Speed channel says wider disks = less HP

[Gooch]

Was watching one of those car mod programs the other night and it was stated that wider disks (diameter) lead to less HP at the wheels. The kit they installed led to 7 HP less at the wheels.

So does smaller disks = more HP?

[Dirty.Deeds]

It's all to do with sprung and unsprung weight.If you really want to get a performance advantage for little or no money then strip the car of unnecessary items to reduce the weight and that will increase the power to weight ratio.

[Craig]

You mean brake disks? And when you say wider, you mean larger in diameter?

Even if that's true, bigger brakes help you go faster on a road course so presumably anyone upgrading to larger brakes is driving on the track so is still coming out ahead.

[darthmaul]

nothing to do with overall weight.

i think it was on Sports Car Revolution right? those cooky canadians!

they installed brake rotors which were actually the same weight (or lighter) than the stock rotors. the important thing with bigger wheels, rotors, or anything that spins around, is WHERE the weight is concentrated. when the total weight's the same but the concentration of the mass is closer to the outside then you will lose power because of the inertia of that mass. it takes more power from your engine to turn that bigger rotor so it eats up some hp.

i went to a clublexus dyno event where this dude actually gained some hp going from 17" wheels to 20" wheels. the dyno guys claimed it was because there was a lot more momentum from the heavier wheels which needed less power from the engine to speed up.

i'm sure even if you gained some hp that way...your car would be slower due to the fact that it'd take more hp to actually get them spinning from a stop... i could be wrong though...

but it was funny how someone yelled, "Everyone get DUBS!!!!" after they saw the dyno chart....hahaha

i don't think i'd go for the 20" wheels that give me an extra second in the 0-60

[Craig]

i went to a clublexus dyno event where this dude actually gained some hp going from 17" wheels to 20" wheels. the dyno guys claimed it was because there was a lot more momentum from the heavier wheels which needed less power from the engine to speed up.


Should be the other way around- heavier wheels require more power to spin. Same for flywheels, which is why everyone gets a lightened one.

There could have been something else going on that caused the increase in power that coincidentally happened when he switched wheels.

[darthmaul]

more power to start spinning...but less power to increase their speed once moving.

i think that's why lightened flywheels are made for track use and not for driveability. they slow down too quickly for smooth driving...

[632 Regal]

has less weight towards the outside and smaller rims have more rubber (weight) to the outside?

[Craig]

more power to start spinning...but less power to increase their speed once moving.



The effects of inertia is the same regardless if it's spinning or not. It takes more power to cause a change in rotational speed, either speeding up or slowing down, in a heavier wheel.

[632 Regal]

The effects of inertia is the same regardless if it's spinning or not. It takes more power to cause a change in rotational speed, either speeding up or slowing down, in a heavier wheel.