So the wife and I are picking up a '99 528iT Sport in the coming days.....fired up about it...as it sits on sport suspension, and the 17" wheels, and still fulfills the needs of our family.

Here's the catch... The wife thinks the ride is a bit rough, and is lobbying for swapping the wheels out for the non-sport wheels. :nono I LOVE the look of the car as it sits, thus my question....

Is it at all possible to fit tires with a larger sidewall (vs the 235/45/17s) on the 17's to soften up the ride a bit but retain performance/look? I'm not looking to double the sidewall, or anything drastic...I'm just curious if there is some middle ground that I can reach.

I searched online, but was unsure of the fitments...

Any opinions are appreciated...:help

Anyone? Jim@TireRack, you out there?

There are some tires that ride rougher than others. Check out the ride rating of the current tires and shop for something that has a better ride for the same size. Believe me, tires do make a difference in ride and I've had some 40-series tires that rode better than some 45-series tires.

good avice, and I've been checking them out....thanks.

I still wonder if say, a 55 sidewall would fit...or if it would look right...

good avice, and I've been checking them out....thanks.

I still wonder if say, a 55 sidewall would fit...or if it would look right...

I wouldn't suggest altering the OD of your wheels/tires. Your speedo wouldn't read right and the odo wouldn't register the correct mileage......if ever these kinda things matter to you.

:b_blue

I wouldn't suggest altering the OD of your wheels/tires. Your speedo wouldn't read right and the odo wouldn't register the correct mileage......if ever these kinda things matter to you.

isn't there a way to have this mechanically corrected to read the proper speed/mileage?

As far as tire ride, some extreme performance tires have very stiff sidewalls, and ride much rougher. You may want to see what kind of tires are on there right now (or post the brand/model here and we can help) and then decide if the culprit is the tires. If that's the case, and you had something like a Max Performance Summer tire on there now, then you'd likely satisfy your wife by simply switching to a high performance all season or even a less performance summer tire.

If you really want to go with a higher sidewall, you can't mechanically account for the increase in ratio, AFAIK. In that case, I would just calculate the circumference ratio between your new tires and stock tires and use that as a speed multiplier.

This would work like this:

Your stock tires are apparently 235/45R17s. This gives them a circumference of:

17" + (.45x235x2)/25.4 = 25.327 diameter
2Rpi = pi*diameter = 79.57 inches

If you upgraded to say a 50 series tire it would be:

82.47 inches

So the ratio would be

82.47/79.57 = 1.036

So at 50mph (indicated on your speedo) your actual speed would be:

50 * 1.036 = 51.82 mph

As far as tire ride, some extreme performance tires have very stiff sidewalls, and ride much rougher. You may want to see what kind of tires are on there right now (or post the brand/model here and we can help) and then decide if the culprit is the tires. If that's the case, and you had something like a Max Performance Summer tire on there now, then you'd likely satisfy your wife by simply switching to a high performance all season or even a less performance summer tire.

If you really want to go with a higher sidewall, you can't mechanically account for the increase in ratio, AFAIK. In that case, I would just calculate the circumference ratio between your new tires and stock tires and use that as a speed multiplier.

This would work like this:

Your stock tires are apparently 235/45R17s. This gives them a circumference of:

17" + (.45x235x2)/25.4 = 25.327 diameter
2Rpi = pi*diameter = 79.57 inches

If you upgraded to say a 50 series tire it would be:

82.47 inches

So the ratio would be

82.47/79.57 = 1.036

So at 50mph (indicated on your speedo) your actual speed would be:

50 * 1.036 = 51.82 mph


Hey, thanks...... I can handle a mph or two of speedo error, heck, these car usually miss by 3 or 4 anyway.

Just wondering if it would bring the ride more to her liking...just a tad bit softer, and still allow me to keep the suspension/ride height/wheels....

So the question remains.... Outside of a small difference in speed calibration, would a slightly bigger sidewall improve the ride?

Yes, it would.

Thanks JW1, I'm walking the line between having a setup that I favor, and keeping the wife happy..........

BTW, the tires that came on the car are Mich Pilot Sports, 235/45/17's...... per your earlier response.

Thanks JW1, I'm walking the line between having a setup that I favor, and keeping the wife happy..........

BTW, the tires that came on the car are Mich Pilot Sports, 235/45/17's...... per your earlier response.

Do you know what the stock size is? That's the important part when trying to keep speedo accuracy.

Stock = 235/45/17

Duh, I spaced that. What exactly are you asking now?