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Old 05-10-2010, 03:20 AM
ard ard is offline
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Great post.

You lose handling performance- a feeling of being less 'sure', poor grip on rough roads on turns. Hard to quantify unless you are running track times

IMHO, only reason to upsize wheels is to increase the size of the brakes you an fit under them.

This whole 'group think' to 'big rims' is a pet peeve. Check out this car- almost laughable (IMO)

http://www.xoutpost.com/bmw-sav-foru...-spirit-p.html

Dainty rubber, puny looking rotors- car seem precariously perched above the tires-



A



Quote:
Originally Posted by JCL View Post
I believe that you are asking about measurable performance differences such as acceleration, braking, and fuel economy, vs subjective differences in turn-in, handling, and ride. Grip can be measured, but it isn't really relevant, so let's leave that out.

Acceleration and braking won't be impacted directly by wheel weight, but they will be impacted by rotational inertia of the wheel/tire combination. A plus size wheel is often heavier, but it also tends to have the weight of the rim at a greater radius, so it has more inertia, resulting in slower acceleration, and longer braking distances (ignoring traction effects). If you find larger wheels that are actually lighter than stock, then you will have minimal impacts (lighter weight will be offset by larger radius to the rim centre of mass). If you have heavier wheels, with larger diameter rims, you are compounding the negative impacts.

You will not see any differences in steady state performance from the different wheels due to these factors, only in the transient performance.

Because we don't tend to drive in steady state conditions,there is usually some negative fuel mileage impact with larger wheels. You will also see some reduction in fuel efficiency even in steady state conditions, due to the larger frontal area and the higher rolling resistance of the bigger wheels.

Drivers often note that they can tell the difference in acceleration with larger (heavier) wheels, but really, how often are you measuring your 0-60 times? You will be more likely to notice impacts on ride quality, harshness over bumps, and tramlining due to the wider tires following imperfections in the road surface.
ts
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