Changing tyre sizes....

[Gr44]

Got a question, not that I could really afford to do it - espically since the tyres are near new anyway.

But if you changed to 15" to 17-18" or whatever surly then the speedo will be out? which is my main question, is it easy/cost much to get it re-calibrated. Surly people who do this don't drive around with buggered speedos?

Is it a common thing you could just nip into a garage and ask them to do for 50 quid or?

Cheers

[Konan555]

You put a lower profile tyre on the new wheel to make sure the overall rolling radius is the same.

[Gr44]

Ahhhh, that makes sense, what if you upgraded them to a larger size than your existing wheels though?

[Konan555]

As in the new rims being bigger than your current Wheel AND tyre put together?

[Gr44]

yeah, just have to ask to be a pain in the arse

Hey, it could happen - atleast one dumb chav must have tried putting 22" wheels on his nova

[Konan555]

I can see it now - first lump in the road said nova hits and the wheel bounces up and rips on the arch.

the speedo is probably the easy bit

Sometimes there's just a gear you can change for the speedo cable in the box, this allows companies to use the same box and speedo combination on differnt final drive ratios.

Talking of which - gotta find out why mine's undereading...... at 60mph I'm getting a nice indicated 40mph!

[XTR]

http://www.polo-gt.co.uk/mechanical/tyrecalc.html

[Butuz]

Generally anything more than 2" bigger than the alloys that were on the car as standard is going to make the car handle like a bucket and will generally be too big.

As konan says, when you increase the size of the wheels you decrease the profile fo the tyres.

Eg on mine i got 205/55/16 if i put new 17's on i would put 255/40/17, dont forget if you put wider tyres on you may need to reduce the tyre profile a little bit extra, as 255/45/17 will have a larger rolling radius than 205/45/17 so i would need to go down to 40s.

Butuz

[Konan555]

Depending on the car you'd have to be carefull with increasing the tyre width aswell! 205 to 225 on some vehicles could end up with some shredded tyre.

[Shad]

That's where the offset comes into play, but only if your arches can handle the wheel being 'further away' from the hub.

[Konan555]

Like I said - Speedo's the last consideration

You've also gotta think about the effect of altering the shape of the contact patch.

[Gr44]

ahhh i see, some interesting stuff - now to ask the really dumb question

255/45/17 ? I assume that means 255 mm thick tyre? 45mm wide and 17 inches ?

I should really start reading up on cars
Thanks for the response - and who said chavs want good handling, some of them drop their cars by 80odd mm

[Konan555]

255/45/17

255mm wide (as in wall to wall)
45 is the hight of the wall as a percentage of the width
17" is the size of the rim it'd go on.

[Gr44]

ahhh I see, the help

edit

that was meant to be 'thanks for the help' btw bit of a typo