Heavy versus Light wheels - Acceleration Tests and their results

Have you ever wondered how much difference it makes if you would exchange your wheels for lighter ones?

This weekend I had the opportunity to test these differences. I had a set of 17/18 BBS-RSII wheels on my NSX which came with the car when I bought it. Although the wheels look nice, the model (IMHO) is a bit dated and they are also quite heavy. I had set my mind on a set of the new OZ Racing Ultraleggera wheels, also in the 17/18" size. I used the opportunity to measure the difference in makes in acceleration between heavy and lighter wheels.

First: The weight.
I measured the weight of all the wheels, all measured on the same scale.

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

So, just by changing the wheels on the car, I am saving 12.4 kg in the total weight of the car or 27.3 lbs of unsprung weight. Which is always welcome of course.

How the tests were done:
I tried to minimize all the variables while testing.
To measure the acceleration times, I am using a AP22 accelerometer from Race Technology (http://www.race-technology.com/ap22_2_82.html). This device measure acceleration times using a G-meter with an accuracy of 0.01G.
All acceleration runs were done in second gear and the acceleration measured was from 20 kph to 100 kph. This speed interval was chooses because it can be done in one gear, avoiding the human error that is introduced by shifting into a next gear.
To do the test, I used the following procedure:

- Tape the AP22 to my dashboard so that it is mounted correctly.
- Fill up the gas tank completely
- Drive to the straight stretch of road chosen for the test. (Gave the engine time to warm up completely).
- Start the AP-22, set it up to measure 20kph to 100kph acceleration, and let it calibrate.
- Start driving in 1st gear. As soon as the car is rolling, shift to second and let the car roll forward in 2nd gear at idle rpm without touching the throttle. Idle is around 700 rpm on my dash.
- Wait until the car is rolling forward smoothly and with a constant speed. This took about 5-10 seconds.
- Then, press the accelerator down to the floor and let the car accelerate until the AP-22 displays it has finished the acceleration run.
- Bring the car to a standstill, store the data on the AP22, turn the car around, calibrate the AP22 again and do the next run.
- With every set of wheels, this test was repeated about 10 times.

After the test with my original BBS wheels were completed, I had a tire shop change my tires from one set of wheels to the new OZ Ultraleggera wheels. So, the same tires were used to avoid any issues with grip.
After that, the gas tank was filled up completely again and the NSX was taken to exactly the same piece of road and the test were repeated using the exact same procedure.

The results, well, read on for yourself. All times are in seconds.

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

Road conditions during both tests were the same. The only difference was that the outside temperature was about 2-3 degrees Celsius lower during the second set of tests.

To be really honest, I found the results to be a little disappointing. I expected the differences between the two set of wheels to be much more noticable. Measured over all four wheels, the OZ wheels are 28% lighter than the BBS wheels, and 25% when compared with just the rear wheels.
Judging from the results, the difference in these acceleration runs was ONLY about 0.05 seconds.
The fastest times were exactly the same for both wheel types. However, the slowest times were noticably longer with the BBS wheels, 5.88 versus 5.74 seconds. Also, the standard deviation with the BBS-tests is much larger than the tests with the OZ wheels.
I don't believe this had to do with me getting better at it, because, as it was done, the test was relatively simple. Just roll the car at idle RPM and then press the accelerator down.
In all, what I learned from these tests is that the differences between heavy wheels and light wheels might be a lot smaller then one would expect. Perhaps the weight differences is negated partly because it seems that the BBS wheels have a lot of their weight centered around the hub due to the complicated spoke design. Of course, the effect of extra weight increases the further it is to the outside of the wheel.

Please post your comments on these test because I would like to know how other people feel about this.

Here are some pictures to illustrate the tests:
This is my car with the old BBS-RSII wheels.


This is my car with the new OZ Ultraleggera wheels:


The AP22 acceleration measuring device attached to the dashboard.


The stretch of road used for the tests.


Old BBS-RSII wheels in close-up:



New OZ Ultraleggera wheels in close-up:

On the rear, I have the 303x23mm 1997+ brakes, just look how small they look now.


Now, I still have the new ProSpeed Stage 2 ECU on my desk. So, maybe some new tests are in the making...

Wow, thankx for posting that Maarten.

Always wondered how much wheelweight REALY made for a difference. There is lots of talk about it, peeps spending fortunes on light wheels, but without any real life numbers for backup.

After seen so much talk about light weight wheels, i'm very suprised with your outcome. I expected much more difference, just as you did.

