MOT brake test results question

[leorest]

The Wedge has just passed again!
Figures quoted for breaking efficiency were
Service brake 70% (50)
Handbrake 30% (18)
Numbers in parentheses were the quoted minimum pass level.

When I asked what 70% is a measure of I got a poor answer.
Without being funny, to be a competent tester (and he was) does not require full understanding of the physics involved, so I didn't embarrass him further

I've just Googled for half an hour and still not answered my question so hope someone out there can help.
What does 100% represent?
Leo

[leorest]

Thanks
So...
(Total brake effort / Vehicle Weight) * 100 = % efficiency
Does that mean that 100% = 1 g
Leo

[leorest]

GreenV8S said:

Only approximately, since they test front and rear wheels separately. In the real world you would get loads of weight transfer so the weight on the front wheels goes up and the weight on the rear wheels goes down under heavy braking. In a static test on the rollers you don't get this weight transfer so each wheel just carries its static weight, presumably it is this static weight which is used in the formula given above.

In this instance the test was done by driving the car at 15mph on the road and the measurements being taken buy a box of tricks placed in the passenger foot well (Tapley?). This obviously takes into account weight transfer.
Considering the crap origins of the front brakes and the state of the disks I'm impressed that they achieved 0.7 g. Even more impressive is the handbrake holding a third of the weight of the car. Luckily my drive is less steep than 1:3
Thanks for the help
Leo

[leorest]

steve_D said:

Have they gone electronic or is it still a drum that revolves inside a window? Steve

Couldn't tell, it was a small wooden box with a handle on the top.
Leo

[leorest]

steve_D said:

If you can get it to fall over you don't bother with a reading.

...in the good old days they used a house brick

[leorest]

Yep
The tallest one you can find
L

[leorest]

ifc63 said:

Should I take a house brick with me?

Yes and if he starts to put it on the rollers hit him with it
Seriously though. I'd check with the dealer or factory and make sure you let them know when you book the MOT.
Leo