Herr Otto Partz says you're all nothing but pipsqueaks!

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Custom Cars with Stressed / Car tests megathread
August 09, 2023, 02:11:41 AM
This is a thread for sharing test reports of Stunts cars: all cars are fair game, and everyone is welcome to contribute. It is a spiritual successor to the "Trying out Ryoma's cars" thread from the 2022 preseason, and accordingly tests from there will be linked from here as well.

Index of tests:

*: Test from the "Trying out Ryoma's cars" thread.
†: Retest pending due to major changes in a newer version of the car.
Stunts Chat / The Magic Lamp powergear experiment
June 03, 2023, 07:08:26 PM
Here's a report on a little experiment ran a while ago, with support from @Daniel3D and @alanrotoi . The first two CCC races of this season, Magic Lamp and Free The Genie were set up so that we could gauge how much difference powergear makes to the performance of powergear cars. The extent of powergear availability is a major confounding factor in the sort of bulk comparison I attempted during the ZakStunts preseason rules discussion (which is otherwise fairly accurate). In this experiment, a complementary approach was taken: Magic Lamp is a (mostly) PG-free track, while Free The Genie is a PG speedway, so the differences in relative performance between the tracks can give us a view of influence of PG.

To begin with, these are the results for Magic Lamp. Those were NoRH laps (except for redoing the finish with the flexible PG cars to avoid getting PG on the final loop) driven by me with roughly the same effort on each of them (laps and tracks are attached). For the flexible PG cars, powergear was intentionally avoided on the final loop. The final column is the bonus percentage, ZakStunts-style, corresponding to the laptimes. P962 (fixed at 0%) and LM002 laps have also been included for reference:

PMIN    1:35.85    -5.7
P962    1:41.30    0   
XCFX    1:42.90    1.6   
PFCR    1:47.30    5.6
FGTO    2:09.40    21.7
VETT    2:10.60    22.4
ANSX    2:11.35    22.9
LM02    2:19.95    27.6
PACK    2:33.55    34.0

(XFCX is the Xylocaine, PFCR is the Crown Victoria, PACK is the Packard 8.)

This comparison puts non-PG Indy at -6%, the other original PG cars fairly close to each other around 21-23%, the Xylocaine at a pretty low 2%, the Crown Victoria (which isn't quite a PG car) at 6%, and the Packard at 34%.

Next, the Free The Genie results. I drove this with RH so that a comparison of full PG laps would be realistic, again putting similar amounts of effort in each lap (though the Xylocaine one might be a touch stronger than the others):

PMIN    1:07.55    -28.6   
XCFX    1:12.45    -19.9   
PACK    1:19.45    -9.3   
FGTO    1:20.10    -8.4   
VETT    1:20.85    -7.4   
P962    1:26.85    0   
ANSX    1:29.20    2.6   
PFCR    1:48.85    20.2   
LM02    2:28.60    41.6   

Both the Crown Victoria and the LM002 lose heavily here due to not having been fast enough to cut the second u/d cork (even the P962 barely made it). As for the PG cars, we see gains of over 40% for the Packard, around 30% for the Vette and GTO, and around 20% for the Acura (as expected, gains are limited by the lack of powerslides), Indy and Xylocaine (which are a little less dependent of powergear thanks to better handling).

These are results obtained by one specific driver on two specific tracks, so they are certainly affected by idiosyncrasies and chance. Still, they should give a rough idea of what to expect when it comes to the influence of PG on e.g. bonus percentages.
General Chat - R4K / R4K40 - Westwood
May 01, 2023, 05:42:46 PM
Kevin Pickell's Westwood is a great retro pick! Between here and CCC, I also like seeing the Xylocaine get some regular use -- I feel we've kinda done it dirty back when it made it to ZakStunts years ago.
Stunts Forum & Portal / Forum language options
April 21, 2023, 01:27:09 AM
A bug report from @Erik Barros a while ago made me realise the language packs for the forum interface weren't working well, as they had been made for a version of the forum software much older than what we currently have. I have just reinstalled the language packs with up-to-date versions, which should provide a better experience if you ever feel like switching the preferred language in your profile. Below is a before-and-after comparison:

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Competition 2023 / Unstable replays at ZakStunts
April 10, 2023, 02:48:47 AM
2023-04-22 update: The proposal below is being updated to better reflect our current understanding of unstable replays. To avoid invalidating the next several replies, removed passages will be struck out, while additions will be in italics. For a rundown on when instability arises and how to work around it using the replay controls, see this post.

I'd like to start a discussion about the unstable replays rule, motivated by the replay invalidations at ZCT260 (see the shoutbox posts from April 8th and 9th for what happened there, and the end note at the bottom of this post for an explanation of what unstable replays are). I will open it by putting a rule change proposal on the table for your (and dreadnaut in particular, of course) consideration.

The proposal

Change the relevant passage of the rule which makes unstable replays invalid (rules page, section "The System", bullet point #2) from:

"[...] and [a replay] should play correctly when loaded in Stunts, from 'Options → Load replay'."


"[...] and [a replay] should show as complete upon loading in Stunts from 'Options → Load replay', rewinding to just before the finish line, and continuing from there."

2023-04-22 update: While checking how the replay ends upon loading from Options should be the primary means of validation, the current procedure of watching the lap from the beginning, with multiple cameras if necessary, should be kept as a fallback. That being so, it might be appropriate to concisely describe the validation procedure and how it is supposed to work in a separate item.


