Biggest tyre radius wise

[asoni]

I have oem 20” alloys which take quite a low profile tyre which obviously compromises comfort a bit. I’m not willing to go down to smaller alloys to fit a bigger profile tyre but I was wondering, is there any reason you can’t fit bigger profile tyres on these 20” wheels to make ride a bit more comfortable? I also actually like the chunky look on 4x4’s.

Reason I ask is people fit anything up to 22” alloys to these cars which must increase the radius even if paired with very low profile tyres. So I guess  there is no technical reason why the overall radius can’t be increased on 20” wheels, assuming they are actually available.

[X5Sport]

The rolling radius does not change as you increase the hub size, hence the profile number coming down as the hub gets larger.  All of the wheels and tyres offered by BMW on the E70 have the same overall diameter.  My 19” wheels are the same diameter as my 20” wheels but have a different profile to ensure that.

If you change the profile away from factory you will change the speedo calibration and will very likely mess up the transmission to the point it breaks.  Your speedo is not permitted to under read, but can over read by 10%.

In theory I can fit 19” on the front and 20” on the rear with their correct tyres (as per the factory plate) and the transmission and speedo won’t care as their circumferences will match.

[asoni]

Thanks, that make sense however with people that put 22" wheels on, the profile must have to be incredibly small in order to not increase the overall radius!.

[X5Sport]

It is /30 front /15 rear.  More like rubber bands than tyres!

[asoni]

I thought my 40 and 35 were bad!!