F3 tires vs F Renault tires

[jedrinck]

I need to replace the tires on my 8V F Renault which I use only for trackdays, so rules are not a problem. I could get Kumho F 3 tires at roughly the same cost as Michelin F Renault tires. The F 3 tires are a little wider and I hope to be faster with them. The fronts have 20mm more diameter but that can easily be adjusted for with the pushrods. Is there any data about the coefficient of friction of these tires accessible to help evaluate if it is worth trying them? Or, has anybody tried exactly that and is willing to talk about it?

[AU N EGL]

Michelin tires have far great grip then Kumhos. Cost more too.

[jedrinck]

Are you talking about these specific racing tires or just about the general reputation of the brands? As you may know, Michelin provides spec tires for the F Renault euroseries and Kumho for the F3 euroseries.
These 13" slicks for light single seaters have absolutely nothing to do with the range of road legal tires made by these companies so no conclusions can be drawn about how well they work just buy saying that Michelin generally makes better tires.

[AU N EGL]

Originally Posted by jedrinck

Are you talking about these specific racing tires or just about the general reputation of the brands? As you may know, Michelin provides spec tires for the F Renault euroseries and Kumho for the F3 euroseries.
These 13" slicks for light single seaters have absolutely nothing to do with the range of road legal tires made by these companies so no conclusions can be drawn about how well they work just buy saying that Michelin generally makes better tires.

Their respective race tires. If you have a spec tire then you use that.

When competitors have a choice, Kumhos are chosen more for cost benefit then for speed. Michelin are chosen for speed, up to 2 sec a lap faster, but are much more expesive.

If the price is close, go with the Michelin.

[tristancliffe]

It's hard to say as the F3 cars have probably never run of the spec/compound/size of FRenault tyre and vice versa.

Be aware that a taller sidewall will stiff affect suspension geometry. You can get the ride height back again, but the outboard ends of the wishbones will be higher off the ground. That could benefit, but it's more likely to make things worse (what things are a different matter though!).

I'd say stick with the Michelin spec rubber. At least then you can vaguely compare yourself with official FRenault laptimes

[jedrinck]

Thanks for the comments so far. Tristan, judging from your avatar you use F3 tires, are they kumhos and if yes, how many track miles do you use them for? Also, how many heat cycles can they handle before they get significantly worse, because that is really something where the Michelins shine. The 10mm ride height change necessary is the range people use to adjust for bumpier tracks, there are obviously geometry changes but I guess I won't notice them. Some classes require to run these cars at 40mm ride height and I read that costs one or two seconds a lap, most of that being attributed to the higher cg while I will have the same cg as before. So maybe MS would notice, but DC wouldn't..

[tristancliffe]

I use Avon tyres with A24 compound. They lasted all season (albeit about a second slower at the end), and my season mileage was around the 700 miles mark.

Next year I'm planning on using softer A53 tyres, and having two sets for the year. Not thought about Michelins or Kuhmos. I have no idea of the cost, sizes, compounds etc of them. I know Michelins are considered unforgiving by a rival of mine.

I don't believe in heat cycles. The only data available on them shows the effect to be miniscule, and is provided by teams that throw tyres away after one or two runs on them. Sure, rubber hardens with age, so a brand new tyre is quicker than an older one, but I don't believe using them makes that much difference until they wear out. But that's a personal feeling. I'm some still believe the unsubstantiated myths about heat cycles.

[jedrinck]

I haven't experienced the adverse effects of repeated heat cycles either, the FRenault club racers say the current Michelin spec tire is very durable while the one from a couple of years ago would deteriorate quickly.
One can get the Michelins or the Kumhos for about 40 Euros a piece used with about 90% of rubber left, so it would be a rather cheap experiment. I don't know about unforgiving, my 97 tatuus with the Michelin tires is an easy car to drive fast. Sizes for the Michelin FR spec tires are 16/53/13 and 23/57/13. Sizes for the F3 spec tires are 180/550/13 and 240/570/13. The front Kumhos are 10mm wider and the rear ones 20mm wider than the Michelins.

[THR]

heat cycles matter!! big time
Id stick to FRen tyres tho, y change... the Fr tyres easy to come by and cheap enough really, and do seem to last pretty well.
the F3 tyres must be more expensive or the same, so y bother changing!
I know they are very different in handling! as you would expect really.

[tristancliffe]

How did you measure the effect of heat cycles, and how did you separate those results from the effects of general wear and UV light deterioration? The professional teams can't (and don't), so I'm curious as to how you worked that out.

Tyres age and get slower, but there is no evidence that the number of heat cycles has any effect. E.g. do two test days on the same tyre of tyre. On one day do 50 two lap sprints and allow to cool to ambient between each run (i.e. 50 heat cycles). On the next day do 2 runs of 50 laps. Ignoring the effects of getting better at a circuit or car, fuel loads and all that and you'll probably find there is not much difference in lap times.

[THR]

ok i cant prove it :P
but it makes sense that every time you get the tyre hot and they turn to blu tac rather than rubber that the composition changes due to heat.

[tristancliffe]

It only makes sense because the myth is popular. It's equally plausible that the rubber turns to blu-tac and then simply sets again, with whatever changes to the composition being negligable when it next turns to blu-tac.

[JamesH]

On a related subject, is tyre softening of any help here to increase performance at lower cost?

[ubrben]

Originally Posted by JamesH

On a related subject, is tyre softening of any help here to increase performance at lower cost?

I've only ever seen marginal benefit in improving heat cycled tyres. I know for a fact that Michelin treated MotoGP tyres to improve the initial grip of hard tyres. I don't know what they used though.

Heat cycling has a measurable effect. In the case I'm aware of the cross link density of a used tyre was higher than that of a new tyre.