My proposal tries to strike a compromise, keeping replay viewing and validation reasonably easy while excluding as few valid-as-driven replays as possible. To expand a bit on that, I'll consider the two goals which, as far as I understand it, motivated the 2021 rule change:

  • Ensuring competition management can validate replays by following a simple procedure with reproducible steps.
  • Avoiding confusing replay watchers who play laps from the competition archives.

Goal #1 is fully addressed by my proposal. In fact, as far as manager convenience goes it even improves upon the status quo, as it is no longer needed to watch the whole lap to be sure it is valid -- just loading from Options, rewinding a little bit, and continuing to the evaluation screen is enough. (This streamlined procedure is what I have always assumed managers short on time would default to on race closing, which partly explains my mix-up when replying to Friker at the shoutbox on April 2nd.) Besides that, unstable replays which are valid according to this procedure (i.e. the vast majority of them) can be watched to the end on normal speed through the well-known replay controls trick of rewinding a little around shortly after the point of divergence and resuming play, and are reproduced correctly by the repldump tool, and usually, with an adequate choice of starting frame, when played at double speed as well. (And conversely, Overdrijf's extraordinarily hard to verify replay from ZCT232, which triggered the rule change, fails the streamlined verification.)

2023-04-22 update: Considering what we have learned over the past two weeks about unstable replays -- in particular, that divergent timelines are system dependent, and that replays such as Overdijf's ZCT232 one aren't as rare as previously thought -- it makes sense, as suggested by Friker, to keep the current, play-from-the-beginning validation as a fallback method. It is fairer to drivers to accept as many unstable replays as we reasonably can, and keeping the current method as a fallback won't noticeably increase admin workload. The main caveat is that, since divergent timelines are system dependent, if a replay is only finished on a divergent timeline and not on the load-from-Options/fast-forward one there is no guarantee that the manager will be able to watch the lap being completed. That being so, it seems appropriate to keep the new wording of the rule as it was in the original proposal, recommending pipsqueaks to check if their laps show up as complete upon loading from Options -- if they don't, there is a nonzero chance of them being ruled invalid, even though the fallback validation might rescue them.

As for goal #2, there are two aspects to consider. Firstly, there being a reproducible way for managers to validate replays means every one else can check them in some way, and as pointed out above that also translates to reasonable ways of actually watching the laps. Secondly, I feel we should not penailse, in multiple ways, pipsqueaks in the here and now for the hypothetical benefit of a future visitor who might be confused by archival replays -- specially considering that the pipsqueaks have valid-as-driven laps and are at no fault, and that we can provide easy access to information that clarifies the matter to visitors (through Wiki articles, replay package readmes, and so on).

If need be, I can go into further detail on the points above, and in particular on what makes it so taxing to verify replays in the way specified by the current rule. But I have talked for long enough for an opening post, so it's time to give the floor to you. 

End note: what is an unstable replay?

An unstable replay is a lap, usually a RH powergear one, which plays differently in-game depending on how the replay controls are used. In the most common scenario, the player completes the lap normally without noticing anything strange, and the replay shows up as complete upon loading from the Options menu and looking at the end of the tape. However, rewinding to the beginning and playing at normal speed shows the car as crashing or veering off track.
Stunts Chat / Controller tests
February 17, 2023, 06:33:02 AM
If you looked at the ZakStunts shoutbox on the ZCT258 deadline day, you may have noticed that @Erik Barros , @Overdrijf and me have been doing a few test with playing Stunts on alternative controllers. I'll open this thread with a report on using a Xbox 360 controller.

Setting it up

First, here is how I (with some help from Erik) have set up the controller on DOSBox. I'm currently using DOSBox Staging 0.80.1 on Linux. The operating system shouldn't matter much; however, DOSBox Staging has improved support for controllers, including the ability to have more than two analog axes recognised as such (see the 0.75.1 release notes).

With the default configuration, DOSBox Staging will map the x and y analog axes (steering and accelerator/brakes) to the left analog stick, and joystick buttons 1 and 2 (shift up and down) to Xbox buttons A and B. While that is reasonably faithful to what you'd get with the kind of joystick originally supported by Stunts, it is also suboptimal in that it is not very comfortable to have steering, accelerator and brakes on a single analog stick, specially given the wealth of options offered by the Xbox controller:

Xbox 360 controller diagram. Source:

Changes to the controller layout are done through the DOSBox mapper, available by pressing Ctrl + F1 in DOSBox. DOSBox Staging, allows you to remap the controller however you like, removing some limitations found with plain DOSBox (please reply if you run into difficulties with that!). My favourite mapping so far, which should work with no further configuration in both plain DOSBox and Staging, is a hybrid one: accelerator and brakes on buttons (as analog makes no difference for them), and steering on the left stick:

  • Joystick axis x-/+ (steering): left stick x-/+
  • Joystick axis y- (accelerator): A button
  • Joystick axis y+ (brakes): X button
  • Joystick button 1 (shift up): RB bumper
  • Joystick button 2 (shift down): LB bumper
  • Esc key (menu): Start button, or Y button

With the mapping done, select joystick input in the Stunts option menu, and perform the in-game calibration as usual.

Compared to the standard Stunts input devices, this hybrid setup is rather like an improved version of mouse controls (steering on x axis, accelerator and brakes on the buttons), free of the jerkiness that makes using the mouse so unwieldy.

Test drive

A natural thing to ask about using analog controllers in Stunts is whether the input is actually analog. After all, replay files store input in a digital format, a direct transcription of keyboard key presses. In the case of accelerator and brake input, there is indeed nothing analog about the input, even if you map an analog stick or trigger to the joystick y axis. As for steering, however, Stunts has a trick up its sleeve. In joystick mode, steering without moving the analog stick all the way left or right will keep the car wheel in an intermediate position as well. The game achieves that by sending key presses in the appropriate rhythm to keep the wheel roughly at the same place. That is demonstrated in the attached JOYTEST5.RPL, in which I spent more than a minute moving in circles, with the LM002 wheel held at one fifth of the way left.

