More on wheels and tyres (stay awake at the back!)

[Blurredman]

Settle down boys and girls while I tell you a tale that will raise your neck hairs.

My little saga started last week, after I had done a spirited drive from Leeds to Birmingham (sometimes but not always completely below 70mph). I had noticed that the car seemed a bit vague and so took it to my mechanic brother to have a look at it on the ramp while I tootled off to give blood.

When I came back he silently beckoned me over to look at the underside of the car. As he pointed out the 3 cracks in one wheel, and four in the other - plus an ominous bulge in the rear passenger side tyre wall - my remaining blood drained from my face, as I realised that the M6 might have become my final resting place but for the tenacity of a bit of rubber to cling to the rim of a defective alloy for a few miles longer.

Getting home and shaking the piggy bank, I realised that I had been spending too much on craft ales and not enough on my Z4-will-eventually-need-fixing-for-some-reason fund. I weighed up my options. Should I shell out on 2 new BMW 326 9" x 19" rims? Or ditch the stock wheels entirely and get a spanking new set of alloys? Then Mr True-Blue of this parish threw in a suggestion: "pick up another front pair of 326’s and run them on the rear in a square set up". Hmm, I thought, that's not a bad idea.

Some eBaying later, I had acquired a couple of decent looking fronts and through my brother and his nice company discount scheme, some Uniroyal Rainsport 5s non-runflats. Time to actually get the old boots off. The scene inside the old wheels/tyres was unpretty. Both rear tyres could have been imports from Ukraine judging by the devastation wrought on them by rubbing against the metal. They were ready to let go, and give me a merry-go-round experience in my Z.

I am happy to say that the car now handles wonderfully (albeit needing tracking) and the non-runflats are a revelation. The square wheel, 225-front 235-rear combination doesn't seem drastically different to the OEM set up and a jaunty drive out to Worcester on Saturday taking in motorway and B-roads restored my faith in the car. All done for around £650 too, so the marriage is intact.

Anyone considering a square(ish) set up with all-round 8"x19" wheels and standard tyres - give it a go. The risk of cracked alloys isn't zero, but I like to think it is scaled down a notch or two.

And thanks to all you peeps who chipped in with ideas last week on this. Turned out not to be such a sorry tale after all!

 

[Pondy]

Must admit I wouldn't tell the difference unless someone pointed it out. Oh hang on.....you did!

 

[B21]

Salutary tail…so many 326M wheels crack and you see from the MOT reports so many E89s driving around on goosed tyres..

Captain Pessimistic points out that front 326Ms crack also..but judging by the ratio of fronts available not so much…

Enjoy the ride / handling..

On the lower power cars the wider rears are not as compelling an option..

 

[enuff_zed]

Captain Pessimistic points out that front 326Ms crack also..but judging by the ratio of fronts available not so much…

But that could be due to location on the car............... he says, jumping on the glass half empty bandwagon. :roll:

Maybe the rears crack because they are on the rear, not because they are wider?

Well we now have two members testing the theory anyway.

 

[B21]

Captain Pessimistic points out that front 326Ms crack also..but judging by the ratio of fronts available not so much…

But that could be due to location on the car............... he says, jumping on the glass half empty bandwagon. :roll:

Maybe the rears crack because they are on the rear, not because they are wider?

Well we now have two members testing the theory anyway.

Could be …suggest you run squarely (pun) over some severe speed humps multiple times at say 50 mph ensuring both sets of wheels sit across the rising part of the hump..

My wheel doctor assures me that’s the best stress test for alloy wheels..

 

[Blurredman]

As has been pointed out, the cars with 17" wheels run a square set up anyway. I tend to agree that on the 20i the lower power gives less cause for concern with running the narrower rears. I may yet add 5mm spacers on the back, but will see how it goes without for a few weeks first.

 

[Mr Tidy]

It looks like you dodged a bullet there!

 

[Pondy]

I honestly believe the wider rear wheels/ tyres are nothing to do with power, only to do with 'show'.
Other manufacturers NEVER put wider fronts on a fwd car, do they?

