What Size 18" Tyres?

[EViS]

My run-flats will need replacing soon and I'll be ditching them for non runflats. What size rubber should I be fitting to my 18" 107's? Currently I have 255/35 R18 on the rear and 225/40 R18 up front. Is this correct, or should I have 225/40 R18 all around?

Edited with correct rear tyre size.

 

[Dav the wheel nut]

They are 8'' fronts and 8.5'' rears so you could easily go 225/40/18 fronts and a wider 255/35/18 rears which was a standard set up on 108s.

 

[EViS]

What's the benefit of wider rears?

 

[ben g]

What's the benefit of wider rears?

Bit more grip, I guess. People say the rears handle skinnier tyres fine.

I just stick with the OEM specs in terms of tyre size.

The 255's look better than 225's from behind too.

 

[philbo909]

My run-flats will need replacing soon and I'll be ditching them for non runflats. What size rubber should I be fitting to my 18" 107's? Currently I have 225/35 R18 on the rear and 225/40 R18 up front. Is this correct, or should I have 225/40 R18 all around?

I think you have 255/35/18 on the rear. Just replace with oem size rubber and you'll be fine

 

[Piper1]

What's the benefit of wider rears?

Wider back gives wider foot print therefore more grip in back for less tail kick out resulting in touch more understeer than square stance.

 

[Tyreman]

You could go up in aspect ratio like on the M and that will improve ride quality too

 

[Mr Tidy]

I think you have 255/35/18 on the rear. Just replace with oem size rubber and you'll be fine

Yes, I think you'll find this is what you have - they are the standard BMW sizes for those wheels. Rears are wider because the rear rims are wider as someone said.

But if you find the ride firm, as tyreman says you could go up slightly on the aspect ratio - I'm pretty sure someone recommended 245/40 x 18 for the rears.

 

[Tyreman]

I think standard M sizes are

F 225/45R18 & R 255/40R18

 

[EViS]

Yes, I do in deed have 255/35's on the rear. Thanks for all the replies folks! :driving:

 

[ben g]

I think standard M sizes are

F 225/45R18 & R 255/40R18

Indeed. They cost a lot more than standard Zed sizes aswell.

 

[MACK]

I think standard M sizes are

F 225/45R18 & R 255/40R18

Indeed. They cost a lot more than standard Zed sizes aswell.

Having run both the standard sizes and the M sizes in non runflats, there's no doubt the M ones with their extra 5% of side profile do give a much nicer ride and seem a bit quieter, particularly at the rear. However to my eyes they do look a bit too chunky and make the wheels look smaller. Well at least they did on my 107s with michelin ps3 and goodyear f1 a2. Currently I've got a set of mv2's on mine which I've been trialling which came with bridgestone non runflats in the standard size. Going back to the original size again has definitely improved the look, but has certainly killed the ride quality and they're noiser to boot. Some of that maybe down to switching from goodyears to bridgestones, but both sets of tyres have a good 6mm of tread on them, so it's not that the bridgestones are more worn down etc.
As a half way house option Im going to try some of the afore mentioned 245/40/18 on the rear. I recently fitted some of these on the back of the wife's 1 series which previously had some 35 profiles tyres on. They do seem to be a good compromise between increasing ride quality and not ruining the look with too much sidewall. The added bonus is the price. As Ben mentioned the M spec tyres sizes are very pricey for an 18 incher. The rear 255/40 michelin ps4 from blackcircles will set you back £185 each. The same tyre in the standard 255/35 is £145. However the 245/40 comes in at £130, so it seems a win win on the face of it.

 

[Steve84N]

245/40/18 is a very good size for the Z4. It gives less understeer, better ride and a more accurate speedo.

 

[mr wilks]

When pondering the Msize rear of 255 40 looking slightly oversized on some Bmw 18s its worth noting the stock 224 rear wheel off the ZM is 9j wide as opposed to 8.5j for 107,s 108s MV2s etc 245 40 18 is a perfect fitment for non M 18inch alloys , far better than 255 35 18 in every aspect :wink:

 

[MACK]

When pondering the Msize rear of 255 40 looking slightly oversized on some Bmw 18s its worth noting the stock 224 rear wheel off the ZM is 9j wide as opposed to 8.5j for 107,s 108s MV2s etc 245 40 18 is a perfect fitment for non M 18inch alloys , far better than 255 35 18 in every aspect :wink:

Good point Mr Wilks. I'd not given it a second thought the effect the extra half an inch of wheel on the rear has on the look of the tyre etc. On this subject what would you run on the front? I was getting catching with 225/45 M spec on m sport suspension with 15mm spacers. After I refreshed the suspension and lowered it slightly with Eibachs this actually improved, much to my surprise (shows how knackered the shocks were :rofl: ). But the rubbing was still there to some degree. Switching back to 225/40 has got rid of it and I have to admit looks better, the M spec did look like too much sidewall to my eyes on the front aswell as the back. Its a shame as the ride is so much harsher with the 225/40 on. As a halfway house for the front I'm thinking about going down the 215/45 route as im pretty sure 235/40 wI'll rub etc. I'm just not sure if I will also get rubbing with the 215/45 option running the eibachs and 15mm spacers.
Any thoughts?

 

[mjennings23]

Another vote here for 245/40 on the rears, still has ample rim protection and adds that bit extra comfort. Stuck with 225/40 on the fronts however.