Aftermarket wheels and MPG

758 Views 3 Replies 3 Participants Last post by OPS, May 13, 2004

OPS

Discussion Starter · May 12, 2004

Hi,

I've just put new wheels on the car. Original setup was 225/45x17 Contisports on 17x8 Type 44 BMW wheels (Offset: ET 47) New setup is 225/40x18 T1-S on 18x8.5 BBS RK wheels (Offset: ET 38).

My MPG went down from 23 to 20 MPG at a constant rate of app. 100 mph.

What I can think of:
- Change in tire tread design
- Change in offset (tires stick out app. 1/4 inch more)
- Anything else not related to tires

Any of you have ideas, experiences?

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SteelBlueXI

· #2 · May 12, 2004

What do the RKs weigh? They may be heavier than your old wheels. Even if they are the same weight or lighter, you still went up a size. This pushes the rotational mass further from the wheel hub and closer to the edge of the wheel.

More rotational mass = more work to do = less MPG

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Staszek

· #3 · May 12, 2004

The BBS should be lighter I think but I dont know, since the width is the same what kind of tires are you running now. The stickier the tires the more friction is created, causing more effort to turn the wheels.

A grand touring tire with limited grip will get MUCH better gas mileage then a high performance tire of the same size.

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OPS

Discussion Starter · #4 · May 13, 2004

The wheels should be lighter, although weight is more at the outer part of the wheel. Old wheel/tire were 46lb combined, BBSs are not more than 19lb. T1-S tires are also said to be one of the lightest tires. And since MPG in this case is measured at a constant speed, weight should not be a factor (I guess...).

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