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Discussion Starter · #1 ·
ok, so there are two wheels Im looking at.
They are both 18", but one weighs like 20# and the other is like 17#.

My question for the guru's is...does the three pounds make THAT much of a noticable difference? BTW, driving mostly on the street, not sure about track or drag....dont really have time for them.

thanks in advance
 

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Additional wheel weight alone doesn't just impact suspension. Though the suspension gurus could have a field day on that issue alone . . .

I think it's the combination of the additional unsprung weight + excess rotational inertia. Rotational inertia is very bad for acceleration.

rotational acceleration = torque / rotational inertia.

less rotational inertia means faster acceleration given the same torque.

So yes, you'll notice the penalty of heavier wheels on the streets in terms of sluggish acceleration and sloppier handling. I'm sure somebody here has already crunched the numbers. ;)

Dave.
 

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It mostly depends on where you put the weight. I don't think we would like a 3lb lump on the rim of our wheels.
 

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Discussion Starter · #4 ·
yeah,
like I figured the weight does make a difference. I already knew about the rotational inertia and the other physics that goes along with that. I understand that the larger the wheel the more it is required to make it move.

But still, is the difference in accelaration that noticable? between 17 and 20 pound wheels??:confused: :confused:
 

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I don't remember the equations exactly but it's an exponential thing. So a total of 12 pounds (3 x 4 wheels) rotating is something like putting a 144 pound guy in the car. Same goes for suspeension - it's exponential.

Chris
 

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I've crunched the numbers and found that over 80% of the rotational inertia is in the tires. So you most likely won't feel a difference between a 20lb wheel and a 17lb wheel during acceleration. My numbers showed about a 2 or 3 equivallent hp difference at max acceleration in 1st gear. Don't worry about it if you aren't trying to shave 10ths of a second off your race times. The heavier wheels may even have less rotational inertia depending on how the bulk of the weight is distributed.

I race my car and my race tires and wheels have about 1/2 the rotational inertia of my street tires and wheels and even that amount isn't that noticeable from the butt dyno.

I'm not sure how much it affects your handling due to unsprung weight but again, if you aren't racing you should just pick the wheel that looks the best to you.
 
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