Vehicle handling, particularly drifting, is affected by framerate. The higher the framerate, the more the car will slide. In normal cars, it also slows down more during a slide. This isn't the case in drift cars, but I haven't done any real testing on those. TL;DR lower framerates are better.
Below are the results of some testing from the past couple days, performed using a CCXR with full eBay bonuses on Nürburgring GP Circuit. Each test pass simply consists of going around the first corner as fast as possible. The game is recorded, the recording is gone through frame by frame, and the minimum speed (in km/h) the car dropped to is logged. Minimums were chosen because using the average of each test pass would unduly minimize the differences caused by different framerates.
Full disclaimer, it isn't possible to test this with 100% accuracy, but I did my best and spent several hours doing a few hundred passes to try to average out any inconsistencies.
I'm no statistician, but this should be enough to get some idea of what's going on. The most important thing here is the average without outliers (average of the minimum speeds of each test pass), which shows a clear downward trend in speed as the framerate increases. This is also reflected by the minimum without outliers (lowest minimum speed of any test pass), which follows the same trend.
The maximum (highest minimum speed of any test pass) is notable because it actually stays relatively consistent. Unfortunately, I can't show this easily in data, but the reason is that these fastest test passes don't involve drifting. There still seems to be a slight downtrend with higher framerates, but I can't conclusively say that lower framerates are faster—more research is warranted.
Even assuming high framerates can be as fast as low framerates, the data proves their consistency isn't equivalent. Despite me being objectively worse at the game at lower framerates (due to a combination of heightened input latency and motion sickness), the minimum speed at 15 and 30 FPS was significantly higher than at 120 or 240. I attempted to show this in the rightmost column, standard deviation, with mixed success. The low-speed outliers only existing at higher framerates also supports this. (If you're wondering, 0 km/h is a spin—and I was unable to spin the car at lower framerates no matter how hard I tried. Maybe initiating a drift is more difficult?)
Finally, to touch on the sub-30 FPS numbers, these are below console performance and generally considered unplayable. However, I suffered through it to see whether scaling continues beyond 30. Long story short, they appear to have diminishing returns. Despite this, there were some results that were out of line, like the 121 km/h result at 20 FPS, and so out of caution I have to recommend that framerates below 30 FPS be officially banned from use in speedruns to maintain parity with consoles (and also to be fair to people who can't take the abuse of low framerates).
Anyway, that's all for this loveliness. Let me know what you guys think. Thanks @Night_95 for insisting the problem exists.
Edit 2024-03-10: Apparently all cars have a "skid type" and drift cars don't lose speed because they use the drift skid type. They're still less consistent at higher framerates, but the extra sliding might be beneficial if you're going for high scores.
Also, just to be clear, the decrease in consistency scales linearly with framerate. That means going from, say, 30 to 60 FPS is less impactful to your times than going from 120 to 240 FPS, even though it's visually more impactful. That's why I'd still recommend playing at 60 if you can't handle 30. Funnily enough, that also means ultra high framerates like 1000 FPS could make the game literally unplayable.
