List 1A Tyre Pressures
Discussion
I've been racing my caterham since March 2010, with finishing positions improving from 11th of 15 at the beginning to scoring my first few podiums this season. It has been hugely satisfying but through all of this I have never managed to find the 'correct' tyre pressure- It seems that whatever I do with them, they always 'go off' in the second half of the 20 minute races. I have been progressively lowering the pressures until now I feel they are as low as I can run them, but still I have this problem. Other competitors run their tyres anywhere within a 9-10PSI range of each other, which is obviously quite a significant variation!
I can't do a lot of testing due to finances but I'd be very grateful if anyone can shed some light on the behaviour of an ordinary road tyre used for racing, and the various ways in which their performance can drop off?
More specifically, while i understand the basic principle of tyre pressures increasing with heat and reducing the size of the contact patch, other competitors have told me about tyres generating heat due to 'squirming' of the tread blocks at lower pressures etc and the rubber itself getting excessively hot?
I can't do a lot of testing due to finances but I'd be very grateful if anyone can shed some light on the behaviour of an ordinary road tyre used for racing, and the various ways in which their performance can drop off?
More specifically, while i understand the basic principle of tyre pressures increasing with heat and reducing the size of the contact patch, other competitors have told me about tyres generating heat due to 'squirming' of the tread blocks at lower pressures etc and the rubber itself getting excessively hot?
looks like you are not comparing apples with apples there. 25 hot, 18 cold, is probably the same.
I would have thought for a caterfield type car, 27-29 hot is where you need to be, which would probably be about 22-24 cold.
are you confident in the accuracy of your pressure gauge?
what about your damper settings, have you got too much rebound?
have you condsidered going up in rear tyre pressure?
what about your driving style, are you to aggressive with steering input.
road tyres are a bit s
t anyway, they will always drop off in grip, IMHO all that changing the cold tyre pressure does is delay the point at which they go off, and in some cases they will go off a little bit slower.
so with this last point, I would check on which lap you feel the car is starting to loose grip, and whether that is later than with the tyre pressures. By lap 15 or so they will be bks anyway.
I would have thought for a caterfield type car, 27-29 hot is where you need to be, which would probably be about 22-24 cold.
are you confident in the accuracy of your pressure gauge?
what about your damper settings, have you got too much rebound?
have you condsidered going up in rear tyre pressure?
what about your driving style, are you to aggressive with steering input.
road tyres are a bit s
t anyway, they will always drop off in grip, IMHO all that changing the cold tyre pressure does is delay the point at which they go off, and in some cases they will go off a little bit slower.so with this last point, I would check on which lap you feel the car is starting to loose grip, and whether that is later than with the tyre pressures. By lap 15 or so they will be b
ks anyway.The gauge I use is an accurate analogue gauge with nice big 1psi increments. Obviously it can be difficult to measure the tyre pressures when they are hot, due to time taken to get to paddock, get out, find gauge etc- but I tend to get them hot and then equalise the pressures all round (i.e. to 21psi hot, or ~18psi cold). The increase in pressure when hot is actually quite small probably due to the fact they were at a low pressure to begin with, so in my experience 18psi cold to 25psi hot is about a 4psi range.
As I say most drivers use low pressures like me and there is the odd one or two who are competetive (i.e. winning!) and having their tyres at 30psi hot!
I know it's a case of experimenting but with the limited testing I have had, I haven't managed to get a clear trend in tyre pressure vs. time taken to cook them- it seems so variable circuit to circuit, so I just want to understand what happens and why.
Damper rebound is fixed
Geometry has been set up
corner weighted
re: driving style, here is some on-board footage of one of my more recent efforts
http://www.vimeo.com/m/#/21938949
As I say most drivers use low pressures like me and there is the odd one or two who are competetive (i.e. winning!) and having their tyres at 30psi hot!
I know it's a case of experimenting but with the limited testing I have had, I haven't managed to get a clear trend in tyre pressure vs. time taken to cook them- it seems so variable circuit to circuit, so I just want to understand what happens and why.
