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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).
The amplitude of wheel wobble, comparing balloon tyres with high-pressure tyres.

Identifier  ExFiles\Box 28\4\  Scan346
Date  1st August 1925
  
R.R. 493A (50m) (D.B. 175 25-9-24) J.H.D.

EXPERIMENTAL REPORT. -3- Expl. No. REF: Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}2/LG25. 8.25

the wobble dies out.

We carried out a test with the Chronograph to ascer-
tain the respective amplitude of the two sets of wobbles which we
were investigating in the tests with the hydraulic dampers. We
found that while a wobble with balloon tyres would have an
average amplitude of about 14° to 15°, that with high pressure
tyres it would not have an amplitude above 7° to 8°. We do not
mean by this that the amplitude of the wobble with high pressure
tyres cannot exceed 8°. What we mean to infer is that we can
get continuous high speed wobbles with high pressure tyres with
amplitudes of about 8°, whereas the same sort of wobble with
balloon tyres, whilst naturally occurring at a lower speed, also
must have a larger amplitude. Under exceptional conditions
with high pressure tyres we have had a wobble build up to an
amplitude of 15°. This has only occurred on four or five
occasions and in every case the brakes have been applied. A case
in point was the one we quoted where the wheels left the ground
for 10 ft. in turn.

It appears to us that owing to the greater amplitude
of the wobble with low pressure tyres, it is easier to damp out
because we have more movement to deal with. On the other
hand, there is always the fact that with high pressure tyres we
have a definite out of balance force of 1 lb. being rotated at
high speeds tending to produce wobbles - the low pressure on
the other hand being in balance.

We are improving the Houdaille shock absorbers and
are repeating our tests.

contd :-
  
  


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