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[BMWNTHZST]

My 335i sport came with 225/35/19 front and 255/30/19 rear. My question is if I went to a 255/35/19 rear wouldn't this screw up the odo reading due to the fact that the tire has a larger area to cover now for each rotation?

The tire shop told me this was a recommended tire size by BMW

[BTM]

Odometer reads from the transmission if I'm not mistaken, so wheel/tire diameter won't affect it

Edit: guess not, speedometer reads from transmission then? I'm confused

[The HACK]

Originally Posted by BTM

Odometer reads from the transmission if I'm not mistaken, so wheel/tire diameter won't affect it

Wrong.

[BTM]

Ok, so what's right then?

[alex2364]

Your tire shop doesn't know what they're talking about. I would stick with OEM sizes.

[alex2364]

Originally Posted by BTM

Ok, so what's right then?

OP is right. Odometer and speedometer readings are calculated by the rotation of your wheels.

[BTM]

Strange. I could've sworn I read that one or the other was calculated from the transmission or driveshaft. Oh well

[MusclezMarinara]

dont mess around with tire sizes on XI models but def stick with OEM sizes

[BMWNTHZST]

my car is a 335i convertible not an x model.

If I go with a 275/30/19 will that work or will it rub? I'm thinking I will be ok.

[BTM]

Originally Posted by BMWNTHZST

If I go with a 275/30/19 will that work or will it rub?

Try posting here

[The HACK]

Originally Posted by BTM

Strange. I could've sworn I read that one or the other was calculated from the transmission or driveshaft. Oh well

It is. Therefore it is affected by the size of tires. Taller tires means each mile travelled, the odometer will indicate LESS than the actual mile travelled, and shorter tires means each physical mile travelled the odometer will indicate MORE than the actual mile travelled. The odometer is calibrated to convert the signals from the transmission based on an overall diameter of 25.0". A 235/35/19 tire would result in a 26.0" diameter. A 4% difference, and your odometer will read 4% too slow based on the tire change (for every 100 physical miles travelled the car will only report 996 miles).

[BTM]

I guess that makes sense but seems less than ideal to me, something as common as changing to snow tires can affect your mileage and possibly warranty? It's not like there is a snow tire option from BMW, nor are the stock RFT recommended for snow

[The HACK]

Originally Posted by BTM

I guess that makes sense but seems less than ideal to me, something as common as changing to snow tires can affect your mileage and possibly warranty? It's not like there is a snow tire option from BMW, nor are the stock RFT recommended for snow

No. You're suppose to change tires to the same aspect ratio, or tires that retain OEM overall diameter. So when you go from a 255/35/18 OEM tire to 225 width snow tire, you SHOULD buy 225/40/18 or 225/45/17 to retain the same overall diameter. If you need to buy 205 size snow tires ('cause, you know, skinnier tires give better grip in snow) you buy 205/50/17s.

The opposite is true. If you want to buy WIDER tires for performance reasons, you need to go from a 255/35/18 to say, a 265/30/19 to retain the closest overall diameter.

[BTM]

True, I understand the benefits of keeping the overall diameter as close as possible. Still, just seems like an easy way for a dealer to say "mileage is questionable due to different tires" and try and shaft you...

[BMWNTHZST]

Thanks for your help guys. I've gone ahead and ordered 225/35/19 front and 265/30/19 rear

[NoWr2Go]

If you go 265-30-19s in the back you should go with 235-35-19s in the front and not 225s.

[Gary@TireRack]

Originally Posted by BTM

True, I understand the benefits of keeping the overall diameter as close as possible. Still, just seems like an easy way for a dealer to say "mileage is questionable due to different tires" and try and shaft you...

As long as the tires are the same overall diameter, he would look like a fool for trying to claim that. Its not about having 'different' tires (brand or model of tire is irrelevant), its about having the wrong size of tires.