The science behind tyre width for trackdays - who can help?
Discussion
Evening all,
I've tried quite a few different tyre sizes on my DC2 track car, but I'm not sure how to work out exactly what size should be best.
The standard car came with 195/55/15 tyres on the earlier models and 215/45/16 tyres on the later model (same chassis). On trackdays, I've myself ran various different widths from 195-225. I know most people run a 15" wheel with 195/50/15 as they are always the cheapest for good track tyres, but are they going to be down on cornering performance?
I've just seen some Toyo R888's (old design) brand new for £69 each which is ridiculously cheap, but would I not be better paying more and getting the 205/215/225? How do you work out how much width you actually need? I need to know the science. The price difference would be a good £50 per tyre!
I'm planning on going to Cadwell this month and currently have either 205/45/16 Federal RSR, 195/50/16 Yoko A048 and 205/50/15 Yoko AD08R at my disposal on various rims.
So, from not a very clear post comes a clear question, how do I pick what size tyre will give me the best performance? (ignore compounds and brands for now as I'm pretty sure I understand that area
)
Cheers
Dan
I've tried quite a few different tyre sizes on my DC2 track car, but I'm not sure how to work out exactly what size should be best.
The standard car came with 195/55/15 tyres on the earlier models and 215/45/16 tyres on the later model (same chassis). On trackdays, I've myself ran various different widths from 195-225. I know most people run a 15" wheel with 195/50/15 as they are always the cheapest for good track tyres, but are they going to be down on cornering performance?
I've just seen some Toyo R888's (old design) brand new for £69 each which is ridiculously cheap, but would I not be better paying more and getting the 205/215/225? How do you work out how much width you actually need? I need to know the science. The price difference would be a good £50 per tyre!
I'm planning on going to Cadwell this month and currently have either 205/45/16 Federal RSR, 195/50/16 Yoko A048 and 205/50/15 Yoko AD08R at my disposal on various rims.
So, from not a very clear post comes a clear question, how do I pick what size tyre will give me the best performance? (ignore compounds and brands for now as I'm pretty sure I understand that area
)Cheers
Dan
motco said:
DanielJames said:
I've just seen some Toyo R888's (old design) brand new for £69 each which is ridiculously cheap
May I ask where please? Unless, of course, it's a one off and only one set. ThanksThanks for the replies, the second response I've read a few times but 4am probably isn't the best time for it
I'll re-read tomorrow. The most interesting point for me is tyre pressures, something that I do enjoy "fiddling" with on trackdays. I'm going back on track Monday so will be sure to have a play with the pressures. I'll re read the responses in the morning, thanks chaps.
Ray Luxury-Yacht said:
Dunno if this will help or not, but I used to race bikes, and have been a TD instructor too, with a bit of car experience thrown in...
With regard to tyres, there are several main things to consider. Size is only a small part of that equation. If you don't understand fully what I write below - then have a Google round about each point, to give you a greater understanding about the things I am discussing?
1) Assuming the tyres you are using can firstly deal satisfactorily with the transmission of power, especially out of corners - then one of the main considerations is suspension and wheel geometry. I might suggest that the vehicle's camber, castor and weight distribution have some of the greatest effects on both grip and traction, above all else. Secondary to that is whether you have a limited slip differential or not. Without this, it is likely that in a front-wheel-drive vehicle, the inside front wheel might spin up and waste power when accelerating out of a turn.
After all the many thousands of hours I have spent (wasted?
) at race tacks, I can confirm that one of the primary features of a good lap time, is effective acceleration out of turns, especially slower ones. It's (usually) more important than corner speed, and even late braking. The simple fact of the matter is that early traction and acceleration out of a turn will equal a higher top speed along the next corresponding straight. Amongst other things, this is one of the most important factors to consider when cutting lap times. Trust me on this.
2) Tyre pressures have a monstrous effect upon grip and traction too, taking the climate and track temperature into consideration. I bet you that if someone who didn't know what they were doing turned up at a track with a particular car, and I had the same car running smaller / thinner tyres, if I was given some basic setup information and track surface temperatures, then after a bit of testing I would find a suitable tyre air pressure on my car that would blitz the other car with bigger / wider tyres. Not only that, but often a smaller / thinner tyre running at optimum pressures for the track at that particular point can give the driver a better feel too, hence helping to cut lap times even further. Sometimes, compliance is everything - especially in the cold and the wet.
3) Before you go off on a wild goose chase for bigger / wider tyres, consider this: the primary driver of tyre grip and traction, once you have set optimum pressures and decided on compound and sidewall compliance - is the force with which the tyre's contact patch is pushed down into the running surface.
If you don't get that, then you need to think of what's happening at a microscopic level between rubber and ashphalt. Thinking back to those physics lessons at school, friction between two surfaces is created by the irregularities, force and compliance of the two materials. E.g. the tyre and the track have peaks and troughs in them invisible to the naked eye - but it is this interaction and 'keying in' of the two surfaces which creates friction.
You can't really change the track's characteristics, but you can influence the tyre's to create as much friction as possible. A softer more compliant tyre compound, or reduced pressures which allow more running surface deformity, CAN improve this friction co-efficient.
HOWEVER - and providing you have stuck with me - this is NOT ALWAYS improved by just fitting bigger / wider tyres. You might think that a bigger / wider contact patch would give you a greater amount of friction, grip and traction, right? Well, no - as per the physics, it depends upon the WEIGHT of the body (i.e. the car) which is pushing / forcing the tyre down into the track.
