[parish8]

I found this website that helps to understand the effects of rotational weight. We have all heard how getting rid of rotational weight is like getting rid of “4” times normal weight. Well it is a little more complicate than that. The calcs at the bottom of the page give a much better idea of rotational weight effects. It gives you mass equivalents.

Here are some of the numbers.

Tires = 1.9
Rims = 1.3 - 1.4
Rotor = 1.1
Driveshaft = 1.01

Dropping weight on a tire you get almost double the effect. Dropping weight on the driveshaft give you virtually no additional effect. Nothing on our cars is over 2 equivalent ratio.

http://hpwizard.com/rotational-inertia.html#wheelstires

[JFM-jr]

This makes sense the larger the diameter and the further out the weight sits on that diameter is going to have a larger effect. The closer to the center the less benefit. An axle shaft or driveshaft has no real turning circumference to speak of vs let's say a 30" slick. Cool info in that link

[62nalide]

Yep my main focus for the past 10yrs thats how I managed a 6.55 @ 104mph in the 1/8 on a heads and cam setup in a 5th gen....

[parish8]

The stock front wheel/tires are 59lbs each. A 17” front skinny with a bias ply tire weighs 27lbs. 64lbs total off the front of the car. Looking at those calcs I am going to average the wheel and the tire ones and call it a 1.65 mass eq ratio.

1.65 x 64 = 106lbs of equivalent loss. Putting that into a hp/et calc shows .11 et reduction in the 1/4 mile on a stock car and .09 for a car more like mine. This does not include loss of rolling resistance or the fact that you will likely hook better getting some weight off the front of the car.

[laynlo15]

My Rears were 64 lbs, fronts 62 lbs. I saved 100 lbs with my Race Stars and Hoosier slicks and skinnies. Plus my car ran 3 tenths quicker and several mph over the stock wheels and tires. The track temps and air were about the sam so pretty accurate comparison.

[cmitchell17]

So switching to non run flat Michelin Pilot sport 4S dropped 5lbs per tire from the stock goodyears. So 5X4=20, 20X1.9=38lbs

[vtirocz]

Originally Posted by cmitchell17

So switching to non run flat Michelin Pilot sport 4S dropped 5lbs per tire from the stock goodyears. So 5X4=20, 20X1.9=38lbs

Wow. Are you comparing worn tires to new tires?

[cwebster]

Great topic! I've read this before in various other literature and online. The information on the linked page is very thorough and I like that it includes calculator tools. You can easily demonstrate the concept with a few bicycles if you turn them over and pedal them by hand. Larger, heavier wheels take a lot more effort (power) to turn. This goes hand-in-hand with gear reduction as the effect is multiplied when you change the wheel height or, more accurately, its circumference.

--Cal

[Snowblind]

Originally Posted by parish8

The stock front wheel/tires are 59lbs each. A 17” front skinny with a bias ply tire weighs 27lbs. 64lbs total off the front of the car. Looking at those calcs I am going to average the wheel and the tire ones and call it a 1.65 mass eq ratio.

The 27lb front skinny setup, are you running a 26" tire ? I just got my M&H bias fronts today (28's) and they weigh 17 lbs ea..my 28" M&H radials weigh the same. Scratchin my head here, I thought they would be lighter.

[cmitchell17]

Originally Posted by vtirocz

Wow. Are you comparing worn tires to new tires?

No I'm just going off the published weights by Goodyear and Michelin.

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