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Effect of tyre temperature on tyre grip
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(41 posts, started )
Effect of tyre temperature on tyre grip
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?
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.
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.

Driving on rims = no grip.

You say slicks should have even LESS grip when cold?
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.
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?
Quote from Bob Smith :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.
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:
Attached images
graph_noline.jpg
graph_line.jpg
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
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.
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.
:munching_Waits in anticipation

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
Quote :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.
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
Attached images
graph_noline_super.jpg
graph_line_super.jpg
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
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.
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
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.
Those are some nice graphs, AndroidXP!

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)
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 ) to answer it.
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...
Quote from tristancliffe :Good question Bob, and I look forward to clever people (with time on their hands ) 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...
Quote from Becky Rose :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.
:bump:

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


R3 @ [COLOR="Green"]91°C[/COLOR]: 1.50g
@ [COLOR="Olive"]99°C[/COLOR]: 1.43g

R4 @ [COLOR="Green"]99°C[/COLOR]: 1.46g
@ [COLOR="Olive"]106°C[/COLOR]: 1.40g


R2 @ [COLOR="Green"]80°C[/COLOR]: 1.58g
@ [COLOR="DarkOrange"]90°C[/COLOR]: 1.49g
@ [COLOR="Red"]100°C[/COLOR]: 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.
#25 - 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/attach ... id=4791&d=1136410311). 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.
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Effect of tyre temperature on tyre grip
(41 posts, started )
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