Anyone know a bit about tyres?

[Canary_Yellow]

Increased the diameter by 8mm, but increased the circumference about 25mm.

215/40 would be 540mm circumference, and 225/40 would be 565, an increase of 5%. If the speedo does depend on this it would read under speed which isn't ideal with all the speed cameras about.

Maybe BMW's are clevererererer, or they use the rear drive wheels for speedo?

It's only a 1.27% difference.

The tyre has a diameter of 172 (in a 215/40) and the wheel is 457.2mm (18 inches). So 629.2 diameter.

Plugging that into a 2 x pie x r calc gives a circumference of 1976.7.

A diameter of 637.2 gives a circumference of 2001.82.

The difference of 25.12/1976.7 x 100 = 1.27

EDIT: I think your calc might have left out the wheel?

 

[Region3]

It's only a 1.27% difference.

The tyre has a diameter of 172 (in a 215/40) and the wheel is 457.2mm (18 inches). So 629.2 diameter.

Plugging that into a 2 x pie x r calc gives a circumference of 1976.7.

A diameter of 637.2 gives a circumference of 2001.82.

The difference of 25.12/1976.7 x 100 = 1.27

EDIT: I think your calc might have left out the wheel?

Only an idiot would forget about the wheel

 

[stevelev]

Asda tryes always a good place to try, always good to ask your local dealer if they can price match, if not Asda are using most national fitting conmpanies and dealerships to provide the service

The have a variety of your size, though not run flat, there are part worn run flATS ON ebAY

http://www.asdatyres.co.uk/215-40-18

aND FOR THE GEEKS AND THE op HERE IS A SITE THAT GIVES YOU ALL THE OPTIONS WITH THE RELATIVE VARIANCE(S)
https://www.mcgrefer.com/sizeinfo/2054018

 

[D4RK1]

Before you buy have a look at Goodyear efficient grip performance. We've had 4 of these in 225/40/18 on the wife's gti and I can confidently say they are the best tyre I've driven. I was never impressed with potenzas. Had them on the golf and on my caddy van. The good years are amazing in wet conditions and come out at £85 a corner fitted and balanced. I'll be going for these on the van when it's due some new shoes.