Hi, Just tried my brakes with an old style Tapley meter. The type that measures G force as a percentage. I get 50% with the footbrake & 60% with footbrake & hand brake together. Does anyone know what figure would be a pass with the old MOT please
Thanks. Kevin

Location: S yorks

I believe it should be 50% on service brake (footbrake) and 25% on secondary/emergency (handbrake).

See section 3.7 & 3.10 here:
https://www.protyre.co.uk/media/486070/vosa-inspection-manual-classes-3-4-5-7.pdf

It would be different for uncoupled brakes. From memory I think 30% on one and 25% on the other. I don't think it matters which. Though I may well be wrong on the numbers.

Very useful information as I have one of these meters and will propose a club run to my place for a competitive brake test; when I get back there.
Imagine cars one at a time, clubmembers partners lining the road (we don't want the extra weight), barking discouragement, Boo!
If time permits we'll swap drivers and the boo will be on the other foot. Think on it, bound to be fun, educational and improve safety. cheers Russell

Location: oz

Blimey RR, no wonder they dont want to test old cars.

The post ” Standard Brakes do Work... “ quotes several old road test percentages worked back from stop distance. Many Sevens struggled to attain much more than 50% lightly laden, probably with full force on everything. With appropriate linings some now apparently manage to lock all (narrow) wheels even on pre Girling, which suggests 85% or so.

The NZ requirements, probably international, are based on distance from a low speed (30 kph, and correspond to a constant 50% for all wheel braking, supposedly laden, and unassisted by engine braking etc. But a vehicle which can only achieve this will be disconcerting to drive.
The Tapley seems to somehow assess average rather than peak deceleration; I think the instructions may require the final jerk to be avoided.

For those who did not get past the 5th form, or who have forgotten, for surfaces which do not significantly cog together, the maximum decelerating force matches the weight, giving 1G deceleration maximum, taken as 100%. (Just as for a falling object). Modern wide tyres will exceed this esp at lowish speeds. Most post war hydraulic cars will approach or attain 100% from low speed unladen. In normal driving 70% is seldom exceeded. However if it takes a lot of effort such cars are not very reassuring. With rear only brakes on a car, the NZ requirement for these is an idealistic 40%; requiring these brakes to be super effective, esp as only half or less vehicle weight may be on the rear wheels under braking.

From 30 mph 100% deceleration throughout the braking represents 30 feet, 50% corresponds to 60 feet etc.
Older books did not enthuse about really powerful brakes, considering them a danger. More than 50% for buses was considered a threat to passengers. At least until quite recently many/most heavy vehicles laden would not achieve 50% at speed.

Linings are certainly key. I run a 1960s car. The handbrake has dwindled seriously over the decades as replacement shoes from the 1980s etc have been fitted. I had a set of 1970s Ferodo MZ with some zinc for another car so in desperation redrilled the leading shoes and fitted. The effect was immediate. Can drive in the city on handbrake alone, and lock wheels, as originally.

Location: Auckland, NZ