Effect of tyre temperature on tyre grip

[Niels Heusinkveld]

Hi all,

I'm trying to find documents on 'rubber grip vs temperature' but all the pdf's that seem like they might contain some info cost $ to buy online.. I think that the road tyres loose too much grip with temperature. Around 90/100c it really has reduced a lot, although its hard to say if this is the 'general tyre model issue' (that Scawen is aware of :)) or the tyres loosing too much grip with temperature.

Does anyone have some data on grip vs temp of tyres?

[AndroidXP]

IMO cold tyres are really awkward to drive on. It's no problem driving with road normals at a temp of well, 30° or so, but driving with slicks at that temperature feels like driving on rims.

Hot tyres feel weird too, but I can see that blistering could cause a severe drop in grip. But even then, tyres shouldn't fully regain their performance once blistering occured.

[Gentlefoot]

Yep - my experience is that road compounds operate in a much wider temperature range than slick compounds which offer virtually no grip when cold.

Road tyres do not loose too much grip when they get overheated, instead they just wear away incredibly quickly.

I agree this isn't modelled perfectly in LFS. I believe the slicks when cold should have less grip than at presesnt. Also that when road tyres go above 105 degrees they should wear out much faster than they do but also offer more grip than at present at 20 degrees over ideal temperature.

[AndroidXP]

:confused:
Driving on rims = no grip.

You say slicks should have even LESS grip when cold?

[Gentlefoot]

Yep - in LFS they seem to have proportionately the same amount less grip when cold compared to hot as road tyres do. This is wrong.

Ofcourse the well documented low speed grip problems in LFS would be made even worse if this was changed.

[Bob Smith]

OK, try taking out, say, the FOX, do some racing to get both tyres up to temperature, then burn out the rears and pit for fresh rear tyres. Now attack the lap as before and see how the back end behaves.

Edit: I see your point is more about grip less when cold versus grip loss when hot... well that I don't know about but they seem to loose plenty. Perhaps they loose too much when hot instead of not enough when cold?

[Gentlefoot]

Perhaps they loose too much when hot instead of not enough when cold?

Thats what I mean. Slicks are too grippy when cold and road tyres lose too much when hot.

[AndroidXP]

Okay, I just made a quick 'n dirty test, driving around on the Autocross field with the FZR on R2 tyres. I made four replays, putting out RAF data and then analyzing it via the RAF Tyre Extractor, taking guesses at reasonable looking values.

Replay 1: 45-55°C tyre temp
Replay 2: 60-70°C
Replay 3: 80-95°C
Replay 4: 120-140°C

I basically looked at the lateral grip vs. slip angle graph, roughly making out lowest and highes cornering forces. Then I assigned the lower value to the worse temp and the higher to the more optimal temp. Finally I hacked everything together to an Excel diagram. Here's the result:

[Niels Heusinkveld]

great work! :) How much work is it to do this for a street tyre car as well? :O Its cool what you can get out of RAF files it seems..

top stuff!
/N

[AndroidXP]

I'll do one for street tyres when I come home. Which car should I take? FZ50 for consistency? Basically any RWD car is fine.

Just remember that this is all done by hand, so the accuracy might be somewhat questionable, but I think it doesn't look too far off of what we experience in LFS.

[Gentlefoot]

Great work my man! Looking fowrward to seeing a curve for a road tyre on the same graph as the slick! If it reflects real life accurately it should be a flatter curve.

[B2B@300]

:munching_Waits in anticipation :D

Hey I can use that smiley for once as I really am sitting at the PC eating noodles-in-a-box on my lunch break with nothing better to do :razz:

[Becky Rose]

You say slicks should have even LESS grip when cold?
I remember doing a race a few years ago now where I was stationary in the pits because of a delay refuelling. On the way in to the pits I had been setting times closest to the fastest lap, on exiting the pits at the 1st corner it felt like I was driving on ice - I turned the wheel and nothing happened.

