AFAIK even the fattest, lousiest comfort slime tyres have a max of 300kpa. Low profile stuff usually can go much harder. stay below 80% max pressure for safety.

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Added on February 23, 2008, 2:27 am

Those tractor tyres are supposed to be soft and wobbly. Truck tyres run around 500+ kpa

Nothing will happen wan lah.. as long as u pump it to spec @ 420kpa..

PS. Personally I have seen a saga pump 400kpa, yes, 400, into 4 of his normal tyres (was waiting for him to finish using the airpump)