Lightweight wheels - really a 20:1 benefit?

[Atty]

So, I'm looking at new wheels for my Mk7. Apparently VW has a fetish for heavy wheels, from what I've read the mk7 wheels are 29lbs each. Crazy!

I'm looking at some Enkei wheels and on their website it looks like they claim every 1lb of weight saved unsprung equals the equivalent of 20lbs of weight savings from sprung weight. If that were true, and I lost 12lbs per corner with the wheels I'm looking at, I would be saving the equivalent of 960lbs...which is a ton of weight!

When googling for the real answer I found a lot of talk, some backing it up others disproving it. Thought I'd ask here.

Has anyone made substantial weight savings with wheels? If so, what was the noticeable differences?

 

[Kelvrick]

I went from 24lb wheels to 18lb wheels. Yes, it felt substantial. Friend of mine added 4 piston big brakes, and it felt the opposite.

Don't have any numbers for you. Just feel wise, the before was like your car has 5 people. After is like just the driver. 20:1 seems a little high in my opinion. My butt dyno guestimate says 10:1.

 

[Zivic]

So, I'm looking at new wheels for my Mk7. Apparently VW has a fetish for heavy wheels, from what I've read the mk7 wheels are 29lbs each. Crazy!

I'm looking at some Enkei wheels and on their website it looks like they claim every 1lb of weight saved unsprung equals the equivalent of 20lbs of weight savings from sprung weight. If that were true, and I lost 12lbs per corner with the wheels I'm looking at, I would be saving the equivalent of 960lbs...which is a ton of weight!

When googling for the real answer I found a lot of talk, some backing it up others disproving it. Thought I'd ask here.

Has anyone made substantial weight savings with wheels? If so, what was the noticeable differences?

it will make a noticeable difference. keep in mind tire weight and overall diameter if you are going with a bigger wheel. this could offset some of the weight savings

 

[Atty]

it will make a noticeable difference. keep in mind tire weight and overall diameter if you are going with a bigger wheel. this could offset some of the weight savings

I'm 18x8 now and the wheels I was looking at are 17x8. 29lbs stock and 17lbs for the new ones.

 

[tortillasoup]

Unsprung weight vs sprung weight. I think it's a factor of 10X difference. (Unsprung weight being worth more)

 

[kitatech]

My 17" alloys + performance tires weigh the same as my OEM tires on 15" steelies...much improved ride.

 

[Zivic]

I'm 18x8 now and the wheels I was looking at are 17x8. 29lbs stock and 17lbs for the new ones.

yes, the overall difference should be noticeable, but it isn't going to be an OMG, MY CAR RUNS TEN. I think for the most part you will notice the car being a bit more nimble/responsive to your inputs.

 

[Bull Dog]

I remember looking into this issue before and the consensus is that unsprung rotating mass, generally has a 3:1 ratio. That is: three pounds of sprung weight is roughly equivalent to 1 pound of unsprung rotating weight.

 

[Kelvrick]

I remember looking into this issue before and the consensus is that unsprung rotating mass, generally has a 3:1 ratio. That is: three pounds of sprung weight is roughly equivalent to 1 pound of unsprung rotating weight.

I think there is more to it than just weight though. You have to factor in the rotational inertia of the new setup vs the old regarding how far out the weight is. Not just rim size, but tire size too. So the OP going from 18x8 29lbs to 17x8 17lbs is going to save 12lbs a corner, but he could also gain from the fact that the weight is closer to the hub.

Oh yeah, OP, don't forget about speedometer accuracy if your new setup is different from the old.

 

[twinrider1]

What exactly are they saying improves at such and such ratio?

 

[PieIsAwesome]

I remember looking into this issue before and the consensus is that unsprung rotating mass, generally has a 3:1 ratio. That is: three pounds of sprung weight is roughly equivalent to 1 pound of unsprung rotating weight.

This seems more correct. 20:1 is difficult to believe. The true value will depend on the moment of inertia of a particular tire/wheel, and that will depend on how the mass of the tire/wheel is distributed, as another poster suggested.

 

[Midwayman]

I remember looking into this issue before and the consensus is that unsprung rotating mass, generally has a 3:1 ratio. That is: three pounds of sprung weight is roughly equivalent to 1 pound of unsprung rotating weight.

This sounds way closer to reality. 20:1 is just absurd. Even 10:1 would be really pushing it, and only certain situations.

 

[Insomniator]

I went from 25lb 17" stock wheels on my Mini S to 17lb 17" Konig feathers. No way was the difference that astounding. Barely noticed it honestly. I think 3:1 was the number I found in my research.

Still not a bad deal for something that also happens to be asthetic.

 

[monkeydelmagico]

I'm 18x8 now and the wheels I was looking at are 17x8. 29lbs stock and 17lbs for the new ones.

I've never gone -1 on rim size always +1 or +2 . Didn't really notice a difference in acceleration but certainly noticed ride (compromised) and cornering (improved) differences

 

[yhelothar]

There was this magazine article about this where they tested a really light weight wheel ~11lbs and a moderately heavy one ~17lbs on a miata and went through an autocross track. The subjective test, the drivers reported noticeable differences in handling. But when it came to the autocross times, they were identical.
I'd have to say the difference is marginal at best.

