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trakktapedude
trakktapedude New Reader
10/29/18 12:09 p.m.

Having done a lot of research on this topic for both cars and motorcycles, I found several evaluations on both applications with light wheels. One interesting item that surfaced a few times was the comment that pulling one pound out of unsprung rotating mass has an overall effect similar to taking FOUR pounds of sprung mass. 

I have been tracking my 2006 Elise for over ten years and recently went from a set of Rota Slipstreams (a great wheel for the money, in spite of comments by some) to a set of 15/16 Volk CE28's. The effect on acceleration and ride quality is noticeable. The effect on turn-in or cornering is harder to feel, but must certainly be there. With two piece rotors and the Volks, I think I have pulled about 36 pounds out of unsprung weight. Also, by going 15/16, they are a little lighter than a 16/17 setup. I like 15/16 for several other reasons, as well. There is a wider variety of DOT legal competition tires available like the RA1 and it allows me to run the car at a bit lower ride height without having bumpsteer issues from the stock steering rack. 

Now, if I could just get a set of wheels for the Lotus like I just bought for my KTM 950 SuperMoto! 

On a motorcycle, the difference is astonishing as the gyroscopic effect from the wheels is greatly reduced at turn-in.   All fun stuff!

ebonyandivory
ebonyandivory PowerDork
10/29/18 12:56 p.m.
OldGray320i said:
sfisher71 said:

2 - Is there anyone here wouldn't sell his or her grandmother for half a second per minute? 

Me.  Half second won't help.  I suck.

Mine are all dead sooooooo....

ebonyandivory
ebonyandivory PowerDork
10/29/18 12:58 p.m.

From flipping around at Ecomodder, it seems wheel weight makes a signal difference in mpg.

I suppose that could factor into racing but maybe not until you get into the more expensive type racing where the rules are tighter?

BA5
BA5 Reader
12/4/20 11:31 a.m.
OldGray320i said:

I was wondering how much difference a pound or two makes in performance and feel. 

The 11lbs per corner is  LOT in my mind.  But going from 14lb wheels to 11 or 12 probably isn't going to be a huge difference, at least based on the test.  Looks like it averages a little over a tenth of a second per couple pounds in change.

I suspect the car would ride better with lighter wheels, on the inane theory that wheel inertia plays a part - kind of like the difference between a 3lb sledge and a 5lb sledge - when the 5lb hits, it hits with more force given the same rate of motion.  Of course, the opposite might be true in that it's harder to start moving 5lbs than 3.  My ignorance shining through.

In any case, since I'm not starting with 20lb wheels, and given that I'm just not that competetive in auto-x at this point (and probably won't ever be, really), might as well focus more on what I like than how much it weighs.  Current 15x7 wheels are 14lbs, and between the 15x8s I'd like to get, 6UL's, Hypergrams, S1 Storms, Dial-ins, etc, it's 2-3lbs a wheel.  Probably not setting my world alight.

The effect is linear, as the 'm' term in pretty much any acceleration/Force equation is linear.

So for their 'average' driver in this particular test the difference is ~ 0.03 sec/lb.

Going from a set of Giovanna wheels from 1998 to a set of Kosei wheels would make a pretty good difference.

Going from the Kosei to Volks is definitely going to net diminishing returns for your money.

Reducing the diameter is a whole different story, though....

Jesse Ransom (FFS)
Jesse Ransom (FFS) UltimaDork
12/4/20 11:39 a.m.

How much does speed influence the impact of weight?

The faster you're traveling, the more the wheels are accelerated upward over every bump, and the faster they have to accelerate to contact every dip.

I imagine from a grip and suspension-performance standpoint, wheel weight matters more in road racing than in autocross.

I might also wonder whether in testing this you actually need to twiddle damping to test for improvement from a meaningful change in wheel weight?

David S. Wallens
David S. Wallens Editorial Director
12/4/20 2:08 p.m.

I'd like to redo this test on a bumpy surface. I think that will reveal a few things, too. 

spitfire4gp
spitfire4gp New Reader
12/4/20 11:10 p.m.

I recall when I began road racing someone mentioned that in a competition engine we get rid of that heavy steel flywheel for a light aluminum one so the engine will spin up faster.
And the light bulb went on that I basically had four flywheels on the corners of my car. That's when I dropped the coin on new wheels. As for the old heavier wheels, now I had something to mount some rain tires on! laugh

Error404
Error404 Reader
12/4/20 11:49 p.m.

