Track Day Merc - tyre pressures
Discussion
Hi all,
I'm doing a track day at my local track Castle Coombe this Saturday. Has anyone any advice on tyre pressures please?
I've done one track day before and some driving tuition, but am really going along for the fun and to go round safely rather than for out and out full speed all day long. This is partly because I don't have the confidence in the car to really nail it - last time out a rear Pirelli P6000 blew. So I want to make sure I set the right pressures to ensure tyres don't overheat or blow or anything again! Also if I get carried away and start trying to keep up with my friend's Elise s1 I'd like to know it's not all going to go pear shaped underfoot.
I attended a carlimits day recently and was advised to add 10 psi (IIRC) to the standard pressures because otherwise the tyres could be a problem. Does that sound right? I can't remember the factory specified pressures off the top of my head. The car weighs 1300kg or more, and shouldn't be too front heavy being a lightish four-cylinder. Also if you know the affect it has on handling/turn-in and so on that would be interesting to know but primarily I'd just like to go safe, since Coombe isn't exactly a slow track and the Merc carries quite a bit of speed since I rebuilt the engine.
I will be running standard brakes too, what signs do I look for when they start to overheat and should back off? They were actually fine last time because I went easy on them.
thank you!
I'm doing a track day at my local track Castle Coombe this Saturday. Has anyone any advice on tyre pressures please?
I've done one track day before and some driving tuition, but am really going along for the fun and to go round safely rather than for out and out full speed all day long. This is partly because I don't have the confidence in the car to really nail it - last time out a rear Pirelli P6000 blew. So I want to make sure I set the right pressures to ensure tyres don't overheat or blow or anything again! Also if I get carried away and start trying to keep up with my friend's Elise s1 I'd like to know it's not all going to go pear shaped underfoot.
I attended a carlimits day recently and was advised to add 10 psi (IIRC) to the standard pressures because otherwise the tyres could be a problem. Does that sound right? I can't remember the factory specified pressures off the top of my head. The car weighs 1300kg or more, and shouldn't be too front heavy being a lightish four-cylinder. Also if you know the affect it has on handling/turn-in and so on that would be interesting to know but primarily I'd just like to go safe, since Coombe isn't exactly a slow track and the Merc carries quite a bit of speed since I rebuilt the engine.
I will be running standard brakes too, what signs do I look for when they start to overheat and should back off? They were actually fine last time because I went easy on them.
thank you!
Start with 10psi over recommended inflation pressure. Mark the shoulders of the tyres to 1/4" of the sidewalls with white liquid shoe polish or chalk. If the tyre rolls enough to abrade the marks that you have made on the side wall, you may need to raise the pressures a little. This advice is pretty basic as there are other factors that affect how much the tyres roll on to the sidewalls.
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If you're pushing on road tyres will inflate by about 5psi once warmed up so bear that in mind.
I've always started on stock pressures and adjusted accordingly through the day. I normally end up around stock pressures when hot.
The brakes going will be obvious. If the pads glaze/overheat you'll have to press the pedal harder and harder to slow the car down. This will probably lead to the fluid boiling which will result in your foot going to the floor and a change of underwear required!
I've always started on stock pressures and adjusted accordingly through the day. I normally end up around stock pressures when hot.
The brakes going will be obvious. If the pads glaze/overheat you'll have to press the pedal harder and harder to slow the car down. This will probably lead to the fluid boiling which will result in your foot going to the floor and a change of underwear required!
I dont understand or have got the wrong end of the stick? I thought that as the tyre air heats up the pressure is increased under hard driving. So wouldn't you do the first few laps under higher pressure to redcue too much side wall flex but then reduce it as the tyres warmed? Otherwise you would reduce grip by having overinflated tyres?
I drive a 1700kg CLK55 amg and have only increased tyre pressures on skid pans - have I been doing it wrong? (The tyres are Dunlop SP9000s 265x30x19 and 235x35x19 running day to day pressure of 41PSI all round and 45PSI all round on skid pans).
I drive a 1700kg CLK55 amg and have only increased tyre pressures on skid pans - have I been doing it wrong? (The tyres are Dunlop SP9000s 265x30x19 and 235x35x19 running day to day pressure of 41PSI all round and 45PSI all round on skid pans).
petermansell said:
I dont understand or have got the wrong end of the stick? I thought that as the tyre air heats up the pressure is increased under hard driving. So wouldn't you do the first few laps under higher pressure to redcue too much side wall flex but then reduce it as the tyres warmed? Otherwise you would reduce grip by having overinflated tyres?
