View Full Version : tyre preasure
Opening up the debate again see as I just put on the Uniroyal rainsport 1 a couple of days ago.
What tyre preasure to use? I've been using 36psi front and 35psi rear. Have been told that its a bit on the low side for the 45 profile tire. What is everyone else using?
Dormouse
08-02-2003, 13:45
Yup 36 on the front, although the sidewalls feel a little soft at that pressure.
Dor.
Really didn't notice ubtil I got the rainsports, but now that you mention it the sidewalls do feel on the soft side. I thought it might be the tread.
I believe Seat recommend 36 MAX for the fronts on a 45 profile tyre.
Ben
Pedro Merengue
09-02-2003, 12:43
What about the 32 and 30 written on the Fuel cap side.....
what do they mean by that?
I live in a pretty hot country and I am running on Michelin Pilot Sport and the pressure I found to run best on is just like you guys said about 35 front and 36 rear.....(I have the front at a lower pressure for the UNDERSTEER thingy).
:cheers:
Pedro
Having lower pressure at the front will INCREASE understeer. Its a bit strange really as I've read two books which claim that increasing pressure at the front will reduce understeer and reducing pressure at the rear will increase oversteer.... however, in the same books it also says that lowering the tyre pressure will increase the size of the contact patch and therefore give more grip!
So, which is it, does lowering pressure increase grip or does raising pressure increase grip?
Cheers
Ben
I always thought increasing pressure = increased grip.??
I remeber reading a article/study on driver habits, where they said that most driver (something like 85%) never check pressure and that 90% of those are running with low pressure in the tyres causing excessive wear, higher fuel consumption , and longer braking distances. This would surely mean less pressure = less grip ??
ncarring
10-02-2003, 12:18
My understanding is that initially increasing tyre pressure helps to minimise understeer by reducing the sidewall buckling caused by the transfer of weight onto the offside tyre. However some deformation is obviously needed to compensate for surface irregularities - a solid tyre would have less grip because it would slip more (apart from shaking out your fillings of course :-D). So it's a balancing act.
Over inflated tyres will wear from the centre outwards, under inflated ones from the edges in. Bump up your pressure if you need to but keep an eye on tread wear.
YMMV
Pedro Merengue
10-02-2003, 12:28
Originally posted by prc
I always thought increasing pressure = increased grip.??
I remeber reading a article/study on driver habits, where they said that most driver (something like 85%) never check pressure and that 90% of those are running with low pressure in the tyres causing excessive wear, higher fuel consumption , and longer braking distances. This would surely mean less pressure = less grip ??
Well think of it this way
less tire pressure--> more contact surface---> more friction---> more power needed to overcome theses friction forces---> more fuel consumption.
but regarding less or more understeer with less or more tire pressure, it all depends on the road conditions and the speed at which the car is being driven.
soft and skiddy road need softer tire ----> less pressure.... but here the speed is definetly lower......and so on....
I have tested the car myself on Autocross track which were dusty, shiny, ...and all you could think of in terms of bad tarmac.
Every one was running on 45 psi ( 40-45 series profiles) and you could not beleive the understeer. even with EVO VI and VII AHH...
when we went in a TVR Chimera we gained a 2 sec lead on a track where 1st and 2nd gears are only used , and that was by reducing the front tire pressure to 30 psi ...it was great I am telling you.
So it all depends on the road and speed
Pedro
:cheers:
Originally posted by Pedro Merengue
So it all depends on the road and speed
Roads suck and the speeds are high;) I guess ambient temperature is also important. As the temperature hear is normally higher than the UK, I guess a bit less pressure would be fine.
I'll keep it as is for now.
Dormouse
10-02-2003, 15:25
Having lower pressure at the front will INCREASE understeer. Its a bit strange really as I've read two books which claim that increasing pressure at the front will reduce understeer and reducing pressure at the rear will increase oversteer.... however, in the same books it also says that lowering the tyre pressure will increase the size of the contact patch and therefore give more grip!
Buy a set of track wheels and sticky tyres for track days and keep the road tyre pressures set to cope with the variety of road conditions not hooning it around everywhere....that's my philosophy :p
Dor.
max_torque
10-02-2003, 16:06
Usually biggest change it tyre grip with pressure is actually 'caused by heat!
(low pressure = deformed sidewalls + tread block shuffle) = more work into tyre carcase = more heat, opposite for high pressure)
(the more the tread moves the worse the steering feels, so high pressures tend to generate a more precise turn in feel for the driver, improving "handling" if not actual grip)
Hence typically in wet you run lower pressures (less absoulute loads anyway as less lateral G on wet suface with a lower Mu value) this heats up tyre, increases softness of compound.
It's a balance, depends upon basic construction of tyre wall, stiffer more reenforced tyres need less pressure to withstand deflection.
Also remember that the bigger increase in area when tyre pressures are low is in the front / back plane (contact patch lengthens), not across the width of tread, although tyre will "balloon" slightly.
If you thought suspension design was tricky, tyres are more of a black art even today!
Dormouse
10-02-2003, 16:32
tread block shuffle
The Official Cupranet Dance? :D :D
Dor.
Originally posted by Dormouse
The Official Cupranet Dance? :D :D
Dor.
LOL:D :D
Cuprasport2000
21-03-2003, 12:14
So for an Ibiza running 45 profiles then, is it safe to assume that fronts should be 36PSI and the rears should be 35PSI, regardless of tyre make?
Not really as different tyres like different pressure. I would say that 36/35psi is a starting point. You might want to experiment a bit up or down. If you look at the following thread you'll see that some of the guys have lowered the 40 series tyres on the cupra R down to 30psi.
http://www.seatcupra.net/forums/showthread.php?s=&threadid=15273&perpage=20&pagenumber=2
Cuprasport2000
21-03-2003, 12:41
:cheers: I had 4 x 195/45/16 Toyo T1-S's fitted yesterday and want to check that the pressures are correct as they look a little low at the moment. Should I then take them to 36PSI - Front and 35PSI - Rear, and then see from there then?
BTW - these tyres are unbelievably quiet compared with the Pirelli's I had on there before. They are much more forgiving on the bumps too. Its like driving a new car!
I would take them up, then see how the car reacts. If it becomes too harsh and bumpy lower is 2 psi and try again. They might look low, but that doesn't mean they are.
I have no experience with toyos. Probably won't either as they are very expensive hear. I used to run 36/34 in my '98 ibiza (same size your running).
Cuprasport2000
21-03-2003, 13:23
Cheers for the info Paulo. Have a good weekend mate.
:cheers:
If i'm doing a long M-way run I'll put the pressures up a couple of PSI all round. In the winter I run the rears at book pressure cos it's funny to lose the rear all the time. Now it's drier I'll put the rears slightly over book pressure cos it feels less snappy on the limit in the dry.
My rears now have so little grip that at 80+ in the wet on a private M-way the rear dances all over the place.