I also posted this as a follow up to the previous post.
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I purchased the 245/40X20 and 275/35X20 from Tire Rack (not Tyre Rack)
They will email you and tell you that the tires are not standard sizes. Just respond “okay “you know.
Local tire shop mounted them up with no issues.
Factory wheels, no spacers.
Everything fits, no clearance issues.
Just for reference... many vehicle manufacturers have put wider than tire manufacturers recommend tires on narrow wheels as original equipment. Both BMW and Porsche have done this.
Because the wider tire has a higher load carrying capacity at a lower inflation pressure.
You can reduce front and rear tire pressure by around 3 psi to carry the same weight as the original equipment tire to coincide with what BMW decided to use. By reducing the inflation pressure a couple of psi that will also help compensate for a wider tire on a narrow wheel wanting to bulge in the center and give you a more even tire wear.
Original tires
Front 215/45X20 load index 95XL @32psi=1227 lbs
Rear 245/40X20 load index 99XL @32psi=1371 lbs
New tires
Front 245/40X20 load index 99XL @28psi= 1243 lbs
Rear 275/35X20 load index 102XL @29psi= 1388 lbs
I decided on running 30 psi in the front and 30 psi in the rear. (The tire pressure monitoring system is happy down to -25% or 24 psi.) Just as a starting point, and see how it feels and how the tires wear.
So far, so good.
Load index vs inflation pressure:
https://www.toyotires.com/media/2125...s_20170203.pdf
Tire size comparison chart:
https://tiresize.com/comparison/