what are the effects of lighter rims??
05-09-03 | 10:40 PM
#1
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Joined: Aug 2002
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From: Austin, Tx
what are the effects of lighter rims??
i was wondering if the affects where the same as just reducing weight on your car or does it get you a betteradvantage from reducing the weight.
05-10-03 | 05:23 AM
#2
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Joined: Dec 2001
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From: San Lorenzo, California
Lighter wheels = less unsprung weight. This means the suspension can control the wheels + tires better which means better ride AND handling. It also will improve acceleration as you will effectively gain horsepower due to there being less mass to accelerate.
05-11-03 | 03:01 AM
#3
WWFSMD
Joined: Jun 2001
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From: SoCal
I agree with rynberg's answer.
Lighter wheels&tires allow the suspension to keep the rubber on the ground better, for more traction and higher grip (especially when there are bumps).
Lighter wheels also mean a better ride because the ratio of sprung to unsprung weight it higher when you lower the unspring weight. Also, when the wheel+tire is lighter, it will rise over a bump easier, which transmits less severe impact vibrations to the chassis.
Rotational inertia is a factor as well, but its affect on acceleration will be less than double the static weight of the wheel+tire. It is still more than one, since the wheel will be both rotating and translating (moving forward with the car). But the outer diamater is moving just as fast as the car is translating, which means most of the wheel's mass is rotating as a linear speed that is less than the speed at which the car is moving. That means the effect is less than double, but perhaps 1.5 times or so. I write this only because this affect is often overstated, like 200 lbs of wheels are like 800 lbs of chassis weight or something (wrong). Using the 1.5 estimate of the effect, 200 lbs of wheels is like 300 lbs of chassis weight. Or adding 40 lbs to your wheels + tires will affect acceleration in about the same way that adding 60 lbs of weight in the car (non-rotating parts). The effect is much more pronounced for things that spin faster than the wheels (like the flywheel), but for wheels, the effect of the rotational intertia is no more than twice the static weight, and probably more like 1.5 times the static weight (the exact multiplier depends on the distribution of mass in the wheel+tire assembly).
-Max
Lighter wheels&tires allow the suspension to keep the rubber on the ground better, for more traction and higher grip (especially when there are bumps).
Lighter wheels also mean a better ride because the ratio of sprung to unsprung weight it higher when you lower the unspring weight. Also, when the wheel+tire is lighter, it will rise over a bump easier, which transmits less severe impact vibrations to the chassis.
Rotational inertia is a factor as well, but its affect on acceleration will be less than double the static weight of the wheel+tire. It is still more than one, since the wheel will be both rotating and translating (moving forward with the car). But the outer diamater is moving just as fast as the car is translating, which means most of the wheel's mass is rotating as a linear speed that is less than the speed at which the car is moving. That means the effect is less than double, but perhaps 1.5 times or so. I write this only because this affect is often overstated, like 200 lbs of wheels are like 800 lbs of chassis weight or something (wrong). Using the 1.5 estimate of the effect, 200 lbs of wheels is like 300 lbs of chassis weight. Or adding 40 lbs to your wheels + tires will affect acceleration in about the same way that adding 60 lbs of weight in the car (non-rotating parts). The effect is much more pronounced for things that spin faster than the wheels (like the flywheel), but for wheels, the effect of the rotational intertia is no more than twice the static weight, and probably more like 1.5 times the static weight (the exact multiplier depends on the distribution of mass in the wheel+tire assembly).
-Max
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