Larger Rims affect acceleration?
So I've always been curious about this, maybe someone on this thread can help me out. Disregard the plausibility of my hypothetical numbers here.
Say you start with a 17" wheel/tire combo that weighs 30 pounds. If you move up to an 18" wheel/tire combo that is a larger overall diameter than the 17" wheel/tire combo but is the same 30 pounds, will the car be quicker? I would imagine so because turning the axle one revolution now causes the car to move a longer distance. And the weight of the wheel/tire combo is the same, so it's not adding weight and slowing down the axle's revolution. But you're also incurring things like added friction and wind resistance since you're moving a longer distance for the same revolution of the axle.
Lot of things going on there, which is why I'd love to learn how it all plays out. My guess is moving to a wider diameter wheel/tire combo while staying the same weight will make the car quicker. But moving to a wider diameter combo that weighs more (which of course is the more likely scenario) is a toss-up as far as its impact on the quickness of the car.
Say you start with a 17" wheel/tire combo that weighs 30 pounds. If you move up to an 18" wheel/tire combo that is a larger overall diameter than the 17" wheel/tire combo but is the same 30 pounds, will the car be quicker? I would imagine so because turning the axle one revolution now causes the car to move a longer distance. And the weight of the wheel/tire combo is the same, so it's not adding weight and slowing down the axle's revolution. But you're also incurring things like added friction and wind resistance since you're moving a longer distance for the same revolution of the axle.
Lot of things going on there, which is why I'd love to learn how it all plays out. My guess is moving to a wider diameter wheel/tire combo while staying the same weight will make the car quicker. But moving to a wider diameter combo that weighs more (which of course is the more likely scenario) is a toss-up as far as its impact on the quickness of the car.
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I believe its all about weight. If you have the same 17 combo and 18 combo and they both weigh the same and the overall diameter with the tire on is the same, there is no difference on the distance when one rotation of the axel is turned. But if you ever turn a wheel of any sort or size. the weight is what causes the extra toughness in turning it.
I believe its all about weight. If you have the same 17 combo and 18 combo and they both weigh the same and the overall diameter with the tire on is the same, there is no difference on the distance when one rotation of the axel is turned. But if you ever turn a wheel of any sort or size. the weight is what causes the extra toughness in turning it.
What I'm asking is when one of these - either the weight or the diameter or both - change, what is the effect on the quickness of the car. Specifically, which is quicker (all else equal): a car with a 17" wheel/tire combo that weighs 30 pounds and a car with an 18" wheel/tire combo with a larger diameter but the same weight.
That's a complicated question Calvin, and quite frankly, probably beyond my scope of knowledge, But, I'll give it a shot with my 1 year of mechanical engineering education. 
A larger rolling diameter should actually slow your car down because you get less torque. Think of it like starting your car in 2nd gear. You would, however, have a higher theoretical top speed. This is also why you try to match the rolling diameters as close as possible, so you don't mess up your speedometer.
If you had a 17" vs. 18" setup with identical rolling diameters, identical tire widths etc, there could still be a difference due to the moment of inertia implications. Think of a bicycle wheel that just happened to have all of its mass near the outside diameter and compare it to another wheel with the exact same outside diameter, but with all the mass concentrated toward the center. The latter one would respond better to torque, and thus result in fast acceleration.
So you have overall weight, moment of inertia factors, wheel widths, tire properties, etc. Lots of variables at play.
A larger rolling diameter should actually slow your car down because you get less torque. Think of it like starting your car in 2nd gear. You would, however, have a higher theoretical top speed. This is also why you try to match the rolling diameters as close as possible, so you don't mess up your speedometer.
If you had a 17" vs. 18" setup with identical rolling diameters, identical tire widths etc, there could still be a difference due to the moment of inertia implications. Think of a bicycle wheel that just happened to have all of its mass near the outside diameter and compare it to another wheel with the exact same outside diameter, but with all the mass concentrated toward the center. The latter one would respond better to torque, and thus result in fast acceleration.
