275 width in the rear?

[Chrakaknox]

has anyone tried 275/35/18 or 275/30/19's on the rear yet? I'm looking into ordering aftermarket 18" or 19" wheels - still haven't decided. Most I'm looking at are 9.5" wide on the rear with a 35 offset. If a 255 width fits without much trouble, would the extra 20mm (.78 inches) cause any issues in the rear? BTW, I would be sticking with 225 or 235 in the front either way. Thanks in advance...

[soapman72]

I probably wouldn't go that wide in the rear. Although it would definitely look cool, all you will do is cause the vehicle to understeer more, and you definitely want to confirm that the O.D. of whatever front tires you pick match up exactly with the rear , or you risk causing issues with the AWD and ABS due to wheel speed differences.

[HotRodW]

You'll lose about 1/2" in overall tire diameter with either of those sizes.

[richb811]

265/35 is closer to spec, its within 1.1% of OEM spec.

285/30 is also better than the 275/35 but might be a tad wide for the fenders. It's also around 1% of spec.

I wouldn't recommend the 275/35 as it is going to screw with your X-drive system being over 2% out of spec.

[Chrakaknox]

thanks for the info...

[Chrakaknox]

Originally Posted by Rich@GTBPerformance

265/35 is closer to spec, its within 1.1% of OEM spec.

285/30 is also better than the 275/35 but might be a tad wide for the fenders. It's also around 1% of spec.

I wouldn't recommend the 275/35 as it is going to screw with your X-drive system being over 2% out of spec.

the 18" OEM spec is 26" diameter and the 19" OEM spec is also 26" or is it 25"? The BMW ordering sheet is confusing me, the upgraded 19 inch sizes convert to 25":

Front/Rear
225/35/19 255/30/19 25 in diameter
225/45/18 255/40/18 26 in diameter

[richb811]

Originally Posted by Chrakaknox

the 18" OEM spec is 26" diameter and the 19" OEM spec is also 26" or is it 25"? The BMW ordering sheet is confusing me, the upgraded 19 inch sizes convert to 25":

Front/Rear
225/35/19 255/30/19 25 in diameter
225/45/18 255/40/18 26 in diameter

Exact outside diameters I couldn't tell you.

These are percentages based off your OEM spec tire sizes and if you want your X-Drive to work properly, you are going to need to keep within 1%

[Chrakaknox]

Originally Posted by Rich@GTBPerformance

Exact outside diameters I couldn't tell you.

These are percentages based off your OEM spec tire sizes and if you want your X-Drive to work properly, you are going to need to keep within 1%

Oh, Ok, I'd always thought the most important number to stay closest to was the overall diameter and that's 26" for the standard 18" wheels on the 35i....but the upgraded 19" package you can order with the msport line converts to something like 25.1" which is a pretty big difference (approx. 4%)in my eyes.

[soapman72]

I wouldnt be too concerned about a slight increase or decrease in diameter as long as the front and rear still match perfectly. You can find the O.D. for various sizes/manufacturers on tirerack.com. Our tires in the factory size are EXACTLY the same diameter, so that is the way I would keep it. Even ABS braking performance will be affected by mismatching diameters.

[Chrakaknox]

looks like 245/35/19 fronts and 285/30/19 rears at 25.8" diameter should fit the bill...

[Chrakaknox]

Originally Posted by soapman72

I wouldnt be too concerned about a slight increase or decrease in diameter as long as the front and rear still match perfectly. You can find the O.D. for various sizes/manufacturers on tirerack.com. Our tires in the factory size are EXACTLY the same diameter, so that is the way I would keep it. Even ABS braking performance will be affected by mismatching diameters.

Wow, after doing more research on several sites, I'm surprised to find out that even in our stock 18" staggered sizes, there are many tire manufacturers that list their overall diameter as NOT exactly the same. I.e. 25.9 in, or 26.1 in, and not always exactly 26 inches for the same size. I didn't realize there was a slight difference in the same size from manufacturer to manufacturer. I always thought the tire would have the exact O.D. no matter who made it, as long as the size was the same....

[Chrakaknox]

ONLY the Conti DW's (out of 10 different max summer tires on tire rack) in 225/45/18 - 255/40/18 have the exact same diameter - 26.0 inches. So does 0.1 of an inch matter that much from front to back if it measures 25.9 inches? The other 9 out of the 10 tires do not match exactly.....

[Twix]

The reason for the slight difference in outer O.D. is the tread depth.

[Chrakaknox]

I thought so too, however, I believe all 10 tires I researched were listed as 10/32" tread depth....

[HBWT]

Originally Posted by Chrakaknox

So does 0.1 of an inch matter that much...

it matters not in the least.