Tyre width - time to go W I D E?

[Felixlamb]

Hey guys,

I’m finally at the stage where I can chuck the ghastly run flats in the bin (probably mainly due to the remap I got done last year). One question remains… what to replace them with?

As it stands, the stock rear 255 tyres, if pushed, will light themselves up even in the dry, and haven’t got a hope in hell once it’s remotely damp. Given I don’t have an LSD installed, I ideally need to be minimising slip.

With that in mind, I’m considering upping the width of the set of tyres I buy. I’ve seen on the forum that people have gone to 235 on the front, and 265 or 275 at the rear.

I’m looking at probably getting a set of SportContact™ 7s put on. 235/35/19 at the front, and either 265/30/19 or 275/30/19 at the rear.

A couple of questions…

• 
  I assume these sizes will fit on my 326m wheels without issue?

• 
  Will 265s or 275s rub at the rear? Can’t imagine the fronts at just 235 would.

• 
  As the sidewall profile will have to stick at 30, I’m conscious that the speedo will over-read less than before. However I don’t believe, even with 275s on, that it would ever read less than actual GPS speed?
  For me on stock sizes, 60mph is 57mph GPS - a 5% over-read, whereas 275s compared to 255s have a difference of around 1.9%, so presumably still an over-read of 3.1%?

I’m in no immediate rush to get this all arranged as I’ve got my winter set on, likely until March, but it would be good to get everything sorted in advance. Why didn’t I think of doing this around Black Friday?

Thanks in advance!

 

[B21]

Every rim has a range of possible tyre widths…you should stick to the recommended aka middle recommendations…

326M has 8j and 9j rims..

So a 225 is really the ideal width…235 is possible but it’s the limit


Ditto on the back 255 is the recommended size..265 or 275 is possible but it’s the limit

Ideally if you want wider tyres you need to go to 8.5j/9.0j front and 9.5j/10j rear..

Changing the tyre sizes to those suggested usually means the speedo is just very fractionally short of spot on..



https://blobs.continental-tires.com/www8/servlet/blob/3897892/69977261017e17f2a1dc8054655a4bcf/databook-continental-pt-data.pdf

 

[Pondrew]

I have found out to my cost recently, 265 widths are not common, so only a few manufacturers do them and they tend to be VERY expensive. 275 is not recommended for a 9" wheel, it's too wide.

This website gives recommended tyre widths for any given wheel size https://www.tyres-pneus-online.co.uk/tyre-equivalence-advice.html

 

[Busterboo]

I’m finally at the stage where I can chuck the ghastly run flats in the bin (probably mainly due to the remap I got done last year). One question remains… what to replace them with?

How many bhp are you putting through the rear tyres now?

 

[Marcoose]

As it stands, the stock rear 255 tyres, if pushed, will light themselves up even in the dry, and haven’t got a hope in hell once it’s remotely damp. Given I don’t have an LSD installed, I ideally need to be minimising slip.

Are you going to track ?

 

[Felixlamb]

Thanks guys. Ok so sounds like really 265 is the max for a 326 really. Luckily Continental appear to do this size, and most tyre companies are pricing the 265s at around the same as the 255s. Either way, I'm probably looking at close to £800 for a set of 4, however honestly it's long overdue, and it's the one thing you can't cheap out on. I've got new MTEC discs and EBC pads on the way too, so would be good to marry them up with some good rubber. I'll get a full alignment too, as I've been getting far too much camber wear for my liking.

I'd say I'm between 260 bhp - 270 bhp, but I don't know for certain. It was dyno'd back last year on a humid summer day so heatsoak really affected the IATs (and I also later discovered that part of my undertray was obscuring my intercooler, which wouldn't have helped either... fixed now though.). It'll pull on a B48 330i (which is a similar weight and also around 260 bhp) so it's likely around that power. It's definitely enjoying the cold weather we've been having recently though.

Haven't tracked it yet, but I'd really love to do a track day in it, so it's definitely in the cards for next year.