What about actual driving, though? Though effective driving with non-keyboard controls will surely take a lot of getting used to, the first impression was far better than expected. After some warming up and acclimatising, for instance, I got the attached XBOX4.RPL: Default, Indy, classic line, 1:07.40. Slower than on keyboard, but a very normal lap, all things considered -- and the potential to improve is certainly there.

One difference between joystick and keyboard steering in Stunts is that with the joystick mode the movement range of the car wheel is only about half of what we get with a keyboard, presumably so that the analog steering wouldn't become too sensitive. That will probably mean a disadvantage in full powergear tracks and other scenarios which require extreme sliding tricks. On the other hand, I expect that it will be possible to put analog steering to good use in different situations, specially in OWOOT + NoRH driving.

(A practical detail worth mentioning: there seems to be a minor Stunts bug such that accelerating with joystick controls doesn't interrupt the leaving-the-truck animation. One way of skipping it without losing any time is holding the accelerator and then pressing shift down.)

Space and Enter

On a final note, these experiments made me think of a (perhaps obvious) hypothesis for why the keyboard controls have two pairs of keys for shifting (A/Z and Space/Enter). It sounds plausible that A/Z were originally meant as the "proper" shifting keys. However, as the two joystick buttons must handle both shifting and menu confirmation, it makes sense for a joystick button press to be translated to both. Given a reversible mapping, we'd end up with Enter (and Space) playing both roles on keyboard as well.
I'm happy to announce the opening of the Arrabona project: an archive for previously inaccessible parts of the UnskilledStunts records. Right now that includes track-and-replay packs for all 137 races of UnskilledStunts competitions (USC, USL and Christmas Cup) so far, as well as the scoreboards for UnskillesStunts 2021. Thanks to CTG for green-lighting this project!
Now that I'm finally doing the sorely needed behind-the-scenes cleanup of the Southern Cross site, it is probably a good thing to decide what should happen to the car collection there -- and your input will be very helpful for doing so.

For several years, I had tried to maintain Southern Cross as the primary place to download custom cars. However, except for adding the 19th Anniversary Melange, I haven't updated the collection there since May 2021. To make matters worse, many of the Ryoma cars there aren't in their final versions, and I'm not even 100% sure if the downloads of them are replay-compatible with the ones used at CCC.

As things stand, the best maintained car collection around is clearly @KyLiE 's (see the Stunts Custom Cars page at ), and in fact I have recently added a note to the Southern Cross page recommending it. That, however, probably means I have to find some other role for the Southern Cross collection, as I'm not sure if there's much point in me (re)creating a second collection of individual car downloads with basically the same scope. Some of the alternatives include:

  • Shutting down the main part of the Southern Cross collection, leaving only the old-school cheat cars and the historical curios.

  • Switching the focus of the collection to car packs. (That would be a big U-turn, as the point of the Southern Cross collection originally was to offer individual downloads, so that people could easily pick just what they needed. However, the existence of Simple Garage increases a lot the usability of car packs, making this a more attractive option than it was ten years ago.)

  • Figuring out a way to collaborate on a shared collection, set up so that it can be easily made available on different sites. (This is wild speculation, as right now I have no clue about what would be a good way to achieve that.)

  • Restoring the Southern Cross collection in something like its current format. (You'd probably have to persuade me there's a point in doing so, though.)

So, how should the Southern Cross collection evolve? Is there any other possible role for it that I have overlooked? Please let me know of your thoughts, as I don't think I'll manage to find a good solution without considering your views.

I'm delighted to finally release the ZakStunts Folyami ratings, an Elo-like rating system for ZakStunts! You can check the ratings right now at the Southern Cross site. Below is a quick Q&A about the ratings -- if you have extra questions, feel free to ask them!

Why are there two rankings?

Given that Folyami ratings are pretty dynamic, responding rather quickly to changes in form/current performance, it felt appropriate to have something the more permanent to go along with the ranking of current ratings. That being so, there is also a historical ranking, which lists the highest ever rating reached by pipsqueaks.

Why am I not showing up in the rankings?

There are basically two possibilities:

  • Firstly, at least five completed races are necessary to be included in the rankings, so that ratings have at least a few rounds to stabilise.

  • Secondly, pipsqueaks leave the current current ranking after four races of inactivity, and rejoin upon returning to the competition. (Note that there are a few rules for discarding race results that aim at removing unrepresentative ones, such as those reached with an obviously uncompetitive car. That being so, race entries might, in special circumstances, not be counted for the ratings.)

So don't worry: no one gets excluded from the rankings, and you just have to keep racing for (re)joining it  :)

How do the ratings work?

Here are links to a summary of the ZakStunts-specific aspects of the rankings and a technical overview of the rating system. (I have attached the latter here as a PDF, in case you find that easier to read.)

Can other competitions be included in the ratings?

The Folyami project began as an offshoot of my earlier investigations about race strength, which is why the ratings came into being as ZakStunts-only. Ideally, it would be nice to follow illustrious predecessors such as WRL and SWR and make Folyami an omni-rating covering all Stunts competitions. While I do want to explore ways of achieving that at some point, it can't help but be a project for the long term. Not only there are decades of competition results to be reviewed and formatted, but also harmonising the competitions into a single system could prove challenging, especially given how much the currently active competitions differ from each other.

Will there be an update of the race strength ranking?