 

[JulesMaximus]

Must resist urge to buy carbon fiber wheels for my Ducati...

 

[Wuzup101]

Don't resist Jules... Those look baller. What does a set cost lol? I'd be scared more of carbon fiber's failure mode on bike wheels on the street.

As far as the op's question... I'd guess more around 5:1 or less but thats just a guess from anecdotal "research." 20:1 is way too high IMHO. You also have to factor in that an equivalent tire will be slightly heavier in a higher aspect ratio if you downsize rims due to the larger sidewall... Probably not a huge difference but there.

Check out enkie rpf-1's if you want something that is both relatively inexpensive, strong, and lightweight.

 

[yhelothar]

Here are two tests which both did not find a performance increase with lightened wheels.
http://www.nsxprime.com/forum/showt...t-wheels-Acceleration-Tests-and-their-results
http://forum.miata.net/vb/showthread.php?t=419599

The miata test was through a publication with Grassroots Motorsports. You'll need a subscription to access it unfortunately.
http://grassrootsmotorsports.epubxp.com/i/282662/110#

On the other hand, it's been shown that wheel stiffness is a more important factor to consider for performance than lightness.
http://forum.miata.net/vb/showthread.php?t=370186

 

[michal1980]

Here are two tests which both did not find a performance increase with lightened wheels.
http://www.nsxprime.com/forum/showt...t-wheels-Acceleration-Tests-and-their-results
http://forum.miata.net/vb/showthread.php?t=419599

The miata test was through a publication with Grassroots Motorsports. You'll need a subscription to access it, unfortunately.
http://grassrootsmotorsports.epubxp.com/i/282662/110#

On the other hand, it's been shown that wheel stiffness is a more important factor to consider for performance than lightness.
http://forum.miata.net/vb/showthread.php?t=370186

and yet c&d found a difference

http://www.caranddriver.com/features/effects-of-upsized-wheels-and-tires-tested

 

[yhelothar]

and yet c&d found a difference

http://www.caranddriver.com/features/effects-of-upsized-wheels-and-tires-tested

That's interesting. In this test, not only the weight is varied but the wheel size is as well. It shows that the distribution of weight is significant. Larger wheels with smaller sidewalls means more of the weight is outwards from the center of rotational mass. This would require more force to rotate this mass.
The links I provided was done with similar size wheels but with different alloys and manufacturing processes leading to different weights. In those cases, no difference in performance was found.

 

[JulesMaximus]

Don't resist Jules... Those look baller. What does a set cost lol? I'd be scared more of carbon fiber's failure mode on bike wheels on the street.

They cost a couple thousand dollars for a set.

Very expensive.

 

[tracerbullet]

and yet c&d found a difference

http://www.caranddriver.com/features/effects-of-upsized-wheels-and-tires-tested

Nice link, I've searched this particular subject in the past but not seen it.

It shows that the distribution of weight is significant.

I think this is key.

 

[halik]

I thought it was 4x or so? I went from 24lb stock 18s on my old M3 to 16lb SSR comps and the difference was pretty noticeable. Direzza StarSpecs helped also, till the next owner wrapped it around a tree. Wah, wah.

http://www.s2cars.com/bmw/m3/13177183

 

[cbrsurfr]

I felt a huge difference from my stock 17's (28lbs I think) on my old GTI to 18" RPF1 (18.1lbs). The difference between the Raijin's I also had and the RPF1's was 2lbs and that wasn't really noticeable. The differences I noticed between those setups was due to different tire compounds.

There's no set ratio though and there's no way it's 20:1 on a GTI. Commonly accepted estimates are 3-4:1.

Have you changed the suspension yet? It may look like a 4x4 if you put 17's on it when it was setup with 18's from the factory. I think 18's look just right on a GTI. 17's a little small and 19's can look goofy.

 

[JCH13]

20:1 is silly.

The 'difference' as in measurable performance difference, is in the realm of a 3:1 - 6:1 ratio. That is that losing one kg of unsprung and rotating mass is worth 3-6kg of sprung and static mass.

The rotating part is important. The gyroscopic effects of the wheel/tire tend to mute steering feel in addition to requiring more energy to accelerate and brake. While the performance difference is present and measurable, the difference in feel is what more people will notice. It will be easier to feel the steering wheel's feedback and to modulate the brakes the throttle; the overall response of the vehicle to drive input will be faster and more direct. Unless we're talking about a track car this is all you'll really care about.

Keep in mind that as the wheels get lighter you may notice a degradation in ride quality. For the same reason that added mass makes the suspension unresponsive to the drive, it also makes it unresponsive to road roughness and impacts (in a good way). Lighter wheels/tires will likely reduce ride quality. This can be somewhat mitigated by down-sizing the wheel, the extra tire sidewall will cushion the ride more at the sacrifice of steering and braking feel. It's all a compromise!

As someone mentioned, you don't want to sacrifice much stiffness to reduce weight. Adding the compliance of a 'floppier' wheel can completely eliminate the mass advantages of a lighter wheel. Suspension parameters will change under load, steering feel is lost, etc.

TR has a good article on this: http://www.tirerack.com/wheels/tech/techpage.jsp?techid=108&