agreed.
Acceleration test AFTER weight reduction with some WEIRD results !!
- Thread starter MvM
- Start date
agreed.
MvM, no you are quoting the accuracy of the base measurements (acceleration and time), not the accuracy of speed. From your tests, you are really comparing the time it takes to get from one speed to the next. The error is not in time, it is the integrated error of calculating speed. The AP-22 does not measure speed, when you integrate the acceleration to get speed, there is error that keeps building on itself due to road grade and the vehicle pitching due to a component of gravity acting in the longitudinal direction. The AP-22 has built in “fudge factors” to try to account for the rearward pitch of the vehicle, but this further pollutes the calculation of speed due to any changes in acceleration at the vehicle launch and before your real measurement begins. They also have built in triggers to begin the integration when you launch that varies from run to run, which also alters the calculation of speed.
I have written two technical papers on different measurement methods and this subject. I don’t have them at home, but from memory, the technique that the AP-22 uses which is the same as the very common Vericom units can produce errors as large as 3 mph. Any GPS based system would do much better for what you are trying to do. That is why the new AX-22 and the newer Vericom units have incorporated GPS.
Bob
The aftermarket 17/18" wheels and tires is probably your biggest (negative) variable.
Even though those OZ wheels are light, they most likely are heavier. Even if they are the same weight as the super light OEM wheels (probably unlikely) they will have a higher rotation mass -which makes it harder to accelerate or decelerate, thus making the car slower.
I think the wheel/tire change is your biggest variable in the pretty scientific system of testing you are doing over any said aero change or weight distribution possibility or suspension change.
0.02
Even though those OZ wheels are light, they most likely are heavier. Even if they are the same weight as the super light OEM wheels (probably unlikely) they will have a higher rotation mass -which makes it harder to accelerate or decelerate, thus making the car slower.
I think the wheel/tire change is your biggest variable in the pretty scientific system of testing you are doing over any said aero change or weight distribution possibility or suspension change.
0.02
Billy, he had already done a test of before and after the wheel swap and the difference was in the hundreth of a second range when he went from oem to aftermarket wheel swap. What is puzzling the OP is that after he got more power mods and had some weight reduction done, he was a few tenths slower than he was.
I read the thread a week ago and havn't been up to date but new (heavier) tires can affect the performance as will not doing the tests on the same road.
Some variables:
Humidity (not stated)
Engine oil (was it changed between all this testing?) -what oil is used?
Oil Temp (not measured or stated, granted measures were taken to have consistent 'warm up' time, but its not quite accurate enough or consistent enough to be called a constant)
Trans oil temp (same as above)
TIRE PRESSURE (was this checked to be exactly the same for all the runs, especially when mounted with new tires)?
Was the (slow) times with the weight reduction and 17/18 setup done on the NEW or OLD Falken Tires? What was the tire size?
What was the condition of the (faster) times on the OEM 16/17 tires? What tire model, how worn, what size, and was the TIRE PRESSURE the same as on the 17/18 setup?
It would be interesting to:
1) Do the run the moment the car gets warm with the needle in the middle (basically cold) then drive around hard for a while then do another run on the same road 10 minutes later.
2) Do the run in the EARLY morning and then at 1pm.
The above can see the variables of engine temp and air temp. be sure to record the air temps. While these tests also have flaws, it would be interesting to see the magnitude of the variables.
0.02
Last edited:
I also have to agree it's the measuring equipment/operator error. Reminds me of folks who attempt to fix their "overheating" issues with a new radiator, t-stat, water-wetter, etc., only to find out their temp guage was defective/miscalibrated.
Have you removed a "Type R" or "24V twin turbo" sticker ?
Have you changed the colour ? Everybody knows that reds are faster !
:biggrin:
Have you changed the colour ? Everybody knows that reds are faster !
:biggrin:
- Joined
- 15 May 2004
- Messages
- 6,898
MvM states that he has mounted the same tire on the rear, the same size, the same Falken model, no chance, just more thread. I guess the tire pressure is the same as before.
Most of your questions point to the same direction as mine: the new tires in the rear.
This has been an interesting post to say the least and there have been mentions of small brains of which I my have the smallest.
My thought is something which I have been wondering about for some time and you may easily test. My thought is that the gain in weight savings of removing the spare tire and bracket/tray in front of the battery is offset by the increased drag of the large hole produced under the car. My old little brain seems to recall that increses in drag take increases in hp to the cube to overcome, so small changes make larger results.
Anyway, before everyone laughs themselves off their chairs you could simply add the tray and tire back on and see if there is any difference at all plus or minus. At least it is simple to test and if nothing else I gave a few bigger brains a good laugh.
My thought is something which I have been wondering about for some time and you may easily test. My thought is that the gain in weight savings of removing the spare tire and bracket/tray in front of the battery is offset by the increased drag of the large hole produced under the car. My old little brain seems to recall that increses in drag take increases in hp to the cube to overcome, so small changes make larger results.
Anyway, before everyone laughs themselves off their chairs you could simply add the tray and tire back on and see if there is any difference at all plus or minus. At least it is simple to test and if nothing else I gave a few bigger brains a good laugh.
I don't think anyone has mentioned that wind will affect acceleration. Probably a pretty small effect to add to the list unless it was very windy, but yet another variable.
- Joined
- 15 May 2004
- Messages
- 6,898
Yes, it has but up to 60 mph the effect is neglegible and certainly not strong enough to explain differences MvM found.
I overlooked this post.
So there has been a back to back OEM 16/17 vs. 17/18 setup with very little difference - correct?
If you can point out the change in suspension as the variable from the fast acceleration times to the slower times with the lighter setup, that might be your answer due to Bob's comments of how the AX-22 system operates.