Sure! I will add race strengths to the site as soon as I figure out a few details about how to best present the data. By the way, if you have any suggestions of additional features and visualisations for the ratings and the historical data thereof, please do let me know!
General Chat - ZSC / Title decisions in ZakStunts
January 12, 2023, 01:34:07 AM
When in the season are titles decided? That is an interesting question -- specially during the season itself! -- which isn't always easy to answer just by looking at the season scoreboard. Discards mean that pipsqueaks can have different amounts of points available from the final races of the season, so just looking at the Real score and the number of remaining races isn't quite enough to make projections. The experiments with point systems from a few weeks ago gave me a good opportunity to look at title decisions in past years.

Here goes a list of ZakStunts seasons, ranked by how many races were remaining when the title was mathematically decided. When it comes to tiebreakers, it makes sense to use the number of discards and the total number of races, in that order.

Three rounds early

  • 2008 (2 discards from 11 rounds)
  • 2010, 2016, 2017, 2019 and 2022 (3 discards from 12 rounds)

Two rounds early

  • 2004 (2 discards from 13 rounds)
  • 2009, 2013, 2018 and 2021 (3 discards from 12 rounds)

One round early

  • 2007 (2 discards from 9 rounds)
  • 2005 and 2006 (2 discards from 12 rounds)
  • 2003 (2 discards from 13 rounds)
  • 2011 (3 discards from 11 rounds)
  • 2012 (3 discards from 12 rounds)

Decided on the final round

  • 2001 (0 discards from 9 rounds)
  • 2002 (0 discards from 12 rounds)
  • 2014, 2015 and 2020 (3 discards from 12 rounds)

And here are the seasons sorted chronologically, with a few extra details. The Available columns show how many points were available to champion and opponent before the deciding round, and Gap is the difference between them. Note that, thanks to discards, the opponent in the strongest position isn't always who was in second place at the deciding race -- for this table, I picked whoever had the largest difference between their available points and their gap to the leader.

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A few notes on specific seasons:

  • Unsurprisingly, the most impressive early decision is 2008. After ZCT87, Ayrton would have won the title even with a non-discarded missed race.

  • While five seasons were mathematically decided in the last race, due to various circumstances only 2015 and 2020 really had a final round battle.

  • 2009 is a bit of a special case. While CTG wouldn't have been able to overtake me in the final two races, in the most favourable scenario for him we would end with the same score. Since there are no tiebreakers in the season scoreboard, I counted the season as being a two-rounds-early one.

  • You might be wondering why have I listed 2001 as being decided in the final round if the points available to Ben Snel were smaller than the gap to Roy Wiegerinck. The answer is that in 2001 (and 2002) average points over races joined were a major component of the season scores. That being so, a pipsqueak might lose points by entering a race and getting a sufficiently bad result in it. While the title wasn't mathematically decided before ZCT9, Roy could guarantee the title by skipping the race, which is duly what happened.
Stunts Questions / Who created the Coconut cars?
January 04, 2023, 06:53:31 AM
Who created the Coconut cars? That has been a nagging question that I have been reminded of every few years. Stumbling upon the readme I once wrote for the Coronet Pulsar ("created by an unknown designer in a bygone era") made me realise I had never made a serious attempt at finding out the answer. Back in my newbie days, when I got to race with the Coronet at SDR, or even when I started the Coronet Wiki article a while later, it felt like those old school cheat cars had always been there. The distance of a handful of years now tells me I should have known better. Time for some digging, then!

The oldest source on the live Internet for the Coconut cars is probably the cheat cars package at ZakStunts' downloads page, which was added to the site somewhere around August 2001:

The package includes nine cars, helpfully displayed on this table (thanks Alan for adding it to the Wiki!):

We might divide those cars in three groups:

  • The five cars attributed to Mr Eriksson, whose files in the zip have modification dates from March and April 2000;
  • The two Coconut cars: Coconut Car Coronet Pulsar STi-R, and Coconut Car GTR 7.5 GT IMSA. Their files date from August 2000; and
  • The two remaining cars. The Ditsch car in-game description includes both authorship and a dedicatory ("for Magnus by brainSteen"). Though the Wooden wireFire has neither, the file dates (May 2000 in both cases) and the use of camelCase ("brainSteen", "wireFire") suggest they belong together.

The cars themselves provide no further clues on who Mr Eriksson, Magnus or brainSteen are, or whether they have anything to do with the Coconut cars. To remedy that, we can take a ride on the Wayback Machine and turn to the who's who of people in the community around the turn of the century: Kalpen's directory of Stunts links! It doesn't take long to discover that both brainSteen and Magnus not only had Stunts sites, but also offered a common set custom cars for download:

Unfortunately, brainSteen's site wasn't archived, and neither was the car downloads page on Magnus' site. Wandering along the other sites linked from Kalpen's, we can find a surprising number of custom car downloads; however, in all cases I have looked at there is enough information on the pages, even when the car files themselves weren't archived, to figure out the Coconut cars aren't among them. That includes the Supercar .zip from the TSST (The Swedish Stunts Team) site, which likely packaged some of the cars by Royforever:

That's not the only relevant information in the TSST site, though:

So Magnus joined TSST in March 2000. But wait! Have a look at the site footer:

Now compare with the full name of the Coronet Pulsar  :)

The contact info on that footer points to Red Baron, team leader dictator of TSST:

And now, the finishing touch: the list of URLs from Magnus' site captured by the Wayback Machine includes several PDFs with paper models of cars and other vehicles. These models are credited to...

