Tyres - What influences 'grip' the most?

[greenamex2]

I know this is possibly an old recurring theme but what factors influences tyre grip the most?

I am talking about the tyre itself and NOT the suspensions exploitation of it.

My guess would be -

1. Tread compound
2. Tread pattern
3. Number of heat cycles
4. Carcass construction
5. Profile
6. Width (because of the age old "wider tyres change the shape of the contact patch, not the area" argument)
7. Outside diameter

[Al Weyman]

I would put width a few places higher.

[dtype38]

Grip has a lot has to do with the running temperature, and that depends on how hard the tyre is being worked, so car weight and power, and ambient conditions have to figure in there somewhere. And what about tyre pressure?

[greenamex2]

I was thinking more about the sort of things you should look when choosing between X and Y manufacturers tyres, or even A and B of the SAME manufacturers tyres, not so much the subsequent exploitation. But yes I agreed that temperatures and pressures can be what makes the difference between winning and not winning.

Al, or ANYONE, have you ever run an identicial brand and model of tyre of identicial 'age' but different widths against each other and scientifically measured the difference (eg lap times, skid pan times etc)? The width arguement has always intrigued me and I would love a practically tested answer.

[Al Weyman]

No but Gerry has and he reckons width is king.

[Lukin]

Originally Posted by Al Weyman

No but Gerry has and he reckons width is king.

So does my ex-missus.

[Al Weyman]

[Cameron Winton]

I am not sure profile & outside diameter have much effect on grip. Profile may affect sidewall stiffness (But that's getting into construction) which may only affect "feel."
I thought that larger diameter wheels & tyres was the result of pushing for bigger brakes and had little to do with grip. Al may have something to say about this as I have noticed him complaining about the small wheels & tyres he has to run on his yellow car.

[greenamex2]

Cameron, I think Al is just looking for an excuse not to get beaten in Mod Prods when he is complaining about wheel sizes ;-)

Al, I have noticed that the big cars in our series don't tend to 'damage' their tyres as much as us tiddlers. I always put this down to a wider tyre running cooler than a narrow one. Could that be where he believes the advantage is?

[dtype38]

Originally Posted by Denis Bassom

I was thinking more about the sort of things you should look when choosing between X and Y manufacturers tyres, or even A and B of the SAME manufacturers tyres, not so much the subsequent exploitation.

I put that in because I run on 225/60s and a chap I've raced against uses identical tyres but in 205/60s. He swears that I'm over-tyred for my car, but I don't think I am. I think the difference is that his car is about 100kg (10-12%) lighter than mine. I've also found that swapping a set of worn tyres for new ones makes an enormous improvement in grip on my car, so tread depth and heat cycles are quite important.

[HiRich]

Dennis,
It's not my field, so I may not be exactly correct on this, but my understanding is that (almost) everything comes down the the nature of the rubber. A particular rubber compound gets 'softer' (and therefore 'stickier') as it gets hotter. But at a certain temperature the rubber itself starts to break apart. What you are looking for, therefore, is to run as soft a rubber as you can get away with. Factors that influence this are:
- Surface pressure: If each square centimetre carries less load, you can use a softer, less durable rubber. Fitting wider or larger diameter tyres would achieve this (as in all cases here, assuming ideal, lab, like-for-like conditions). However, just fitting wider tyres will not give you more grip automatically - the benefit is in the ability to run a softer compound. Then you gain grip.
- Heat Cycles: Fresh rubber is partially cured (especially soft rubber). Each heat cycle increases the curing, and this creates a 'harder' compound. More significant with soft race tyres designed to last just a few miles, than more cured road tyres designed for many thousands.
- Carcass construction: In the tread, sidewall and shoulder, this is still about maintaining as much of the tread area at the optimum pressure (load/square centimetre, not air pressure) as possible. Some will be under-loaded, and therefore does not run in its optimum 'stickiness'. Some will be overloaded. You need to optimise this. This is also why instantaneous camber is so important (and tied to the construction of tyre you use), and why you might adjust camber for different circuits. Similarly, lower profile tyres potentially show a benefit by by reducing distortion, but only if you tune the suspension to suit. If the suspension has been tuned (with lots of camber change) to accommodate the profile distortion of a high profile tyre (e.g. historic), an ultra-low profile tyremight just stand up on its inner shoulder the moment you turn = tiny contact patch = rapid overheating = sliding plus a destroyed tyre.
- Hysterisis: Stretch and release a piece of rubber, and not all of the energy is released. It is retained as heat. Bend an eraser repeatedly, and it warms up. A tread block is repeatedly being stressed and released - heat builds up inside the block. You can use that to heat up the tyre, but the risk is that you overheat the rubber (losing grip). A tall (new) block can move a lot, and generates more heat as a result. Shave new tyres and you have squatter blocks = less sub-surface heat build-up = less risk of overheating. Wider blocks (e.g. Avon ACB) are stiffer in lateral movement, and therefore there is less heat build-up from hysterisis (assuming the same rubber compound). A slick is one huge block. You can therefore use a much softer compound.

