Wheel Weight

[spetz]

Hi,

Can someone tell for sure how much faster a car with 1kg lighter per wheel would be?

I keep reading things like 1kg at the wheel is equivalent to 10kg in the cabin etc.
Any truth to that?

[trism]

Correct. Do to serious laws of physics, like angular conservation of momentum, it is well known that 1kg of rotational weight is equivalent to about 10kg of static weight.

[vtecing]

Unsprung mass is what your talking about. Anything that is not,directly attached to the chassis and does not rebound from the shocks. Hence why some people pay $200 for wheel nuts, not because theyre blue but because they are light weight.

On my old car it had 17" chromes and I swapped for 15" 5zigens. Made a world of difference, even reduced my torque steer. Then when I put 16s on to sell it the car felt like it needed more momentum to get it going and understeered more frequently.

Also keep in mind that ur tyres are likely to weigh more than ur rims, so if ur prepared to research what wheels u need, dont neglect your tyres. I believe my 15" 5zigens were 6kg each and the re001 195 50 r15 were 9kg each which brang the total weight to 15kg, which was only 2.5kg less than the 17" chromes, but still made a huge difference

[spetz]

Well I was looking at the buddy club wheels. I can't remember their names but there are 2 which look the same, but one set is twice the price because they are stronger and lighter.
Just wondering if that 800+ price difference is worth it?

[vtecing]

Not for street use. Maybe if ur trying to go 0.01 seconds faster on ur lap time

[dougie_504]

So saving 1kg/corner is like saving 40kg in the cabin? Interesting...

[Rudy]

1kg wont notice squat. But im all for wheel weight reduction... i get a bit obsessed with it at times.

[spetz]

I am more interested in the acceleration benefits than handling to be honest

[trism]

Unsprung mass is what your talking about.


Unsprung mass is not the same thing as rotational mass. Unprung mass is as you correctly described and greatly affects handling of the car, especially over uneven surfaces.

Rotational mass only applies to the things that rotate. So the wheel/tyre combo and the disc brake rotor are the only things.

[trism]

So saving 1kg/corner is like saving 40kg in the cabin? Interesting...

Well not so much just "in the cabin" but throughout the entire car.

[trism]

I am more interested in the acceleration benefits than handling to be honest

Well less wheel weight means less rotational inertia, which means it'll be able to get spun easier. Its the same story as a lightened flywheel.

[dougie_504]

Thanks trism, can't rep you again yet though unfortunately :thumbsup:

[mugen_ctr]

And this is were expensive, exotic manufactures come into play :D

The only buddy club rim that i know thats forged, is the P1 QF, all the others are of cast design. have u considered Rays te37? I do believe those are of much higher tolerance than Buddy clubs, buddy clubs look like sticks compared to te37 lol

[spetz]

I like the TE37s as well but I think they look good in bigger sizes whereas I am looking at 15-16" max.
So in that size I think buddy club look the best

[gumus89]

Well less wheel weight means less rotational inertia, which means it'll be able to get spun easier. Its the same story as a lightened flywheel.

Less weight doesnt always mean less rotational inertia. A wheel may be lighter, but it may contain more of its mass on the outer edge to make the rotational inertia greater.


*trollface.jpg*

[nigs]

Less weight doesnt always mean less rotational inertia. A wheel may be lighter, but it may contain more of its mass on the outer edge to make the rotational inertia greater.


*trollface.jpg*
From a design point of view, isn't this stupid when talking lightweight/performance wheels?

[horse]

Well less wheel weight means less rotational inertia, which means it'll be able to get spun easier. Its the same story as a lightened flywheel.

+1. Another thing to consider is where that extra mass is sitting. If the extra mass is closer to the hub, the impact on rotational inertia is less when compared to extra mass sitting further out. I had a mate who had that down on his check list when he was looking for wheels. I have no idea how he would have measured that though. I'm not smart enough to figure that one out.

[vtecing]

Well I bought a new car recently, eg5 vti. It had 17"s on it which I replaced for 15" enkei RPF1 which weigh 4.3kg each. Made **** all difference lol. Does look nice though :D