Slick tyres do not work very well when they are cold, when you're doing an endurance race and the sun has long since set and you do a long pitstop - they're no longer tyres at all... They're just suspension bump stops.

In the race I mention I found myself doing 2 F1-style warm up laps after leaving the pits, jittering from side to side whereever possible to try and regain the heat as quickly as possible. It was that bad.

The difference with road tyres is a matter of relativity. The surface contact area of a road tyre is much smaller than a slick because the rain grooves do not make contact with the ground, therefor the gain in grip of a slick tyre at operating temperature is much larger because it has more surface area - even if the compounds used are the same as a road tyre.

A slick tyre doesn't have less grip than a road tyre when it's cold ... (except that the pressures you tend to run a slick tyre in comparison to a road tyre mean that in practice they do when compared to a road car). What a slick tyre has over a road tyre is that when it is hot, it has more grip than a bucket full of araldite.

[AndroidXP]

Okay, this time it was FZ50 on ROAD SUPER tyres, following the same procedure as yesterday. I wish I had more data to work with, because here the result was very vague again, but it looks somewhat similar to the slick curve.

Finding the correct values from the RAF Tyre Extractor graph isn't too easy either, and there's very much interpretion from my side influencing this, so don't cry when Scawen comes in and says that this is complete BS :D

[mrbogeyman]

I had a thought about the grip levels in LFS, e.g. when people say it feels like driving on ice.

I know the heating patterns and other aspects of the tyres in LFS are incomplete, but I am talking specifically about basic grip levels here (even although they are all related :schwitz:)

BUT, it is a big BUT, what if the grip levels are also do to with the track surface in LFS? I assume that Scawen assigns a friction value to the track/surface so that there is a difference between grass/tarmac/gravel, so what if the level of grip on the track is just too low?

I know this can probably be answered or negated pretty quickly, but of course it is one of the factors involved in the grip levels. Anyway, it was just a thought :D :shrug::scratchch

[AndroidXP]

Erm? That's all relative. There's not really a difference between "the tyres don't have enough grip" and "the tarmac doesn't have enough grip". Besides that, the road supers were pulling 1.27g at a slip angle of 10°, much more than normal street tyres would archieve. I doubt the tyres have too much/not enough grip, it's rather the way how grip is lost and regained.

In the end, we can only wait for the patch and see what Scawen has to say about the improvements. Then we know for sure.

[Niels Heusinkveld]

Thanks for those.. Even though they have to be taken with a grain of salt, you seem to know what you are doing so I'm sure they're 'close enough to say something about' ..

Thats one big drop! I don't *know* but I think this isn't so bad in reality, but I could be wrong.. 0.2G drop sure feels like a lot in LFS: some fun powersliding in a FZ50 only lasts 1 lap or less before I spin with overheated rears :) But if this does turn out to be real, I'll shut up of course ;)

So we have the 'game data', now the even harder part, real data.. :o

[AndroidXP]

I think overheated tyres lose grip almost linear, maybe the curve flattens far more down. It does look a bit simplified and I have no idea how real tyres work regarding temperatures.

Ever tried making a burnout to heat all 4 wheels to 198°C? You ain't going nowhere with those tyres.

IIRC, they should be quite ok even when overheated (a bit) but as soon as blisters build up your day is ruined. If you heat them up more at that point, they will start to dissipate - letting them cool down instead will form hard spots where the blisters were, reducing the flexibility and with that the grip.

[bobvanvliet]

Those are some nice graphs, AndroidXP! :thumb:

Seems like the right thread to ask a question I've been having lately: Does an R3 tyre at 90 degrees have more grip than an R2 at 90? 90 is 'optimum' for the R3, but is that grip actually more than that of an an R2 at 10 degrees above optimum?

(same q for R3-R4 of course)

[tristancliffe]

Or in other words - when does a harder tyre offer more grip than an overheated softer tyre? Should I change my 100 degree R2's for R3's that might run at 85 or 90?

When racing I can never decide whether or not it would be worth going for a cooler running harder compound, wear rates (do they change with temp too?) not withstanding.