So, here is what I think the events were: Magnus, aka Mr Eriksson, is a Swedish pipsqueak and car designer. He joined TSST in March 2000, in between creating the Škoda Felicia and the Лада Нива. Several months later, someone in the team made a couple of СССР cars in tribute to their organisation.

Even after tying those threads, it's hard to identify a single author: it could have been Magnus, though the Coconut cars are very different in style to the Mr Eriksson ones; it could have been Red Baron, though the copyright footer on the site is clearly part of an in-joke rather than anything personal. In any case, it seems certain that the Coconut cars are a TSST project. I guess I finally have something meaningful to write in that readme! I can't help but wonder, though, if @zaqrack or any of you who were around at the time would confirm, or deny, my speculation :)

Custom Cars with Stressed / Trying out Ryoma's cars
December 27, 2021, 02:55:11 AM
In the Cars and rules for 2022 topic, there was a consensus for having at least one of Ryoma's cars in the next season. For that to work smoothly, however, we need to do some testing in order to make an informed choice. To get things started, I will (try to) test one car from Ryoma's Mega every day, and report the results here. If some of you join me in doing that, I'm sure we'll get to figure out suitable choices in no time.

Here are the cars tested so far:

To begin with, here are some words on the Ferrari 456 GT (forum topic):

  • Gears: 6
  • Powergear: No
  • Flat track top speed: 196 mph
  • Real top speed: 218 mph
  • 0-60 mph: 5.1 s
  • Time to hill at Default (auto gears): 12.55 s (References: Countach - 12.40 s; Skyline - 12.45 s; Acura - 12.70 s)
  • Default test lap (NoRH, classic line): 1:32.45
  • First impressions: A moderately fast sports car, whose closest match is probably the Skyline (the 456 should have the upper hand on faster tracks, though). Next to other cars from that class, its handling feels nice and responsive, though there doesn't seem to be much extra grip, and it is easy to get overconfident on the corners.
General Chat - ZSC / Race positions dataset
October 30, 2021, 08:36:20 PM
Extracting the race positions from all ZakStunts scoreboards is not a straightforward matter, even with database access. The positions are computed from the replays rather than stored, and there are all sorts of corner cases to look out for -- name changes, draws, disqualifications, and so forth. For my ratings and race strengths project, I opted to review all the scoreboards and prepare the dataset by hand. A CSV file with the data is available at my project's GitHub repository (attached below is a version of the same file as of ZCT243).

The Track, Racer and Rank columns of the CSV contain what it says on the tin. pipsqueak aliases and name changes have already been unified. The Ghost column value is 1 if the pipsqueak is a known ghost, and 0 otherwise. Lastly, the Status column records the following occurrences about a race entry:

  • DSQ: Disqualification, from a 00's ZakStunts race (back then, disqualifications were handed by setting the laptime to 9:99.99 rather than deleting the race entry outright).
  • INV: Invalid replay, discovered upon review.
  • MSC: CTG's 2014 races.
  • EX1: Laptime beyond the "300% and 2 SD" cutoff.
  • EX2: Lap driven under an alternative ruleset, such as GAR.
  • EX3: Lap driven with a clearly uncompetitive car.

Edit, 21:53 ZakStunts time: I have updated the attached file after re-adding a few 2014 season status notes I had accidentally deleted.
In my previous thread on pipsqueak performance modelling, I reported optimistically on modelling lap times over repeated attempts with a gamma distribution. Back then, all I had for empirical evidence was a set of lap times driven in a minimal four-corners track. To better understand the model and the problem space, it would make sense to gather data on more realistic conditions. Soon enough, the perfect opportunity came up with Alpine, R4K's October race: great car, great (and not too difficult) track, and a real OWOOT NoRH race going on.

From October 11th to the deadline day, I had one (occasionally two) NoRH session on Alpine every day, and recorded all of my valid lap times. I tried my best to keep a consistent driving style, going for the most effective reproducible racing line I knew of, and not giving up on laps unless I crashed or left the track. The following set of box plots show what my lap times on each session looked like (for a closer look at the data, you can look at the attached CSV file):

I would divide my racing in three main stages:

  • On sessions 1 to 5, I was still learning both car and track. In particular, I got under 83 seconds after figuring out a good line through the second and third corners, and under 82 seconds by  understanding how the second fast chicane should be approached.
  • From sessions 6 to 14, there was largely stability, with perhaps some very slow improvement, culminating with a 81.00 on session 14.
  • On sessions 15 to 18, there was modest but marked improvement, which I attribute to either realising I could be a touch more aggressive with my lines upon rewatching the laps I had posted to R4K, or to being in better shape by no longer doing late night sessions. I drove my final R4K time of 80.55 early on session 15. After that, I only managed one more lap under 81 seconds: an 80.75 on session 18.

With the lap times at hand, the next step is attempting gamma fits on stretches in which I had consistent performance. A good place to start could be sessions 15-18, in which I was perhaps closer to my best. Here is a first attempt:

Fitting of the distribution ' gamma3 ' by maximum likelihood
Parameters :
        estimate Std. Error
shape  5.5682015 1.79934095
scale  0.3520632 0.07724456
thres 80.2265133 0.24903711
Loglikelihood:  -115.9133   AIC:  237.8267   BIC:  245.612
Correlation matrix:
           shape      scale      thres
shape  1.0000000 -0.9492797 -0.9041436
scale -0.9492797  1.0000000  0.7526068
thres -0.9041436  0.7526068  1.0000000

A recap on what the gamma parameters mean in our context:

