New Alloys But What Size

[shagpile]

I am getting some new alloys for my 05 plate is200 sportcross,I want 18'' wheels but am confused as to what tyre size mainly the profile. I been told 225/40 18 will fit and keep the speeo in sync. questions are will these work and is the speedo run off the road wheels or does it run off the gearbox. Any help would be appreciated guys.

[BenIS]

This is something ive always wanted to know really. I think what you do is when you go up a wheel size, you just reduce the profile of the tyre. I look into it more then let you know. (if someone doesnt beat me to it in the mean time )

[BenIS]

http://www.avon-tyre...heels-and-tyres

http://www.carbibles..._bible_pg4.html this link is brill. it lets you calculate what size you need. it also tells you the difference that your speedo will show you. So you just put in your normal wheel and tyre size and then your new wheel size, then change the tyre size to get the closest match you can I guess. Then you just have to take into account the difference on the speedo when youre driving. Go down to 2/3 of the way down the page.

Hope this helps

[doberdog]

There are plenty of websites out there that will assist you on this matter - the rolling size is what's important. Going from say a 16 to a 18 would mean decreasing the tyre wall size to keep the same rolling dimension. Altering the rolling dimension will change the performance characteristics of the car and the speed reading.

Google tyre size calculator and you will find a plethora of sites to assist you. Some people will say not to worry too much - ignore them go for the nearest rolling dimension you can.

Also take into account off sets etc when buying new wheels

As I said there are ****loads of sites to help you out there