Tyre pressures, can you go too high?
Discussion
Hi All.
Tried searching but couldn't find an answer specific to my situation.
Car is an Impreza P1 - tyres are Michelin Pilot Super Sports in 225/35/18. Car is about 1300-1350kg.
The recommended pressures on the car are 35 front 26 rear but that is on 205/45/17 tyres.
In road trim I usually run at 35psi (cold) all round which seems fine, if I go lower it feels like an antiroll bar has fallen off.
On track I do a few warm up laps and come back in and check pressures and bleed back down so they are 35 hot. This had been working well on a few days but they have all been in the rain. The last day I did was bone dry. The rears seem to have worn perfectly to the marker by the tread but the fronts have gone past it to the top of the sidewalls.
So I guess in theory I need to put them up higher to stop them rolling over? I have found some info saying Prodrive suggest 38 front 35 rear on my size tyres but I'm getting differing opinions from people as to if this is wise?
Everyone I speak to at tracks thinks I'm already high at 35 but they all run on track/race tyres that need less pressure, eg a friend runs his E90 m3 on about 28psi (hot) but on track tyres and that is quite a bit heavier than my car.
Is it a case of just increasing the pressure to a point where the tyre is wearing where it should and never mind what the psi actually is or is running them at 38-40psi silly? It says on the tyre max pressure 50psi, so am I ok to throw whatever into it as long as it stays below 50psi or is 40ish psi and track use just asking for a blowout?
Advice from Michelin is to run them a few psi over manufacturer figures so that would have me at about 40-42psi is this too high to be safe?
I'm also looking to have the geometry changed from standard to a recommended fast road/ light track setup which gives a bit more -ve camber (-1.4-5 compared to the standard setting of -1.1-2) . Would I be right in assuming this would help with the tyre wear and let me run a lower pressure?
Thanks for any help
Tried searching but couldn't find an answer specific to my situation.
Car is an Impreza P1 - tyres are Michelin Pilot Super Sports in 225/35/18. Car is about 1300-1350kg.
The recommended pressures on the car are 35 front 26 rear but that is on 205/45/17 tyres.
In road trim I usually run at 35psi (cold) all round which seems fine, if I go lower it feels like an antiroll bar has fallen off.
On track I do a few warm up laps and come back in and check pressures and bleed back down so they are 35 hot. This had been working well on a few days but they have all been in the rain. The last day I did was bone dry. The rears seem to have worn perfectly to the marker by the tread but the fronts have gone past it to the top of the sidewalls.
So I guess in theory I need to put them up higher to stop them rolling over? I have found some info saying Prodrive suggest 38 front 35 rear on my size tyres but I'm getting differing opinions from people as to if this is wise?
Everyone I speak to at tracks thinks I'm already high at 35 but they all run on track/race tyres that need less pressure, eg a friend runs his E90 m3 on about 28psi (hot) but on track tyres and that is quite a bit heavier than my car.
Is it a case of just increasing the pressure to a point where the tyre is wearing where it should and never mind what the psi actually is or is running them at 38-40psi silly? It says on the tyre max pressure 50psi, so am I ok to throw whatever into it as long as it stays below 50psi or is 40ish psi and track use just asking for a blowout?
Advice from Michelin is to run them a few psi over manufacturer figures so that would have me at about 40-42psi is this too high to be safe?
I'm also looking to have the geometry changed from standard to a recommended fast road/ light track setup which gives a bit more -ve camber (-1.4-5 compared to the standard setting of -1.1-2) . Would I be right in assuming this would help with the tyre wear and let me run a lower pressure?
Thanks for any help
Road car running road tyres, id stay close to manufacturers recommendations. If it says 35/28 cold, then thatll probably be 40/ 33 hot. So rears would be fine at 35 hot, id probably put 3psi more in the fronts as youve been recommended.
Dont worry about cars running track tyres, very different parameters. They also likely have suspension and geometry changes to allow them to run low pressures.
But 40 psi hot wont hurt tyres. Normally higher pressures mean less grip, but if you arent suffering a loss of grip then youre fine.
Dont worry about cars running track tyres, very different parameters. They also likely have suspension and geometry changes to allow them to run low pressures.
But 40 psi hot wont hurt tyres. Normally higher pressures mean less grip, but if you arent suffering a loss of grip then youre fine.
brillomaster said:
Road car running road tyres, id stay close to manufacturers recommendations. If it says 35/28 cold, then thatll probably be 40/ 33 hot. So rears would be fine at 35 hot, id probably put 3psi more in the fronts as youve been recommended.
Dont worry about cars running track tyres, very different parameters. They also likely have suspension and geometry changes to allow them to run low pressures.
But 40 psi hot wont hurt tyres. Normally higher pressures mean less grip, but if you arent suffering a loss of grip then youre fine.
......... the way the tyre wears can also be relative to the way which you drive! If you leap off the brakes. turn in, and hard on the power, then that will confuse matters.Dont worry about cars running track tyres, very different parameters. They also likely have suspension and geometry changes to allow them to run low pressures.
But 40 psi hot wont hurt tyres. Normally higher pressures mean less grip, but if you arent suffering a loss of grip then youre fine.
RB Will said:
I tend to trail brake into corners with some weight on the nose as otherwise you end up with understeer. Power is quite damped as it comes back in as I have quite a bit of turbo lag
...... that's good, so it elimates that factor!! Some people don't have the understanding of the physics of how the car works, hence the reason I asked! 35psi cold would for most cars on track be way to high for track use but the pilot super sport is very normal road tyre so will need a higher pressure to maintain its side wall stability. Sadly because its not designed as a track tyre it will get hot quickly and loose grip quickly plus wear its outside edge faster.
