Hi there.
There was a big discussion going on about general tyre physics :

http://www.lfsforum.net/showthread.php?t=8619

But I wanted to ask especially about the acceleration thing.

I think LFS is quite perfect to a slip ratio of about 0.8 or so.

So there seems to be a drop of force between the perfect point somewhere between a slipratio of 0.1 to 0.2 and the slipratio between 0.3 to 0.8. But the difference is quite low as it is in real life. Finding the perfect spot at 0.1 to 0.2 is very very difficult and doesn't result in MUCH better acceleration.

So far correct.

BUT I think the problem is with high slip ratios. The force should drop much further at slip ratios of 1.0 to 8.0.


Example :
This seems to be kind of a real tyre with a late peak at about 0.3.

http://www.performancesimulations.com/files/longslip.JPG

Now look at the difference there from 0.2/0.3 to 0.8. Tyre loses about 10% force from slip ratio 0.2 to 0.8 or lets say 1.0 to make it easy.

Slip ratio is defined as wheelSpinVelocity/groundVelocity-1. So that means if tyre goes twice as fast as car it has a slip ratio of 1.0 (100% spin you could say)

Now lets take a start with the XF GTI. Reving up at the limiter, which is about 50 to 60 kph. Lets say 50 kph at limiter.
Then get off the clutch. You'll notice, that there is no blue clutch sign left. So clutch is fully engaged.

Tyres are now spinning at 50 kph, while car starts from 0. Lets say car is now at the beginning moving with 5 kph.

That means, tyres are spinning 10 times as fast as car is moving. This means 10/1-1 = 9.0

Now watch the graph. It seems that it will decent even faster. But lets say it is linear. This means the loss of force is about 9 times as big as from 0.2 to 1.0.
This would mean only 10% force left, which is a bit off, because the curve eventually stops at some point to drop force even further.
But something like 60% force left or so seem to be quite realistic ...

In LFS its more like this examination :
http://www.lfsforum.net/attach ... id=11060&d=1149423472

Of cource these are R2 and street tyres are a bit different. But I think it is the same there. Force doesn't drop anymore between a SR of 0.8 or 9.0.

Changing this would have a great effect on races and general realism. I admit it is hard to find the perfect spot. But people just going full throttle at the start would be significantly worse than people trying to get a good start ...

What about that in next full patch (V)? Shouldn't be really hard to implement, just changing this drop off at high slip ratios ... but in my oppinion it would improve LFS a lot. Racing experience and realism. And it would improve Acceleration lesson in Training a lot

Perhabs also changing this automatic start signal to a free start. But I don't want to ask for to much

Greetings
RIP

EDIT : I meant data instead of date in the title.

EDIT2: These are the tyre data of formula1 2002 : http://www.racer.nl/images/pac_f12002.jpg
And I think they had some real source ... goes down to about 70% to SR 2.0 and then staying about there ...

Sorry for dropping out of the other thread. I do want to clarify a couple of things:

1) The curves I showed were taken under braking rather than acceleration, so the slip ratio of 1 is a fully locked tire at 20mph. (And yes, it was a real tire, not "something like" a real tire ) Traction curves can look a little different than that, but the total amount of drop off in that range is pretty similar. I've got data at three or four different speeds on that tire and the curves all look a little different. So what do the curves look like at 0 mph and slip ratios 0-10? I couldn't tell you for sure. Maybe somebody with a G-Tech or accelerometer and a powerful car could make some tests. Just show us the acceleration rate for the first few seconds with a lot of wheelspin versus trying to modulate it. That'd give some indication of it at super high slip ratios if you wanted to know.

Just to clarify, there will indeed be a drop off. The question is how much? I would be cautious about making an attempt to extrapolate the data I showed for braking at 20mph out to a slip ratio of 10 and assuming that's going to be the same as 0mph under traction... It's likely to vary quite a lot in reality. The curves at 5 mph are not the same as 20, 40, 60, etc., in reality.

2) Actual traction data is pretty rare, really. Most data is shown under braking as tire companies and automobile engineers have historically been interested in much larger numbers in road safety than getting quick starts off the line. I.e., braking performance gets a lot of attention.

Another reason traction data (slip ratio under acceleration) is pretty rare is that you need a machine with quite a lot of power in order to generate it. In contrast, for braking you just need a really powerful brake, essentially.

The link below shows some different tire testing machines as well as some measured results for one tire out to 28 degrees slip angle, and other tests for traction and braking slip ratio (where you can see the curves look pretty similar). In this case you can see a bit of a force drop off at high loads and high slip angles. I've seen another one like that all the way out to 35 degrees that was absolutely pancake flat, so there's some variance there:

http://rclsgi.eng.ohio-state.e ... Model%20-%20ME%20794G.ppt

Concerning the F120002 curves:
http://www.racer.nl/images/pac_f12002.jpg

I highly doubt this is real data from an actual F1 tire. I'd be surprised to find slip ratio +2 data available even to Ferrari F1, let alone find that the data was handed out to a video game company. They're unbelievably secretive. I could be wrong of course, but it's not safe to assume that's a real curve for any tire at all.

Concerning the LFS curves in slip ratio:

http://www.lfsforum.net/attach ... id=11060&d=1149423472

Looks like there already is quite a drop off there. It'd be a good idea to run in the car park and just keep an eye on the acceleration (F9 display) over the first couple of seconds to see what happens with a lot of slip versus more optimal slip.

One other source of info you might look into is 0-60 foot times for drag racing cars. Be careful here though as wrinkle wall drag slicks are likely to be very different from road racing tires, so make sure the data you find is done with something somewhat comparable to a road racing tire. A lot of drag racers log nearly every run they ever make, including their 0-60 foot times and so on along with weather conditions, whether they had a good launch or a lot of wheelspin and so on. If you can find somebody that has logged data like that you could get a pretty good idea how much of a drop off you should see.

Just some ideas

Thx for clarifying that

I didn't know it was under braking. As I said the first bit of a drop seems to be completly right, but I really think the drop should continue on high slip ratios and not stay there.

If someone in a race falls behind at the start, this doesn't seem to be just 0.5 SR but a lot more. Cars with just small amounts of spin still get away pretty good. They aren't all near their peak value, which is really small like in LFS.

I agree it is very very very VERY hard to find good data. I tried it a lot. I also looked at a lot of drag sites. I just found that spinning wheels are really significantly worse. Even if you correct them immediately after the start and don't stay full throttle it makes a difference of 0.5 to 1 seconds on the 1/4 mile. (with street cars ... not those drag monsters)