  • thres, short for threshold, is the predicted ideal time, the one the model assumes it is impossible to go below.
  • shape indicates how hard it is to improve as you get closer to the ideal time. It is associated with track length and track/line difficulty.
  • scale reflects how consistently the pipsqueak manages to drive. Smaller values make for a narrower gamma curve, squeezed closer to the ideal time.
While the diagnostic plots show the gamma fit is pretty good, the parameter values are all over the place, as the following bootstrap confidence intervals indicate:

Nonparametric bootstrap medians and 95% percentile CI
          Median      2.5%      97.5%
shape  5.2026795  1.965190 10.9580942
scale  0.3649339  0.222748  0.6145803
thres 80.2609610 79.615182 81.0369308

Ultimately, is is a bit much to try fitting those three parameters at once with the available amount of data; there is too much wiggle room. From the three parameters, the one we are in a better position to estimate by other means is thres. The sum of the best sectors over the fifteen laps I had saved for posting to R4K is 80.05; that being so, 80.00 is a reasonable, if conservative, ideal lap estimate. Fixing thres to 80.00 results in the following gamma fit over sessions 15-18:
Fitting of the distribution ' gamma3 ' by maximum likelihood
Parameters :
       estimate Std. Error
shape 7.0919246 0.98618134
scale 0.3083916 0.04444141
Fixed parameters:
thres    80
Loglikelihood:  -116.1671   AIC:  236.3341   BIC:  241.5244
Correlation matrix:
           shape      scale
shape  1.0000000 -0.9650934
scale -0.9650934  1.0000000

The 95% confidence intervals look a fair bit tamer now:
Nonparametric bootstrap medians and 95% percentile CI
         Median      2.5%      97.5%
shape 7.2104854 5.4284800 10.1456150
scale 0.3034129 0.2069173  0.4084368

While thres is the easiest parameter to estimate through different means, the one it would be arguably more interesting to keep fixed is shape, as it is supposed to be the one most closely associated to the nature of the track. Given the more believable estimate of shape we have just obtained for sessions 15-18, it is worth trying to fits for other sets of sessions with shape fixed at 7.1. Here is a fit for sessions 6-9...

Fitting of the distribution ' gamma3 ' by maximum likelihood
Parameters :
        estimate Std. Error
scale  0.4312479  0.0320152
thres 80.1501134  0.1939291
Fixed parameters:
shape   7.1
Loglikelihood:  -142.3025   AIC:  288.605   BIC:  293.6915
Correlation matrix:
           scale      thres
scale  1.0000000 -0.8532844
thres -0.8532844  1.0000000

Nonparametric bootstrap medians and 95% percentile CI
          Median       2.5%      97.5%
scale  0.4276147  0.3703891  0.4924684
thres 80.1722529 79.8464586 80.5086957

... and 10-14:

Fitting of the distribution ' gamma3 ' by maximum likelihood
Parameters :
        estimate Std. Error
scale  0.3832479 0.02554952
thres 80.0632570 0.15585001
Fixed parameters:
shape   7.1
Loglikelihood:  -171.2663   AIC:  346.5326   BIC:  352.1242
Correlation matrix:
           scale      thres
scale  1.0000000 -0.8591264
thres -0.8591264  1.0000000

Nonparametric bootstrap medians and 95% percentile CI
          Median       2.5%      97.5%
scale  0.3800133  0.3260546  0.4442169
thres 80.0765083 79.7532830 80.3593560

Keeping the shape fixed, the fits point to a noticeable reduction of the scale parameter (suggesting more confident and consistent driving) across the sets of sessions. The difference in thres (which might be ascribed to refinements of the driving line) is too small to be clearly meaningful.

Parameter estimation for my proposed model is challenging: pining down those three significantly correlated values without huge amounts of lap time data is nontrivial, and  if it can be tricky to extrapolate from one day to the next, let alone doing so across different pipsqueaks or driving lines... On the flip side, the results of the experiment do suggest the gamma distribution is a reasonable model for lap times, and that it is worth it to keep pursuing this idea.
Competition 2021 / ZCT244 - Crazy Eight
October 18, 2021, 03:41:01 AM
Z244 has a two-tile switching shortcut, which is illusrated by the attached diagram and Trueno lap. As per tradition (ZCT202, ZCT146, ZCT136, etc.), now it's that time in which we sit down and decide whether it should be forbidden.

My take: while this shortcut isn't as destructive as the ones seen in past cases (it affects less than half of the track, and might not even be advantageous with faster cars), I think it should be forbidden anyway (it is as ugly as any of those two-tile cuts, and ruins a perfectly good section of the track). For a more objective rationale, we might invoke the "it shouldn't be allowed to drive the same section of track in both directions" principle, originally suggested by afullo back in ZCT202.
General Chat - R4K / R4K15 - Alpine
October 14, 2021, 05:42:44 AM
As some of you have already found out, this is a very enjoyable track, which fits the car and the rules like a glove. It's a great opportunity to try out the Corvette CERV III!

(Incidentally, this race is also perfect for carrying out my performance model experiments, so expect a lot of NoRH laps from me this month :D)
Stunts Chat / Räcer performance modelling: an update
September 25, 2021, 06:39:25 AM
Here is a long-delayed progress update on my race strength estimation project, more specifically on its performance modelling side. Besides improving my ratings framework, the findings I will talk about here might even bring extra insight about racing in practice. How so? Let's find out!

What do you mean by "performance modelling"?

I will start with a recap of what I was busy with at the beginning of the year. The primary goal back then was setting up a metric for the strength of races. To a first approximation, how strong a race is depends on how strong its field of pipsqueaks is -- how many people take part, and how well they are racing at the time. The latter part can be dealt with an Elo rating. However, while Elo ratings can be a decent indicator of the expected performance of pipsqueaks, they don't easily translate to a meaningful rating for race strengths. That's because the Elo system is based on head-to-head matches, while in a race everyone involved is competing at once. For that reason, my chosen strategy was using the Elo ratings to tune probabilistic models of how well each pipsqueak was likely to do in a certain race, and use said models to compute how well someone would be likely to do if entering that race.

