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Effect of tyre temperature on tyre grip
2
(41 posts, started )
Look, I just drove around the skidpad with a setup that resulted in the tyres being equally loaded during cornering. I tried using "normal" tyre pressure and generally a pretty normal race setup.

If those g values are attainable in a race is a different question, but I was more interested in showing how temperature affects tyre grip. The "measuring" of grip was very much done by eye, taking the broadest "strip" of usable data and assigning the lowest value to the less optimal temperature while the highest g value got linked to the more optimal temp. I know this is very inaccurate, but it was enough to form a curve, which was and is the most interesting part IMO. It doesn't look like the load affected the grip that much anyway.

If you know how to do it more accurate, then please, nobody is stopping you from doing it
#27 - w126
I'm sorry, what I wrote previously sounded too rude. :ashamed: I know doing such measurements requires lots of work. This method is good to get info about temperature effect, which alone is probably not load dependent.
Hey, no offense taken.

I will do some further tests for other temperature ranges on R3/R4 tyres later, so we can see a combined diagram.
#29 - axus
Grip is different laterally and longitudinally. And it also varies with slip angle (lateral) and slip ratio (longitudinal) and normal load... not to mention camber and temperature and tyre pressure.... so many variables. Here is a look at plot of lateral grip (x-axis) vs longitudinal grip (y-axis) for the front tyres of a FXO on a skidpan. This is from a programme currently in development in its early Alpha stages. The green shows the Right front tyre and the red shows the Left front tyre. Rear tyre plots are also available but they look a little dodgy, so I won't add those.

On the graph 1 block demonstrates a coeficient of friction of 0.33 on both axes (3 blocks = 1) - sorry for the poor number visibility, as I say this is early Alpha stages. It is a JPG so it is a little fuzzy. As you can see these road supers can achieve 1.26g longitudinally and 1.33 laterally. The values within the "circle" are caused by high slip ratio - I did a wheelspin off the line so that I would get accurate data for longitudinal coeficient of friction. IIRC they were heated to about optimal temperature when I was doing these tests.
Attached images
Very nice, from that you can also see that we really have a traction *circle*. I don't know how it IS in reality but many knowlegable people suggest it should be more of an oval, with more grip long longitudinally.
Interesting guys!

I don't have data for it but Grant Reeve (simmer /ex papy staff) owns a .. MR2 I think, and he got noticable higher long. grip (1.3g I think) than lateral grip (1.1 iirc).

Another point to make, can we see how quickly the rubber (i.e. not the inside of the tyre) heats up? If this reacts quickly to wheelspin this means that it might explain that 'once you have wheelspin you can keep it going through the gears' feeling especially with the F08.. If first gear wheelspin heats up the tyres you loose enough grip to continue spinning them in most gears!

I think, but again I'm plagued by not having data, that rubber doesn't peak that much but has a wider 'near optimum' range until it gets really hot probably..
#32 - axus
Tyre pressures would affect that - a low tyre pressure should give you a lot more longitudinal grip. I will do another quick test in a minute and get back to you. (or tomorrow - I'm not quite sure if I'll have time now as I am about to go out)

EDIT: Here it is - lowered pressures and more road-like cambers and the grip is more longitudinal than lateral. (In this picture each block represents 0.4)
Attached images
^ The difference is very small, though. Maybe you need more data? Try driving multiple laps - I know the tyre temperature and pressure will vary but I think there are still too many vague values with short peaks of force

Anyways, I've finished my R2-R3-R4 temperature graph. Trying to get comprehensive values when testing hot tyres is even more annoying because the "grip band" you see gets very broad, also when you slide the tyres it seems that you lose grip pretty abruptly. These values you'll see are all pretty theoretical and you'd have to be the master of smoothness to actually get that much lateral grip with 135°C hot tyres.

Oh well, here it is - the triangles mark the optimum temperature. I was quite surprised how much grip overheated R4's give...
Attached images
Thanks for all the work guys, this is one of the most interesting and useful threads in ages!
#35 - axus
Hmmm.... not too sure about that graph - I shall conduct my own research, however if that graph is correct why do so many people choose to drive on slicks that work above their opperational temperature? It seems the R2 graph crosses the R3 graph at about 90deg which is the optimum temperature for R3 slicks. That would mean that as soon as your tyres actually start warming up to 90deg it makes sense to go to R3's but no-one does that. Same goes for the R3's and R4's.
#36 - axus
EDIT: Double post - sorry.
#37 - axus
Just tested R3's at 70deg and they produced 1.46lateral g at best so the graph looks a bit off...

Sorry - that was actually R3 tyres

Here's the actual data that I got:

R3's:
70 deg - 1.46
85 deg - 1.55

R3's:
70 deg - 1.39
85 deg - 1.48
Yeah, I'd very much appreciate if you try to reproduce my data, because I'm not at all sure if it has any accuracy.

Why people don't chose R3 and R4? Because until R2 reach an average of 90°, they have alot more grip to offer than R3 and R4. Also, at some point they will cool down again, going back into the extremely grippy temperature zones.

^ Just remember, I was using the FZR, that not only has pretty high load on the rears, but also always a little bit of undertray downforce. I had to always drive in the 60-100 km/h range, or else either the downforce would influence the result too much or the low speed issues woud f*ck things up.

But heads up, if you find that my curves show too high G values all over the board, then I'm glad if you tell me how to correct them. The main aim was to get the curves and where they intersect. If you move that up and down on the force scale it's not that tragic
Erm actually, your data - my data:

R3:
70 deg - 1.46 - 1.42
85 deg - 1.55 - 1.49

To help you a bit with the comparison (the bold values are actually measured values, the others are interpolated)
Attached images
#40
Quote from AndroidXP :Why people don't chose R3 and R4? Because until R2 reach an average of 90°, they have alot more grip to offer than R3 and R4. Also, at some point they will cool down again, going back into the extremely grippy temperature zones.

I could also add, that (at least in the small FWD GTRs) it might be beneficial to ease off the throttle a bit and gain in grip a lot (through not overheating the R2's at all or very slightly).
Very interesting read, keep up the good work guys.
Also with R2s slightly over temperature the inside air warms up a bit too which seems to help somewhat as well.

I'd like to re-itterate what AndroidXP said about cooling temps - if you don't get the tyre over-temperature after the first few laps, the tyre will be too cold by the time it's coming around for replacedment. I've used R3s on a race which barely hit 92 at best during the race, by the time I pitted they were down to the 60s and my lap times were not faring too well.
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Effect of tyre temperature on tyre grip
(41 posts, started )

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