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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Analysis of brake efficiency changes, tests on a Buick Century 8, and conclusions on front/rear braking ratios and overheating.

Identifier  ExFiles\Box 141\2\  scan0335
Date  10th September 1940
  
Rm{William Robotham - Chief Engineer}/MHR.{M. H. Rigby}1/ET.10.9.40 - 3 -

Front wheels

1. Change to pressed steel wheels, 30% drop to 60% efficiency.

Rear wheels

2. Change to double discs on wire wheels, 20% frop to 70% efficiency.

3. Decrease of air gap drum-wheel, 30% drop to 45% efficiency (including 7% estimated drop due to difference between discs on wire wheels and real pressed steel wheels).

4. Addition of cowls, 30% drop to 35% efficiency.

Addition of air deflectors gave an improvement of over 50% on the COMET, but only 5% on the CRESTA.

TESTS ON THE BUICK CENTURY 8.

These were inconclusive due to the failure of the brake shoes, which are not anchored at the bottom ends, to return to their correct positions after each application; The result was that sometimes the linings were rubbing the drums, giving slow cooling and, in order to stop this the adjustments had to be slackened off considerably, giving on occasions a large air gap with artificially fast drum cooling. It was definitely found, however, that on the Red Gate Road, exceedingly high temperatures were obtainable, the fronts sometimes being hotter than the rears, since the rears probably cool almost as fast as the fronts due to the high ground clearance.

CONCLUSIONS.

Returning to our own cars, it is not only the fast cars that exhibit the unequal wear, but also cars such as the RIPPLE, in which case the rears not only cool much slower than the fronts, but are also called upon to provide nearly half the braking torque, the ratio of front/rear braking being only 1.2 : 1, as against 1.85 : 1 on the CRESTA and COMET.

In the case of our high performance cars, the front/rear braking ratios have been increased by 30% by allowing the leading shoes on the front to wrap. Thus on overheating the brakes, the rears will fade badly, whilst the fronts may be only partly affected; and it may be that only by removing the links have we saved the fronts from burning out as quickly as the rears.

Another possibility is that although serious over-heating is as bad on the front as on the rear, when once the linings have been burned
  
  


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