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Wheel-Tire Upsize

Discussion in 'Wheels & Tires' started by bert shirey, Aug 9, 2009.

    bert shirey guest

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    Hey guys:

    I would appreciate some advice on upgrading the wheels and tires on my 08 328xi sedan, no sport package. What I am thinking is to replace the standard 16"/Conti RF package with the optional 17" style 161 BMW wheels. That gives two options: 225 front and rear and the staggard 225/45 front and 255/40 rear. I figure the 255 would be about 2" wider than the stock 205s. The main reason for the change is that I think the larger wheels look better than the 16s. While I am at it, I may switch of the RFs, probably to Michelin Primacy MXV4 A/S GT.
    Other than the inability to rotate a staggard tire setup, are there any negatives to going with the larger rears, especially on the x-drive without sport package? Could the wider tires upset the camber or cause balance problems or mess up the awd performance, or what?
    I only do about 5K miles a year, probably no snow unless I get careless. No what you might call performance driving, but I do appreciate the great feel of my BMW even as it is. Thanks,

    Bert Shirey
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    az3579

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    Other than not being able to rotate the tires, you also increase understeer a bit with a staggered setup. I don't know how the X-drive equipped models handle to begin with, but I'm sure there's some understeer present at times. If you don't want that, I'd stick with the same size all around.


    Besides, larger tires in the rear costs a little bit more (if you were to buy all 4) than to just buy 4 of the same size.
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    CRKrieger

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    X2.

    Without the commensurate changes to the suspension that the Sport package has, staggered tire sizes will simply increase understeer. But they'll look bitchin' and your dates will all be impressed that they get to watch the weeds as you slide off the road into them ...

    bert shirey guest

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    Thanks, AZ3/CRK:

    That`s helpful advice. The X-Drive is so well behaved I just hate to mess it up only to get a better look, not to mention make an expensive mistake; so I`m going to think this out, then do it.
    I`m new to BMW issues, but you guys look like you know what you`re doing. Maybe a bit of understeer is built in to the stock sedan keep garage cats like me straight ? Since I don`t push it, I`ve never really noticed and maybe wouldn`t notice a bit more. Road manners aside, even going up only one inch both ways, the larger wheels and fatter tires look a lot better than the 16 inchers. I notice those 2' wider rears on other BMWs immediately.
    Impress my dates. Into the weeds...hmmm. Let me see. Last time I had what you would call a real date was 1965. (Yeah, I know.) Back then, returning from a date I made a lasting impression on my soon to be wife by sliding my Bugeye Sprite off the road into a cornfield. The thing cornered like a roller skate on those skinny, bias ply tires. Learning the purpose of "grab handle" that night, the girl insisted the Bug had to go ASAP after the honeymoon, such as it was.
    So I traded it on a new MG. Same old wife, same old MG. Why did I wait so long for the BMW. Cheers,

    Bert
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    az3579

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    Yes, it is my understanding that most if not all manufacturers of regular road cars dial in a bit of understeer from the factory to keep regular 'folk out of trouble. I don't think the serious manufacturers like Ferrari and Lamborghini do that, but your run-of-the-mill make does, BMW being no exception.

    HA! Good one. :p

    A couple of things:
    1) Yes, fatter tires in the rear are badarse, but those are usually on the cars that mean the business, like an M3 for example, and I think actually serve a purpose on those cars because of how powerful they are. Fatter tires in the rear help with off-the-line traction on a RWD car, and controls the oversteer a little bit in the corners with the added understeer it introduces. You won't have this problem because your N52 isn't powerful enough to cause serious trouble, and it being AWD definitely lowers the risk.
    2) I don't think rear tires are 2 actualy inches wider, though I haven't counted. I think most of the time staggered setups have rear tires that are two "sizes" wider, so for example: 245 front 265 rear.




    Anyway, I agree that a staggered setup is badarse, but also keep in mind that you'll have to find two rears that are wider than the fronts, but I get the feeling that the wheels you're looking at are already the correct sizes?
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    CRKrieger

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    It takes years of practice to make stuff up and have it sound believable ...
    Yes, it is. It's considered better for most drivers because it never occurs to them to use the power oversteer recovery technique - and most cars, including all FWD cars, simply can't do it. The techniques that work for understeer are slowing down and unwinding the steering until the front recovers traction. Both are fairly safe compared to mashing the accelerator to swing the tail wide and point the car where you want it to go. :eek:
    Actually, it might surprise you how much you do feel. Even at fairly reasonable cornering speeds, you might detect a difference. Maybe so subtle that you can't even put a finger on it. I know I have, just going between two FWD cars; one my daily driver and the other a race-prepared GTi tuned for maximum oversteer (OK; minimum understeer ...).



    So, did it go taillights or bugeyes first? Of course, in those days, a "perfect 4-wheel drift" was everyone's goal on those tires, so if you were really cookin' it like the pros, you went off sideways.
    Any woman who hangs around after you crash with her is worth keeping. ;) The technological advances in cars, and tires in particular, since we were that young are staggering. Your street BMW can outcorner and outbrake Mark Donohue's 1970 Trans Am Camaro - mostly due to the tires that we have now.

    bert shirey guest

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    Wheel -Tire Upsize

    After all, I decided to go to the 225/45 17s front and rear on the 8" wide alloy wheels. That gives me a modest 1' wider tire than the stock 16 205s all around. The point that the wider 255 rears on the X-drive the way I use it would amount to a comprimise to vanity over sense makes sense. As I said, although I`ve been playing with British cars for almost 50 years (an probably know 10% more now than when I started) , my BMW experience is pretty slim. But I do think that wheel/tire choice can make a huge difference in enjoyability of the car, even in everyday driving. For performance situations, I would expect having the right tires would be critical. Last year I put a set of new Michelins on my AWD Mountaineer without any change in size and the difference in handling and comfort over the OEM tires was night and day. Thanks again. This forum is a great resource.

    Bert

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