Acceleration test AFTER weight reduction with some WEIRD results !!

[MvM]

On NSXPrime, there are many threads about improving the performance of the NSX.
One popular item, apart from tinkering with intakes, headers and exhausts, has always been about reducing the weight of the NSX. After all, light weight has always been something the NSX is known for.
For me also, this has always been a favourite item since reducing the weight of the car doesn't necessarily have to cost much.

Having recently become the owner of a stock 1998 NSX-T, I decided to do some testing.
My first test had to do with the effect of replacing the stock 16/17 wheels with larger 17/18 wheels (with almost the same weight).
The result of that test was that the larger wheels made the car slower but not by very much (about 0.05 seconds for 20-100 kph runs in 2nd gear).

Since those tests, I have been replacing several parts of the car to loose some weight and by calculation, the total weight I have lost is about 30 kg from stock.
In addition to loosing weight, I decided to change my normal procedure of filling up the gastank completely before doing the test. The NSX has a capacity for 70 liters of fuel and this equals about 50 kg. So to increase the effect of reduced weight, this time I did the tests with about a quarter of gas left in the tank.

Before doing the test I had the car weighed at the same scale as when I first bought it.
The result was a weight of 1360 kg / 2998 lbs.
The original weight with a full tank was 1418 kg / 3126 lbs (with NSX-R rear wing).
Total weight loss is therefore 58 kg / 128 lbs LESS than stock.

EDIT:
The test-procedure is as follows and is the same as I have been using when comparing same-sizes heavy versus light wheels and the comparison between small and bigger wheels.

I tried to minimize a much variables as possible.
To measure the acceleration times, I am using a AP22 acceleration meter 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.
- 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.

However, after doing the tests, the results were exactly the OPPOSITE of what I was expecting. MY CAR HAS BECOME SLOWER !!!
(And that, of course, is NOT my intention...)

Here are the results:

First test:
Orginal weight: 1418 kg / 3126 lbs
Test results:
6.18 - 6.24 - 6.07 - 6.20 - 6.18 - 6.18 - 6.14 - 6.23 - 6.14 - 6.14 - 6.15 - 6.17 seconds
Average: 6.17 seconds
Deviation: 0.05 seconds
Maximum: 6.24 seconds
Minimum: 6.07 seconds

Second test:
Weight after weight reduction: 1360 kg / 2998 lbs
Test results:
6.28 - 6.50 - 6.28 - 6.46 - 6.40 - 6.45 - 6.29 - 6.45 seconds
Average: 6.39
Deviaton: 0.09
Maximum: 6.50 seconds
Minimum: 6.28 seconds

To say that his was NOT what I expected is an understatement !!

I did not really expect any serious improvement but this is totally unexpected.
According to the calculations of Bob Butler from some time ago, the loss of 90 kg ( 200 lbs) would reduce the 0-60 mph acceleration about 0.33 seconds. Since my weight loss is less than 200 lbs I expected something like 0.10 seconds.

Now being back at home, I am trying to think of reasons why the results are WORSE than before, even after shedding some 58 kg from the car. Normally speaking, with a starting power to weight ratio of 4.98 kg / HP (the car has been dynoed at 285 HP on the engine), 58 kg would be roughly equivalent to 11-12 HP.

Here is a quick summary of the things I have changed on the car:
- Changed the OEM wheels with OZ Ultralegger wheels in 17/18 size (used in both tests)
- Replace the OEM battery with a (brandnew) Odyssey PC925
- Taken of the European foglights
- Removed the spare tire and bracket
- Replaced the heavy NSX-T double-lid engine-cover with a carbon/mesh cover
- Replaced the OEM suspension with the TEIN-RA suspension
- Replaced the OEM front sway bar with the NSX-R bar
- Added the NSX-R lower chassis bar

I have SPECIFICALLY NOT changed anything having to do with the engine that might have increased (or reduced) the engine power.
So, NO CHANGES in air filter, intakes, headers, chips, exhaust or Turbo-stickers !

Piece of road used for testing - Same
Road conditions for testing - Same (dry)
Type of fuel used for testing - Same
Procedure used for testing - Same
Acceleration device used - Same
Cothes worn during the test - Same :wink:
Outside temperatue: NOT the same, but within 3-4 degrees Celsius in both tests (around 23 degrees Celsius).
Wind conditions: Same (no perceptible weight).
Ride-height of the car: The same to within 0.25" of the stock suspension

The ONLY thing that was different are the following two things.
Last Saturday, I replaced my almost worn rear tires with new ones. In both cases, brand and type are the same (Falken FK 452 in 265/35/ZR18.
I have used these new tires for about 320 km (200 miles). From previous measurements, I know that the difference in weight between a new rear tire and a worn out one is about 2-2.5 lbs. Since the NSX has not enough power to spin the tires in 2nd gear, I do not think this can be the cause.

