Help with Tyre sizes

[SBN]

Got a 2009 m3 with 18" alloy set up

The summer setup on the fronts (8.5 wide) is a 245 40/18. Will it be wise, ok, crazy to use a 235 40/18 as I have some for a winter set up on this rim?

[SBN]

Thanks, called BMW they were kind of helpful but wouldn't couldn't recommend It. Same with Ats as well.

Thing is a 8" BMW alloy on the e90 takes a 225 as standard. This is a 8.5 so why jump up to a 245 surely a 235 would work??? But then BMW puts a 245 on for a reason and must contribute to handling, turn in etc having the 245 vs 235

[SBN]

B'stard Child said:

SBN said:

Got a 2009 m3 with 18" alloy set up

The summer setup on the fronts (8.5 wide) is a 245 40/18. Will it be wise, ok, crazy to use a 235 40/18 as I have some for a winter set up on this rim?

That's a significant difference in rolling radius

I'd be looking more for 235/45 18

Interesting comment I thought the profile combined with diameter of the alloy attributes to rolling radius?? Am I wrong in my limited understanding as I thought the 235 is how wide not how round a tyre is?

[SBN]

Sounds veeeeeerrrryyy complicated so I think I will pass on these and look for something that is the same as what I have.

Had no idea that the three measurements on a tyre were not as straight forward as you'd guess them to be. Thanks for your help.

[SBN]

I'll have a look at the handbook later but I did speak to BMW and they would only specify the tyres I have on the car without another option being available.

[SBN]

TA14 said:

SBN said:

I'll have a look at the handbook later but I did speak to BMW and they would only specify the tyres I have on the car without another option being available.

Predictable - they didn't say that it wasn't OK though. You'll be running with the same radius that you run when the 245s are quite worn (but still legal) and a width which won't bother you unless you're at more than 9/10s of the handling capability. Unless there's some weird electronic sensor issue or something you should be OK - that's why you could just do with a BMW expert to confirm it. You need a good independent BMW specialist or a friendly tyre company engineer that knows the car to remove that 1% of doubt; I guess that most people would just try the tyre.

It's £300 against 1% doubt good odds but I'm not the expert. Love the help on here guys it's really useful but will instead look for the correct tyres and then I won't get any warranty issues or similar etc

[SBN]

Ok another question related but this time is based on the correct tyre sizes needed.

I want to fit michelin alpin all the way round... Found some almost brand new 265 alpin pa2 for the rear on eBay but as they no longer sell these, finding some matching 245 alpin pa2 is proving difficult.

Is it ok, to mix pa2 and pa3/4 if the axles are the same models eg pa2 rear and pa3 or 4 upfront?

Reason I say this is there is a lot of threads online about summer ps2 and PS3 mixing because the replacement to the ps2 was the pss. The PS3 was noted as having softer sidewalls and therefore not recommended to be mixed with a ps2 on another axle. So does the same apply to winters as it does to the summer models?

[SBN]

Ok so there appears to be 235 40 18 setup for the m3 but it's on a 8j alloy not the 8.5j alloy I have. The winter set up is square all the way round where as mine is staggered.

So reading all the above does the 8j provide a better rolling diameter than my 8.5j because BMW fit as standard the 235 40 18 to these, all be it on 8j wide rather than 8.5j

Thanks

[SBN]

Also if deviate away from BMW's recommendations will IT invalidate my warranty...? Would my insurance company care or use it against me if I wrote it off etc?

[SBN]

B'stard Child said:

Have you tried using the search facility?

https://www.abi.org.uk/Insurance-and-savings/Produ...

Just seems you want answers to a lot of questions that have been covered a lot before

Thanks for that had a quick look and the key words is within the manufacturers specification so will check my handbooks to see if the 235/40 is an optional tyre fit in the guide?

[SBN]

Just looked in the manual and it specifies 235/40 but only on the winter set up with the same size all round. For the staggered set up like mine it specifies the 245/40

Will probably end up getting what the manual says and avoid all shadow of doubt