Tyre pressure change on after-market wheels?

dcGT

Hi All,
2 questions here: -

1. Does the correct tyre pressure for a given car change when bigger wheels & lower profile tyres are fitted? (I thought it does slightly???)

2. If this is the case, is there anywhere or any way you can find out the correct pressure for new size wheels & tyres on given a car?


Thanks,

DC.

Pimp Ninja

I'd assume that you could ask the shop that you are buying them from what the correct pressures for your tyres should be.

A word of warning, have your speedometer and odometer re-calibrated after changing your tyres because it will affect the mileage displayed on the odometer if your going to a lower profile tyre.

My brother never bothered to get this done when he changed his, and now, by doing the exact same journey in 3 different cars (2 had factory tyres) we discovered for every 80 miles he does it adds an extra one onto the clock.

HashSlinging

Depends on type of car, tyre, weight, road travelled and importantly speed. too high will cause a blow out. I'm running Bridgestones 205/55/16 @ 32 and they're fine. tried 28 but found they heated up when doing 85 - 120mph on motorway and also could feel the back end coming out. So im back to 32 PSi and they're fine. Tyres are the only thing between you and the road so make sure you've plenty of thread (at least 4mm) before you do any testing.

dcGT

Thanks lads.

@ Pimp ninja - Yeah I'm aware of the change in rolling radius, cheers. Also, your take off from the lights is killed with bigger wheels too

@HashSlinging - Yeah I've heard of the factors involved, I was just wondering is there a way of calculating the pressure, having obtained all the necessary information car type/car weight/tyre type/tyre size etc.

Also, do tyre pressures vary dramatically on road cars, or do they keep within a certain range at least?

Cheers,

DC.

JohnCleary

Originally posted by Pimp Ninja
I'd assume that you could ask the shop that you are buying them from what the correct pressures for your tyres should be.

A word of warning, have your speedometer and odometer re-calibrated after changing your tyres because it will affect the mileage displayed on the odometer if your going to a lower profile tyre.

My brother never bothered to get this done when he changed his, and now, by doing the exact same journey in 3 different cars (2 had factory tyres) we discovered for every 80 miles he does it adds an extra one onto the clock.

I'm upgrading from 14" with 180/60/14 to 17" 205/40/17 ... Should I have my speedo re-calibrated?

dcGT

Personally I wouldn't bother, just be aware of the difference when driving, use this to work out the difference: -

http://www.miata.net/garage/tirecalc.html

It would probably cost a good few quid too!

DC.