So you're saying that the 17" RPF-1s on my soon-to-be running Frankenstang are a double whammy improvement over the 18" SN-95 Bullitt style wheels? There is surely no way that that extra confidence will end up with my rear end on top of another tire wall....

flatlander937
flatlander937 HalfDork
12/5/20 8:24 a.m.

Very cool test.

I have two Mazda2s - one has a reverse stagger set of 15x9 - 15x7.5 Konig Dekagrams with 225/195 Hankook RS4s, the other has 15x7 Advanti Storm S1s and Conti ECS. The steering feel is world's different between the two cars. Also of note, the wide front tires seem to have caused a ~4mpg drop or so vs a normal 15x7.5 all around with 195s. 

With only 97whp, I suspect I'll be buying some 15x8 wheels and 205 whatever slicks for track use in the future until more power is added.

 

matthewmcl (Forum Supporter)
matthewmcl (Forum Supporter) HalfDork
12/5/20 10:39 a.m.
OldGray320i said:

I suspect the car would ride better with lighter wheels, on the inane theory that wheel inertia plays a part - kind of like the difference between a 3lb sledge and a 5lb sledge - when the 5lb hits, it hits with more force given the same rate of motion.

This analogy works if you think about swinging the hammer sideways. You move the hammer, but the hammer also moves you. You can swing the 3lb with less reaction in your shoulders.

You hit a bump and the bump pushes the wheel up. The suspension wants to push the wheel back down on the other side of the bump (gravity is too slow ffor good hadling and good ride). The distance the wheel has to go back down is the same whether the wheel is light or heavy, but how hard the car has to push the wheel back down changes a lot. Imagine standing on a skateboard and throwing the 3lb sledge to land in a bucket 10 feet away. Now do the same with the 5 lb sledge. It is pretty easy to see that you will roll back further when you throw the 5 lb. The extra amount you moved with the heavier sledge is the difference in ride quality. Wheel goes down over the bump, but the car is still going up with the effort of pushing the wheel down. Shock dampers complicate the simple analogy, but that is still the underlying principle.

Carbon (Forum Supporter)
Carbon (Forum Supporter) UltraDork
12/5/20 11:09 a.m.

Rigidity is super important too. 

jimbbski
jimbbski SuperDork
12/5/20 7:14 p.m.

I have a VW race car and I had two sets of "race tires" for it with two different kinds of wheels with different brands of DOT race tires. One set were RFP-1's at 9.2 lbs each. The other was something I can't remember but they were heavy! The difference in "feel" between the two sets of tire/wheel combo was easily noticeable on track. The car accelerated faster, stopped easier, and responded quicker. BTY the weight difference between the sets was on the order of 50-60 lbs total.

On a more poweful car a 50 lbs difference may not be that noticeable but when you have a light car with barely 100 HP, every little bit helps.

David S. Wallens
David S. Wallens Editorial Director
12/6/20 9:45 p.m.

It's hard to put a number on "feel," but you're right that lighter wheels often do feel better. Will you notice a few tenths saved on the autocross? But you do notice the feel. (Spoiler alert: We might be discussing a follow-up wheel test.)

codrus (Forum Supporter)
codrus (Forum Supporter) UberDork
12/6/20 9:56 p.m.
David S. Wallens said:

It's hard to put a number on "feel," but you're right that lighter wheels often do feel better. Will you notice a few tenths saved on the autocross? But you do notice the feel. (Spoiler alert: We might be discussing a follow-up wheel test.)

Probably depends on how bumpy your autox lot is.  

David S. Wallens
David S. Wallens Editorial Director
12/6/20 9:57 p.m.

In reply to codrus (Forum Supporter) :

Have you been reading our e-mails? smiley

Cedricn
Cedricn New Reader
12/7/20 10:19 a.m.
Carbon (Forum Supporter) said:

Rigidity is super important too. 

“That which we manifest is before us.”

I heard from a reputable racing company that they measured significant camber loss from super light wheels. So the lightest wheels weren't actually the fastest.

Wheel inertia will be important when acceleration rate is large, for example in autoX. For high speed driving with small accelerations the inertia will have less effect. I talked to a very reputable race engineer about this, he wasn't that bothered with large unsprung mass, as long as he could revalve the dampers to match it. It would be interesting if GM could talk themself into a shake rigg to do this test just to see how the system response changes with wheel weights, and if some adjustments could mask out some of the drawbacks. 

