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E39 525i Sport Tire Options

Discussion in 'E39 (1997-2003)' started by 336572, Apr 19, 2015.

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    My daughter recently purchased a 2003 525i Sport with 235/45R17 tires. We need to replace the tires before summer. She says she does not want another set of "low profile" tires; I assume she considers the 45 Aspect ratio "Low profile". Question: Can we increase the aspect ratio to 50? 55? 60? without impacting the handling geometry of the car?

    Recommendations please.... Thank-you.
    Charles Jones, Raleigh, NC
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    Any time you adjust the tire size the handling can be effected. Is there a certain reason the low pros don't work for her? Also look at the tire place card on the drivers door sill and see what other sizes your vehicle was optioned with.
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    You could also check tirerack.com, they are pretty good at showing what sizes are available.
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    You can use this to compare some changes - http://www.rimsntires.com/specspro.jsp

    I was also wondering why - if you keep 17's and start upping the aspect ratio with more sidewall height, you might start running out of wheel-well space and have the tires rubbing on the fender liners, suspension parts, wheel-well, etc. That kind of route you end up increasing overall height - taller sidewalls, generally, means some loss of steering-response immediacy, among other things. Increasing the overall height of the wheel/tire combo, you raise the car's center of gravity slightly, that affects handling. Probably something with roll center too. Increasing rolling diameter makes for an effective gearing change, the tires turn less rpm's, so the speed showing on the speedometer would show lower than actual speed, compared to a stock size (& BMW speedo's usually show a little higher than actual speed). That can also make for probably a barely perceptible increase in highway gas mileage, unless sticky tires negate that. Again probably barely noticeable, but the effective gearing change means there would be slightly less torque at any given speed & from a standing start. That's some of the stuff that changing o.d. does.

    A small change, probably not too critical a difference, but that's where the why for the change may be a more important consideration - if the goal is a somewhat softer ride quality or less-expensive replacement tires, or decreasing the chance of blowout/rim damage due to potholes, then a better route to go would be to downsize the wheels and go with a smaller-size stock wheel, keeping overall diameter close to stock specs.

    Tirerack.com shows 16x7 as an original size for an '03 E39 525i - if 16's clear the brakes (assuming the sport pkg. didn't have upsized brakes requiring 17's, & the 17's were primarily a handling improvement), then the stock 225/55-16 has 4.87" of sidewall height vs. 235/45-17's 4.16" sidewall height. So, going to 16's, you get .7" more sidewall height (just shy of 3/4 inch). One plus of a downsized wheel should be a decrease in unsprung weight, via 16" wheels/tires weighing something less than 17's, that allows the suspension to work better. Smaller dia. wheel keeping to o.e. setup, no chance of rubbing/clearance issues, and speedo accuracy should remain as is.

    I didn't check Roundel classifieds, but found a couple sets on ebay - local craigslist or any junkyards or local pic-n-pulls might be worth a look-see, if going the 16's route is an option.



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