Fitting non standard tyre sizes?

[Phateuk]

Need some new rears for my M3, I really want some PS4s but nowhere seems to have any stock in 265 35 19, there's plenty of availability for 275 35.

I've always fitted like for like replacement with tyres sizes, and never considered anything else - is this doable? I'm thinking 1cm extra width won't make much/any difference?

Thoughts/comments?

[Pica-Pica]

I personally would always stick with recommended sizes. However here is a good site for calculating rolling circumference differences to compare speedo differences. Beware other sites that only calculate STATIC and UNLADEN diameters and circumferences.

http://www.wheelcalc.com/

[gizlaroc]

What is the front tyre size?

The M3's traction etc. is all set up for a certain rolling radius, changing that radius on one axle 'may' cause issues.

The reason I ask about the front tyres size is you might be better to go 255.35.19 than 275, or if going 275 then you may need a 30 profile instead of 35.

[Phateuk]

The fronts are 245 35.

I hadn't considered the rolling radius being affected by changing only the width, I'd assumed that was only if changing the tyre profile.

If it will cause issues I guess I can just get some PSS instead as there seems to be plenty of those

[gizlaroc]

Just checked, it is 245.35.19 on the fronts, so 265.35.19 is giving a spot on rolling radius for front and rear.


Personally I will stick with 265.35.19, and make sure it is exactly the same PS front and rear. I had a newer pilot sport on the rear of my M3 when I got it and it was a twitchy mess. Took new control arms, dampers and springs, top mounts and all bushes before we realised.
Put the new PS on the front as well and Bingo!! Handled perfectly.

[gizlaroc]

https://www.camskill.co.uk/m55b0s2172p145769/Miche...

[Liamjrhodes]

as long as you change both tyres on the same axle there will be zero issues going from a 265 to a 275. It is such a small change. I will pretty much guarente you could buy two different manufacturers 265 and they wouldn't measure the same

[d_a_n1979]

As above

Going from a 265 to a 275 will cause no issues at all; in fact it'll offer you better sidewall protection for your alloy and in some cases, it can actually make your speedo more accurate!

Use a tyre calculator online to check; as long as it's with +/- 2.5% of the original measurements; you're fine

FYI I run 275/35 and 245/40 18" tyres on my E39 when OEM spec tyre sizes are 265/35 and 235/40 for 18s; I have zero issues and the ncar actually handles that bit better etc...

Check Camskill and Tyreleader for tyres too; they usually offer the best prices by far, you just need to get them fitted

[Pica-Pica]

Phateuk said:

The fronts are 245 35.

I hadn't considered the rolling radius being affected by changing only the width, I'd assumed that was only if changing the tyre profile.

If it will cause issues I guess I can just get some PSS instead as there seems to be plenty of those

Yeah, the profile height is the % of the width (when unladen) so 275/35 would be 96.25mm, and 265/35 would be 92.75mm. As said, I would stick with prescribed sizes, especially on that car and especially with regards to insurance company’s view.

[d_a_n1979]

Adding the 275s will not cause ANY issues whatsoever

Pica-pica; sorry, but it's like you're scaremongering when you don't really know what you're talking about

Many folk run a tyre one size wider; as already mentioned, it offers a better, straighter sidewall and better rim protection

Your insurers will also not bat an eyelid over them; obviously mention it to them, but it shouldn't change a jot

[Herbs]

d_a_n1979 said:

Adding the 275s will not cause ANY issues whatsoever

Pica-pica; sorry, but it's like you're scaremongering when you don't really know what you're talking about

Many folk run a tyre one size wider; as already mentioned, it offers a better, straighter sidewall and better rim protection

Your insurers will also not bat an eyelid over them; obviously mention it to them, but it shouldn't change a jot

Out of interest, what are the downsides in comparison?

[gizlaroc]

Herbs said:

Out of interest, what are the downsides in comparison?

The downside is that many think the E92 and F80 don't feel quiet oversteery enough as it is, those who have run a square set up on 18" track wheels, so 245 front and rear, have said it feels better, a bit more like you would expect from an M3.

Going wider you will exaggerate that even more.

They do tend to tramline a bit more too.

Having said that, some may prefer the extra grip a wider rear offers, it is after all the reason BMW put the wider rear on in the first place.

[gizlaroc]

I should add though, the PS4 is not a particularly wide tyre anyway, it will actually have less central tread than many other brands 265 wide on a 275 wide.

[gizlaroc]

Phateuk said:

The fronts are 245 35.

I hadn't considered the rolling radius being affected by changing only the width, I'd assumed that was only if changing the tyre profile.

If it will cause issues I guess I can just get some PSS instead as there seems to be plenty of those

DO NOT MIX TYRES FRONT AND REAR ON AN M3!!!!!

[d_a_n1979]

gizlaroc said:

DO NOT MIX TYRES FRONT AND REAR ON AN M3!!!!!

I agree...

My pal ran PS4s on the rear of his E46 M3 but had Eagle F1s on the front (IIRC) and it was bloody awful. That was on 19" alloys FYI

He ended up putting the F1s on the rears too, they weren't a good tyre for the car IMO; gripped fine, but lethal in the wet

[gizlaroc]

Problem with F1s is they grip well, but when they let go they do it with a hell of a snap.

They work great with AWD cars, but a tyre that lets go progressively is far nicer for an M3.

[Prinny]

My 2-p.

I agree with Dan about the sizing - i’ve run +10mm on all tyres on my 335d, z4, 760, and when the M6 needs new boots, it’ll be going up 10mm too. It makes the speedo more accurate (less over-read, 30 is 30, etc) and it also has slightly more protection for the rim when parking badly. Not had any issues otherwise.

I also agree vehemently with Gizlaroc! Don’t mix brands on anything with an M-Diff. They really, really don’t like it.

[Olivera]

d_a_n1979 said:

He ended up putting the F1s on the rears too, they weren't a good tyre for the car IMO; gripped fine, but lethal in the wet

Eh? Eagle F1s (every generation of them) have consistently been amongst the best in the wet in tyre tests, and have always been EU wet A-rated.

[Pica-Pica]

d_a_n1979 said:

Adding the 275s will not cause ANY issues whatsoever

Pica-pica; sorry, but it's like you're scaremongering when you don't really know what you're talking about

Many folk run a tyre one size wider; as already mentioned, it offers a better, straighter sidewall and better rim protection

Your insurers will also not bat an eyelid over them; obviously mention it to them, but it shouldn't change a jot

I am just advising that the insurance company may have a view on changing tyre sizes from specifications. Then you say the same, that is “obviously mention it to them”. WTF?

[Pica-Pica]

gizlaroc said:

DO NOT MIX TYRES FRONT AND REAR ON AN M3!!!!!

You mean ‘keep the same tyre brand and tread design all round’