To define the model, I used the one probability distribution with sensible characteristics that I happened to recall. It looks like this:

The horizontal coordinate is for lap times, in arbitrary units since concrete information about the tracks is not being dealt with. Time zero, at the leftmost edge of the plot, stands for the ideal lap, and so moving rightwards means increasing deviations from the perfect lap. The vertical coordinate is for the probability (strictly speaking, the probability density) of reaching each lap time. In the example plot above, there are distributions for two pipsqueaks. The red curve pipsqueak is expected (though not guaranteed) to perform better than the blue curve one, as their probability density is squeezed closer to zero overall. Given these two distributions, winning probabilities for red and blue can be obtained; with more pipsqueaks, it is also possible to calculate things like the probability of one pipsqueak reaching a top five result against the others (that is, losing to at most four of them).

It is also worth reviewing what I meant by this model having "sensible characteristics". Firstly, the probability density at zero time is zero, which means the perfect lap is taken as an unattainable ideal. Secondly, the drop leftwards from the peak reflects how improvement becomes increasingly hard as the perfect lap is approached. Thirdly, the gradual decay on the tail to the right of the peak expresses the range of possible mistakes that might affect a lap, even quite big ones.

OK, so what's new?

I managed to improve a lot my approach after learning that the model I had chosen is a gamma distribution. The chart below, taken from Wikipedia, shows a few example distributions from that family of probability distributions:

Gamma distribution pdf
Cburnett, CC BY-SA 3.0 <>, via Wikimedia Commons

In particular, the blue curve here with k=3 is (save for a scaling factor) the same as the distributions I had been using (note the visual similiarity with the curves from my example plot above). from my example plot. k, the shape parameter, controls the shape of the curve: distributions with larger k are more symmetrical around the peak, and drop off more sharply towards zero on its left. (The other parameter, theta, is the scale parameter, controls how compressed or stretched out the curve is -- it is the one I let vary according to the Elo ratings, while keeping the shape parameter fixed.)

The Wikipedia examples also illustrate how setting k=1 collapses the distribution a plain exponential. Exponential distributions could conceivably be used instead of the more plausible-looking ones with higher k that I chose. The interesting thing about that possibility is how the winning probabilities for a pair of pipsqueaks with exponential distributions of lap times look exactly like those in the Elo formulas, with the scale parameter being inversely proportional to the Elo rating. Going the other way around, it is possible to replace the conventional Elo winning probability formula with the one for my favoured k=3 model and, with a few tweaks to the system to keep things in scale, have everything working as smoothly as before -- except without the need for an awkward conversion from the Elo ratings to a seemingly unrelated model, and with a much better understanding of what is going on.

And why should any of that be taken seriously?

So far all I have reported here was me toying with equations, with nothing to show that the talk about performance models corresponds to reality. At this point, a little serendipity comes into play.

One of the Stunts experiments I wanted to do back in January was investigating the cornering speed differences between left and right turns. As alluded to elsewhere, I prepared two minimal four-large-corners tracks, one clockwise and one anticlockwise, and went about driving them repeatedly with the Corvette. After seeing no difference whatsoever over quite a few attempts, it dawned on me that I had been doing the tests with the 1990 Mindscape version for no particular reason (I happened to be playing on that version for the competition at the time). Once I switched to 1991 Broderbund the difference immediately became obvious. In any case, at that point I already had recorded a few dozen lap times around those tracks on 1990 Mindscape, so I figured I might as well keep driving a few laps per day until I had enough data to see if the empirical distribution of lap times actually looks like a gamma distribution...

The plots below show the histogram of the lap times (224 completed laps -- attempts in which I left the track or crashed were discarded) and the fitting of a gamma distribution to it. In order to fit a gamma distribution to the data, it is necessary to guess what the ideal lap time is, so that the zero time on the model can be set. I have assumed 23.25 (which is 0.05 below the best I managed) as the ideal lap time, and so the "data"/"quantile" values on the plots should be read as time gaps to 23.25.

That looks fantastic! Incredibly, even the fitted value for the shape parameter was 3.35, which is pretty close to my almost arbitrary initial choice of k=3 for the model. (I should note that a fitted k further away fro 3 wouldn't actually be a problem, for reasons I will soon get to; what truly matters is that a gamma distribution is a reasonable fit for the observed lap times.)

What else there is to investigate?

Given what I have learned so far about the model (through not only the investigation described here but also various attempts at tuning my rating system), I believe gamma distributions with shape parameter 3 form a good basis for an Elo-like ranking of pipsqueaks and a race strength metric derived from it. It remains a pretty bare bones model, with the limitations of using a single parameter as an evolving rating that stands for pipsqueak performances that I had alluded to in my earlier post about race strengths remaining the same. Furthermore, in spite of the incredibly good results I obtained in my attempt to fit a gamma distribution to real data, there is a large gap between a series of single laps by a specific person on a very simple track and whatever happens when people take part in a real race. Depending on what one wants to use a performance model for, ways in which this gap might be narrowed become relevant. Here I will briefly discuss two aspects of this matter: tracks and repeated attempts.