The second thing is that becaus of road work going on, I had to take a detour to the stretch of road I use for these tests. The area is rather rural and this caused me to travel an additional 15 miles to the road I used. I drove in normal fashion.
My first thought was that since the engine might be hotter this might cause a reduction in power (even though my water temperature was where it always is, right at the middle). So my last two measurements were done after parking the car and waiting for 15 minutes with the engine hatch and lid open to give it a bit time to cool down. The results were not any different than before. To add to that, I still use the OEM airbox.

So my question is this - ANYONE got any ideas ???

 

[swerve2007]

in my opinion, the biggest factor here are the wheels- larger wheels have the mass spread out to the outside which takes longer to accelerate rotationally with the addition of more weight of a larger tire. i have noticed the same going from oem 16/17 to oem 17/17 but i did it for purpose of tire selection. the effects of larger wheels are reversable but it involves gearing change to recover the performance. for those reasons folks who go to larger wheels for cosmetic purposes are usually sacrificing performance.

 

[MvM]

in my opinion, the biggest factor here are the wheels- larger wheels have the mass spread out to the outside which takes longer to accelerate rotationally with the addition of more weight of a larger tire. i have noticed the same going from oem 16/17 to oem 17/17 but i did it for purpose of tire selection. the effects of larger wheels are reversable but it involves gearing change to recover the performance. for those reasons folks who go to larger wheels for cosmetic purposes are usually sacrificing performance.

Thanks for your input.
HOWEVER, the wheels used in both tests ARE THE SAME !!

The results from the test with the OEM wheels and the OZ wheels can be found here:
http://www.nsxprime.com/forums/showthread.php?t=138309

 

[CL65 Captain]

Temp AND humidity (dew point) effect power output of the engine. :smile:

 

[MvM]

Temp AND humidity (dew point) effect power output of the engine. :smile:

I know that, but do you think that 3-4 degrees Celsius can make THAT much of a difference?
For the record, humidity is very much the same over here (Netherlands).

 

[CL65 Captain]

I know that, but do you think that 3-4 degrees Celsius can make THAT much of a difference?
For the record, humidity is very much the same over here (Netherlands).

no. Have you been eating a lot and putting on weight? :biggrin:

 

[mskrotzki]

Phase of moon?:biggrin:
Sunspots?:biggrin:

 

[shawn110975]

had you waxed the car before or after? these tests?

what kinda of fuel used?

I dont think they made a diesel NSX but i might be wrong. lol

 

[greenberet]

When new, my Falken FK-452 tires had a tread depth of about 7 mm on the inside edges. If you replaced yours when that was gone, then the car should travel about 2.2% further for every revolution of the wheel.

Edit: 2.2% longer gearing will reduce the torque reaching the road by 2.2%. Is that enough to account for your results?

 

[RYU]

The biggest factor I think you're forgetting about is the human factor. You're measuring such a minuscule difference imo. I dunno... I guess I'll play... How about your shifting? Variances in clutch engagement? How about hygrometer rating of your clutch fluid? I don't know. I have a small brain

 

[N Spec]

How are you testing the 0-60? I thought the 97+ NSX were in the low 5 seconds? What RPM are you launching and how is your shifting? Those are a lot of launches, I hope you are not launching hard that hard those many times lol.

I used my Ipod touch with dynolicious and got something like low 6 second 0-60s with launching at around 2500 rpm or so. I don't know how accurate that is, but I also did a low 14 sec 1/4 mile going slight uphill towards the end with with heavy 17/18 wheel combo and no weight reduction (I have a 95 targa!). I would have to get my ipod to give exact numbers, but the ipod did say I was making around 260 hp lol, based on my vehicle weight input and drivetrain loss.

 

[MvM]

Hi Guys,

Thanks for the inputs so far.

I have edited my first post to include the exact discription of how I do these tests.
I do all the runs in 2nd gear so NO shifting is involved.
Simply speaking, after calibrating the AP22 acceleration meter, I start the car rolling, shift to 2nd gear, let it roll at around 1000 rpm and then simply floor the pedal. And then let the car do the work.

0-60 tests would be nice, but it would first of all be very bad for my clutch :biggrin: And second, it would simply involve to many variables like rpm for shifting, shift speed, wheel spin, keeping the car straight etc.

 

[goldNSX]

The ONLY thing that was different are the following two things.
Last Saturday, I replaced my almost worn rear tires with new ones.

Here you go.

You may have a little loss here and a little loss there but greenberet is nearest to the result: your tyres. As you're wearing down the tires the thread pattern becomes less flexible (less loss of power) and the tire becomes smaller. They're in their fastest acceleration shape. 5 mm less thread HAVE an effect. In the past I always noticed it on my NSX right from the very first meters after my tech mounted new tires. Flexibility in the tire thread costs power to be lost on the road.
Just imagine that we're not driving wheels in the age of Fred Feuerstein (Firestone). Tyres are flexing and walking.