Anyway, again thanks for posting and doing the tests. Now i dont feel so bad about the weight of my rims.

Very nice reading, (Though a bit dissappointing results)

Question though; is there any difference in "feel" when driving the car with the lighter wheels?

The fact that he once had both the same times (5.57) probably means the test should have been done up to a faster speed more than 62mph.

And 0.05 is quite a difference, Multiply that times 10 for an autocross and you get half a second, which can be the difference between 1st and fourth place.

Thank you for your test MvM, I wonder how the test would have been with the typical 30lb 19" cast/three piece wheel.

I wanted to test the 20-120 kph runs, but the engine whould hit the revlimiter before that. And I sincerely wanted NOT to shift during the testing.
Perhaps it would have been better to do the test in 3rd gear because it would have given me the opportunity to test something like 30-150.
However, I would have needed a different piece of road for that.

As far as the differences are concerned, you will notice that even though the fastest times are the same (5.57 seconds), there is a difference of 0.14 seconds between the slowest runs. Maybe that with warmer weather the differences would have been smaller.
Now, the big difference is the standard deviation suggests that I should have done more runs for each test.
What I might still do, for example, is compare the times for the 40-100 kph interval.

As for the feel with the lighter wheels, so far it feels like the car jitters a bit more on rough and unever roads. Turn in is also slightly more crisp but since the weather is rather cold now (around freezing) and with my rear tires needing replacement soon, I am not yet ready to try the limits.

MvM said:

Now, the big difference is the standard deviation suggests that I should have done more runs for each test.
What I might still do, for example, is compare the times for the 40-100 kph interval.

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WOW! Thanks very much for your testing. Now you are Professor 'wheel-weight' on this forum and on the internet (to me at least :wink.

Your testing has been very scientific. Avoiding shifting was very important to keep the standard deviation low. Changing the tires onto the other set of wheels is perfect!

A little statistical analysis: Set 1 (BBS) has 10, set 2 (OZ) has 11 values. I've deleted the last value (5.74 or the highest one) of set 2, in favor of the lighter wheels to do a statistical test. 'In favor' means here that I see that it's hard find a difference anyway. Have this in mind. You normally delete a run (something like 6.20) IF YOU KNOW that something went OBVIOUSLY wrong (BUT ONLY THEN!) Attention: Deleting runs opens the door to very cheap tricks if you want something to show. That's why I guess that most dynos of a product are more or less biased.

The variance in set 1 of 0.11 is higher than set 2 (0.06). Is there any explanation for this? Instead of running more runs in both tests I would repeat the BBS-test. 10 runs per test are fine.

One note: The tires could perform a little bit different on 10/18 than 9/18 but not sure by how much. I guess it's minimal.

This is a simple t-test analysis: one-side, heteroscedasticy

BBS (heavy) OZ (light)
5.76 5.66
5.79 5.69
5.75 5.57
5.60 5.69
5.57 5.57
5.66 5.71
5.57 5.69
5.88 5.64
5.58 5.72
5.80 5.61
Mean 5.70 5.66
StdDev 0.11 0.06
t-value 0.16

t-value is .16 which is statistically not significant to 0.95, means that the difference of 0.04 is more a result of CHANCE than a REAL effect. Deleting another value of set 2 gets the thing even worse. There is NO EFFECT of lighter wheels on acceleration.

That's a little disappointing. All people who stay with the heavy ones can now be pleased and the ones like me who went for lighter ones (still waiting for the bloody wheels!) have to agree that there is NO effect on acceleration of lighter wheels. But what about other tests like ride-comfort or fuel savings, traction over bumpy road or braking distances between the two? :wink:

This also opens the question if lighter tires (same size) AND lighter wheels do a difference. The weight of the tire is most far from the wheel.

I still think it's the tire diameter (maybe also roll resistance) that let's you feel that the OEM 15/16 is much faster than 18/19.

Again, you're my Prof. Phd. wheel weight now! :wink:

Thanks for the compliment, but I don't think I did anything special. Just wanted to know it the difference could be measured, doing it as objectively as I could.
It would be nice if I would be able to repeat the same tests with the same car using for example the original 16/17 wheels instead.

