235 and 265 on non-M E85/6?

RossT

RossT

Member
 Worcestershire
I recently bought some new wheels for my 2007 3.0 si coupe, and planning to get tyres fitted soon.

The specs of the new wheels are 18x8" front ET42, and 18x9" rear ET40. Fairly conservative offsets, but the rears being 9" wide will add that 6mm or so to how far they stick out compared to stock, plus the offset. Basically the fronts are exactly the same as BMW style 224 wheels and the rears are also the same but inwards by 10mm.

I'm most likely to get the standard 18" fitments of 225/40 front and 255/35 rear as I'm not looking to add spacers and I know they'll be safe, but I do also like a meaty looking tyre so was toying with the idea of 235/40 on the front and 265/35 rear?

The reason I'm slightly hesitant is that tyre/wheel fitment calculators can't always give a reliable indication of how a tyre will fit your specific car as tyre dimensions vary slightly by manufacturer, and the outer tyre edge is the most critical part of wheel fitment as it's closest to your arches. Increasing tyre width by 10mm will add 5mm on the outer edge a bit like having a 5mm lower offset, which should be perfectly safe on the front (seeing as my car originally had 10mm spacers fitted and the new wheels are only like using 5mm spacers), but the rears could be a little bit close for comfort depending on the exact tyre chosen?

I'm sure others must have tried these tyre sizes before so any thoughts/feedback welcome. Like I say, the standard sizes will be a no-brainer and look decent (especially at the back) so I still think I'm more likely to go with those, but interested to discuss.
 
I fitted a set of E89 wheels to my second 3.0Si that had 8.5J ET40 rears with 255/35 tyres and there was still plenty of room in the arches so I don't think you'd have a problem with 9J and 265 tyres.

I realise the offsets are totally different on an M but the arches are the same size on all E86s and I'm running 265/40 rear tyres on 224s without an issue. As BMW fit 255 tyres on 8.5J rears I thought on a 9J a wider tyre made more sense, and I got a bit more sidewall protection as a bonus!

Have you tried "willtheyfit" - they seem pretty accurate.
 
The extra 10mm will be fine, the slightly increased radius will bring your speedo closer to dead-on. Tyre widths are nominal anyway - take two different makes of a given width and they'll be quite different in tread width.
 
Thanks for the reply fellow Mr T, yes 8.5J ET40 rears with 255/35 tyres would be the same as when I had the 10mm spacers with my standard wheels and there did appear to be a bit more room to play with, just wondering about that roughly 11mm or so extra from the 9J wheel plus wider tyre. It doesn't sound much but you're getting close to a 224 wheel on a 3.0si E86 which I know are tight but work due to the 255s leaning in. I have directly compared to a 224 rear fitment on willtheyfit and it looks very similar/close in the tyre edge area!

Thanks as well Scott, I think the wider tyres would fit as you say but I suppose the other question is whether I really need that width with stock power, when 225 + 255s will be cheaper...
 
Hah. As someone who objects to spending more then necessary on rubber, I'd be sticking with 225s!

On my first car (997cc Nova) I went from 135R13 to 155/70 13 and did revel in the chunkier stance and profile. I suspect that 15% increase was far more noticeable than 10mm on our steam roller wheels ever will be!
 
Isn't 245mm wide the preferable tire width for a 9" wheel? At least for grip and handling.
 
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Rsipad said:
Isn't 245mm wide the preferable tire width for a 9" wheel? At least for grip and handling.
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I'd have thought that would look a bit stretched.

How would it offer better grip than a wider tyre? Surely more unsprung weight from a wider rim would just make handling worse?
 
Mr Tidy said:
I'd have thought that would look a bit stretched.

How would it offer better grip than a wider tyre? Surely more unsprung weight from a wider rim would just make handling worse?
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An oversized tire = more tire rollover and more shoulder = less responsive. A tire with a slight amount of stretch makes it roll over less during cornering which means its more responsive. In terms of raw grip, you're not gaining anything with an oversized tire either as your contact patch is the width of the wheel, that extra tire "width" just becomes more shoulder when cornering.

Wider rims = more contact patch = more space for tire to operate. Tire can stick to the ground and release heat in more area. Also, if you go with forged or flow formed wheels, the difference in weight between narrow and wide wheels isn't too much (and the extra grip via more contact patch more than makes up for the slight weight gain).

In the case of the M, going from stock 224s which are 24lbs front and 26lbs rear but my 18x9.5F and 18x10R setup is 19.2lbs and 20.2lbs respectively.
 
245 would fit fine on 9" width wheels as in RMB's table, but I've also seen people on here fitting that width on 18x8J wheels at the rear and not having any problems. I doubt most would notice much difference between 245/255/265 unless going for fastest laps on a track.

It makes sense that cornering response is a little better with tyres that aren't wider than necessary for the wheel width, but as BMW puts 255s on 8.5J rears for my car as standard I'm planning to stick to 255s for my new 9J wheels (PS5 tyres ordered but not fitted yet).
 
RossT said:
t makes sense that cornering response is a little better with tyres that aren't wider than necessary for the wheel width, but as BMW puts 255s on 8.5J rears for my car as standard I'm planning to stick to 255s for my new 9J wheels (PS5 tyres ordered but not fitted yet).
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That's why I decided 265s on 9J rears would be fine on my car. It's only 10mm more tyre width on a rim that's 12.5mm wider!
 
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