I have owned a few cars with a lot more power (and more importantly torque) than any Z4 will have. All (except BMW) had skinnier tyres than 255mm. I had a 420bhp (500nm) Jap car with 215mm tyres (iirc). They were fine. It didn't end up in a ditch and would go through B roads better than any German car at full chat.

30 years ago you could get 400bhp and 600nm torque (plus) from a Ford Cosworth engine. Not many changed the wheels and tyres cos they couldn't handle the power. They were 205mm.

 

[True-Blue]

Captain Pessimistic points out that front 326Ms crack also..but judging by the ratio of fronts available not so much…

But that could be due to location on the car............... he says, jumping on the glass half empty bandwagon. :roll:

Maybe the rears crack because they are on the rear, not because they are wider?

Well we now have two members testing the theory anyway.

Need to get two of the four 326’s I’ve acquired for the Mrs lightly refurbished, but no concerns at all about running a square set up.. have done it before and all good

 

[coldel]

Until I bought a beemer I never realised these wheels were so prone to cracking, shocking really. Shame because I think they look stunning on the car!

 

[flybobbie]

All those cracks more manufacturing fault.
How are they made, forged, it looks like the alloy is stretched too much and finally splits.
Otherwise each crack would have a strike point on the rim.

 

[flybobbie]

Interesting, die cast.
https://www.youtube.com/watch?v=WNoeLRFS7Zs

 

[Marcoose]

...I tootled off to give blood...

...I had been spending too much on craft ales...

Two major mistakes right there. You sell blood, and ales is for pigs.

:lol: :lol: :lol:

 

[Blurredman]

...I tootled off to give blood...

...I had been spending too much on craft ales...

Two major mistakes right there. You sell blood, and ales is for pigs.

:lol: :lol: :lol:

At risk of causing an international incident, I should point out that in my part of the world Pigs sit on Walls and help to sell ale

 

[B21]

As has been pointed out, the cars with 17" wheels run a square set up anyway. I tend to agree that on the 20i the lower power gives less cause for concern with running the narrower rears. I may yet add 5mm spacers on the back, but will see how it goes without for a few weeks first.

BMW are paranoid about oversteer..so they tend to use bigger boots on the rear and a lot of camber..doesn’t worry Mercedes ..

 

[Mr Tidy]

Two major mistakes right there. You sell blood, and ales is for pigs.

Actually on our side of the pond we are much more generous - we donate blood!

 

[Marcoose]

Two major mistakes right there. You sell blood, and ales is for pigs.

Actually on our side of the pond we are much more generous - we donate blood!

I thought that since Brexit it was all for one and one for himself.

Oh, wait, you want back into socialism again. Never mind. :lol: :lol: :lol:

 

[sars]

As has been pointed out, the cars with 17" wheels run a square set up anyway. I tend to agree that on the 20i the lower power gives less cause for concern with running the narrower rears. I may yet add 5mm spacers on the back, but will see how it goes without for a few weeks first.

BMW are paranoid about oversteer..so they tend to use bigger boots on the rear and a lot of camber..doesn’t worry Mercedes ..

Two things, it's more to do with aesthetics than a worry about oversteer and it's BMW UK who decide on what we get, go to the German website and they have a lot more wheel choices, you can even get 225/45 R18 x 255/40 R18 wheels on the M40i. Also my last two Mercedes both had staggered set ups, as do most sports cars.

Both the e85/86 and e89 had a square set up as standard

 

[Pondy]

Also my last two Mercedes both had staggered set ups, as do most sports cars.

My diesel E class estate had staggered wheels and that was by no means a sports car (nor is the Z4 IMO). It had staggered wheels purely because it was an "AMG line" model. All for show, not for go!

 

[Mr Tidy]

My diesel E class estate had staggered wheels and that was by no means a sports car (nor is the Z4 IMO). It had staggered wheels purely because it was an "AMG line" model. All for show, not for go!

Exactly! My 330i is an SE so has a set of Square 17s - had it been a Sport it would have had Staggered 18s despite being fundamentally the same car.

But I like to think a Z4M is a sports car!