jono300

iTrader: (8)

When fitting aftermarket alloys with a new set off tyres to a car just wonder how you know what tyre psi to run ?? personally run my tyres at 30psi on the hyundai coupe fitted with 17" alloys with 205/40/17 tyres but to be honest sure this was the psi that they were at when fitted and not 100% sure what exactly they should be ??

is there a chart or so that a given tyre size should have the psi set to ??

reason I ask is that after only around seven months off having the tyes fitted one off them has cracked around the sidewall enough to require replacing, was advised that the main cause off this is more than likely down to running low tyre psi.

bit confused if anyone could offer any advice as dont really want to have to shell out on another new tyre in just another few months !!

funny enough -off the four new tyres that were fitted just before xmas one has had a puncture on the sidewall requiring replacment and as above the other developed cracking to the sidewall enough to also require replacing, the brand new alloys were kerbed within the first week off being on the car even though I managed to own my last set off alloys for something like six years without litteraly getting a single mark on them- sods law eh ??!!

corradoboy

The tyre pressure is relative to the sprung weight of the vehicle. As that hasn't changed, nor do the pressures. You could consider that the internal volume of larger wheel/tyres would require a higher pressure under Boyles Law (physics) but you must also consider that usually people increase wheel size and thus reduce profile to retain a suitable rolling circumference, and the reduced tyre wall will offset much of the required increase in pressure through having a higher structural rigidity.

Run them at the recommended pressures as stated in the handbook, and adjust them to suit the driving characteristics you prefer. High pressures feel pointy and direct, but will break loose quickly. Low pressures will be grippy, but vague and wallowy.

I used to play about towards the end of the tyres lives. I always enjoyed 2psi under at the front, and 3psi over at the rear so it gripped on turn-in, but the back-end would break loose easily at the slightest provocation. Ordinarily I ran 1psi over all 'round.

jono300

iTrader: (8)

Appreciatte the informative reply - thanks again .

ALi-B

iTrader: (1)

You may want to change the pressures a little; For example the tyre plate on many BMWs have different pressures according to the size of wheels/tyres fitted.

Its only 3 to 4 psi between each extreme though.

As for kerbing your alloys, make sure the tyres have rim protectors on (thicker rubber on the sidewalls), I've inadvertantly replaced a pair of tyres like for like (same brand, size and model) but forgot to specify the version with rim protectors. I didn't notice the difference until after I kerbed the alloys a few days later.

BOB.T

30 PSI won't make your tyre crack, I suggest crap/old stock tyres.

J4CKO

iTrader: (1)

Use the female approach, has the car stopped or is it on fire due to the tyre heating up, are there sparks coming off the rim as it grinds against the tarmac ? then its fine, minor noises can be cured by turning up the radio, remember having to buy new tyres will compromise your shoe budget !

speedking

What was the tread wear like on the tyre where the pressure was so low that it caused cracking of the sidewall?