Correct. Why are you confused?petermansell said:
I dont understand or have got the wrong end of the stick? I thought that as the tyre air heats up the pressure is increased under hard driving. So wouldn't you do the first few laps under higher pressure to redcue too much side wall flex but then reduce it as the tyres warmed? Otherwise you would reduce grip by having overinflated tyres?
I drive a 1700kg CLK55 amg and have only increased tyre pressures on skid pans - have I been doing it wrong? (The tyres are Dunlop SP9000s 265x30x19 and 235x35x19 running day to day pressure of 41PSI all round and 45PSI all round on skid pans).
It's true that the pressure in the tyre increases as it warms up. The recomended pressures for road driving take this into account for the road. You dont however corner as hard on the on the road as you do on the track(hopefully!). When cornering at max attack the tyre on road pressures might deform far enough to put the sidewall on the tarmac. Now the increase as suggested is about 5psi when on track. (In my case 26 to 32 psi). The increase on the road is probably about 3psi. But you'll not be anywhere near the cornering force. So you only get a small pressure increase even though your activity is much higher. To stop the sidewall running more air will be needed to start with so that when hot on track all is ok.I drive a 1700kg CLK55 amg and have only increased tyre pressures on skid pans - have I been doing it wrong? (The tyres are Dunlop SP9000s 265x30x19 and 235x35x19 running day to day pressure of 41PSI all round and 45PSI all round on skid pans).
The above makes sence to me, but I'm sure someone can put it better!
To me 10psi over normal running would result in tyres vastly overheated & awfull no grip handling, walshy does say do it for his handling days & hes said the same to me, but that is very difrernt to trackdays.
I personally would start at near recomended pressures do a session & see how I got on & check pressures as soon as I got in. You need to play around & see what works for you.
For ref my old Golf circa 30 ish hot has seemed the best, for e30 325i at similar weight to yr merc, I find 35 ish HOT all round is great, It takes a session or 2 for them to stabalise & will rise up to 10 psi from cold pressure at 1st session so bleed down, but if im aiming for 30 one have done a session to get them warm, I then bleed to 25, then see how they look, & later on seem to start session at somat like 27 before the session & end at say 33.
Slicks & the 888s bit diferent, seem to like lower psi but not as low as some folks have recomended me, but just a tad.
Remember to pump up to road pressure before you drive home, good way to wreck yr sidewalls if you don't.
I personally would start at near recomended pressures do a session & see how I got on & check pressures as soon as I got in. You need to play around & see what works for you.
For ref my old Golf circa 30 ish hot has seemed the best, for e30 325i at similar weight to yr merc, I find 35 ish HOT all round is great, It takes a session or 2 for them to stabalise & will rise up to 10 psi from cold pressure at 1st session so bleed down, but if im aiming for 30 one have done a session to get them warm, I then bleed to 25, then see how they look, & later on seem to start session at somat like 27 before the session & end at say 33.
Slicks & the 888s bit diferent, seem to like lower psi but not as low as some folks have recomended me, but just a tad.
Remember to pump up to road pressure before you drive home, good way to wreck yr sidewalls if you don't.
You only up the tyre pressure if you've got soft sidewalls and need to compensate. If you do it unnecessarily you'll crown the tyre and overheat it. One thing you could do is check the temp across the tyre with a contact pyrometer (I've got a laser one and to be honest its a bit bobbins as you really need to stick something into the tyre). If you know what the hot pressure is for your tyres on the road (most manufacturers quote cold which is tedious) then you could aim for something around that and adjust as necessary.
You say you blew out a tyre last time. Where did it blow out and have you established what caused it? (apart from ragging 2 tonnes of merc around on tyres not designed for it?
You say you blew out a tyre last time. Where did it blow out and have you established what caused it? (apart from ragging 2 tonnes of merc around on tyres not designed for it?