Truly, I expected the difference to be greater than this. After all, the total weight difference is equal to about 3 HP on my car. And also remember that people often state that every lbs or kg of unsprung weight is equal to at least twice that amount of sprung weight.
The stretch of road where I did the tests was not 100% perfect even, but it was horizontal as far as I could tell (after all, almost everything is in the Netherlands :smile: ). But at no point did I experience any kind of wheelspin when starting the test. And doing the tests in both directions should cancel out any differences.
Maybe the positive effect from lighter wheels as being driven by the engine is cancelled out by the fact that you now have lighter wheels trying to push a much heavier object. As in, it's easier for a heavy guy to push a car that for a light guy. So for the engine it's easier to spin the wheels but for the wheels it's harder to move the car.
Or maybe I should have set the starting speed somewhat higher. At 20 kph, the engine is barely running 1200 rpm, which is by all accounts very low and is not a RPM-range where you normally operate your car at all. I will take a new look at those numbers.

As already stated, the car seems to transmit road conditions somewhat more than before, but since the wheels have only been on the car for two days, I am not making any final judgements yet.

Wow, excellent writeup! Thanks for doing that as I know many people have wondered the same thing. Your very clear, thorough and detailed write up certainly answers taht mystery.

If you don't already, you should write for a car magazine in your spare time!

I guess that mesh shift boot won't matter much then...

MvM said:

Thanks for the compliment, but I don't think I did anything special. Just wanted to know it the difference could be measured, doing it as objectively as I could.

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Well, the great thing is THAT you actually did it and as I recall you asking here some time ago how you would/should to it. And that's the GREAT things about it. :wink:

Truly, I expected the difference to be greater than this.
...

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Please don't get me wrong BUT are you still looking to proof the argument that lighter wheels should be faster but couldn't proof it? :wink: That's a normal reaction believe me.

Your test minimized a lot of sources for variance and variance is very bad during testing.

For me: As long as nobody can proof that ligher wheels are faster with a similar testing procedure I believe your results.

I think one thing you may want to keep in mind is that you're doing 5 second tests. A better test would be using a higher gear and trying to get it closer to 10 seconds or more.

There are too many other factors involved to pick up any subtle acceleration differences over 5 seconds. (Unless you expected lighter wheels to be a HUGE difference, which I don't think they are.)

You perhaps should have tried a couple 1/4 mile runs at a local track, anyone will tell you that the lighter wheels will make a difference.

maybe to test the effect of the wheel weights, it would be best to do a 2nd gear pull to redline and then breaking to zero, and then measuring the time. the car will most likely stop better with the lighter wheels, but this would also require a different kind of road/parkinglot/track. i wonder what experimental data would reveal in accelerating the car in a lateral direction with lighter wheels vs. heavier wheels.

nice real-world experiment.

Try the same test with the light wheels and a passenger in the car, I bet you, you will get times similar to the heavy wheels without a passenger.

And yeah, I think weight + the diameter of the taller rear tires is what makes the biggest difference in stock 15/16 16/17 vs aftermarket wheels.

First of all, let me say that this was a good attempt at real science. This is very rare on internet forums. And, please, let's stay on the measurable gains here and not the "how did it feel" which is truly subjective.

When people say that reducing unsprung weight is twice as valuable as reducing sprung weight, I believe they say this relative to road-racing. Having a lighter unsprung weight allows the suspension to keep the tire in contact with the road better. It also reduces rolling inertia and total weight so its a two-way bonus. However, this test was only checking the acceleration so it only "sees" one benefit.

Now, as far as the test. As I've said in previous threads on wheel weights, but didn't get much feedback - the benefit of reduced wheel weight, on acceleration, will be seen when acceleration is greatest. A few % change on a large value is easier to discern than that on a small value.

For instance, acceleration in 5th gear is really low. Less wheel weight will make almost no difference.

Similarly, acceleration when the engine is bogging down, such as at the beginning of this test, is also a point of little acceleration.

A better test is to use a time when the acceleration is highest. That means, in low(er) gears and at higher torque values.

So, in that light, what can be done next time in 1st gear? Can we get a 4000rpm through 7000 rpm pull? I believe the torque (and transmission gear ratio multiplier) is about maxed in this range.

Same for 2nd gear. Eliminate any test data below 4000 rpm and then study only the range between 4 and, say, 7k.

Does your data have individual values for acceleration between 60 and 100 kph only? If so, you will more likely find a stronger correlation.

If you could do 1st gear pulls, say from 20mph to redline, I bet the results would be even greater.

Note that for whatever value the lighter wheels have on acceleration, they will always be a relative factor of the vehicle's acceleration. The values will taper from highest in 1st to almost zero in 5th as acceleration tapers from large in 1st to low in 5th.