However: New tires brake faster because of their higher flexibility as they absorb part of the energy.

The other thing could be tire pressure. More pressure = more diameter. As you like to test scenarios try to measure the acceleration times between different tire pressures, i.e. 40 psi and 30 psi. I can feel a difference even between 40 psi and 35 psi. It was quite extrem when I had only 20 psi in them (not on purpose, the tires simply lost air during months of storing).

Do the tests and you know why I really love my 245/40/17 at low tire pressure.

EDIT: Smaller tires = more acceleration but less cornering-capability. It's a trade-off which likes to be balanced depending on your preferences.

Please remind that using lower than OEM tire pressure is at your own risk! It's certainly a big no-no driving at high speeds.

 

[MvM]

So, what the two of you (GreenBeret & GoldNSX) are saying is this:

5mm difference in thread depth make up for 58 kg of weight loss.

or, to put it in other words:

5mm difference in thread depth equals about 11-12 Engine HP.

I agree that there is a difference between old and newer tires, but in all honesty, I doubt that this difference would all of a sudden mean a (negative) difference in acceleration times of 3% EVEN WITH 60Kg Less weight to haul around.

Perhaps it is a combination of several things :frown:
A higher temperature (around 3-4 degrees Celsius), new rear tires, perhaps a hotter engine.

Does anyone know just how much influence a difference in outside air temperature would make on engine performance?

Also, could it be that somehow the battery could be of any influence?

For the record, please note that when I do these test, aircondition is switched of as is the stereo, cooling fan and that I also do these tests with all windows closed. And yes, the car is running fine.
For the re

 

[goldNSX]

5mm difference in thread depth equals about 11-12 Engine HP.

Yes, it feels like this. I would value the comparison between 245 and 255/40/17 about 20 hp with my buttometer.

Good question about the influence of temperature on horsepower. My car feels having more but not much power at lower temperatures. The influence of the tires is bigger.

 

[MvM]

Yes, it feels like this. I would value the comparison between 245 and 255/40/17 about 20 hp with my buttometer.

Good question about the influence of temperature on horsepower. My car feels having more but not much power at lower temperatures. The influence of the tires is bigger.

Well, actually I would have to disagree.

I agree there is some influence but I doubt it very much it would be this big.
Let me explain my doubts.

As you will remember, in the past I did some these comparing heavy and light 17/18 wheels.
It was noted then that a difference in weight of 12.5 kg in wheel weight did not make any significant difference in acceleration times in these 20-100 kph runs.

About two weeks ago, I did some tests comparing 16/17 wheels with 17/18 wheels in the same manner.
We found out that the slightly larger wheels made the car just a tad slower on these runs. A total of 0.05 seconds to be exact.
The OEM 17 wheels were fitted with 255/40ZR17 tires. The calculated diameter of the wheels+tires should be 63.6 cm.
The OZ 18 wheels were fitted with 265/35ZR18 tires. The calculated diameter of the wheels+tires should be 64.3 cm.
The difference in height is therefore 0.7 cm or 3.5mm when looking at the radius instead of the diameter.
The weight of the 18" OZ wheels was practically the same as the 17" OEM wheels (about 0.3 kg, including the tires).

So, now I ask you this.
Why would an increase in thread (= height) of 5mm REDUCE acceleration with 0.20 seconds with a car that is almost 60 Kg lighter weight of the car whereas a increase of 3.5mm would make a difference of only 0.05 seconds with the car weighing the same??

 

[b00sted]

i for once can tell you new tires can make a BIG difference in how the car pulls on a straight, i noticed that going from worn re010 to a set of new potenza´s s02

 

[goldNSX]

So, now I ask you this.
Why would an increase in thread (= height) of 5mm REDUCE acceleration with 0.20 seconds with a car that is almost 60 Kg lighter weight of the car whereas a increase of 3.5mm would make a difference of only 0.05 seconds with the car weighing the same??

Now, it's hard to tell as both effects are mixed and can't be divided unless you go back to the worn tires.
I still think that the new tires slowed the car significantly down.
Again, the diameter of a wheel is dynamic, it changes with load. It gets lower in the rear with more acceleration. The sidewall stiffness and air pressure are the two main effects. A 255/40/17 offers more flexibility than a 255/35/18 which is the same diameter.

 

[tbromley]

All good points but you gotta think that little minute differences like some of these are hard to put into a file with real substantive, repeatable, results. There are so many variables to tests like this not to mention just driver initiated descrepensies. We aren't robots and so little fractional differences are interesting but you can't hang your hat on .05 of a difference. There are a lot of issues here and overall this is a good test and results are very interesting and have a lot of merit. I've enjoyed seeing this test and continue to get a lot out of it. I also enjoy reading the comments of everyone. Gold is making great points as is MvM.

