Refurb or get rid. What do you think?

Speedo shouldn't need recalibration - 18s will have lower profile tyres than your old 17s so the circumference of the tyre won't change enough to worry about
 
Speedo needs no change as you have lower profile tyres on 18's which maintain the same rolling radius.

Edit - popped to post :)
 
Well my current tyres are 225/45/17 all round, which if I understand correctly, makes my current tyre wall 101.25mm high.

The new wheels are OEM Z4m which I believe (rear tyres) are 255/40/18. This would make the tyre wall 102mm high.

I would have a slightly higher tyre wall and larger wheel diameter. Assuming the speedo measures the rear wheels, would this put the speedo out by much?
 
On the M spec tyres you will have a greater ride height & smaller arch gap with a speedo difference so a reading of 60mph will be nearer 58mph but in reality you need to fit the wheels & then run the car with a satnav to give you the answer :wink:
 
Nice one. Useful tool ekimj10, cheers.

I'll do a sat nav check too when I get the new wheels fitted.

Mr.Wilks, sent you an email last week. Did you want my 17's once I've got the 18's fitted?
 
I wouldn't worry, my speedo is apparently correct with the SatNav plugged in and my wheels are 19''
 
Mark-Z4 said:
I wouldn't worry, my speedo is apparently correct with the SatNav plugged in and my wheels are 19''
Click to expand...


Checked with Tomtom my Z is also reading correct on the speedo with non factory wheel widths & 18inch M spec tyres fitted :?
 
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