Hope this helps.

l8apex32 said:

So, in that light, what can be done next time in 1st gear? Can we get a 4000rpm through 7000 rpm pull? I believe the torque (and transmission gear ratio multiplier) is about maxed in this range.

Same for 2nd gear. Eliminate any test data below 4000 rpm and then study only the range between 4 and, say, 7k.

Click to expand...

I agree on the 'the higher the acceleration the higher the effect' BUT I have to disagree with deleting the data below 4k. Assuming that there is near to none effect below 4k rpm the measured times up to 4k rpm would be the same for both tests and the difference between them in the 4-7k range will be reflected in t2 and therefore in the overall time:

Total time t = t1(1.2-4k rpm) + t2(4-7k rpm)

Assuming t1 is the same for both tests (or better said constant) the difference in total time won't be touched. If the lighter wheels have a lower t1 you would see a difference in t anyway but from the data I don't see a reasonable difference. So it doesn't play a role if you measure >4k or >1.2k from this point of view. Actually I would expect even less significant results just because measuring between 4-7k rpm is a source for more errors. 1st gear pulls is even a bigger source for errors due to traction problems.

MvM choose a very good test.

What MvM was looking for was if lighter wheels result in better acceleration. Honestly we have to say NO. But why do people feels a massive acceleration gain if you switch from 265/35/18 to 245/40/17 or 16'' stock wheels? It's not the weight of the wheels primarly. It's the diameter of the wheel AND the effective radius of the tire on the ground. The smaller the rim the higher the sidewall of the tire -> the more flexible the wheel -> the smaller the effective radius. The effective radius gets even smaller the higher the acceleration because the back of a rear end driven car puts even more force on the tires.
If the engine delivers constant torque means -> the smaller the effective radius -> the higher the force -> the higher the acceleration.
That's the advantage of rear driven cars. In front driven cars it works the other way round.

Proof this yourself: Change the rear tire pressure (not below factory specs) and do some acceleration runs. The lower the tire pressure the higher the acceleration.

The AP22 measures the acceleration in 10 Kph intervals (or 10 Mph if you set it up for miles).
I have taken a look at the raw data from the tests for the 40-100 Kph and 60-100 Kph.
This means starting the measurements at around 2300 rpm for 40 Kph and 3500 rpm for 60 Kph. Unfortunately, when downloading the data from the AP22 sometimes the data gets out a little garbled for reasons which are unknown to me. This results in some of the interval-data is missing in the final output. Which means that two sets of the 40-100 data is missing for the OZ wheels (none for the BBS) and for the 60-100 data two sets are missing for the BBS wheels and three for the OZ wheels.
However, when I take a look at the data for these runs, the results are even closer for both set of wheels.

Runs for 40-100 Kph with BBS Wheels (10 runs):
Average: 4.135
Minimum: 4.03
Maximum: 4.24
St.Deviation: 0.08

Runs for 40-100 Kph with OZ Wheels (9 runs):
Average: 4.123
Minimum: 4.05
Maximum: 4.20
St.Deviation: 0.06

Runs for 60-100 Kph with BBS Wheels (8 runs):
Average: 2.718
Minimum: 2.64
Maximum: 2.81
St.Deviation: 0.06

Runs for 60-100 Kph with OZ Wheels (8 runs):
Average: 2.714
Minimum: 2.66
Maximum: 2.76
St.Deviation: 0.04

So the differences between the BBS wheels and the OZ wheels gets even smaller. Of course, the time intervals get much shorter so the differences are smaller as well, but this data just supports the original conclusion that just the changing of these set of wheels does not change acceleration times in a significant way.
Now, if someone would lend me a set of original 15/16 or 16/16 OEM wheels, we might redo these tests, using the same car. And if someone has a better and longer piece of road for me, we could do these tests for a larger speed-interval, like 40-150 Kph in 3rd gear.

Now, anybody interested in a same kind of test with different chips (like OEM chip versus Dali versus ProSpeed chip) :smile: :smile:

MvM said:

As already stated, the car seems to transmit road conditions somewhat more than before, but since the wheels have only been on the car for two days, I am not making any final judgements yet.

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A little bit off-topic I know but the occasion is too good to miss:

I was wondering that you feel more road irregularities and how this could be explained as I first thought it was the opposite way: Lighter wheels -> more comfort.

The wheel/suspension/car combo reminds me of my very old days where I've used to listen to records with my analog turn-table. The pick-up sounds much better/detailled (!) at higher frequency the lower the mass of the stylus is all else held constant (stylus shape, 'suspension' that holds the stylus, tone arm etc.). It prevented the stylus from skipping over musical information on the record, giving it better contact to it.