 

[Pondrew]

One thing I would say, having very recently done it, is increasing the widths can make the car feel less 'nimble' in the corners as there is more rubber to push around and if 'overtyred' they will sit flatter on the road.
I have gone from 225 front and 255 rear to 245 and 275 (not a Z4 and wider wheels). The extra 20mm on each wheel is quite noticeable. Great in a straight line, not so good on twisty roads TBH. Mine were done for looks more than anything, though.

Worth bearing in mind.

 

[Felixlamb]

Hadn’t noticed before, but the G29, even in 20i form, runs 255s at the front and 275s at the rear (but on 9J and 10J respectively). Wonder why they decided to do that.

https://www.bmw.co.uk/en/all-models/z-series/roadster/2022/bmw-z4-technical-data.html#tab-0-0

I suppose I’m not specifically looking for outright performance, perhaps more the aesthetics of meatier tyres, but the perks of that are of course a plus.

 

[plenty]

265 vs 255 won’t make much of a huge difference tbh. Tyre compound will make a much greater impact, and LSD of course. 255 Conti SC7s will be a night and day difference over RFs in the dry. 265s will actually be more prone to aquaplaning.

 

[B21]

Hadn’t noticed before, but the G29, even in 20i form, runs 255s at the front and 275s at the rear (but on 9J and 10J respectively). Wonder why they decided to do that.

https://www.bmw.co.uk/en/all-models/z-series/roadster/2022/bmw-z4-technical-data.html#tab-0-0

I suppose I’m not specifically looking for outright performance, perhaps more the aesthetics of meatier tyres, but the perks of that are of course a plus.

If you go with the 265/30 rear best to marry it to a 235/35 front..keeps the DSC happy ..

SC7s are probably the grippy-ess tyres short of a track oriented tyre ..you won’t be disappointed..

G29 chassis was a complete rework so logical to put bigger boots on as they improved the chassis quite a lot over the E89..

 

[Felixlamb]

Sounds like a plan then. 235s and 265s married to a set of SC7s should be a huge improvement. Thanks guys

 

[flybobbie]

I'm not into fancy tuning of suspension, but as a general car i always feel the front tyres are too wide.
Reason why steering is awful.
Like go kart tyres.
Would narrower tyres make steering lighter and more nimble.
Seems to me wide is just a fashion thing.

 

[sars]

I would say that the g29 is over tyred, yes you can take corners at ridiculous speeds, however tyre noise on those 275’s isn’t great. Also the g29 is available as standard 17” & 18” with 225 fronts and 255 rears, which I believe would make driving a little more exciting. Those 19” rears are also very heavy, I would say almost half again on the Ispiri’s now fitted

 

[brillomaster]

I'm not into fancy tuning of suspension, but as a general car i always feel the front tyres are too wide.
Reason why steering is awful.
Like go kart tyres.
Would narrower tyres make steering lighter and more nimble.
Seems to me wide is just a fashion thing.

i will say, my E85 handled and steered best when it was on narrow 225/45/R17s all round. did feel a lot more nimble. Outright lateral grip was better on the 245/255 track tyres i ran for trackdays, but driving to and from the track on those tyres when i wasn't pushing the limits of grip it wasn't as nice to drive.

 

[Argyll Andy]

however tyre noise on those 275’s isn’t great

Big improvement on the Conti 7’s Sars

 

[B21]

IMHO for a N20 powered Z4 probably 235/265 is as much / need for power on hooning …for the N54 powered Z4 with so much more power and weight especially over the front end the 245/275 combo is better for hooning albeit at the expense of heavier steering and an increased propensity for tram lining especially when warm..

With tyres like MP4S and SC7 and the new GY Assy 7 the level of grip is quite phenomenal compared to the old Potenza run flats..

So 225/255 would be no great limitation..again IMHO

If going around corners with lots of throttle on then a LSD would be a very good option..

 

[mr wilks]

Going 255 35 as opposed to 265 30 will increase the amount of rubber on the tarmac if that's the main criteria for the OP :?
doubt 99% of owners 99% of the time would notice but if it makes you feel better

 

[B21]

Going 255 35 as opposed to 265 30 will increase the amount of rubber on the tarmac if that's the main criteria for the OP :?
doubt 99% of owners 99% of the time would notice but if it makes you feel better

How would that work?

The 255 tyre is till 255 wide so it’s 10mm narrower than the 265….longer contact patch?