So you can see that all of the tyre characteristics (and indeed suspension characteristics) seem to revolve around making as much of the contact patch work within its ideal temperature range (and this in turn also relates to the the circuit/road surface characteristics).
You can also see that you can bully a tyre (with aggressive driving or setup) to heat up quicker, which can be used to get more out of it quickly, but potentially at detriment to its race-life - think Webber in a Jaguar, or Bridgestone's 2005 F1 problems after a safety car period.
In a simialr vein, I remember hearing a story about F1 qualifying tyres from a few years back (possibly Goodyear). Drivers were having real trouble getting them up to temperature on the out lap, and having bullied them they would not last the lap. Eventually it came out that Goodyear used a mould releasing agent. The low friction surface prevented drivers from building up surface temperature, but their bullying built up sub-surface heat. They struggled to wear off the surface in time, and in bullying the tyre to achieve this, the exposed surface was too hot. Shaving off the contaminated surface solved the problem immediately. Then everyone found out that Senna had been doing this for the past six months...

So this is what I've picked up over the years. I think it is correct, but would welcome better-qualified opinion.

[youngoldy]

Well, in the dry, its surface area and compound, pressures, temperature, and in the wet, the same as before will its tread pattern

[HiRich]

Originally Posted by Denis Bassom

Al, I have noticed that the big cars in our series don't tend to 'damage' their tyres as much as us tiddlers. I always put this down to a wider tyre running cooler than a narrow one. Could that be where he believes the advantage is?

Following my theory, and assuming both tyres run the same compound:
- You are probably right that the wider tyres are running cooler (more specifically, slap bang in the ideal temperature range), whilst yours are overloaded, and running too hot.
- Adding an inch to your 'tiddlers' (and tuning setup to suit) might pull your temps into the ideal range. But adding two inches might bring them down too much, and you could be even slower (though the tyres would probably last forever)
- You would probably find that the gap in performance and durability differs between circuits. You are overworking your tyres (it would seem) so a long hard corner like Cadwell Charlies would muller your left tyres. Conversely, Silverstone (all flavours) doesn't really have such long corners, has a lot of left-right work and straights, which all allow the unloaded tyre to recover.

[phoenix]

From what I understand there are three factors and it is hard to put them in order because they are inter-dependent.

The factors are: compound, contact patch and load.

Both a larger width and larger diameter can increase the contact patch (if the geometry permits it) and the load a tyre can take. A larger contact patch means you can run a softer compound for the same load because the load per square inch or mm of the contact patch is reduced.

The grip a tyre gives increases with load in a non linear way, up to a point, and then it decreases with extra load but again in a non linear way. Trying to get this information from tyre manufacturers is, in my experience, impossible; perhaps theyu don't know the answer. But in one example I was able to find the tyre grip increased slowly and then more rapidly as tyre load climbed to araound 1000 Kg and then began to decline, slowly at first and then more rapidly as more load was added.