Audiophile -> Automotive adaption: Your car is the pick-up with four wheels (stylus) and their related suspension driving over the street (record).

The lighter the wheel (mass) the more/detailled info you get from the road. A lighter wheel will follow a bump earlier but jump (no contact to road) less (less travel) over the same road irregularities and will be faster back on the ground -> more control/grip. These are two opposite effects as far as ride comfort is concerned. But the mean force of the wheel on the road is more equally -> more control/grip. Conclusion: With lighter wheels you could (!) use softer springs or less rebound/compression rates on the shock.

-> With lighter wheels you should feel more irregularities but with less harshness. q.e.d.

goldNSX said:

I agree on the 'the higher the acceleration the higher the effect' BUT I have to disagree with deleting the data below 4k. Assuming that there is near to none effect below 4k rpm the measured times up to 4k rpm would be the same for both tests and the difference between them in the 4-7k range will be reflected in t2 and therefore in the overall time:

Total time t = t1(1.2-4k rpm) + t2(4-7k rpm)

Assuming t1 is the same for both tests (or better said constant) the difference in total time won't be touched.
<snip>

Click to expand...

I agree with this, however, my point is that we are looking for a small change in acceleration, and we look over time periods where we expect there not to be any change, then our chance of seeing the change is reduced.

For example, if we have a 1% greater improvement in acceleration over a 10 second test, we see .1 change in time. Baseline is 10 seconds, trial time is 9.9 seconds.

9.9 / 10 = 99%

However, if all of that change was in the last 5 seconds of the test, then we can use a different method that focuses only on the last five seconds. Baseline is 5 seconds, trial time is 4.9 seconds.

4.9 / 5 = 98%. Twice the resolution.

Also, I believe that testing in 1st gear will give you a significant gain in resolution to any difference (78% more effect switching to 1st gear).

(5 - (.1 + .78)) / 5 = 96.44%

A stock NSX can not spin the tires in 1st gear, assuming OEM tires on standard dry pavement. I think it would be worthwhile to try 1st gear tests.

l8apex32 said:

A stock NSX can not spin the tires in 1st gear, assuming OEM tires on standard dry pavement. I think it would be worthwhile to try 1st gear tests.

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I understand your point as well as those from GoldNSX.

Your last remark made me remind that I DID NOT switch of the TCS while doing any of these tests.
For the record, let it be noted that at no point during the tests did the TCS light come on. Nor did the engine at any moment feel like it was bogging down.
But it makes me wonder if the TCS light might not come on if TCS is kicking in only in a very slight way. This is one variable did I did not think of as I did not feel like it would make any difference. Like you state, with 265/35ZR18 tires in the rear, starting at 800 rpm, the engine does not create enough torque to make the tires spin.

Problem for me is that I am not going to redo the whole exercise again (switching back tires to the BBS wheels and then back to OZ because I like the new wheels very much).

l8apex32 said:

I agree with this, however, my point is that we are looking for a small change in acceleration, and we look over time periods where we expect there not to be any change, then our chance of seeing the change is reduced.

For example, if we have a 1% greater improvement in acceleration over a 10 second test, we see .1 change in time. Baseline is 10 seconds, trial time is 9.9 seconds.

9.9 / 10 = 99%

However, if all of that change was in the last 5 seconds of the test, then we can use a different method that focuses only on the last five seconds. Baseline is 5 seconds, trial time is 4.9 seconds.

4.9 / 5 = 98%. Twice the resolution.

Also, I believe that testing in 1st gear will give you a significant gain in resolution to any difference (78% more effect switching to 1st gear).

(5 - (.1 + .78)) / 5 = 96.44%

A stock NSX can not spin the tires in 1st gear, assuming OEM tires on standard dry pavement. I think it would be worthwhile to try 1st gear tests.

Click to expand...

Now I see your point of argumentation. But I still have to contradict. :wink:

Your scenario would hold in the case where there was NO effect below 4k rpm AT ALL. In this case (and ONLY in this) it would be better to just measure > 4k rpm just to avoid measuring errors and reducing the disturbing error variance by other variables. But in your 9.9 / 10; 4.9 / 5 scenario the t-test (ANOVA) would figure out the same statistically not significant value as the variances and the difference between the means are the same. That's the great thing about it.

