Rubber sizes for 17's

V

vortex

Member
Herro ! :)

I got a Z4 3.0i SE which I bought about 7 months ago. After a lot of problems I am considering changing them RFTs as they really make the ride uncomfortable and harsh and the tramlining is driving me nuts.
The car has a stock pair of 17" 103 double spoke wheels.
Currently the car has RFTs of different brands. Front left is a Bridgestone Potenza I think, Front right is a Falken, Rear left is Bridgestone, rear right is a Nokian.
I Image that different types of RFTs are making matters worse than same types of RFTs all around.

One of the things I wanna ask is why I have 225/45 both front and rear.
That is how I bought the car. The bloke who changed my front left tire 3 months ago was insisting that I use 245 in the rear.
I would image this makes the rear very unstable (I can confirm that, once it over steers its uncontrollable).

So I've decided to make the change and go for non-RFTs.

However I'm a bit puzzled. Most websites seem to indicate that I need a 225/45 front, which is the same as before.
For rear tires I would like to go for 255/40.
According to the same bloke who did the change before, I can fit on the 103 (17"x8") a 255/45 tire without any problem or side wobble/rubbing.

Which brings me to the side wall size.
Should I stick with 45? I cannot find many rear wheel 255/45, most seem to be 255/40.
Furthermore, if I go with 40 rear, shouldn't I change the front ones too? But I cannot find front 225/40/R17, the closest being 235/40 or 215/40.

Last but not least, is there a chance I will be compromising ride quality, comfort or cornering if I put 255/40 or 255/45 in the rear instead of what seems to be the recommended 245/45/R17?

:)

PS: Wrong forum, I see now this is for E89. Sowwy
 
Moved into correct forum :thumbsup:

Standard tyre size on the 103 is 225/45 17 front and rear, on the same wheel width - 8J. Personally I would stick with that all round, any increased rear width isn't going to make a huge amount of difference on the same width rim.
 
Thanks for moving it :)

So are you implying I change the rims? :p
The extra 30mm should however make a small difference, no ?
 
Well the E85 always looks better with 18s rather than 17s but at the expense of tyre cost and ride comfort. But the 103s look the best of the 17" wheels available.

Although the tyre width is 30mm wider, the rim width is the same so I don't see that the full 30mm of additional width would be realised, not like if an 8.5 wide rim was used, like BMW does on the 18" wheels.

Maybe I'm wrong on that? But if it did make a difference would you actually notice :idunno:
 
Hehe, yes I was hoping I would notice, it does scare me when I totally lose control of the rear.
Thank you for the input, I guess its completely useless thinking about 40 or 45 without the proper wheels.
As a side note, do you happen to know the load ratings for Z4s?
Thank you!
 
I think your wheels will be fine, a decent set of matched tyres will be a good first step, then probably a proper alignment would be a better investment than bigger wheels at this stage, and maybe a review of the bushes.

Apart from this time of year and the obvious traction issues, a properly set up Z4 with decent non-RFT tyres should handle pretty well.

Load ratings - don't know!
 
Why go with a 40 profile on the rear? It's not much of a difference but still.... think about all the negatives and very few positives....

You cant rotate your tires, rears will wear faster, rear tires will be more expensive.... also rear will sit lower than the front.... not by much but still....
if you change the size, change all 4...
if you go 255, the tire will balloon out with the 17x7.5 wheel size. 225/45/17 is on there for a reason.
 
I thought the 103's were 17"x8.0"?
Yeah I'll stick with 45 all around, just contemplating on wider rear tires.
Will ballooning (lol) them at the rear create problems such as rubbing?
 
We have the 103s with 225 Eagle F1A2s and I cannot get the back end to shift off line, maybe another litre will make a huge difference but I kind of doubt it. Go for extra load, the standards are not quite as sharp as you are used to on turn in. Anyway, wouldn't being able to hang the back out on the corners be a funfactor if the handling is predictable?
 
A 225MM tire is 8.85" inches wide on an 8" wide wheel. A 255 is 10" on an 8" wheel.
It puts a lot of bending pressure on the tread belts and makes the tire slightly bulged in the middle as if it was overinflated. Then compound the wider tire with going to a shorter 40 series profile to maintain the stock diameter. Thus putting even more distorting pressure on your tread.

You can put a wider tire on a given width wheel. But the tire needs to be taller to prevent tread distortion. But then you mess up your diameter and speedometer/odometer, And handling.

Best bet for you is to get a good set of performance tires in the 225/45/17.

The load rating for the stock RFT is 91W 91= 1356 pounds/615Kg's W= 168MPH/270Kph
 
Do as I say. Or I will hunt you down. And force you to watch reruns of Parliamentary debates. :D

I worked at a bike shop for a few years. And an acquaintance in the US owned a tire shop. Had to deal with the weekend moto gp boy racer wider is ALWAYS better crowd. Bikes are far more prone to handling issues when one slaps on an overly wide tire on a stock wheel. But the same principles apply to cars. However. Cars do have a much more forgiving nature as they don't easily fall over like a bike will.
 
Agreed, bigdog sounds like he knows what he's on about. 225/45 all around it is then.
Any recommendations ? I was looking into Toyo T1-sport, Pirelli P Zero, Goodyear Asymetric F1 or Yokohama Advan Neova.
Seeing as you all agree on staying with 225/45 I might as well go for the better performing tires :)

PS: A 16" Space saver wheel should fit both front and rear, right ?
 
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