Can I suggest you monitor it though and avoid them going over 40Psi HOT. I would be inclined to raise the rear pressures to also reach between 35 and 40 HOT. Once you you know the tyres are running at a neutural pressure hot allround i.e 40psi front and rear, that will give you a true balance (assuming your driving is consistent) and you can adjust pressures from there if the car is out of balance. It will always be a compromise though because of the tyres.
If you run a proper track tyre then you'll need to drop the hot pressures significantly and why so many people will be telling you 35 is to high.
Can I suggest you monitor it though and avoid them going over 40Psi HOT. I would be inclined to raise the rear pressures to also reach between 35 and 40 HOT. Once you you know the tyres are running at a neutural pressure hot allround i.e 40psi front and rear, that will give you a true balance (assuming your driving is consistent) and you can adjust pressures from there if the car is out of balance. It will always be a compromise though because of the tyres.
If you run a proper track tyre then you'll need to drop the hot pressures significantly and why so many people will be telling you 35 is to high.
If you are running normal road tyres it’s also worth considering getting them nitrogen filled. It’s the dryness of the nitrogen that’s important not the 20% oxygen by the way.
You will then find that they don’t increase in pressure anything like as much when they get hot. The water vapour expands far more than the gas and so the pressure goes much higher.
I drive my normal road car Boxster on track and always had to let the tyres down after a few laps. Porsche started routinely nitrogen filling tyres and t found that the tyres didn’t go off as they got hot and as long as I only stay out for 15/20 mins at a time there’s no need to let air out.
Plus, tyre pressures stay constant for months. Mine haven’t had to be adjusted since September.
You will then find that they don’t increase in pressure anything like as much when they get hot. The water vapour expands far more than the gas and so the pressure goes much higher.
I drive my normal road car Boxster on track and always had to let the tyres down after a few laps. Porsche started routinely nitrogen filling tyres and t found that the tyres didn’t go off as they got hot and as long as I only stay out for 15/20 mins at a time there’s no need to let air out.
Plus, tyre pressures stay constant for months. Mine haven’t had to be adjusted since September.
SimonMason said:
35psi cold would for most cars on track be way to high for track use but the pilot super sport is very normal road tyre so will need a higher pressure to maintain its side wall stability. Sadly because its not designed as a track tyre it will get hot quickly and loose grip quickly plus wear its outside edge faster.
Can I suggest ...
If you run a proper track tyre then you'll need to drop the hot pressures significantly and why so many people will be telling you 35 is to high.
This, if you are going to do more track stuff, I'd suggest getting a second set of wheels and putting more track focussed tyres on them that have stiffer side walls. Then you can run them at lower pressures and benefit from the grip and not ruin your road tyres on track. Can I suggest ...
If you run a proper track tyre then you'll need to drop the hot pressures significantly and why so many people will be telling you 35 is to high.
888s or AD08Rs (my choice) or RSRs or something.
Wollemi said:
If you are running normal road tyres it’s also worth considering getting them nitrogen filled. It’s the dryness of the nitrogen that’s important not the 20% oxygen by the way.
You will then find that they don’t increase in pressure anything like as much when they get hot. The water vapour expands far more than the gas and so the pressure goes much higher.
I drive my normal road car Boxster on track and always had to let the tyres down after a few laps. Porsche started routinely nitrogen filling tyres and t found that the tyres didn’t go off as they got hot and as long as I only stay out for 15/20 mins at a time there’s no need to let air out.
Plus, tyre pressures stay constant for months. Mine haven’t had to be adjusted since September.
I didn't know that - thanks. You will then find that they don’t increase in pressure anything like as much when they get hot. The water vapour expands far more than the gas and so the pressure goes much higher.
I drive my normal road car Boxster on track and always had to let the tyres down after a few laps. Porsche started routinely nitrogen filling tyres and t found that the tyres didn’t go off as they got hot and as long as I only stay out for 15/20 mins at a time there’s no need to let air out.
Plus, tyre pressures stay constant for months. Mine haven’t had to be adjusted since September.
I was at Donington with some friends on Monday and was surprised to fond that some of our tyres were raising by 10psi over a session.
So effectively going out on 28psi and coming in after 15-20mins with 38psi. It was noticeably wearing the Michelins Cup 2s quicker when they got hot. I find the AD08R more durable and pretty much just as grippy.
So effectively going out on 28psi and coming in after 15-20mins with 38psi. It was noticeably wearing the Michelins Cup 2s quicker when they got hot. I find the AD08R more durable and pretty much just as grippy.
Thanks for the feedback guys.
I'm currently torn between swapping out the tyres for something that I can use on road and track. My only problem with this is my normal road tyres are a 35 profile and anything designed for track is 40-45 so makes them overall diameter a bit more and I'm not sure if it will rub.
Otherwise the option is there for the nitrogen fill but I will have to do a bit of testing first to find the optimum pressure to have them set at as I don't want to be taking a nitrogen tank to trackdays for adjusting on site.
I'm currently torn between swapping out the tyres for something that I can use on road and track. My only problem with this is my normal road tyres are a 35 profile and anything designed for track is 40-45 so makes them overall diameter a bit more and I'm not sure if it will rub.
Otherwise the option is there for the nitrogen fill but I will have to do a bit of testing first to find the optimum pressure to have them set at as I don't want to be taking a nitrogen tank to trackdays for adjusting on site.
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