Lightweight Wheels - Does it really matter?

[ZDan]

Originally Posted by Ro_Ja

Reminded me of this article:

http://www.m3post.com/forums/showthread.php?t=479110

I read through this article, it seems like they removed *all* the weight from the area that bolts to the hub, and the wheel design has the spokes as far offset from the mating surface as possible. They didn't remove the weight from the rim area where the benefits would be greatest. They did remove weight where the reduction in stiffness would be significant, though.

For sure they removed enough material from the wheel that deformation became an issue affecting performance. Anyway the performance difference may perhaps bigger than I initially thought, but the linked Enkei test doesn't seem totally valid to me.

If the less-stiff wheel is effectively losing some camber, what happens when you dial it back in to compensate?

In the end, you design for maximum strength/stiffness for minimum weight. The wheel they took material out of had been designed to work with that material in place! So they were outside of the engineered-in strength right off the bat. I would be more interested to see a test of a forged wheel vs. cast of similar design, both designed to the same loads and the same overall wheel strength relative to material strengths. The Forged wheel would be a bit lighter, the cast wheel a bit stiffer, but the weight difference would be distributed over the wheel instead of concentrated near the hub (where lighter weight doesn't help much, but reduction in stiffness could hurt more). I bet you'd have a *damn* difficult time sussing out the lap time differences, particularly if each setup is optimized separately.

[coyote]

Originally Posted by ZDan

Wheels made to the same dimensions/wall-thicknesses/etc., one 6061-T6, one AC4C-T6 (A356-T6), will have PRECISELY the same rigidity/stiffness. ANY aluminum alloy will have a modulus of elasticity of 10-10.5 Msi, so the *stiffness* is the SAME for a given net shape.

Although the modulus of elasticity is "similar", different alloys and different tempers can have quite different material properties.

Of course that's just the material difference. As I said, manufacturing method also plays a role in why you can make a wheel with similar properties using 20% less metal (as does design).

I would love to see a comparison between say a CE28N and whatever the Rota rip off is called.

[coyote]

Originally Posted by ZDan

I would be more interested to see a test of a forged wheel vs. cast of similar design

Originally Posted by coyote

I would love to see a comparison between say a CE28N and whatever the Rota rip off is called.

Didn't see your post when I made mine :-)

[jwjknorr]

Hmm alot of long answers. Short answer. More mass, less speed, Less mass more speed. This goes for the whole car. Rule of thumb, not always correct so dont flame , but about 100 lbs is a tenth of seconed off a quarter mile time. With anything rotational the affects are even greater becouse your not only loosing weight on the car, but allowing the engine to spin with less resistance.

Rotation mass easy options include, wheels, ours are 20lpb stock but 18's can easily be found at 17 lbs, Flywheels <-- major difference in my opinion, crank pully <-- did on my car , cheap easy and noticeable , and carbon fiber drive shaft <--- nexts years tax refund , never used before, heard great things want to try. What can i say i like trying new things.

Can anyone chime in on if we can hurt these motors by freeing up to much rotation mass.. For example I went with all options i mentioned , which is my plan, no big hp increase maybe 1 hp but will defiantly have a time difference.

I drag all my cars for fun. Not hard core maybe twice a year with 4 runs over 6 hours but this car i plan on learning motor sport tracks, although south jersey sucks for this. SO expensive for 1 day with little return.

[gms]

In 2005/2006 we raced the Honda Civic Type-R Challenge at the Nürburgring Nordschleife. It was a Honda Championship integrated in the VLN Series, including the 24h Race. The Hondas where built up as FIA Group N Cars (around 200whp) with slight modifications due to the long and bumpy Nordschleife.
The cars came with massive and stiff 7x16" ATS Epsilon wheels. The field was very close and hard so we decided to search for a legal advantage. I ordered the RPF-1 which where around 6lbs lighter each corner.
Laptimes where immediately around 5 sec faster and car Response also increased. Three races later nearly the complete Honda field had changed to light wheels and took the ATS as livingroom tables.

[ZDan]

Originally Posted by coyote

Although the modulus of elasticity is "similar", different alloys and different tempers can have quite different material properties.

Ultimate strength, yield strength, elongation properties, yes, they can be *very* different. But MODULUS (i.e., stiffness) is going to be in the 10-10.5 Msi range for *any* aluminum alloy, regardless of temper. If anything, 6061 actually has the slightly lower modulus, ~10.0 average tensile/compressive, whereas cast 356 is at 10.5 for tensile (average would be slightly higher).

[Jesse]

you can notice driving feel improve with wheels that are lighter for sure. 5-10 pounds on each corner can make a difference for sure.

[hal0n]

I didn't see this mentioned. Another thing to consider is that the rotating mass stores energy. This is just like the flywheel. There are some situations where reducing rotating mass can hurt performance such as climbing hills. In general the trade offs are completely worth it though.

[mrk1]

I've always enjoyed light weight wheels, car feels lighter on its feet. Also make sure to keep an eye on tire weight.

Lightweight parts could have more potential to flex as previously mentioned but I would be surprised to see significant flex on street tires on the road.

[ZDan]

Originally Posted by hal0n

I didn't see this mentioned. Another thing to consider is that the rotating mass stores energy. This is just like the flywheel. There are some situations where reducing rotating mass can hurt performance such as climbing hills. In general the trade offs are completely worth it though.

Only if you allow the car to slow down going up the hill. They you get a TINY smidge of "assistance", and you'll coast *slightly* further. If you maintain speed, zero difference. If you try to accelerate, of course you'll be slightly slower with the heavier wheels.

Already mentioned previously, but the rotational energy in the wheel is not that significant relative to the tire. I also had calculated 1.7x as the effective *tire* weight savings multiplier which I've used in vehicle performance modeling for years. Someone else in this thread came up with 1.25x for wheels as a general factor, which seems plausible, but since that's so small I just leave it out.

[gms]

Originally Posted by hal0n

I didn't see this mentioned. Another thing to consider is that the rotating mass stores energy. This is just like the flywheel. There are some situations where reducing rotating mass can hurt performance such as climbing hills. In general the trade offs are completely worth it though.

Dont forget that it takes energy to get a flywheel loaded. As long as this energy
doesnt come from the brakes, it is missed in acceleration. So thats not a real deal.

[Apex Chase]

Originally Posted by coyote

Reducing mass is good.

Reducing unsprung mass is great.

Reducing rotational mass is brilliant.

Reducing rotational unsprung mass is golden.

Just because you have an NSX, doesn't mean you have a clue.

Add a set of wheels that are 5 lbs. heavier to your car and then tell me if you think it matters.

[RazBRZ]

I see it simply as. Lighter wheels = wider wheels and tires for a similar weight = more grip

[GTB/ZR-1]

Originally Posted by Huehuecoyotl

I can totally tell them apart if you had me drive them blindfolded.

Now this could end in tears... lol