I would suggest that if you can't quantify this effect it will have more to do with your test procedures/repeatability than heat cycles not being a reality.

Ben

[tristancliffe]

If heat cycling is as much of a deal as most in paddocks would have you believe then procedures and repeatability don't matter, as they are dwarfed by the whole seconds per lap tyres apparently lose after three or four heat cycles.

If it does occur to any meaningful level then it's probably so tiny that I doubt most drivers bar the very best will be able to feel it.

[ubrben]

Originally Posted by tristancliffe

If heat cycling is as much of a deal as most in paddocks would have you believe then procedures and repeatability don't matter, as they are dwarfed by the whole seconds per lap tyres apparently lose after three or four heat cycles.

If it does occur to any meaningful level then it's probably so tiny that I doubt most drivers bar the very best will be able to feel it.

Just because heat cycling happens doesn't automatically mean it swamps everything else. Just because it's not a massive effect doesn't mean it isn't happening.

How often do you run new tyres BTW?

Ben

[tristancliffe]

Once a year.

Does anyone have any quantifiable data on heat cycling, or will it be one of those things that people believe happens yet have never ever seen any proof whatsoever? No professional teams with the budgets to measure it have ever found it other than the first heat cycle altering the tyre (e.g. scrubbing tyres for a race or using fresh ones as a one-hit wonder qually tyre; these I do not question).

But once the tyre is bedded in after it's first heat cycle I do not believe that 99.99999% of drivers or teams will ever feel the difference due to heat cycling. Wear, changes to tyre profile via wear, damage, UV light degradation, humidity degradation etc. all play their part, but there is no actual evidence of further, noticeable heat cycle degradation.

[ubrben]

Originally Posted by tristancliffe

Once a year.

Does anyone have any quantifiable data on heat cycling, or will it be one of those things that people believe happens yet have never ever seen any proof whatsoever? No professional teams with the budgets to measure it have ever found it other than the first heat cycle altering the tyre (e.g. scrubbing tyres for a race or using fresh ones as a one-hit wonder qually tyre; these I do not question).

But once the tyre is bedded in after it's first heat cycle I do not believe that 99.99999% of drivers or teams will ever feel the difference due to heat cycling. Wear, changes to tyre profile via wear, damage, UV light degradation, humidity degradation etc. all play their part, but there is no actual evidence of further, noticeable heat cycle degradation.

And where's the evidence for all of the other things you mentioned.

I design race car tyres BTW...

Ben

[tristancliffe]

Most teams, ourselves (a team?) included have lap times demonstrating a reduction in outright performance from the first run on a new tyre to the second. But I have not had lap times (or other data) showing a general degradation of tyre over many heat cycles, not that it's fair to compare lap times 7 months apart with changes to the car and the setup (and driver experience). I suppose it would be better to have shore values of the compound - something I'm keen to try and take this year if I can.

Wear - unlikely to be a direct influence unless you are sensitive enough to feel the difference in corner weights and ride heights.
Changes to the profile (i.e. negative camber wearing the inside edge first) will change the shape and load distribution of the contact patch, and would therefore have an effect.
UV light - breaks down the molecule chains causing an increase in hardness with exposure.
Humidity - that was a guess!

I'd love to see what you base the effect of heat cycling on. Any actual evidence/data?

[R59]

I don't have any quantifiable data (because I have never written it down!)
The 18" Dunlop's that I run on my Thundersaloon are the same as they supply to GT teams, and that used to be used in British GT.

After three heat cycles, ie: three uses, they go off big time. 3 seconds a lap around Oulton Park.

Now those three heat cycles could be quite short, or quite long.

Bearing in mind, those tyres would survive 4 hours solid hard racing if need be, and be consistent over that period.

Take them out for a qually, a race, and another qually, and in the next race you'll be going backwards!

Ric Wood found that too with his Holden and his Calibra.

Now, moving on to Avon's. I did most of a season in ASCAR on one set of Avon's, and time wise, they were as quick when they were nearly through to the canvas as they were when they were new - doing low 37's new, and low 37's when knackered around Rockingham.

If anything, the Dunlops were great when brand new, the Avon's went through a "greasy squirmy" phase until they'd done about four or five laps.

The Avon's were also "abused", and often lived outside in all weathers.

[jedrinck]

I had not looked at this thread for a while and when I saw 20 replies I figured there might be an answer to my question...still, it is an interesting read.
R59, I fly air ambulance too occasionally, Beech 350 for the german automobile club (ADAC). I still find the F3 tires appealing, might give it a try.

[ubrben]

Originally Posted by tristancliffe

Most teams, ourselves (a team?) included have lap times demonstrating a reduction in outright performance from the first run on a new tyre to the second. But I have not had lap times (or other data) showing a general degradation of tyre over many heat cycles, not that it's fair to compare lap times 7 months apart with changes to the car and the setup (and driver experience). I suppose it would be better to have shore values of the compound - something I'm keen to try and take this year if I can.

Wear - unlikely to be a direct influence unless you are sensitive enough to feel the difference in corner weights and ride heights.
Changes to the profile (i.e. negative camber wearing the inside edge first) will change the shape and load distribution of the contact patch, and would therefore have an effect.
UV light - breaks down the molecule chains causing an increase in hardness with exposure.
Humidity - that was a guess!

I'd love to see what you base the effect of heat cycling on. Any actual evidence/data?

You've read somewhere that UV light breaks down molecular chains - I doubt you've measured it yourself, but you believe it? Cross link density increases in heat cycled tyres. Measuring hardness values would be a good idea as you've suggested.

Now we could argue till the cows come home about what percentage of each effect is occuring, but heat cycling does cure the rubber, and it is measurable.

Ben