[rick228i]

Hello,
I went to the tire shop to replace my old Pirelli P0, front 225/40R18 rear 245/35R18 on my BMW 228i.
When I got home I realized the tire shop installed 245/40R18 on the rear instead of the recommended 245/35R18
It does not look right to me.
How can I know if this option is still acceptable for my car ?
The tires seems way noisier than the old one I have but this unrelated probably because the brand is different, not Pirelli.
What could be the disadvantage on this replacement ?
I did not even know that 245/40R18 can replace 245/35R18
Thanks for your comments

Rick

[KennyFSU]

It's only a 5mm higher sidewall, which will make handling slightly worse since there's more flex now but ride quality may improve since it will ride softer on harsh roads. If your car is just a DD it'll be fine, just run them until they wear out.

[rick228i]

I'm in California where the speed limit is very low... yes is my DD car and I do not plan to run it faster than 70 or 75mph. Anyway apparently feels like the handling is ok anyway unless I go to Laguna Seca, in that case yes I might notice a difference... you are right.
thankd for your help.

[aerobod]

If the tyre is not rubbing and your car is RWD and not AWD, then the only effect may be very slightly reduced acceleration due to the larger diameter tyre and your speedo may be reading below the posted speed (although BMW speedos typically read a few percent high, so it may be more accurate now).

With an AWD car the increased diameter mismatch between front and rear tyres could be problematic due to the extra strain on the centre viscous coupling.

[rick228i]

228i is RWD, the tire is not rubbing even though my car is not full weight loaded (4 persons + luggage).
So you think I can stay with it ?
Thanks

[GregoryG]

The sidewall hight difference is 12.5 mm, with an overall larger diameter of 25mm, or about 1 inch.

https://tiresize.com/comparison/

As long as it's not rubbing you shouldn't notice any difference.

[Ajowhan]

Originally Posted by KennyFSU

It's only a 5mm higher sidewall, which will make handling slightly worse since there's more flex now but ride quality may improve since it will ride softer on harsh roads. If your car is just a DD it'll be fine, just run them until they wear out.

The 40 is not 40mm sidewall, its a percentage of the tire width which is 245. Its a 12.25mm different.

This is an estimate but, calculating tire specs with 18" diameter, diameter of our wheels is roughly 628.7mm. A 12.25mm different is only about slightly less than 2%. Shouldn't be an issue.