Increasing your spring rate (especially the rear) and decreasing the front droop travel (how much the front lifts up in the air under acceleration) will affect the G-forces the AX-22 system is reading. By maintaining a flatter platform compared to the rear squatting and front lifting in the OEM suspension, the AX-22 could read this difference/variable in vehicle pitch as a difference in acceleration -despite the car being lighter and having the same power. The Tein suspension has much higher spring rates (especially in the rear) and less droop travel in the front which will make a substantial platform difference under acceleration, even from a roll in 2nd gear for the whole test run.
Doing another A-B comparison on 16/17 vs. 17/18 might not be the answer. Instead (although a pain) doing an A-B comparison OEM vs. Tein suspension will probably point out the variable that's causing all the controversy.
Billy
- Joined
- 15 May 2004
- Messages
- 6,898
I agree with all you said except for doing a backup run with 16/17. On the assumption that -60 kg don't have a big effect on acceleration times but only have an effect on the car's front lift factor doing the tests with 16/17 again could give you an idea of how much the TEIN influenced the results or if it's mainly the fresh tires in the rear. Very interesting indeed.
Last edited:
- Joined
- 28 November 2009
- Messages
- 997
This weeks top gear. Worth a watch.
They do a top speed run in the new Bugatti Veyron.
Notice how they wait for the perfect conditions and why and how much difference it makes.
http://www.bbc.co.uk/iplayer/episode/b00t8qfb/Top_Gear_Series_15_Episode_5/?t=39m12s
Also watch the end, tribute to Ayrton Senna.
Ross i'm interested in your comment regarding the corners setup. Are Tein suspension any good? Tein are good for me as i live out in the country, having adjustable stiffness within the cabin is so handy. These 4 wheels laser align centres when they set up the car does it actually improve peformance to a noticeable level?
They do a top speed run in the new Bugatti Veyron.
Notice how they wait for the perfect conditions and why and how much difference it makes.
http://www.bbc.co.uk/iplayer/episode/b00t8qfb/Top_Gear_Series_15_Episode_5/?t=39m12s
Also watch the end, tribute to Ayrton Senna.
Ross i'm interested in your comment regarding the corners setup. Are Tein suspension any good? Tein are good for me as i live out in the country, having adjustable stiffness within the cabin is so handy. These 4 wheels laser align centres when they set up the car does it actually improve peformance to a noticeable level?
- Joined
- 15 May 2004
- Messages
- 6,898
...available in the UK only.
...available in the UK only.
It is widely available on the internet. I just finished watching it here in Colorado. Try StreetFire.
The wind is not a small factor when comparing different runs. I am sure Billy sees this also, but when the wind changes on a track that I am racing on, you can immediately see it in the data. The slope of the acceleration curve changes based on the direction of the straight-away, and any comparison that would be attempted for the time it takes to change speed would significantly be altered.
I also agree with Billy's comment about the pitch change based on a different suspension. The bottom line is that you are trying to measure an effect that is too small to be measured with the method you are using. The differences are much better to calculate, and the rotating mass can be calculated also.
Bob
I also agree with Billy's comment about the pitch change based on a different suspension. The bottom line is that you are trying to measure an effect that is too small to be measured with the method you are using. The differences are much better to calculate, and the rotating mass can be calculated also.
Bob
Wow, I had not noticed that this thread had continued to grow.
First of all, there is no way I am going to go through all the trouble again of switching back and forth between the OEM and TEIN suspension just for testing their impact on this kind of tests. I agree, it might be interesting to see the results, but it simply is too much work for me to do this.
Many reasons have been given to explain the results, some of which I am a bit sceptical about but some certainly make sense.
Probably, the measured effect is a combination of several factors, some of which I have no real control over.
One of the best ideas is that because of the change in spring rate, the tilt setting on the AP-22 should have been changed. However, since I have to way measuring the difference in tilt during acceleration between the different suspensions, tampering with this setting would only introduce another variable.
In the end, I think it comes simply down to this.
I wanted to measure the impact weight differences make upon acceleration.
I tried to do this by combined my planned modifications (lighten up the car) and do the test. The way this was done however, introduced variables which affect the results in several and non measurable ways which spoil the test results.
Like posted before, I will continu modding the car and then redo the tests with just putting in some heavy weights into the car first, run the tests, remove the weights and then redo the tests.
This could be all done on the same day, same road, same conditions.
You will, however, have to bear with me for some time since I'm not finished with the car at the moment :smile:
First of all, there is no way I am going to go through all the trouble again of switching back and forth between the OEM and TEIN suspension just for testing their impact on this kind of tests. I agree, it might be interesting to see the results, but it simply is too much work for me to do this.
Many reasons have been given to explain the results, some of which I am a bit sceptical about but some certainly make sense.
Probably, the measured effect is a combination of several factors, some of which I have no real control over.
One of the best ideas is that because of the change in spring rate, the tilt setting on the AP-22 should have been changed. However, since I have to way measuring the difference in tilt during acceleration between the different suspensions, tampering with this setting would only introduce another variable.
In the end, I think it comes simply down to this.
I wanted to measure the impact weight differences make upon acceleration.
I tried to do this by combined my planned modifications (lighten up the car) and do the test. The way this was done however, introduced variables which affect the results in several and non measurable ways which spoil the test results.
Like posted before, I will continu modding the car and then redo the tests with just putting in some heavy weights into the car first, run the tests, remove the weights and then redo the tests.
This could be all done on the same day, same road, same conditions.
You will, however, have to bear with me for some time since I'm not finished with the car at the moment :smile:
Similar threads