So the weight and cornering speed of the car has to be important, though I think that being over-tyred is unlikely to be a real problem, as restricting tyre width is generally a thing the rule makes do, not designers!

However, if you can't get the tyres up to temperature and there is no softer compound available it must be a sign that you have too much rubber, I would have thought. Conversely, if the tyres run too hot and you are on the hardest compound then it would suggest to me that a larger contact patch is called for. However there are other causes of tyres running too hot - too much or too little camber control for one, wheelspin for another - so elimination of any such problems from your enquiries should be the priority.

[Goran Malmberg]

This is a quite complex question. I should recomend the book of Paul Haney on the subject. This book also tell that tire dynamics is sort of "secret" stuff, and that not even the drivers can speak freely.

I hope that HiRich should not get angry at me for bringing up a few corrections.
Surface pressure. I have been discussing this issue with both Haney and M Ortiz, and also been making a number of experimenting myself.
There is also a scool that tells that the tire pressure sould balance the footprint area, so that wider tires should not end up with bigger footprints.
there are a number of commets to all those mentioned statements.

I campared two size Avon slicks for foot prints with the same size diameter but different widths, and the area to width theory did not showed to be true. After speaking with some tire manufacturer, (even Avon), they agree to this but where not willing to discuss the matter to deepley. Construction and sidwall stiffness is a factor. But in general, wider tires do give moore foot print area. As µ is a result from load per area, this in itself should give a wider tire better grip in about the same range as a load change from using another rollbar, its the same pfenomenon.
The wide tire also show another foot print pattern, beeing moore of an oval shape, shorter and wider. This give another slipfunction that favour cornering. Needs some drawing to show.

Wider tires have greater cooling area and may run softer rubber for the same condition.

Hysteresis.
This is very good explained in the Haney book. The grip become better with a slow recover rubber since it only create force against the "loaded side" of pavemant obstructions.

Its hard to separate the friction capacity strictley from other factors in the suspension system, but I get the point from the questioner.
Performing test to see what happens is a VERY complicateded task.

I better stop here I guess. However, ther are a few examples on my site with footprints. http://hem.passagen.se/hemipanter/
Klick "Wheels and tires."
Goran Malmberg

[greenamex2]

That's what I like about you Goran, you always do the stuff that I can't be bothered too!

Keep em coming guys!

[graham bahr]

as has been said its difficult to seperate the tyre grip itself from the suspension, not to mention the fact that the amount of power your putting through the driven wheels has a huge influence

[COLIN STUBBS]

iv thought about this at great length denis and have to say that the thing that influences grip as far as im concerned is how hard you wang it into a corner.lydden/no lsd/unbuffed toyos/no suspension/oh my god.

[ubrben]

Originally Posted by Denis Bassom

I know this is possibly an old recurring theme but what factors influences tyre grip the most?

I am talking about the tyre itself and NOT the suspensions exploitation of it.

My guess would be -

1. Tread compound
2. Tread pattern
3. Number of heat cycles
4. Carcass construction
5. Profile
6. Width (because of the age old "wider tyres change the shape of the contact patch, not the area" argument)
7. Outside diameter

I would say you're about right, but I'd probably combine the last four things, because they all have a reasonably equal effect on contact patch size and shape.

Wider is better provided you don't end up with too much slip angle drag and you can get the comnpound up to its working temp.

Ben

P.S. Lukin that was the funniest one line post I've seen in a long time

[Al Weyman]

Wider tires have greater cooling area and may run softer rubber for the same condition.

