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Old 08-23-2005, 11:39 AM   #1
RallyBLUSTi
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Default Do Larger Diameter wheels Reduce Power?

OK please bear with me, I am not that s-m-r-t, so please tell me if larger diameter wheels take away power. I am thinking of buying some 19' wheels for my sti, just pimping wheels, cause I am a pimp or something like that , and was wondering if they are gonna take power away, compared to the stock 17's, I am not gonna sell my 17's cause I want to use them for drag racing and autocross, but wanted the 19's for you know pimpin'. And yes it does matter that I have all the power even when I am just, um, pimpin. So please help me out and let me know. Thanks guys.
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Old 08-23-2005, 11:41 AM   #2
subieworx
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Adding rotational mass or even just shifting the same amount of mass further out on the wheel will cause your acceleration to decrease. It is a simple case of physics in where it takes more power to drive the larger and heavier wheels.
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Old 08-23-2005, 12:04 PM   #3
RallyBLUSTi
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Yea that's what I figured, same principle as the Flywheel, just wanted to see what other people's thoughts were.
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Old 08-23-2005, 04:21 PM   #4
Back Road Runner
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Yep, just like a flywheel. It does nothing to power. It's just a matter of rotating mass. It takes more energy from the engine to speed up and takes more braking energy to slow down. It will use up more of the power you have available. If you're not keen on the laws of physics, look up the term inertia.

An engine, drivetrain, even wheels and tires all are bound by the laws of physics and concepts of energy. They all work the same and work together. It's just that a flywheel will have a greater impact on what you feel than a set of tires and wheels. Generally, moving to a different set of tires and wheels will be almost unnoticable, and the gain in grip and handling may very easily outweight any small decrease in acceleration/deceleration you may hardly be able to notice. Just because they are heavier doesn't mean they may be worse. If those heavy rims and tires provide a whole lot more grip and responsiveness, is it worth it? Then again, if the grip and responsiveness gain was almost unnoticable, then the loss of accelerate/deceleration could actually become the larger factor. Pick and choose wisely and figure out which gains and losses weight more heavily.
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Old 08-23-2005, 05:12 PM   #5
mediapig
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Default Great post!

Just wanted to say I've heard this discussed many times, in many ways, and that was the clearest, most thoughtful answer I've ever seen given to this question. Thanks!
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Old 08-23-2005, 06:23 PM   #6
Airborne_J
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Your gut feeling was right on this one, you said you were going to stick with 17" for autoXs.

More technically speaking, from a search for "rotational inertia" on google. (it was the 4th result) (notice how I got around the 10-post rule)
The moment of inertia of a system is defined as:
I = *Integral*( R2 )dm

where R is the distance of the mass element dm from the axis of rotation.

In otherwords if you add weight, or keep it the same but position it further away from the axis you're going to require more work. This is why the weight of your tires is arguably more important than the weight of your wheels. Although tires have certain properties that we don't want to sacrafice just for a few pounds.
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