A car of a certain weight, is pushing every square inch of the contact patches of the tyres down into the track at a set pressure. Forgetting compounds and tyre pressures for a moment - this force is a set force which will not change, unless the car has some serious aero addenda like wings and spoilers. So, you are stuck with what you have.
If you fit wider tyres to the same car, with no other changes or modifications, expecting more grip and traction, then you may be disappointed. This is primarily because you are now presenting, for example, 20% more tyre contact patch to the track surface. However, the weight of the car which is pushing these bigger contact patches down into the track is the same - hence, you actually have a reduced pressure per square inch of contact patch than you had with thinner tyres.
Therefore, in many cases - overall, you have reduced the friction co-efficient available for grip and traction, despite the wider tyres - and will then suffer paradoxically slower lap times....which might even be compounded by less steering / braking feel, and even a greater propensity to aquaplaning in the wet.
Does that all make sense? Sorry for the long physics lesson reply - I've not long come home and was a bit bored, so thought I might offer all my thoughts on the subject, haha! I don't pretend to be an expert, and I may well get shot down in flames by others who know more - but all I am saying is that these basic principles helped me and my team in deciding upon what tyres to run, where and when.
HTH
I've finally had time to read that With regard to tyres, there are several main things to consider. Size is only a small part of that equation. If you don't understand fully what I write below - then have a Google round about each point, to give you a greater understanding about the things I am discussing?
1) Assuming the tyres you are using can firstly deal satisfactorily with the transmission of power, especially out of corners - then one of the main considerations is suspension and wheel geometry. I might suggest that the vehicle's camber, castor and weight distribution have some of the greatest effects on both grip and traction, above all else. Secondary to that is whether you have a limited slip differential or not. Without this, it is likely that in a front-wheel-drive vehicle, the inside front wheel might spin up and waste power when accelerating out of a turn.
After all the many thousands of hours I have spent (wasted?
) at race tacks, I can confirm that one of the primary features of a good lap time, is effective acceleration out of turns, especially slower ones. It's (usually) more important than corner speed, and even late braking. The simple fact of the matter is that early traction and acceleration out of a turn will equal a higher top speed along the next corresponding straight. Amongst other things, this is one of the most important factors to consider when cutting lap times. Trust me on this.2) Tyre pressures have a monstrous effect upon grip and traction too, taking the climate and track temperature into consideration. I bet you that if someone who didn't know what they were doing turned up at a track with a particular car, and I had the same car running smaller / thinner tyres, if I was given some basic setup information and track surface temperatures, then after a bit of testing I would find a suitable tyre air pressure on my car that would blitz the other car with bigger / wider tyres. Not only that, but often a smaller / thinner tyre running at optimum pressures for the track at that particular point can give the driver a better feel too, hence helping to cut lap times even further. Sometimes, compliance is everything - especially in the cold and the wet.
3) Before you go off on a wild goose chase for bigger / wider tyres, consider this: the primary driver of tyre grip and traction, once you have set optimum pressures and decided on compound and sidewall compliance - is the force with which the tyre's contact patch is pushed down into the running surface.
If you don't get that, then you need to think of what's happening at a microscopic level between rubber and ashphalt. Thinking back to those physics lessons at school, friction between two surfaces is created by the irregularities, force and compliance of the two materials. E.g. the tyre and the track have peaks and troughs in them invisible to the naked eye - but it is this interaction and 'keying in' of the two surfaces which creates friction.
You can't really change the track's characteristics, but you can influence the tyre's to create as much friction as possible. A softer more compliant tyre compound, or reduced pressures which allow more running surface deformity, CAN improve this friction co-efficient.
HOWEVER - and providing you have stuck with me - this is NOT ALWAYS improved by just fitting bigger / wider tyres. You might think that a bigger / wider contact patch would give you a greater amount of friction, grip and traction, right? Well, no - as per the physics, it depends upon the WEIGHT of the body (i.e. the car) which is pushing / forcing the tyre down into the track.
A car of a certain weight, is pushing every square inch of the contact patches of the tyres down into the track at a set pressure. Forgetting compounds and tyre pressures for a moment - this force is a set force which will not change, unless the car has some serious aero addenda like wings and spoilers. So, you are stuck with what you have.
If you fit wider tyres to the same car, with no other changes or modifications, expecting more grip and traction, then you may be disappointed. This is primarily because you are now presenting, for example, 20% more tyre contact patch to the track surface. However, the weight of the car which is pushing these bigger contact patches down into the track is the same - hence, you actually have a reduced pressure per square inch of contact patch than you had with thinner tyres.
Therefore, in many cases - overall, you have reduced the friction co-efficient available for grip and traction, despite the wider tyres - and will then suffer paradoxically slower lap times....which might even be compounded by less steering / braking feel, and even a greater propensity to aquaplaning in the wet.
Does that all make sense? Sorry for the long physics lesson reply - I've not long come home and was a bit bored, so thought I might offer all my thoughts on the subject, haha! I don't pretend to be an expert, and I may well get shot down in flames by others who know more - but all I am saying is that these basic principles helped me and my team in deciding upon what tyres to run, where and when.
HTH
I can relate to what you've written, when I fitted the 225s up front the car did drive very differently. The steering was heavier, yet more direct in feeling, but I dare day it felt slower on corner exit.
I'm at Angelesey in a few weeks so I think I'll be taking a few different setups to try out on track and see what I prefer. I know it's only a track day but it's all good fun learning about this stuff. I'm more interested to see how my car will perform with 195 A048s vs 225 ones up front. I did love the 225 setup, but if the 195 can give me the same corner speeds but with added corner exit speed that would be sublime!
Many thanks for taking the time to post that.
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