Two of my tyers (both left hand side ones) looked a little flat during the day so I stopped at a servo to check on them and give them some air. At first I noticed it said max pressure was 51psi!!! And I was like, whoa, that's up there. Finally noticed it happened to say that the max pressure was for USA and Canada, whatever that's about.
In the end I settled on 35psi all round. Does that sound right? These are brand new SP9000's, standard XR 18's.
35 PSI seems about right. I run 36 in the fronts and 34 in the back on my XR8 with the 18 inch wheels and that seems to work pretty well. I run a little more in the front tyres because of the extra weight over the front wheels.
51 PSI in the US might have something to do with driving in snow maybe.
we usually put 38psi minimum in 18s, pref about 40psi, because the stiffer sidewalls put more 'weight' on the outer edges of the tyres, and you have to increase pressure in the center to compensate and get even wear.
but 'normal' commo and falcon tyre wear could be completely different.
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36psi what I would use on normal cars but because the XR8s are not normal cars and they have lower profile tyres, I would actually be using a quite high psi. If you are doing highway driving, it is even recommended that you keep them at around 50-51psi!
Assuming that you don't do lots of highway driving but you live in areas with 80km/h speed limits, I would be setting the rears to something like 45psi and the fronts to 47psi or even higher! This is better for the wet (which we have been getting a lot of lately), even wear and of course she will handle significantly better.
Mum uses what I tell her and she thinks that that was the best compromise. You don't want to get in trouble in a crash for tyres not being inflated enough. Really, the more the better really unless you are doing beach driving (in an XR8?) up till the max psi.
My cars 15"s max is 44psi and yesterday I set the fronts to 40psi and the rears to 38psi. Not very comfortable but who wants to crash in comfort? She handles way better and I can hear them work as they squeal when I take corners tighter than usual. To me you guys with 18"ers setting to 36psi is a bit too low, in general, those ratings should be used for cars like mine with smaller rims and bigger tyre walls.
Remember: Overinflation is when you go over the max psi indicated on the tyres which is 51psi. Tyres are the most important thing to your car so check them at least twice a week with your own metal gauge.
Ok i'm running 17x7 wheels with SP9000 tyres. I seem to be the odd one out in that i set my rear tyre pressure to 38 and fronts to 36. Reason being is that i feel the XR6 with a neutral even tyre pressure all round under steers abit too much for my liking. Therefore putting a tad more in the rear gives it abit of oversteer bias.
What i'm amazed at however is people running there cars with over 40psi. Believe me even with an XR6 running 38psi in the rears results in eaasy wheel spin in the dry.
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A word of warning, if you notice your tyres have lost pressure, take them off the car and repair them immediately. Don't do what I did and think it would be ok to drive them a couple of klms down to the servo to pump them up. I found out the hard way that the rims will rest on the inner wall of the tyre and cause them to chew the rubber down to the wire. The tyre pressure when I got to the servo was 16psi and it didn't look that low.
When I took the tyre in to have the nail removed and repaired was when the problem was noticed. That short trip cost me over $400.
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I used to run 36psi allround in my 17x8 Tickford's(Dunlop's) but I started to notice a quick wear on the inside edge's,so after some discusion's with the boy's at Herrod's and a wheel allignment they advised me to run 40psi all round,I'm hoping this will slow the wear down that these tyre's are bad for.
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