So you have overall weight, moment of inertia factors, wheel widths, tire properties, etc. Lots of variables at play.
Last edited by brociouz; Oct 10, 2011 at 07:28 PM.
That's a complicated question Calvin, and quite frankly, probably beyond my scope of knowledge, But, I'll give it a shot with my 1 year of mechanical engineering education.
A larger rolling diameter should actually slow your car down because you get less torque. Think of it like starting your car in 2nd gear. You would, however, have a higher theoretical top speed. This is also why you try to match the rolling diameters as close as possible, so you don't mess up your speedometer.
If you had a 17" vs. 18" setup with identical rolling diameters, identical tire widths etc, there could still be a difference due to the moment of inertia implications. Think of a bicycle wheel that just happened to have all of its mass near the outside diameter and compare it to another wheel with the exact same outside diameter, but with all the mass concentrated toward the center. The latter one would respond better to torque, and thus result in fast acceleration.
So you have overall weight, moment of inertia factors, wheel widths, tire properties, etc. Lots of variables at play.
A larger rolling diameter should actually slow your car down because you get less torque. Think of it like starting your car in 2nd gear. You would, however, have a higher theoretical top speed. This is also why you try to match the rolling diameters as close as possible, so you don't mess up your speedometer.
If you had a 17" vs. 18" setup with identical rolling diameters, identical tire widths etc, there could still be a difference due to the moment of inertia implications. Think of a bicycle wheel that just happened to have all of its mass near the outside diameter and compare it to another wheel with the exact same outside diameter, but with all the mass concentrated toward the center. The latter one would respond better to torque, and thus result in fast acceleration.
So you have overall weight, moment of inertia factors, wheel widths, tire properties, etc. Lots of variables at play.
Larger diameter wheels will slow the car unless you change the gearing to compensate even if they're the same weight.
Deviating from the design diameter more than 2% brings on a whole host of potential problems. It's not something to just casually do.
Changing the WHEEL diameter means nothing as long as the TIRE diameter stays the same. A larger diameter wheel will have slightly more inertia because the bulk of the mass is at a larger radius, but in the real world, this isn't something you'll be able to say - yeah, the car is definitely slower now. You'll find out when you race a car with stock wheels and they beat you by a small but definite margin.
AFA light and strong AND cheap...Enkei PF01s or RPF01s are great lightweight strong and inexpensive wheels compared to the brands I've seen discussed in this thread. Silver PF01s in the pic below.
Deviating from the design diameter more than 2% brings on a whole host of potential problems. It's not something to just casually do.
Changing the WHEEL diameter means nothing as long as the TIRE diameter stays the same. A larger diameter wheel will have slightly more inertia because the bulk of the mass is at a larger radius, but in the real world, this isn't something you'll be able to say - yeah, the car is definitely slower now. You'll find out when you race a car with stock wheels and they beat you by a small but definite margin.
AFA light and strong AND cheap...Enkei PF01s or RPF01s are great lightweight strong and inexpensive wheels compared to the brands I've seen discussed in this thread. Silver PF01s in the pic below.
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Ok found these wheels I quite like any thoughts?
http://www.ebay.co.uk/itm/18-LEXUS-I...item48418e323b
http://www.ebay.co.uk/itm/18-LEXUS-I...item48418e323b
Joined: Sep 2010
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From: Vancouver, BC / Seattle, WA
Calvin,
Technically a 17" wheel/tire and 18" wheel/tire, even I wonder but I would probably assume the 18 combo would be heavier - assumption, they are same style make...
Technically a 17" wheel/tire and 18" wheel/tire, even I wonder but I would probably assume the 18 combo would be heavier - assumption, they are same style make...
They look pretty nice.
Ok found these wheels I quite like any thoughts?
http://www.ebay.co.uk/itm/18-LEXUS-I...item48418e323b
http://www.ebay.co.uk/itm/18-LEXUS-I...item48418e323b
