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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).
Report discussing tyre wear issues and the effect of tyre inflation pressure on petrol consumption, including a performance graph.

Identifier  ExFiles\Box 53\3\  Scan007
Date  6th January 1927 guessed
  
contd :- -6-

tread makes the tyre ride very harshly when new. In addition, on the Rapson double-tread tyre, when the first tread is finished, it comes off in a series of large pieces which hit the wings of the car and make a tremendous noise. As this continues for many miles it is rather a distressing feature.

III: PETROL CONSUMPTION AND TYRES.

(a) The effect of balloon tyres on consumption.

Balloon tyres are often accused of causing a considerable increase in petrol consumption. We give the results of a test carried out on cord tyres shewing the measured difference in consumption when these are run first at an absurdly high, and then at an exceptionally low inflation pressure.

[Start of chart section]

TYRE INFLATION PRESSURE

EFFECT OF SPEED & TYRE
PRESSURE ON PET. CONSUMPTION

WATER TEMP 60° C
IGNITION STANDARD
MIXTURE CONTROL CENTRAL
AXLE 15 x 52
TYRES STANDARD

Graph data:
Y-axis: MPG / PET. CONS (from 12 to 20)
X-axis: ROAD SPEED MPH (from 10 to 50)
Line 1 (dashed): 60 Lbs/sq in
Line 2 (solid): 25 Lbs/sq in

[End of chart section]

It will be observed that at a normal touring speed of 30 m.p.h. this amounts to about 6%. Now the difference between the rolling resistance of a normally inflated high pressure and balloon cord tyre is less than that

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