Thanks Jim. I guess I meant tires when I said "wheels". Totally makes sense. Is there much of a gas mileage difference or ride difference when you go from 15's to 16's?

 

We've only used 16" wheels on "our" (my wife's) MINI, so I haven't directly experienced any differences in mileage or ride between 15s and 16s. We used to have a '64 Mini Cooper S with 10" wheels, but that was too long ago to remember much.

Theoretically, one should be able to get better gas mileage on OE 15s because they are so much lighter than OE 16s. The OE tires are a little lighter too, so the total weight of 15s could be 7 or 8 pounds lighter per corner than 16s; depending on exactly which OE wheels and tires are compared. That 30# or so weight difference is unsprung rotating mass, so it's probably "worth" about a 100# reduction of sprung weight in the car.

As for the ride, the sidewalls of OE 15" tires are taller than OE 16" tires, which, in turn, are taller than OE 17" tires. Other things equal, taller sidewalls provide somewhat more ride cushioning due to their greater flex.

Maybe someone who's gone from OE 15s to OE 16s can inform us both about any noticeable changes in mileage and ride.

 

Thanks for the info Jim.

 

I have my stock 16's with 205/55/16 tires and didnt notice much ride difference when I installed my (heavy aftermarket wheels) 17's with 215/40/17 tires. It was slightly rougher but even though I added unsprung weight I Increased gas mileage by about 2MPG on the freeway. A larger wheel will increase your rolling resistance but once your moving it will rotate less often than smaller tires increasing fuel economy. If you want to run bigger wheels and tires buy some light weight wheels they cost more but are well worth it in the end. I will be running some 14 pound 17" rims when I can afford them.

 

evanbear, you do realize the 17" wheels you have on are actually smaller than the 16" wheels you had on before? Thus, they are rotating more often.

 

The 17" wheels are bigger, but the 215/40/17 tires are about 1" smaller in diameter than the 205/55/16, so jcauseyfd is right about wheels and tires rotating more often.

 

when I got the wheels they originally had 225/50/17 thats when I compared MPG differences. I think if you do the math the tires are a little bit taller than the 205/55/16 or the 195/55/16 that are the factory size. The 205/55/16 with 6/32 of tread is 24.25 inches tall and a 225/45/17 also with 6/32 of tread was 24.5 inches tall, if you add another 11.25mm to that thats how tall a 225/50/17 tire would be. I soon bought the set of 215/40 to be the close to the same size as the factory 205/45/17.

 

Measuring my friends tires 215/40/17 stretched over an 8.5 inch rim they are sitting a little under a 3/4 of an inch smaller than the 205/55/16. But I am sure the original tires were taller than the stock 195(205)/55/16

 

Really had to search for this tread. I just made a trip in my wife's 2009 MCS and put my GPS unit in. Readout is 4 mph fast on the speedometer above 50 mph and about 3 mph fast below 50. I was surprised as my Lexus 330ES and the GPS always are spot on.

 

Those "over-reads" seem typical for most cars from what I've read and experienced. Maybe your Lexus is the "deviant" by reading accurately.

 

The Speedometer being off is a normal thing in all BMW and MINIs. The factory allowance for this is up to 10% per MINI and BMW. The higher rate of speed you are traveling at the more it will be off. Usually like everyone is seeing, its about 4 to 5 mph off. There is not any correction that can be made to this unfortunately. So set your cruise at 5mph over and you will be perfect!!!

 

You could put taller tires on it and reduce the speedometer error.

Dave

 

Yep, the particular law that MINI/BMW is trying to comply with is that the speedometer isn't allowed to read even 1 MPH too low, but it can read up to 10% high, PLUS an additional 2.4 MPH.

As an example, with a true road speed of 70 MPH, any speedometer reading from 70 MPH up to 79.4 MPH is technically "within spec", so the dealer won't correct it.