I saw this on the NSX forum, and the results just don't seem right.
What do youguys think?
Is the test procedure okay?
Are the results what you would expect?
Anything they're overlooking?

http://www.nsxprime.com/forums...98186

Heres the summary. Details are in the post:
Wheel Weights
The old wheels:
Front BBS-RSII 17x8 : 11.0 kg / 24.3 lbs per wheel
Rear BBS-RSII 18x10: 11.8 kg / 26.0 lbs per wheel

The new wheels:
Front OZ Ultraleggera 17x7: 7.8 kg / 17.2 lbs per wheel
Rear OZ Ultraleggera 18x9: 8.8 kg / 19.4 lbs per wheel

Acceleration Test results
Heavy BBS wheels (one run was not recorded correctly):
5.76 - 5.79 - 5.75 - 5.60 - 5.57 - 5.66 - 5.57 - 5.88 - 5.58 - 5.80
Minimum: 5.57
Maximum: 5.88
Average: 5.70
St.Deviation: 0.11

Light OZ Ultraleggera wheels:
5.66 - 5.69 - 5.57 - 5.69 - 5.57 - 5.71 - 5.69 - 5.64 - 5.72 - 5.61 - 5.74
Minimum: 5.57
Maximum: 5.74
Average: 5.66
St.Deviation: 0.06

 

That's all fine and good, but I think the advantage of lighter wheels plays a bigger part when suspension movement is involved, rather than strictly rotation. I've always heard of light wheels praised as a benefit for unsprung weight. This guy's test could've been done with the same results if he had an iron rod in place of the shocks.

This should really be viewed as an acceleration test comparing overall weight loss of 27.3lbs. He brings up the very important issue of HOW the wheel is designed and where the mass is centralized. There was a similar test with flywheels a few years ago with similarly ambiguous results. Turns out even if one flywheel was heavier than another, if it's mass was concentrated more towards the center it had either similar results or in at least one case, better results than the lighter unit.

 

I think on a heavier car the weight of the wheels would have less effect on the acc. times. I think on a lighter car the differences would be greater, but not by a whole lot. By comparason I went from 17" stock wheels on my MCS to a 15" RPF1 which cut my corner weight by almost 20lbs per corner. It was the most dramatic mod I did to the car even with all the engine work.

I still think turn in speed, braking, and acc. are all affected by lighter wheels, so taking that into account they are still a worthwhile upgrade, when you look at it as a benefit across a wider spectrum than just acc.

 

I've seen a lot of problems in the methodology used in amateur testing. For example:

1. Is the testing done blind, so that the driver doesn't know what wheels/tires are on the car? Otherwise, he may expect to drive faster with the wheels he thinks are faster, and this can affect the results.

2. In most tests, people start with the setup they expect to be slower, then they test the setup they expect to be faster. This ignores the improvement that most drivers see over the course of the day as they run more and more tests. A proper methodology should test one setup, then the other setup, then go back to the first setup again and see if there is any change from the results the first time around.

3. Were the tires used exactly the same (same make/model/size/tread depth)?

4. The other problem is that there are many other variables involved from one test to another - human inputs, weather conditions, pavement conditions, etc. These variables introduce "noise" in the results, so it's tough to tell how much the differences are caused by the different wheels, and how much by other factors.

I'm not saying that lighter wheels aren't better, just that it's very difficult to measure whatever difference there is, and you have to have a testing methodology that removes other variables as causes of differences.

 

Why different widths for the wheels? Different width for the tires too?

 

Sport Compact Car did a story a few years ago measuring the same car on a chassis/roller dyno using different weights of wheels. The results were empirical, measurable and repeatable. The heavier wheels had a significant effect on reducing horsepower and torque. That's why SCC has always published wheel weights in its annual wheel buyer's guides...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thawley &raquo;</TD></TR><TR><TD CLASS="quote">Sport Compact Car did a story a few years ago measuring the same car on a chassis/roller dyno using different weights of wheels. The results were empirical, measurable and repeatable. The heavier wheels had a significant effect on reducing horsepower and torque. That's why SCC has always published wheel weights in its annual wheel buyer's guides...</TD></TR></TABLE>

Yeah, that's what I thought. Thats why I'm thinking something must not be right.

 

forgive my ignorance, but is that unit used for acceleration the seconds from 20kph to 100kph?

the tires are the same, the gear(single) is always the same. while this may not be the best way to test it does show a difference.

i agree that testing the old setup again after the new would be the best way to reinforce the data. however, i understand that it would be a pain in the butt to remount the tires back onto the old rims, then back AGAIN for permanent use.

 

I've seen TRUE back to back dyno testing with light wheel and tire setup vs heavy at the same rolling radius. The difference was astonishing If you can cut 7-10lbs off a corner and keep the same level of grip, DO IT! That car you couldn't keep up with on the straights in the last race might be in your mirrors the next.. . Emphasis on keeping GRIP though.. .

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thawley &raquo;</TD></TR><TR><TD CLASS="quote">The heavier wheels had a significant effect on reducing horsepower and torque.</TD></TR></TABLE>

By how much?

 

If I had remembered, I would have provided the amount. Someone will have to dig thru the back issues for exact figures if they want them...

 

Braking is also better with the lighter wheels. I saw a test a couple years ago on a Denali. I think they went from 18" to 20" to maybe even 22" wheels. Acceleration was worse and the braking distances increased some 20-25' from what I remember.