Chaning to M spec tyres...
- Thread starter nicollow
- Start date
You haven't said anything about the current equipment on the car, or the wheels/tires you are running now. Knowing nothing else other than it's a 3.0i, my recommendation to reduce ride harshness would be to change from the oringal equipment runflat tires (if still equipped with same) ... 
Curious as to why you think the different profile would improve the ride characteristics?
Curious as to why you think the different profile would improve the ride characteristics?
a340driver
Member
Interesting. I have a Z4M and went to Lepsons in Swindon when I needed new rears just last week. They insisted that I had the wrong tyres on my car- as you say +5 front and back. After calling into Dick Lovett(Swindon) next door I was amazed to find that they said the same. After looking at the sticker on the side of my door, talking to Dick Lovett(Bristol) and doing a bit of research it transpires that I do have the correct tyres i.e. 225/45 & 255/40 both R18.
Also when I confirmed my size they said it was an Audi tyre rather than BMW. As long as it fits on the wheel what's the problem.
They seem to want to make something simple into something complicated so that they can charge for their expertise and this just annoys me.
Also it means another week before I get new tyres!
And yes, I think you're right. It does improve the ride judging by my 330Ci with 225/40 & 255/35 R18!
Also when I confirmed my size they said it was an Audi tyre rather than BMW. As long as it fits on the wheel what's the problem.
They seem to want to make something simple into something complicated so that they can charge for their expertise and this just annoys me.
Also it means another week before I get new tyres!
And yes, I think you're right. It does improve the ride judging by my 330Ci with 225/40 & 255/35 R18!
Hi, yeah sorry assumed that an 18" setup was a given. I have 108s on at the moment and although the rims are the same dimensions as the M, the tyres are lower profile. Why?!?!
Good insight a340driver, my last car had a whole heap of different size of wheels/tyre combos available. Hope you get it sorted asap...
Good insight a340driver, my last car had a whole heap of different size of wheels/tyre combos available. Hope you get it sorted asap...
The Z4 is designed to have a tire that regardless of profile or rim size is about 25 inches in diameter. The ///M is designed to have a tire that is about 26 inches in diameter. I previously has a 2003 and 2006 Z4. On both of them I ran 235/40-18 front and 265/35-18 rear. This combination resulted with a front wheel diameter of 25.4 and the rear 25.3 inches. While I can't say so for sure I suspect that had I put a 225/45-18 on the front which has a diameter of 25.9 inches I would have had rubbing issues. Perhaps someone here has tried that and can comment.
nicollow said:So, after looking at tyres for my 3.0i, Ive noticed that the Z4M has +5 on both the front and rear profile section. Why is this? Im thinking that this would be a good way to reduce the harsh riding qualities of the car? Is this sacrilege?
Have to say I'm not really sure why the M has higher profile tyres than the 3.0. I think it might be that there are differences in the suspension parts and/or geometry between the M and non-M, and I guess the M engineers tested the thing as a whole and came up with 45 profile fronts and 40 profile rears as the best option.
From what I understand, it seems that higher profile generally equals less stiffness in the sidewall of the tyre, which would equate to a bit more 'give' in the tyre. After all, Martin Brundle is always saying how much the big sidewalls on F1 tyres account for overall ride-height movement on an F1 car.
But what does seem to be accepted is that the harsh ride of non-M Z4s is caused by the OEM Bridgestone run-flat tyres. Changing these to a non-run-flat tyre (Falken FK 452 or Vredestein Ultrac Sessanta are two popular choices) seems to improve the ride considerably and also reduces the tramlining tendency the car has when on run-flats. Alternatively, changing to a different make of run-flat can also help. Have a search on the forum - there are loads of threads about the subject that will explain the pros and cons of this.
From my own experience, I'd recommend sticking with the original sizes for the 3.0. The main reason I think this is that I recently changed the tyres on my M and had a total bug-ger of a job finding a good tyre that I wanted that came in the right size for both the front and the rear. The choice for the lower profile tyres on the 3.0 seems far wider, and the tyres are cheaper too
Good write up Angus... Yeah, rubbing is an issue I guess, but Ive heard of people putting Z4M or CSL wheels on their car. Do these not have the bigger diameter you mention?
Thanks for the heads up on the Z4M tyres being harder to find anyway. What did you go for in the end, and where did you get them? Im looking at some Goodyear F1s, but cant seem to find anywhere that have them in stock...
Thanks for the heads up on the Z4M tyres being harder to find anyway. What did you go for in the end, and where did you get them? Im looking at some Goodyear F1s, but cant seem to find anywhere that have them in stock...