Good question Bob, and I look forward to clever people (with time on their hands :p) to answer it.

[Bob Smith]

From testing I've done in the past I know each compound (going from R1 to R2 to R3 to R4) loses approx. 0.1g in cornering ability. The optimum temperature goes up 10 degrees in each case. Looking at that graph, the tyres are losing about 0.1g cornering for every 10 degrees.

So my initial conclusion would be that switching tyres and ending up with the same temperature wouldn't affect grip at all, only the rate at which they wear. However, to switch tyre compound and end up with the same temperatures would usually require changing tyre pressures, which of course affects grip...

[bobvanvliet]

Good question Bob, and I look forward to clever people (with time on their hands :p) to answer it.

Well, it seems to me AndroidXP is the man for the job. Having one of those pretty graphs (which probably take the poor chap ages to put together...) for each compound would quickly show the break-even-point.

And on the case of wear: Harder compounds wear slower anyway, don't they? So a harder compound at a temp closer to optimum seems like a double advantage in that area... :shrug:

[Gentlefoot]

A slick tyre doesn't have less grip than a road tyre when it's cold ... (except that the pressures you tend to run a slick tyre in comparison to a road tyre mean that in practice they do when compared to a road car). What a slick tyre has over a road tyre is that when it is hot, it has more grip than a bucket full of araldite.

Road tyre compounds are designed to operate in a wider temperature ranges than a slick tyre. The reason for this is that when my mum drives to the supermarket, and a kid runs out in front of her 50 metres down the road, she needs to be able to stop. She doesn't do burnouts in the driveway to get heat into her tyres. Well, not recently anyway. :)

So road tyre compounds are a compromise, just like road suspension. The compound works at low temperatures, but to get it to do this, without being ridiculously soft, the compound is changed and this results in less ultimate grip compared with a compound that worked in a very narrow temp range.

[AndroidXP]

:bump:

Soo, I didn't make full plottings of R3/R4 tyres but I measured their max grip at optimum temperatures


R3 @ 91°C: 1.50g
@ 99°C: 1.43g

R4 @ 99°C: 1.46g
@ 106°C: 1.40g


R2 @ 80°C: 1.58g
@ 90°C: 1.49g
@ 100°C: 1.40g

From this we can see that R2 at 90°C can compete with R3 at its optimum temperature, but at 100° it loses both to R3 and R4.

[w126]

Do you measure maximum grip for the same value of normal load in every case? I ask because grip is load dependent (load sensitivity http://www.lfsforum.net/attachment.php?attachmentid=4791&d=1136410311) (http://www.lfsforum.net/attachment.php?attachmentid=4791&d=1136410311%29). If you do not use the same normal load in every case than you may get additional inaccuracy because of that. OTOH if you use the same normal load, then it must be rather small value (judging by maximum grip for road super tyres). I think it might have been better to use larger load, for example the normal load of outside tyre in a typical corner, because then you get grip values closer to effective grip of the whole car (outside tyres do most of the work when cornering). For example someone might expect to corner at 1.27 g on road super tyres, but in fact no more than 1.2 g might be possible.

[AndroidXP]

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 :thumb:

[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.

[AndroidXP]

Hey, no offense taken. :shy:

I will do some further tests for other temperature ranges on R3/R4 tyres later, so we can see a combined diagram.

[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. :thumb:

[AndroidXP]

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.

[Niels Heusinkveld]

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..

[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)

[AndroidXP]

^ 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...

[bobvanvliet]

Thanks for all the work guys, this is one of the most interesting and useful threads in ages! :thumb:

[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. :shrug:

[axus]

EDIT: Double post - sorry.

[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

Your data:

R3's:
70 deg - 1.39
85 deg - 1.48

[AndroidXP]

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. :shrug:

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 ;)

[AndroidXP]

Erm actually, your data - my data:

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

;):thumbsup:

To help you a bit with the comparison (the bold values are actually measured values, the others are interpolated)

[maczo]

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. :thumb:

[Bob Smith]

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.