Damper rebound is fixed
Geometry has been set up
corner weighted
re: driving style, here is some on-board footage of one of my more recent efforts
http://www.vimeo.com/m/#/21938949
It will depend on the tyres you are running in the grads.
There is no issue running as low as you mention on some tyres on caterhams.
managing tyre temps on caterhams is key to consistent wins.
Consider also how much tread depth you have and how to tweek you driving style to avoid excessive sliding.
Not sure what other adjustments to the car you can make, from recollection its pretty limited.
There is no issue running as low as you mention on some tyres on caterhams.
managing tyre temps on caterhams is key to consistent wins.
Consider also how much tread depth you have and how to tweek you driving style to avoid excessive sliding.
Not sure what other adjustments to the car you can make, from recollection its pretty limited.
I have used 21psi hot all round in most of the tyres ive used in 4-5 years of racing and track days with caterhams, R888-Kumho Ecsta-Avon slicks. Cold, FL=17, FR=18, RL=15, RR=16 or very near about.Or set them all at 18 psi do your qualifying and as soon as you can after its finished (mate waiting in the pits) set them all to 21psi, then when there cold a day later or so measure them all and see what they are.....hopefully not too far off the ones above. If its very wet set them higher approx 30-35psi this opens the tread up quite a bit and disperses the water. Andy Mcmillan would be the guy to ask im sure he's at all the grad meetings.
Thanks for the help guys and sorry for leaving this thread for a while.
Still struggling but only one race weekend left this season. Was in the running for championship 3rd place until a mechanic's mistake on the green flag lap at 'Combe saw me retire before the grid. Looks like I'll end up with 5th now.
Next is Rockingham- reknowned for cooking tyres! I will experiment with going lower still. I tried 25psi hot again at pembrey but it felt numb and I had a lot of understeer and difficulty getting heat in (perhaps due to smaller contact patch).
A change of tyres from list 1A Yokohama A539 to list 1B Yokohama A021r was discussed in the club but the A539 are going to be retained, so I will be doing some testing over the winter to try and get them working for me using a methodical trial-and-error approach.
I see this as a real obstacle in my driving progress and I really want to understand what I'm getting wrong!
Still struggling but only one race weekend left this season. Was in the running for championship 3rd place until a mechanic's mistake on the green flag lap at 'Combe saw me retire before the grid. Looks like I'll end up with 5th now.
Next is Rockingham- reknowned for cooking tyres! I will experiment with going lower still. I tried 25psi hot again at pembrey but it felt numb and I had a lot of understeer and difficulty getting heat in (perhaps due to smaller contact patch).
A change of tyres from list 1A Yokohama A539 to list 1B Yokohama A021r was discussed in the club but the A539 are going to be retained, so I will be doing some testing over the winter to try and get them working for me using a methodical trial-and-error approach.
I see this as a real obstacle in my driving progress and I really want to understand what I'm getting wrong!
Fair dos that did sound a little stupid. What I forgot to say was I have asked AndyMac and our tyre supplier/oval racing legend George Polley what pressures I should use and both suggested over 25psi hot. I am re-assured that you are successfully using pressures as low as 16psi cold, I will try going lower next time. When I go higher than 23/24 hot it just doesn't go as well. I am also going to try a few setup tweaks to try to kill any understeer.
AndyMac and George Polley both suggested that the tyre needs the pressure to give it rigidity.
AndyMac and George Polley both suggested that the tyre needs the pressure to give it rigidity.
If George and Andy say you need to have them at 25psi or higher hot, you need to have them at 25psi or higher hot. I ran a Super-Grad for two years and started with similar figures as Sam on my A048s but that's the recommended hot pressure for that tyre (I got that from George and Andy).
The understeer you're getting is probably the combination of ARBs you have on (can't remember if Classics have a Rear ARB) - trying going softer at the front for a start until you find a balance that works for you. I can't see the video but your driving style may be a factor too - where in the corner is it understeering?