Pentoman - a bit off topic but i will be at Castle on Sat too. come over and say hi - tatty blue BMW E30, you can't miss it - pic on my profile.
re tyre pressures - i have never found quite the right ones - my cars weighs less than 1000kgs and i start on about 30 and they heat up by 4 - 5 psi hot which seems the trick for me on toyo 888s
re tyre pressures - i have never found quite the right ones - my cars weighs less than 1000kgs and i start on about 30 and they heat up by 4 - 5 psi hot which seems the trick for me on toyo 888s
OK thanks all
2 tonnes of Merc! I should hope not! 1300kg apparently and mine is low spec half leather/manual seats/no AC.
poshgit - Hi, my name's Russell by the way, I'll come take a look at this 'tatty' BMW although at under a ton and with 888s it sounds better than tatty - check my car out for tatty. I'm there with a friend in an Elise and Subaru 22B, plus my GF is passengering me. Tell me more about this BMW?
Below should be a photo of the tyre from last time when it blew out
HI RES LINK: http://bp2.blogger.com/_kg7LwFd8fxM/RdrlU6mH2WI/AA...
this is the tyre
what do you think? This was a rear tyre, blew on powering out of a chicane and under high lateral load.
Hope I don't get flamed for it but I still have a pair of the same set of Pirelli P6000s on the front. The rears however were replaced with Toyo T1-Rs. Am I stupid?
Here's some cornering shots from the guy that was doing pics (I'm cleaning the car this time round!), doesn't look like the tyres are rolling excessively but?
Still unclear on what to do with the pressures - based on what happened last time I'm thinking it loaded the sidewalls too much, and more pressure = more sidewall stiffness so going to go with 5-8 PSI over factory pressure? I don't squeal round heavily rubbing the tyres on every corner so wouldn't think heat would be a problem.
ta
2 tonnes of Merc! I should hope not! 1300kg apparently and mine is low spec half leather/manual seats/no AC.
poshgit - Hi, my name's Russell by the way, I'll come take a look at this 'tatty' BMW although at under a ton and with 888s it sounds better than tatty - check my car out for tatty. I'm there with a friend in an Elise and Subaru 22B, plus my GF is passengering me. Tell me more about this BMW?
Below should be a photo of the tyre from last time when it blew out
HI RES LINK: http://bp2.blogger.com/_kg7LwFd8fxM/RdrlU6mH2WI/AA...this is the tyre
what do you think? This was a rear tyre, blew on powering out of a chicane and under high lateral load.
Hope I don't get flamed for it but I still have a pair of the same set of Pirelli P6000s on the front. The rears however were replaced with Toyo T1-Rs. Am I stupid?
Here's some cornering shots from the guy that was doing pics (I'm cleaning the car this time round!), doesn't look like the tyres are rolling excessively but?
Still unclear on what to do with the pressures - based on what happened last time I'm thinking it loaded the sidewalls too much, and more pressure = more sidewall stiffness so going to go with 5-8 PSI over factory pressure? I don't squeal round heavily rubbing the tyres on every corner so wouldn't think heat would be a problem.
ta
Pentoman said:
Hope I don't get flamed for it but I still have a pair of the same set of Pirelli P6000s on the front. The rears however were replaced with Toyo T1-Rs. Am I stupid?
If you want cronic understeer thats a great set up, if not put the pirelli sh*ite on the back, T1Rs grip, pirelli p6000s dontiguana said:
Pentoman said:
Hope I don't get flamed for it but I still have a pair of the same set of Pirelli P6000s on the front. The rears however were replaced with Toyo T1-Rs. Am I stupid?
If you want cronic understeer thats a great set up, if not put the pirelli sh*ite on the back, T1Rs grip, pirelli p6000s dontBest bet get rid of the p6000, god awful things.
Well, back in one piece.
I went with 39 front and 41 rear, cold pressures. I didn't have any understeer problems, perhaps I was just driving around it or not really going for it, but if you set it up right on the way in you could power on the whole way through the corner in a nice understeer/oversteer balance and carrying plenty of speed at exit.
Poshgit (Guy, who didn't seem especially posh?) was a dead nice guy and came to visit me while I was morose watching the open session at the end of the day. So I decided to go out again and enjoyed it far more in the longer session where I could go for it for a few laps then slow right down to cool it all off then speed up again. Attempted to follow an E46 M3 and R33 skyline that were battling, failed, but it was interesting to watch. It has made me want better brakes for next time though so I can lean on it all a bit more. Didn't even nearly the trigger the ABS once. I'm just glad not to have to fix anything at this point since I couldn't afford it!
Poshgit reckoned my tyres had worn just about nicely too. His BMW looked good, well on the track at least... held its line very well and looked nicely agile, although through every corner it was pretty much on the redline throughout because it had no traction at the rear! He wasn't drifting, it just had no rear grip despite 195 section Toyo 888s.