Hi nicollow,
The standard Z4M wheels are 18 inch diameter jobs. So the overall diameter will only differ from the 18 inch non-M wheels because of the higher profile tyre (if fitted).
The genuine CSL wheel is 19 inch diameter. But it's usually fitted with 235/35 tyres on the front and 265/30 on the rear. So the overall diameter is actually smaller than that of the standard M set up. Here's a link to a handy tyre size calculator that you can play around with to give you an idea:
http://www.tyresave.co.uk/tyresize.html
As far as I know, there's much the same amount of room under the wheel arches of all Z4s, so whether you go with 3.0, M or CSL sizes you shouldn't have too much of a problem. Plus there are quite a few non-M owners on this forum that have fitted M wheels and tyres to their cars without any rubbing as far as I know. Guiseley is one that springs to mind.
In the end I had a rush of blood to the head and broke my piggy bank for a set of Michelin Pilot Super Sports. I was able to get the standard M size for the for the front (225/45/18) but the nearest I could get for the rear was 265/40/18. It's only 10mm wider than standard and, according to the calculator, only 8mm bigger in diameter. Have to say I'm delighted with them so far.
But if I'd been able to get the right size, I'd have gone for Goodyear Eagle F1 Asymmetric 2 based on this:
http://www.tyrereviews.co.uk/Tyre/Goodyear/Eagle-F1-Asymmetric-2.htm
And, according to their website, Camskill have the standard 3.0 sizes in stock (drool at those prices compared to mine
). Here's a link to the page on their website:
http://www.camskill.co.uk/m61b2324s0p0/Car_Tyres_-_MPV_Tyres_-_People_Carrier_Tyres_-_18_inch_GOODYEAR_TYRES_CAR_GOODYEAR_EAGLE_F1_ASYMMETRIC_2_-_
Good luck with all that
The standard Z4M wheels are 18 inch diameter jobs. So the overall diameter will only differ from the 18 inch non-M wheels because of the higher profile tyre (if fitted).
The genuine CSL wheel is 19 inch diameter. But it's usually fitted with 235/35 tyres on the front and 265/30 on the rear. So the overall diameter is actually smaller than that of the standard M set up. Here's a link to a handy tyre size calculator that you can play around with to give you an idea:
http://www.tyresave.co.uk/tyresize.html
As far as I know, there's much the same amount of room under the wheel arches of all Z4s, so whether you go with 3.0, M or CSL sizes you shouldn't have too much of a problem. Plus there are quite a few non-M owners on this forum that have fitted M wheels and tyres to their cars without any rubbing as far as I know. Guiseley is one that springs to mind.
In the end I had a rush of blood to the head and broke my piggy bank for a set of Michelin Pilot Super Sports. I was able to get the standard M size for the for the front (225/45/18) but the nearest I could get for the rear was 265/40/18. It's only 10mm wider than standard and, according to the calculator, only 8mm bigger in diameter. Have to say I'm delighted with them so far.
But if I'd been able to get the right size, I'd have gone for Goodyear Eagle F1 Asymmetric 2 based on this:
http://www.tyrereviews.co.uk/Tyre/Goodyear/Eagle-F1-Asymmetric-2.htm
And, according to their website, Camskill have the standard 3.0 sizes in stock (drool at those prices compared to mine
). Here's a link to the page on their website:http://www.camskill.co.uk/m61b2324s0p0/Car_Tyres_-_MPV_Tyres_-_People_Carrier_Tyres_-_18_inch_GOODYEAR_TYRES_CAR_GOODYEAR_EAGLE_F1_ASYMMETRIC_2_-_
Good luck with all that
Leave the tyre profile alone and don't mess up the gearing, speedo, acceleration, braking, etc. It could even be insurance voiding and claim refusal.
You don't say which model you have but given 108's I'll guess a 3.0. That comes with lowered (15mm) harsher suspension as standard so if ride comfort is the goal then you picked wrong model need to change to a 2.5 or less or fit their springs.
My assumption on why the M has different profile tyres is ton reduces the mass of a bigger rim while getting a large tyre for radius. That's then matched to it's gearing and suspension set up.
You don't say which model you have but given 108's I'll guess a 3.0. That comes with lowered (15mm) harsher suspension as standard so if ride comfort is the goal then you picked wrong model need to change to a 2.5 or less or fit their springs.
My assumption on why the M has different profile tyres is ton reduces the mass of a bigger rim while getting a large tyre for radius. That's then matched to it's gearing and suspension set up.