This is the reason I am complaining about the 225 x 55 x 15 Formula R's I have to run on my heaby car, they are TOOO soft in my opinion for the weight of the thing. They have overheated and chunked up and I have had to reverse fit them to try to get a few more races out of them as I cannot afford £650 in tyres every meeting! I personally think the car went better on Falken road tyres albiet both bigger diameter and width. I have spoke with a few drivers including Camaro and SDI owners and they have gone up from 16 inch to wider 17 inch and even 18 inch wheels (Gerry) and everyone of them have said this single modification has made more differnce than anything else. This is one of the reasons I have not entered the black car back in ModProds as Toyos do not do a 275 x 50 x 16 tyre that I was running so it means thousands to spend on two sets of wheels and has put me off a bit.

[graham bahr]

Originally Posted by Al Weyman

This is the reason I am complaining about the 225 x 55 x 15 Formula R's I have to run on my heaby car, they are TOOO soft in my opinion for the weight of the thing. .

too soft yes i'll go along with that, when i used to hill climb my car the soft soft hillclimb slicks which were actually intended for cars a bit lighter than mine,used to wear out real fast, i was lucky if i could get a season out of a set, which was only around 50-75 competitve miles, when i went circuit racing i found harder compounds gave slightly more grip and would also last about a season, which was now 10 times as far in competive milage.

this year i bought some avons, as recomended by one of the major motorsport tyre retailers, apparently they would of been spot on for the weight etc of my car, when i got them i had my doubts as they were quite a bit softer than i had been running, short races they were ok, and gripped about the same, the longer races which are still only 15-20 mins they would go off big time, without giving extra grip early on.

basically i think what happened is the tyre supplier concentrated on the weight of car and wheel sizes, and didn't sufficently take the power into account, which ment massive braking at the end of the straights as i was carrying around 30mph more speed on the straight than the origonal intended application for the tyres, and just overworked them,

be it extra speed or weight its all extra load on the tyre and if teh compound is too soft it just rolls of the tyre surface like a pencil eraser rather than gripping the track properly.

[greenamex2]

Al, when people have gone to bigger diameter wheels have they also increased width and/or outside diameter and/or reduced tyre profile?

I have a similar dilema with my kit car at the moment. I am leaning towards using current 'standard' size tyres just to future proof the expenditure on new wheels.

[graham bahr]

rim width can have an effect also, i took my 195 slicks off 7x15 inch rims and put them on 8x15 inch and had more grip and far better turn in

[retro_msport]

Originally Posted by graham bahr

rim width can have an effect also, i took my 195 slicks off 7x15 inch rims and put them on 8x15 inch and had more grip and far better turn in

Ive always gone by the rule ....... the tyre should never be wider than the rim. Better turn in as the tyre isnt tucking under and rubbing the letters of the sidewalls

10" wheel width = 9-9.5" tyre

Also a tyre temp probe can tell a lot... not only suspension wise but if the tyre is staying in its recomended temp range.

I set a sprint car up with the temp probe, the driver went out and did a run and came back complaining the car was undriveable, very loose, horrible etc and asking what i had done to make it so bad, untill his brother came back with the time, 3 seconds better than his best time ever.
Next event he had returned his car to his "cast in stone" settings and the time gain was gone... but the car is nice to drive
As for me wanting to tweek his rear axle to give some camber and toe in....
"you want to bend my axle... are you mad"

One other thing to consider is driving style, a smooth driver will make his tyres last, so can run softer, a driver who is hard everywhere will make mincemeat out of the same tyres on the same car.

I think with tyres you have to put all the aspects that change the performane on the outside of the circle and try and get the performance center in the center, if you get me , you add a bit here and it takes a bit away from over there.

[graham bahr]

Originally Posted by retro_msport

Ive always gone by the rule ....... the tyre should never be wider than the rim. Better turn in as the tyre isnt tucking under and rubbing the letters of the sidewalls

.

i couldn't agree more,

infact 'd almost go one step further, as in my example the 7 inch rims were already plenty wide enough for a 195 tyre, but still it was better on an even wider rim, many would agrue the 8 inch rim too wide but it worked