Say Hello to the old man from me
The understeer you're getting is probably the combination of ARBs you have on (can't remember if Classics have a Rear ARB) - trying going softer at the front for a start until you find a balance that works for you. I can't see the video but your driving style may be a factor too - where in the corner is it understeering?
Say Hello to the old man from me
Classic Grad 98 said:
Fair dos that did sound a little stupid. What I forgot to say was I have asked AndyMac and our tyre supplier/oval racing legend George Polley what pressures I should use and both suggested over 25psi hot. I am re-assured that you are successfully using pressures as low as 16psi cold, I will try going lower next time. When I go higher than 23/24 hot it just doesn't go as well. I am also going to try a few setup tweaks to try to kill any understeer.
AndyMac and George Polley both suggested that the tyre needs the pressure to give it rigidity.
Fair shout, sometimes when i was getting understeer it was because the front tyres didnt have any heat in them. When your getting the hot pressures what are you starting with, they should be going up a good few psi from cold. Are your shocks adjustable, and when is the understeer, on throttle (stiffen the back) off throttle/ trailing (soften the front). If your front tyres are making things too rigid then this might be the cause of the understeer. AndyMac and George Polley both suggested that the tyre needs the pressure to give it rigidity.
Just do one change at a time. Have you had your car corner weighted, its not too bad if its a little out but if its majorly based toward the back then this might also be the cause. A quick way is to have the front wishbones parallel to the ground measure the height, go to the rear and have it 12mm higher measured at the end of the chassis where the floor is riveted/ end of the tunnel.
Another thing i done when i started, if at a test or track day, was give it to someone who's getting quick lap times and let them do a few laps. They should be able to tell you whats good and bad, or maybe need improved with the cars handling. I tended to blame the car, only to be shown it could do a lot better.
Best of luck
Season over, now eagerly looking foreward to next year! I'll be doing a bit of testing to do a bit of experimentation with tyres and anti-roll bars over the winter.
I ended up getting 4th in the championship which I'm pretty happy with.
I was at Rockingham at the weekend and the tyres felt great, so I think I may have cracked it. It is very much as Al suggests- I think I found the pressure at which the tyre warms up slower but doesn't overheat. That said, it was nearly 30 degrees all weekend and Rockingham has a weird surface material, but at least it's a start.
Unfortunately you have to drive an in lap, and then there's a long drive to the outer paddock- so I was unable to measure 'hot' pressure accurately. I'll be leaving them well alone, making a note of the cold pressures and then using them as a starting point next time.
I will try 'procomp's suggestion at some point but my previous experience suggests anything over about 25 hot will be too skatey!
Sam- re: chassis setup. It has been Geo'd and flat floored accurately. Spring rates and shock absorbers are fixed. There is no rear ARB, but you can chose from a selection of front ones- I might try my lighter bar to improve the turn-in. I tend to have to use tricks to get the car to turn in at some corners...
I ended up getting 4th in the championship which I'm pretty happy with.
I was at Rockingham at the weekend and the tyres felt great, so I think I may have cracked it. It is very much as Al suggests- I think I found the pressure at which the tyre warms up slower but doesn't overheat. That said, it was nearly 30 degrees all weekend and Rockingham has a weird surface material, but at least it's a start.
Unfortunately you have to drive an in lap, and then there's a long drive to the outer paddock- so I was unable to measure 'hot' pressure accurately. I'll be leaving them well alone, making a note of the cold pressures and then using them as a starting point next time.
I will try 'procomp's suggestion at some point but my previous experience suggests anything over about 25 hot will be too skatey!
Sam- re: chassis setup. It has been Geo'd and flat floored accurately. Spring rates and shock absorbers are fixed. There is no rear ARB, but you can chose from a selection of front ones- I might try my lighter bar to improve the turn-in. I tend to have to use tricks to get the car to turn in at some corners...
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