hey i was just wondering how much my car will be off now sicne i go biggers wheels for my 4x4. the only markings i can see tha indicates size on the old tyres were, 205r16 the new news are 31x10.5x15 thanks

goggle dude

http://www.google.com.au/search?hl=en&q=tyre+size+calculator&btnG=Google+Search&meta=

Yeah, Goggle it... that'll work :nuts:
:bowrofl:

goto the trye shop they will help you otherwise a tyre rolling diameter calculator will help

there's not enough info for us to help you determine the change in size of your wheels.

you need the old sidewall markings that will enable us (or you) to work out what the old rolling distance was and compare it to the new rolling distance.

your new tyres are in Imperial measurements which mean 31" in diameter, 10.5" in section (width) and fit on a 15" rim. so your new outside diameter is 31 x 25.4mm = 787.4mm which gives a rolling distance of 2.473 metres.

your old tyres will have 205/xx R16 on them... without that xx number we can't help.

cheers,
.wook

You need to know the diameter or circumference of both tyres. The tyre manufacturer should be able to supply the fitted diameter figures, if you are using BFG's, they are available on the web.

Assuming that your speedo used to be accurate, take the new tyre diameter, divide it by the old tyre diameter and then times that by the speed indicated by the speedo, this is your actual speed.

Easier still, use a GPS to indicate your real speed while you compare it to the speedo indicated speed.

I've had to change speedo gears a few times for tyre changes on my Jeep.

Ken