That is a big thing; you're not 'riding on the curves', because the result on the road is often a combination of longitudinal and lateral slip. If you have real curves, measured perfectly, and you enter those curves in a sim, the output will only be perfect if the force combining is perfect as well. Since, aparantly (Todd said...
) force combining is tricky and easy to do slightly wrong, likely seen in LFS and ISI, the whole point of realistic curves in sims sort of stops being all that important! The target is not 'real curves', the target is 'exact final force vector'. So I am saying, even if you would find that curves drop a lot after the peak, copying that curve to a sim won't necissarily make it more realistic if the force combining isn't perfect!
I've been spending too much time with rFactor and only when you get to the nitty gritty of it you tend to get some appreciation how changes in the curves (god knows how they are combined), lead to changes in car handling. With the released corvette, sustaining a high angle powerslide is a little nervous; seemingly lateral grip isn't as dependable as I'd like. I've since only slightly changed the shape of the curve. At a slip angle of 26 degrees, the new curve has 1% more lateral grip. Hardly spectacular, but this made a noticable change in the handling; more confidence in keeping the back stepped out at a big angle. Given the likely inaccuracies in force combining, a completely flat curve after it reaches its maximum would probably be a simplification one could defend in court..
Longitudinally I've never really been sure what is going on. Its common knowledge that you can screw up your 1/4 mile time if you don't launch smoothly. The conclusion is that excess wheelspin must mean a reduction in grip, which could VERY well be the case. Thinking on the matter though, say you're doing a drag run, with ''knowledge'' in the back of your mind that wheelspin is bad. When you hear / see the wheelspin, what do you do? Get off the gas to try and stop them from spinning... So where does the lost time come from, the spinning tyres or the gas pedal not being pressed for a few tenths of a second! Not saying this is true, but its worth considering at the very least!
Another longitudinal ''thing'' that I can imagine is the excess heat generated by noticable wheelspin. When smoke comes from tyres, I can imagine the composition of the rubber is sort of fluid and mushy right at the surface of the tyre. This might reduce available grip somewhat, though the extend is open to debate. If you would find data up to high slip ratio, and it would show a drop off to, say, 80% grip at 1.5x slip, this would already include the effect of the rubber heating up. It seems that most sims use base curves and, on top of that, add temperature effects, reducing grip further. Here also, force combining is what makes the driving experience, so some amount of simplification might well be justified.
Attached the current grip curves for the Corvette, plus a comparison (that 1% difference at 26 degrees slip) that you can barely see, yet do notice when driving, of the new curve and the one that is in the Version 1 release of that car.
So in semi conclusion, speaking about tyre curves and how much they drop off tends to assume the force combining is 'perfect' which it probably is not. Secondly, you can't see how the handling will be affected by different amounts of lateral dropoff; you can't predict how a drop to 80% feels just by looking at the graph. From my limited but practical (rFactor that is) experience, 1% difference in grip at a big slide angle of 26 degrees makes a noticable difference. My slightly premature conclusion would be that any tyre that drops noticably towards, say, 30 degrees slip angle, will be VERY hard to drive beyond the limit, unlike what you see so many real drivers do in real (road) cars.
PS: once again, a really informative thread about cars / physics; LFSforum - respect!