Riding in my friend's 22B was interesting - it's very capable, great torque and grip, but it's a rather brutal experience that feels very tough on brakes and tyres. Fast though. I imagine a heavier, less track oriented 'normal' Impreza could be a bit of handful to contain if really going for it. I also find the way you power on to pull out of corners strangle because if you enter too fast and then commit to usingthe power to pull out of your mistake - it could go very pear shaped at this point?
Whatever, great day, thanks for the advice
I went with 39 front and 41 rear, cold pressures. I didn't have any understeer problems, perhaps I was just driving around it or not really going for it, but if you set it up right on the way in you could power on the whole way through the corner in a nice understeer/oversteer balance and carrying plenty of speed at exit.
Poshgit (Guy, who didn't seem especially posh?) was a dead nice guy and came to visit me while I was morose watching the open session at the end of the day. So I decided to go out again and enjoyed it far more in the longer session where I could go for it for a few laps then slow right down to cool it all off then speed up again. Attempted to follow an E46 M3 and R33 skyline that were battling, failed, but it was interesting to watch. It has made me want better brakes for next time though so I can lean on it all a bit more. Didn't even nearly the trigger the ABS once. I'm just glad not to have to fix anything at this point since I couldn't afford it!
Poshgit reckoned my tyres had worn just about nicely too. His BMW looked good, well on the track at least... held its line very well and looked nicely agile, although through every corner it was pretty much on the redline throughout because it had no traction at the rear! He wasn't drifting, it just had no rear grip despite 195 section Toyo 888s.
Riding in my friend's 22B was interesting - it's very capable, great torque and grip, but it's a rather brutal experience that feels very tough on brakes and tyres. Fast though. I imagine a heavier, less track oriented 'normal' Impreza could be a bit of handful to contain if really going for it. I also find the way you power on to pull out of corners strangle because if you enter too fast and then commit to usingthe power to pull out of your mistake - it could go very pear shaped at this point?
Whatever, great day, thanks for the advice
http://www.edpphoto.com/charitytd160208pm.HTML/cha...
http://www.edpphoto.com/charitytd160208pm.HTML/cha...
http://www.edpphoto.com/charitytd160208pm.HTML/cha...
http://www.edpphoto.com/charitytd160208pm.HTML/cha...
Think it's a lot of roll but even the "too compromised for the road" Subaru looks like this
http://www.edpphoto.com/charitytd160208am.HTML/cha...
And poshgit's rat rod!
http://www.edpphoto.com/charitytd160208am.HTML/cha...
http://www.edpphoto.com/charitytd160208pm.HTML/cha...
http://www.edpphoto.com/charitytd160208pm.HTML/cha...
http://www.edpphoto.com/charitytd160208pm.HTML/cha...
http://www.edpphoto.com/charitytd160208pm.HTML/cha...
Think it's a lot of roll but even the "too compromised for the road" Subaru looks like this
http://www.edpphoto.com/charitytd160208am.HTML/cha...
And poshgit's rat rod!
http://www.edpphoto.com/charitytd160208am.HTML/cha...
http://www.edpphoto.com/charitytd160208pm.HTML/cha...
Is it me. Or is the front running on the sidewall here?... 
http://www.edpphoto.com/charitytd160208pm.HTML/cha...
http://www.edpphoto.com/charitytd160208pm.HTML/cha...
And poshgit's rat rod!
http://www.edpphoto.com/charitytd160208am.HTML/cha...
http://www.edpphoto.com/charitytd160208pm.HTML/cha...
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i also think my cr*p driving ability - too fast into the approach of a corner - then scrubbing off speed as i go round, was not helping the body roll.....slower in faster out i keep telling myself!!!
http://www.edpphoto.com/charitytd160208am.HTML/cha...
http://www.edpphoto.com/charitytd160208pm.HTML/cha...
[/quote]
i also think my cr*p driving ability - too fast into the approach of a corner - then scrubbing off speed as i go round, was not helping the body roll.....slower in faster out i keep telling myself!!!
Fishy Dave said:
I was there with you on the day, remember seeing your car. Can't remember the date mind, I was at Combe quite a few days last year - was it at Ben Elliotts charity day?
It was indeed yes. It was extremely dirty last year, and a bit dirty this year (I don't like to turn up giving anybody any expectations!). This one here was Ben Elliot's charity day again too.Gassing Station | Track Days | Top of Page | What's New | My Stuff