Contradiction:

The additional data (40-100 and 60-100) showed even FAR less difference (!) and therefore contradict to your hypothesis. Why this? There are two reasons for this observation: 1. there is an effect < 4k rpm OR 2. the error variance is high < 4k rpm

The second case automatically leads us to the question HOW the test has been designed and HOW they have been performed. Is there any source for unexpected and unwanted errors? The answer is NO. Why?
The testing procedure fulfilled nearly all criterias to avoid disturbing errors as MvM did the runs on the same tires (!), the same fuel level, the same wheater, the same driver, the same car, the same road, no clutch used etc. (and most importantly MvM is not a sales representative of OZ ) The test driver can't improve or fatique by only pressing the throttle 20 times.

So the second case is not very reasonable -> the overall error variance is very, very small which leads to the conclusion that there IS an effect below 4k rpm which you should measure. The data shows this. q.e.d.

Conclusion: If there is no effect expected, don't measure it to reduce error variance. If you expect an effect (even a small one) measure it!

Sorry for the long post!

A few posts up I made the suggestion that one of the reasons the lighter wheels don't seem to give any advantages during acceleration might be because the wheels still have to move a heavy object (eg. the rest of the car). And that it is more difficult for a light object to move a heavy one than it is for a heavy object.

I tried to put it into some number and the results turned out to be more dramatic than I thought possible.
Also, I have taken 9 kg as weight for a front tire and 10kg for the rear tires. This is not 100% correct but these numbers are fairly close to actual tire weights.
Here are the numbers. I have round the numbers for easy reference. Also put the weight in Kg as it doesn't make any differnce for the percentages and/or ratios.

All number are given with a full tank of fuel.
NSX with the BBS RSII wheels: 1360 kg.
BBS wheels total weight: 45.6 kg
Total weight wheels+tires: 83.6
Weight of car MINUS wheels+tires: 1276.4 kg
Weight of wheels+tires of total weight: 6.15%
Ratio of car minus wheels+tires/wheels+tires: 15.27

NSX with the OZ Ultraleggera wheels: 1347.6 kg.
BBS wheels total weight: 33.2 kg
Total weight wheels+tires: 71.2
Weight of car MINUS wheels+tires: 1276.4 kg
Weight of wheels+tires of total weight: 5.28%
Ratio of car minus wheels+tires/wheels+tires: 17.93

In other words, the total weight of the wheels plus tires drops from 6.15% to 5.28% just by changing the wheels, a difference of 0.87% of the total weight.
Also, the ratio of total wheel+tire weight increasing from 15.57 to 17.93.
In other words, with the BBS wheels, the wheels are trying to move an object that is 15.57 heavier than they are themselves. With the OZ wheels that increases to 17.93 times heavier.

Just imagine that you are a 150 lbs guy and that you are trying to move an object weighing 2290 lbs or one that weighs 2690 lbs. Do you think you would notice the difference between those two objects (all else being equal)??

This is much more that I expected before I starting rolling the numbers. It never occured to me before that the wheels + tires on a car are that large a percentage of the total weight of a car.
And NOW I am wondering, when looking at my acceleration test-results, whether it is pure coincidence that that 0.87% difference in wheel+tire weight of the total car weight is very close to the measured difference in acceleration. (BBS = 5.70 seconds average, OZ = 5.66 seconds average, difference = 0.70%)

This is a great thread and I appreciated the testing effort. I have believed for some time that lighter wheels/tires would have little effect on acceleration of the car running on pavement.

If the car were sitting on jack stands, and the only mass the drivetrain had to overcome was the wheels, I think lighter wheels would produce a more significant difference.

But the car is on pavement and the drivetrain is trying to move the 3000+ lbs of car. That mass is gigantic compared to the DIFFERENCE in mass between light and less light wheels.

If the road was a long straight gear ("rack") and the drive wheels were cogs ("pinion") made of solid metal, I believe drilling holes in the cogs to reduce spinning mass by a few pounds would produce no meaningful difference.

MvM said:

Now, if someone would lend me a set of original 15/16 or 16/16 OEM wheels, we might redo these tests, using the same car.
:smile: :smile:

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You know I have 16/17 OE wheels on my just imported car, all you have to do is ask:wink: :biggrin:

MvM said:

I understand your point as well as those from GoldNSX.

Like you state, with 265/35ZR18 tires in the rear, starting at 800 rpm, the engine does not create enough torque to make the tires spin..

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Perhaps you should try a Supercharger???:wink: :biggrin:

How did you get your speedometer to read 320?