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posted on July 18th, 2004 at 09:21 PM
Can anyone decipher a brake analysis?
I had my NSW blue slip done last week and it included a brake analysis. I thought they just drove it and made sure it stopped, and I wasn't too
worried because the front discs (69 bug) still have half the meat on them, and the rear drum shoes are brand new.
The mechanic drove it with some portable setup on the pedal, with a readout on the passenger seat, which printed a test result when he returned. He
said it passed but I'd love to know what the printout means, as in quality of my brakes, etc. Can anyone help?
The printout said:
Newtons Max = 463 (pk = 461)
Decel Max = 78%g
Avge Decel = 54%g
Duration = 1.7 sec
Est Speed = 33km/h
Light Veh. Serv Brake
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posted on July 18th, 2004 at 10:45 PM
Hey there,
now first off, I am guessing here, so don't take this as THE WORD.
Avge Decel = 54%g indicates to me that under the brake, as applied, the car slowed down at about 5m/s/s. That is, every second, the car was going
5metres per second slower. That is, assuming it's a linear decelleration, which is not realistic. But, that *was* an average value. Basically,
you're decellerating at half a 'g'.
Decel Max = 78%g says that the most decelerration your car got is 0.78gees. ie, at some instant, the car was decellerating at about 7.5m/s/s.
Newtons Max = 463 could be the force applied through the tires to slow the car during braking. Now, acceleration is force divided by mass, so... a =
F/m = 500N/1000kg = 0.5m/s/s. This is way smaller (like 10x) than the above mentioned decelleration values (but I don't know whether the mass is
1000kg, and 500 is pretty close to 463). This suggests to me that my hypothesis is incorrect. Perhaps, then... it could be the pressure (sorry,
*force*) applied to the brake pedal. Basically, was the brake pedal stomped on with about 50kg? Seems reasonable. Hence, I am inclined to think
that this value represents the force the brake pedal experienced (from the driver).
I won't speculate on the other values.
Cheers mate,
Aurel
68AutoBug
A.k.a.: Lee Noonan
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posted on July 18th, 2004 at 10:55 PM
They just mean that Your car stopped within the guidelines set down by the RTA ... in NSW...
Your car probably did not stop as well as a car with Vacuum assisted brakes...
One other very important thing.... Most of these figures depend on what tyres You have fitted to Your car... and
We All know there are tyres and then there are Tyres.....
The road surface the test is done on can also change the readings...
so, I don't take any notice of them.....
Lee
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posted on July 18th, 2004 at 11:30 PM
Hi
I have seen people do this test sitting in their office, they just swing their hand around and stop it suddenly while squeesing the brake pedal part
in their hand. As Lee said dont take any notice of them.
posted on July 18th, 2004 at 09:21 PM
