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Advice Sought on Tire Sizes to Replace on 2008 Z4M Roadster

Discussion in 'Wheels & Tires' started by jbmaher, Oct 12, 2014.

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    jbmaher

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    Considering putting Michelin Pilot Super Sports on my 2008 Z4M. Would appreciate any thoughts or inputs on:
    1. The car can take 245/40 front and 275/35 rear tires on the OEM Wheels and the price is almost the same as the 225 and 255's currently on the car (right now, I have run flats and want to replace them - almost worn out). Which pair combination is better for comfort and handling?
    2. Any issues with the car side panels getting rocks or pebbles flying outside the wheel well to damage the paint since these protrude about 3/4" further out?
    3. Any other thoughts? Thanks - John
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    MGarrison

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    Hopefully somebody who's tried that combo on the same car will offer up some insight - I'd suspect if the sidewall height & stiffness is about the same as what you've been running, there wouldn't noticeably different ride-comfort. Increasing tire-patch width, with more rubber on the ground, should translate to increased handling with higher cornering grip, etc. The wider tires might cost a smidge of fuel economy. Would need somebody's comments on what they've found running the same setup as far as any wear from kicked-up road debris.

    Using your current wheels, on paper, they would be a centimeter wider inboard & outboard, which isn't that much, so seems like that might not be much different than anything you're getting now - since there's variability in actual width though, if in reality the tires you get are a good bit wider than what you have, seems logical to think you might be subject to more hashing on body panels.
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    jbmaher

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    This was advice I received from some other technical folks on ZEE Club (Facebook) and would appreciate anyone's thoughts about what they said:
    "Do NOT put 275's on OEM 9" wheels - they aren't wide enough. 265 is the widest you can go without the tire bowing outwards in the middle. Pilot Super Sports are great tires, though not so good in the winter (max performance summer tires = warm weather only). I would recommend 235/40/18 and 265/35/18. 275 width tire works best on a 10" wheel, but it will work on a 9.5" wheel too. Stock M wheels are 8" front, 9" rear = 225 width front, 255 rear tires.


    A general rule:
    8" wheel = 235 +/- 10
    8.5" wheel = 245 +/- 10
    9" wheel = 255 +/- 10
    9.5" wheel = 265 +/- 10
    10" wheel = 275 +/- 10


    FYI, the widest rear tire that will fit without rubbing on a Z4M is a 275, depending on your wheel offsets. 285's can work if they have round sidewalls. Square sidewall 285's (like Star Specs) will rub. You can't go much wider than that without fender rolling."

    I also received a post and then had a chat with Tire Rack.com that a 235/45 front and 265/40 rear ought to also work, and with the slightly additional tire height, it's my understanding that tire height helps with comfort (but I don't want to weaken performance).

    Thoughts?
    • Member

    MGarrison

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    I wouldn't have any reason to doubt their recommendations since they're presumably experience-based; that being the case, it sounds like running 275's means a wheel purchase, which can be just that much more a chunk of change on top of tires.

    A quick glance off Tire Rack of the overall diameter between a 265/35 & 265/40, you get 1/2" more sidewall height with the aspect ratio 40 tires. So, a smidge more sidewall give that might translate into the comfort aspect as far as feeling bumps (& less chance of rim damage from potholes, etc.), at the slight cost of steering & transitional response. The larger overall dia. is an effective differential ratio change, so you'd lose a smidge of acceleration time, but would be at a lower rpm for any given speed & gear, so perhaps a slight mpg gain there, higher top speed for any given gear, or being able to wait a little longer before hitting the rev limit & having to shift. Very slight raise in center of gravity, not sure that the handling aspects of that would be particularly noticeable in street driving.

    265/35's would be the more performance-oriented choice, but slightly less sidewall height vs. stock, so (presumably) slightly increased risk of rim damage & you might feel bumps a bit more.

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