From what I gather my Tom Tom GPS states that my Furby speedo is around +6% out which I assume is accurate.

My thoughts are that if someone was to put wheel/tyre of a larger diameter than std. up to +6% it would be more accurate as well as having the advantage of filling the arches better.

Has anyone done this without having rubbing problems with arches? I'm talking about diameter, not width here (maybe small increase to 215mm tyre).

example of increased tyre size would be -

std 205/45/16 23.26 inch

17's 215/45/17 24.62 inch (+5.75% increase in diameter)

18's 215/40/18 24.77 inch ((+6.43% increase in diameter)

Just curious......

I'll be shoehorning some 18x8 wheels on this week with 215/35/18 on, i'll keep you posted.

I'll be shoehorning some 18x8 wheels on this week with 215/35/18 on, i'll keep you posted.

That's a +2.8% increase in diameter for your tyres.

I'd be very interested to hear your views on moving from 16" to 18" wheels. More in particular the ride quality!

Good to see you have Eibach springs too, same as me so I look forward to hearing from you!

I don't know which is spot on but my GPS was showing 67mph when the speedo showed 70mph (standard wheels/ tyres)

Wouldn't the profile be 40 with 17"s and 35 with 18"s?

Bit is the difference a constant 6%?

And what about tyre wear? There is a potential difference of around 6mm from a new tyre to a knackered one.

I run 215/40/17..............Speedo is spot on with my Road Angel

I run 205/40 R17s - My Navman says I am going just 2mph slower than I really am according to the speedo, when it reads 80mph. I should think using 215/40 R17s on the front next time around will make it a bit closer to spot on, marginally.

Bit is the difference a constant 6%?

And what about tyre wear? There is a potential difference of around 6mm from a new tyre to a knackered one.

It's been 6% out from just about new and it's across the board, at least up to 100 (kph that is )

Although I now have eibachs which look soo much better than std. there is still a gap between the arches. I don't necessarily want to go any lower but bigger wheels and tyres might help a little here and correct the speedo too!

I just think the arch size is a little too big for the std. wheel/tyre diameter size.