RX8driver
RX8driver Reader
12/8/20 8:02 a.m.

I recall reading about how the Corvette ALMS team, during the C6 era, switched wheel suppliers mainly for stiffness reasons. There are a few tests out there where wheels were track tested and the lighter ones weren't automatically fastest. There's one Japanese mag that took an Enkei GTC01 or something like that, lightened one set and ran one set stock, and the stock set was faster, as it was stiffer.

codrus (Forum Supporter)
codrus (Forum Supporter) UberDork
12/8/20 1:28 p.m.
David S. Wallens said:

In reply to codrus (Forum Supporter) :

Have you been reading our e-mails? smiley

Heh.  Back before the 49ers moved to their new stadium, SFR SCCA used to use the Candlestick parking lot for autox.  That was truly terrible pavement, we used to refer it to "autocross with elevation changes" :)

 

BA5
BA5 Reader
12/8/20 1:59 p.m.
RX8driver said:

I recall reading about how the Corvette ALMS team, during the C6 era, switched wheel suppliers mainly for stiffness reasons. There are a few tests out there where wheels were track tested and the lighter ones weren't automatically fastest. There's one Japanese mag that took an Enkei GTC01 or something like that, lightened one set and ran one set stock, and the stock set was faster, as it was stiffer.

Here's a link to where someone posted that Enkei test in another forum.  Interesting read.  Looks like they took a ton of material out of the hub area, which would definitley see a lot of stress and maximize deflection.

The anti-slip paint bit was very interesting.  I've always assumed that tires stay pretty set unless you're cranking out stupendous levels of power.  I may have to put some indicating paint on my wheels to see what comes of it!

 

twowheeled
twowheeled New Reader
12/8/20 2:16 p.m.

On the street my much heavier tire and rim combo on the miata ruined ride quality over bumpy pavement. I suspect I need a lot more damping that the coilovers im using can't provide. And they are probably matched to the cars weight.

SVreX (Forum Supporter)
SVreX (Forum Supporter) MegaDork
12/8/20 2:26 p.m.

For all the vast interest in wheel weight, no one ever seems to look at tire weight. 
 

It's hard to find sometimes, but it is a much bigger variation than most people realize. 
 

And THAT'S rotational weight that is much further from the axle center. 

Granet
Granet New Reader
12/12/20 9:15 p.m.
SVreX (Forum Supporter) said:

For all the vast interest in wheel weight, no one ever seems to look at tire weight. 
 

It's hard to find sometimes, but it is a much bigger variation than most people realize. 
 

And THAT'S rotational weight that is much further from the axle center. 

True, Mazda worked with 'I forget brand' to supply lighter tires for the Miata. 

Great article. 

Snrub
Snrub Dork
12/13/20 9:26 a.m.
SVreX (Forum Supporter) said:

It's hard to find sometimes, but it is a much bigger variation than most people realize. 

Tire rack has that info for every tire they sell. I picked 245/40/18:

Competition class tires: Hosiers are 21-22lbs. Everything else 25-26lbs.

200tw: 25-28lbs.

I think the problem with picking tires based on weight is that a heavier tire may be faster than lighter one. There is info on which tire is faster. There is no performance, or even durability data on wheels, so the only thing people focus on is weight. In the Enkei test it's a .4sec difference on a road course with a non-viable wheel vs. a viable one. Is it maybe .1 between a decent wheel and a worst one?

ProDarwin
ProDarwin MegaDork
12/13/20 10:11 a.m.
BA5 said:

The anti-slip paint bit was very interesting.  I've always assumed that tires stay pretty set unless you're cranking out stupendous levels of power.  I may have to put some indicating paint on my wheels to see what comes of it!

 

Remember, your tires can only put down so much power, so it doesn't need to be that stupendous.  Also, almost all track cars can effectively put down stupendous amounts of power with their brakes.

 

RE: light tires, just like the wheel argument (maybe even moreso), stiffness is a factor.  200TW tires are typically heavier than other tires, but they also have stiffer sidewalls which helps performance.

Tom1200
Tom1200 Dork
12/13/20 2:15 p.m.

I've commented on various posts before about running the smallest wheel & tire you can get away with BUT I'm racing cars that only have 100whp. 

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