[RAV]

The brochures show lower mileage with larger wheels. Im sure their odometers reflect the slightly different diameters. Also the larger wheel is slightly heavier but also the the sidewall of the tire is smaller which will make the tire lighter overall. I would think the loss of rubber in the side wall would weight more the additional length of the spokes of the alloy wheels. Can anyone explain this ?

[Delta0311]

Originally Posted by RAV

The brochures show lower mileage with larger wheels. Im sure their odometers reflect the slightly different diameters. Also the larger wheel is slightly heavier but also the the sidewall of the tire is smaller which will make the tire lighter overall. I would think the loss of rubber in the side wall would weight more the additional length of the spokes of the alloy wheels. Can anyone explain this ?

???? Lower mileage what, on the tire wear?

[RAV]

look at a BMW Brochure on the UK website, they show different mileage ratings based on the size of the wheels chosen.

[Jbrock22]

Originally Posted by RAV

The brochures show lower mileage with larger wheels. Im sure their odometers reflect the slightly different diameters. Also the larger wheel is slightly heavier but also the the sidewall of the tire is smaller which will make the tire lighter overall. I would think the loss of rubber in the side wall would weight more the additional length of the spokes of the alloy wheels. Can anyone explain this ?

Larger wheels & tires = additional weight

[Jamesons Viggen]

Originally Posted by Jbrock22

Larger wheels & tires = additional weight

This.

More often than not, larger wheels increase unsprung weight and make the engine work a fraction harder which will reduce MPGs. If you notice the wheels on true race cars, they are often much smaller than a similar road car.

The exception is when you select a lightweight tire and a lightweight wheel. Many times I have gone +1 and still reduced weight by 2-5lbs per corner. In those cases there is no negative.

[PrematureApex]

It's not as simple as weight, although that's a big advantage...

Even if they weigh the same, or even if the larger wheel setup weighs slightly less, the larger wheel has a larger moment of inertia and will take more energy to accelerate and decelerate vs. the smaller one.

http://hpwizard.com/rotational-inertia.html

For performance, run the smallest wheels that will fit over your brakes. Might come at the expense of some turn-in feel, depending on the tire though, so that might be a motivator to keep the sidewall smaller.

[HighlandPete]

This article may help understand why upsizing isn't best for fuel consumption, or always a performance benefit.

http://www.caranddriver.com/features...d-tires-tested

Also wheel widths and tyre sections change on some wheel upgrades, so drag and rolling resistance can be changing as well.

[Jbrock22]

Agreed.

[0w40X1]

I ordered my 2014 S28i M Sport with 18" wheels for a very good reason.

When the run flats are gone, I'll buy Michelin PSS in 225/40R18 and 255/35R18 which will lower final gear about 4%.

The car is already a low rpm monster, but acceleration will be better, and it'll feel lighter and get better gas mileage.

Of course I have to recalibrate my Sanguage II down 4% or it'll look like I got way better mileage.

Guys trying to keep miles off car wouldn't dream of this, but I barely drive the car.