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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).
Specifications for the S.S. Chassis, including rear axle ratio, tyre options, and gearbox ratios.

Identifier  ExFiles\Box 15\5\  Scan069
Date  1st February 1929
  
EFC. Y7310 BY/Cgh{W Clough}4/G.1.2.29.

S.S. CHASSIS.
-------------

In reply to EFC1/T1.2.29. up to the present it is only intended to have one rear axle ratio for the SS.{S. Smith} chassis viz. 11/41.

Two sizes of tyres are being used on the experimental cars viz.-

33" x 6.75" low pressure tyres on 21" x 5" rims, which have an effective rolling diameter equivalent to 103.25" circumference.

The alternative is 32" x 6.75" low pressure tyres on 20" x 5" rims, and from the information given to us by the Dunlop Co. this size of tyre will have approximately the same effective rolling diameter as the above, owing to the fact that the latter have more rubber on the treads.

The gearbox ratios are :-

1st. Speed ..... 3.511
2nd. Speed ..... 1.998
3rd. Speed ..... 1.360
4th. Speed ..... Direct
Reverse ........ 3.086

BY/Cgh.{W Clough}
  
  


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