Tyre pressures.
Discussion
My Chim has non-standard wheels, with 17" fronts (215/40 ZR17) and 18" rear (245/35/ZR18). The tyres needed air (looked a little low and the rear was really squirming under full throttle). I have gone for 30psi/ 2bar front and back as a starter. Anybody care to advance on this as there's no real guidance? 
I'm no expert on tyre pressures, but if you have the same area of rubber in contact on the ground, i.e. the same width tyres as standard, regardless of the diameter of the wheel / tyre I would have assumed that the original tyre pressure would equally apply.....22 front, 24 rear. I could be totally wrong so check. But if you run too high you will just wear the centre of the tyres out and have less grip.
I'll deflate them a little tomorrow. 
At the end of the day it's how they feel on the road but even on much lower profile tyres I'd have thought that 30psi would be excessively hard.
What did you use as a pressure gauge though? The forecourt ones aren't very accurate at lower pressures and don't even bother with the ones built into 12v compressors - the only thing they're any good for is making sure that you're at least consistent from side to side.
I ended up buying a couple of accurate rubber-cased glycerine-filled gauges (one that covers 0 - 15 psi for a quad that I had and one that covers 0 - 45 psi for the car) about 15 years ago and never regretted them - makes getting consistent pressures a doddle ...
What did you use as a pressure gauge though? The forecourt ones aren't very accurate at lower pressures and don't even bother with the ones built into 12v compressors - the only thing they're any good for is making sure that you're at least consistent from side to side.
I ended up buying a couple of accurate rubber-cased glycerine-filled gauges (one that covers 0 - 15 psi for a quad that I had and one that covers 0 - 45 psi for the car) about 15 years ago and never regretted them - makes getting consistent pressures a doddle ...
They don't seem to bad if I'm honest, but it was nice and dry today when driving her. I used one of those awful Cig Lighter manual tyre inflator gauges and pushed until the hit 29/30psi. I gather they're probably around the 27psi mark. Have just looked at the glycerine-filled gauges as suggested, but are a tad on the expensive side. I was thinking of one of these:
http://www.amazon.co.uk/Draper-69924-Pressure-Gaug...
http://www.amazon.co.uk/Draper-69924-Pressure-Gaug...
Edited by chris1972 on Saturday 16th February 22:49
Can I be cheeky and extend this a bit?
I have three sets of wheels and tyres and need pressure advice on all three please:
1. 15/16 inch Imolas running normal road tyres (typical standard saloon tyres, which I use for winter). I had been running these at 22/24 psi
2. 17 inch wheels on which I have Yokohama Parada Spec 2s. I had these also at 22/24 psi, only because I didn't know better. Ran the car on them all summer on road and track. However, they felt good.
3. Just bought 17/18 inch SP12s with Toyo R888s. 215/45 ZR on the front, 235/40 on the rear. Track days only. Just got them. Not a Scooby what to run them at.
Thanks
I have three sets of wheels and tyres and need pressure advice on all three please:
1. 15/16 inch Imolas running normal road tyres (typical standard saloon tyres, which I use for winter). I had been running these at 22/24 psi
2. 17 inch wheels on which I have Yokohama Parada Spec 2s. I had these also at 22/24 psi, only because I didn't know better. Ran the car on them all summer on road and track. However, they felt good.
3. Just bought 17/18 inch SP12s with Toyo R888s. 215/45 ZR on the front, 235/40 on the rear. Track days only. Just got them. Not a Scooby what to run them at.
Thanks
£12.50 each? http://www.oilybits.com/pressure-gauge-glycerine-f...
... but the Draper looks fine too.
... but the Draper looks fine too.
Edited by Bassfiend229hp on Saturday 16th February 23:02
SILICONEKID350HP said:
No idea what standard Draper calibrate them to but I would expect they'd not be far out - it's the gauges on cheap 12v compressors that I've always found to be a little "special"...
Back to the original question, I also have 18" rears and 17" fronts and the car came back from tyre fitting with 30lbs all round. And was horrible, nervous and twitchy on bends that weren't smooth as a baby's..
Dropped to 24 front 26 rear and much happier now, nice and calm and smooth. Amazing the difference a few pounds can make.
Dropped to 24 front 26 rear and much happier now, nice and calm and smooth. Amazing the difference a few pounds can make.
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