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got chance of some 18" chrome wheels for the celsior(91) brand new, but how do you get the tyre size for the new wheel to keep the same circumference,at present there 16" with 225/60/16 tyres,bit thick when it comes to this as ive never changed sizes before,will 18's fit ok or are 17's a better bet,help would be appreciated. thanks. Ian

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Hi,

This site might be of help,just tap in the standard size/profile of your tyres and it should tell you all the sizes that are the same or close to yours :)

http://www.performancetyresdirect.co.uk/co.../converter.html

Chips.

It's easy to work out...

205x65 on 15" =

15" x 25.4/2 = 190.2 (wheel radius in mm)

205 X 65% = 133.3 (aditional radius of tyre on top of wheel in mm)

Total = 323.5mm

Same for 18"

18" x 25.4/2 = 228 (wheel radius in mm)

225 X 45% = 101 (aditional radius of tyre on top of wheel in mm)

Total = 329mm

Bigger wheels and wider rubber needs smaler profile to keep your speedo something like!

I Checked my speedo with GPS and at 70mph indicated the actual was 65.5. This is 7% out, this means that a little larger rolling radius should only go towards correcting the speedo example above increased rolling radius by 2% so you could probably even go up to 225x50 on 18's

Hope I'm not just stating the obvious ;)

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Hi,

I was never really any good with maths :D

But i have great common sense.

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