wheel size diameter variations!

[Jcerb]

I was looking earlier on a tyre calculator http://www.tyresave.co.uk/tyresize.html and was puting in the standard 16" saturns(which are bang on a sat nav for accuracy)compared to 17's(rl7) and 18'(spiders) with recomended tyres and they are miles out on diameter. This must affect speedo massivly, for example: spiders with 40 profile tyres are 34mm bigger than saturns on the recomended 45'. Has anyone calibrated their speedo's after? Must slow acceleration too. Were all the calibrations done from the factory depending which wheel size you chose?

[ttmr]

Thought the 4.5s were 17's standard with optional 18's,so should be correct,don't know about 4.2's or speed six?

[kirknisbet]

based on front tyres

225-45-16 against 225-40-18

with this combination youre speed will be 4.6% greater than indicated

when youre speedo reads 30mph you will be actually doin 31.4mph and when youre doin 60 it will be 62.8mph

hope this helps plus if the wheels are heavy may notice the fuel being used slighty more

245 45 16 against 255 40 18

will be 5.5% increase speedo 30mhope this helps plus if the wheels are heavy may notice the fuel being used slighty more it

will be 31.6 mph and at 60 it will be 63.3mph

Edited by kirknisbet on Sunday 12th June 11:18