I think it's great that you guys do this stuff. Kind of like Car&Driver or Road&Track right here on Prime. Cool stuff.

 

[nsxtasy]

The biggest factor I think you're forgetting about is the human factor. You're measuring such a minuscule difference imo. I dunno... I guess I'll play... How about your shifting? Variances in clutch engagement? How about hygrometer rating of your clutch fluid? I don't know. I have a small brain

I guess I have a small brain too. You are indeed trying to measure differences that are absolutely tiny, and are affected by human actions which can vary in timing. The variable you are trying to measure is easily swamped by many other variables.

 

[goldNSX]

STOP!
Before claiming that there are thousands of variables esp. the human factor please re-read MvM's post fully. I've to say that MvM DOES hold nearly all variables constant. I'm working in statistics and we've designed the tests pretty well. Holding all variables constant takes more money and there's a simple restriction. So we can't hold the outside temp constant as we're no weather gods and have no laboratory.
The differences are small but that's why MvM does 10 runs and takes the mean and standard deviation of it. If there was a major error factor like engaging the clutch the standard deviation would be high. But in MvM's runs it is very low. I'd not say that 0.1 seconds are big but 0.33 sec. are. And if you call for the hypothesis that there's no effect and you see one then BINGO.

 

[DutchBlackNsx]

Humidity has been said a few times and waved off as well, but the weather has been pretty on and off lately here.

Interesting info though.

 

[Cap'n Carl]

You've done a great job of controlling as many variables as possible. There's a rule of thumb in drag racing, where each 100 pounds lost is good for a tenth of a second lost in the quarter mile. You've lost a little over a 100 pounds, but your measured distance is less than a quarter mile, so let's say your weight loss has knocked maybe .05 seconds from your 20-100kph time. That's a lot to a drag racer, but not much in the real world. You could have erased that performance gain thru the things that have been mentioned: tires, temperature (big factor), humidity, etc.

You probably know this, but the weight loss has benefitted you in many ways: turn-in response, roadholding, braking, wear on tires, wear on suspension, mileage, wear on engine, etc.

 

[W]

...

 

[StmpoRaceProducts]

wow... 21 posts and no one figured this out yet....

128 lbs off the car.. 2 Major changes were made and not mentiond.

Im going to guess at the numbers below... 100% correct weight numbers won’t change the fact of why this is happening.

I don’t know KG's since I'm in the states and I never sold large (or small) amounts of cocain for a living so I wil explain this in LBS... sorry America is stupid when it comes to weighing things and socket sizes

Here is a quick summary of the things I have changed on the car:

- Changed the OEM wheels with OZ Ultralegger wheels in 17/18 size (used in both tests)

close to even weight change front to back

- Replace the OEM battery with a (brandnew) Odyssey PC925

minus 15 lbs Front

- Taken of the European foglights

minus maybe 4 up front

- Removed the spare tire and bracket

minus 32 up front

- Replaced the heavy NSX-T double-lid engine-cover with a carbon/mesh cover

center of the car - non-relevant to the problem

- Replaced the OEM suspension with the TEIN-RA suspension

even weight change in all four corners... but also the parts that could cause even more problems to this is a specialist didn’t install them

- Replaced the OEM front sway bar with the NSX-R bar

no clue on weight but sways only come into play on turns

- Added the NSX-R lower chassis bar

plus 5 but a TIGHER FRONT WILL ADD TO THE PROBLEM

There are 2 noticeable variables other than tires, tire pressure, temp, humidity ect...

Problem 1) FACT - so you tightened up the front if the car and took 45-50 lbs off the already very light front end.

When you correct the weight problem with spring aqdjustment.. your investment will help rather than hurt... Not as much as if you purchased a better part at a better price.... which would be another net loss in weight.. also up front. found here...

http://www.stmpo.com/product.php?productid=16135&cat=250&page=1

Test my theory... remove the tool tray and rear bumper beam... that should equal around the same weight at apox the same distance from the center.

I cant say you will be lower... but the numbers will be better... I'll bet you fall right in between

Since you have that heavy bumper off... your half way to installing this back on

http://www.stmpo.com/product.php?productid=16150&cat=253&page=1

Problem 2) Your TIENS have changed the weight distribution without you knowing it... so adjust your spring rates to place more pressure evenly at all four corners with the change in weight up front in the equation... corner balancing will fix this problem.

At the track... race teams don’t just do practice laps to "get a feel for the track"... hell.. you can do that on Gran Turismo.

It's mostly done to change tire pressure and suspension...

My $.02... I’d be willing to give you $100.00 off my rear bumper if I'm wrong... (since putting money where your mouth is" seems to be something rarely done these days)

just keep all variables consistent with the first tests though... and make suspension and spring rates changes after you try my theory.

Regards