When it comes to tracks, the Elo-like rating system I am working with is entirely indifferent: races are seen as events in which pipsqueaks compete and are ranked, with everything else, including the nature of the track on which they compete, being abstracted away. Turning our attention to the performance model, though, we might consider how the probability distribution of lap times might change according to the track. One way to approach that invokes an useful property of gamma distributions. Suppose we have, rather than a lap time distribution, gamma distributions for the section times that make up a lap, with the distributions having the same scale parameter but possibly different shape parameters. In that case, the lap time distribution will also be a gamma distribution, and its shape parameter will be the sum of the shape parameters for the sections. That points to a way of accounting for basic track characteristics in the performance model, namely using higher shape parameters for longer and/or harder tracks. As I mentioned earlier, higher shape parameters mean a sharper drop in the probability density as we move from the peak towards the ideal time, which intuitively reflects increased difficulty. (One way of thinking about this is seeing each track section as a potential source of mistakes which increase the lap time, and the overall lap time distribution as the result of combining these sources of mistakes.)

As for the matter of repeated attempts, we know that even in a NoRH race what reaches the scoreboard is not the result of a single attempt, but the best result from a set of completed laps. That being so, if we want to use the performance model to think about, for instance, racing strategy, it would make sense to consider, given a single attempt lap time distribution, what the distribution for the best lap time out of a number of completed attempts would look like. While I haven't worked out the details yet, playing with the formulas suggests the resulting distribution is very similar but not quite precisely a gamma distribution, but pretty close. As the number of attempts gets larger, the distribution becomes more symmetrical -- much like it happens when the shape parameter grows in a gamma distribution -- and gets squeezed towards zero -- as expected, as repeated attempts are supposed to improve the results! How fast do the results improve as the number of attempts increase, one might wonder? The preliminary calculations I have done starting from a k=3 single lap distribution suggest the expected gap to the ideal lap time is, approximately, inversely proportional to the cubic root of the number of attempts. In other words, if you want to cut by half the gap to the ideal time, you should be ready to try eight times as many! Note that I'm assuming 3 as the initial shape parameter, which, as the results of my four-corners minimal track suggest, should amount to a fairly easy track; for harder tracks the foreseen number of attempts should grow even faster.

There should be plenty of interesting questions like those I have just mentioned that might be posed in terms of a performance model; I'm all ears for your suggestions!
Custom Cars with Stressed / BMW 850 CSi (E31)
April 18, 2021, 07:06:30 PM
Okay, let's make this officialy a thing!

I already have a dashboard generously contributed by Ryoma, a 3D model prototype from 2010 (which I will reevaluate later in the week, when I reboot into Windows), and a torque curve (obtained from this page, and which matches this BMW page about the engine). I already know in which direction I want to go with the RES, so I will begin working on and testing it today.
General Chat - ZSC / GAR rules draft
March 24, 2021, 06:16:12 AM
I have drafted a set of written GAR rules for use in ZakStunts, to hopefully clarify edge cases and give us an unified document to refer to. Here is a link to it. I plan to have it kept as a draft at least until the Z236 deadline, so that you can review it. In the meantime, I will prepare screenshots to illustrate some of the rules. Criticism and suggestions on all aspects of the draft are most welcome.

To begin with, I would highlight the following rules as deserving extra scrutiny:

  • Topics recently discussed at the shoutbox: 3.28.1 (airtime on banked roads), 3.55.2 (entry and exit of l/r corks), 3.42.2 (jumping over tunnels), 3.71.1 (jumping over slalom blocks), 3.44.4 (airtime inside pipes).
  • Extra rules I am proposing, mostly based on analogies: 3.40.2 (loop exit), 3.44.2 to 3.44.6 (various edge cases involving pipes), 3.4a.1 and 3.4b.1 (extent of the track on crossroads and splits), 3.6d.2 (edge cases involving highway dividers), 3.73.2 (dodging slalom blocks by the outside).
(Don't worry, there aren't hundreds of rules, as the high numbers might suggest; it's just that I have used track element hex codes for indexing.)
Stunts Chat / Penalty oddities
March 23, 2021, 02:57:35 AM
A while ago, GTAMan pointed out a penalty time glitch that cropped up in one of Marco's lives (here is a direct link). It indeed is a new one for me; AFAIK it hadn't been documented yet. Here's the glitch: if the final track element is a split (and not a rejoin) connected to the finish line through the straight path, three seconds of penalty are always given, as if the final track element had been skipped. I guess it took so long for anyone to notice it because the only non-decorative reason for having a split immediately before the finish line is if you are making a Le Stunts track, and in the case no one will actually cross the finish line during the race.

This glitch joins a list of known penalty time oddities, one in which all entries so far have to do with splits and multi-way tracks:

  • Instant finish: if the first element after the start line is a dual way split, the entire track can be cut without penalty by driving back to it. Exploiting this one is generally forbidden through rules and precedents (Z85 was one race in which the issue had to be raised), though competitions relying on a checkpoint system independent from penalty time have on occasion accepted it. Two examples I know of are Funny (SDR-RH 2007) and FTT0111 (FTT 2008).
  • Three-element cut: a split doesn't count for penalty checking if the track is rejoined through the non-straight path. I had forgotten about this one until watching my recent USL round 3 lap and noticing that I fully skipped the split at the 180° turn, by a gap of a few metres. Given what we know about the penalty algorithm, I suspect this one is closely related to the glitch in Marco's live.
  • Dual way switching: Quoting the Wiki, "on tracks where the road splits, it is possible to leave one of the paths and re-enter the track through any point of the other one without penalty time, provided at least one track element is crossed before the paths rejoin". Examples abound; entire classes of track designs are shaped by this one.

Then there's Nagasaki, an USC 2014 track full of splits and crossroads which featured bizarre shortcuts skipping large parts of the track. I still have no clue about what was going on there.