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story and photos by alan cesar
We always hear that lightweight wheels are better. Reducing unsprung mass theoretically helps a car’s suspension work more effectively. Reducing …
Good timing with this post.
I'm thinking of getting some 15x8s, and was trying to go as light as reasonably priced wheels would allow, in part because I thought it might help a bit when I auto-x.
At 12lbs per corner (!?), only between a 1/4 and 1/2 second, I shall seek out wheels I like the look of and worry a lot less about weight.
I'm not competitive enough at this point to worry about a couple lbs a corner.
Every time this topic comes up, I relate the story of basically revalving the Koni's in my Neon IT car by going from stock wheels with RA1's to Slipstreams with Goodyears. Lost about ten pounds per corner, and the shocks were perfect after that.
Lap times may be one thing, but ride quality on the real world streets are another. Heavy wheels make for a less compliant ride when it comes to the daily drive. However, with less weight, one also should consider strength of design. If you sacrifice rigidity for less weight, you might be risking bent wheels if you happen to catch the wrong piece of road debris or an unseen pothole.
Perhaps the biggest thing I notice is steering effort and quality are much better with a lighter setup. Also, lighter wheels are easier to change, for what that's worth. I store my off season wheel / tire combos in the basement, which means a flight of stairs, one trip per corner. Less weight is better in that case!
All I know is when I went from the original steel wheels to miata alloys on my 90 miata the ride vastly improved. I lost almost 10 lbs per wheel and it really made the car feel better in rider comfort. I guess the lighter wheels have less gyroscopic effect because steering effort into tighter turns also decreased. This car was a Club model with no frills like A/C or power steering, I think it weighted 2100 lbs, so weight changes were very noticeable.
Awesome test!
We’re braking distances tested?
Great article, thanks for quantifying. This topic while much discussed in digital and print almost never includes test data. In fact I don’t recall ever seeing any data contained in the many thousands of words written on this topic until now. So once again GRM for the win!
My main want for light wheels is to get my wagon as far away from it's original 4,000lbs self as possible.
Being ever so slightly faster w/ improved MPG is also a big bonus in my eyes.
It depends on the type of racing. On circle track for instance where contact is a normal thing, I've found the mid weight wheel offered the best performance. Ultra light spun shells deformed to easily with light contact and having an out of round wheel was just as bad as the flat that might also happen. A heavy weight or (stock junk yard steel rim) wheel made it harder to turn slowed the cars reaction time and tore up the front end and bent frame rails if you tested the wall that day. Mid-weight wheel had better on-track resistance to damage but lessened the damage to other components when You got in to a nasty wreck like testing concrete wall strength...
Reading between the lines, I'm thinking my fatass losing 40 pounds is good for about 15 hundreths on my 0-60 times. 
To cheeseburger, or not to cheeseburger for lunch...
Just throwing wider tires on the same wheels adds a lot of weight something some might want to consider. I went from 195s to 215s and gained about 10 lbs per corner (same aspect ratio which meant a taller tire by an inch, so that effects things further). Ride comfort and cornering grip, braking seem improved but gas mileage and power suffered
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.
In reply to xflowgolf :
Adding 40 pounds of sprung weight would require another test :-)
We ran "Factory Fours" on a "split 8" oval at http://www.racesandia.com , and our Mitsubishi MightMax/ Dodge D50 came with the heaviest steel wheels I had encountered short of an E-350 Class-C RV. When we switched to Toyota 4X4 alloy wheels we went from running 7th place to winning. The butt dyno didn't register the increase in acceleration, though it did notice the extra traction in the turns which are a bit bumpy. I was able to carry more speed through the center of the turns, and pick up the throttle about half a car length earlier. Big difference.
Several thoughts:
1 - Wow, the difference between the light and heavy wheels is greater than the weight of each (bare) 15" RPF-1 I mounted on my last Miata.
2 - Is there anyone here wouldn't sell his or her grandmother for half a second per minute?
3 - I recall, from the old autox list on Team.Net a billion years or so ago, that somebody quoted the mathematical formula for calculating accelerative performance improvements from reducing rotating mass. ...No, no, it was more recently, when I was writing the PRI feature on cooling systems and in particular, C&R Racing's new Hustler fans for classes that require engine-driven fans. This Web site has a few JavaScript calculators for those who want to estimate for themselves:
http://hpwizard.com/rotational-inertia.html
Though it basically concludes by saying that, when it comes to handling effects, math is hard. I'll stick with half a second per minute as a rule of thumb.
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.
Thanks for the great test!
In reply to xflowgolf :
I keep hearing words to the effect that the most effective modification is driver improvement. 
...And I, too, have 40 lbs I could live without.
I’m wondering how the “butt Dyno” feels it? And I’m not talking “sear of the pants acceleration”, I’m talking “wow, my steering wheel feels incredibly light and the whole chassis seems to respond to my every flick!”
sfisher71 said:2 - Is there anyone here wouldn't sell his or her grandmother for half a second per minute?
I think the interesting thing in this test is that that 1/2 second came with wheels that are 12 POUNDS (!) heavier per corner. When most of us look at wheels that size, almost all the options are in the 10-12lb range. If the difference is linear, a 2lb weight difference is probably averaging in the 0.05second range - which would probably fall in the noise on a test like this.
In reply to Trackmouse :
Steering effort gets noticeably easier the lighter you go, in my experience. Kinda figure it's like trying to hold a hammer out at arms' length. The lighter the hammer, the easier it is to move it around where you want it. =)
Lighter wheels/tires give the biggest benefit on the driven axle. The reduction in rotating mass produces an improvement EVERY time you accelerate.
200mph said:Lighter wheels/tires give the biggest benefit on the driven axle. The reduction in rotating mass produces an improvement EVERY time you accelerate.
This affects the wheels / tires on all axles, driven or not. They all have to spin up the same as you accelerate regardless of whether they're directly powered or not.
rslifkin said:200mph said:Lighter wheels/tires give the biggest benefit on the driven axle. The reduction in rotating mass produces an improvement EVERY time you accelerate.
This affects the wheels / tires on all axles, driven or not. They all have to spin up the same as you accelerate regardless of whether they're directly powered or not.
Not if you lift them off the ground :P
sfisher71 said:2 - Is there anyone here wouldn't sell his or her grandmother for half a second per minute?
Sell? No. Rent?... Possibly.
What about braking data. 60-0 distance and maybe 3 or 4 hard stops then measure for heat soak.
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