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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).
Confirming a telephone conversation regarding modifications to frame width, axle design, and tyre specifications for 'Japan III'.

Identifier  ExFiles\Box 58\1\  Scan109
Date  19th October 1931
  
DA{Bernard Day - Chassis Design}/EV.{Ivan Evernden - coachwork}
c. Hs.{Lord Ernest Hives - Chair}
c. BY/Cgh.{W Clough}
c. BY/SS.{S. Smith}
c. BY/HEB.{H. Biraben}
c. BY/TWD.{T. W. D???Aeith}

XS820.
BY.4/G.19.10.31.

XS770
XS820.

TELEPHONE CONVERSATION WITH VV. 19.10.31.

JAPAN 111.

We wish to confirm our telephone conversation in which you informed us that in order to keep the clearance between the brake drum and the frame or body in proportion to the Phantom 11. it will be necessary for us to reduce the width of the frame from 46" to 45".

We will make similar allowances on Peregrine, for which we had practically completed the axle design, and were starting to detail it.

Arising out of the above modification comes a question as to whether you propose to reduce the spring centres by a like amount i.e. 1". This is important as it affects our axle tubes, which we have actually in hand for Japan 111.

With reference to the question of the wheels, the difference on diameters between the silent tread and the 'Fort' silent tread, Balloon Tyres, for the 20/25 HP. chassis is only .250". The 'Fort' silent tread has been standard since the Balloon Tyre was introduced.

I understand that the adoption of the 'Fort' silent tread was the result of continued enquiries for this type of tyre from customers to Sales, and the difference in dimension being so small it was agreed between the Experimental Department and Sales that the 'Fort' Silent tread should be our standard for the 20/25. This does not account for the difference in diameters which you mention and we are inclined to think that you are over-looking the fact that the sizes given in all tyre catalogues are "nominal". The nominal size of 'Fort' silent 20/25 is 31 X 6" whereas from actual measurements the tyre measures 32.130" over the maximum. We took this matter up ourselves some time ago and obtained from them dimensioned drawings of the section of the tyre. We attach hereto blueprints for your guidance.

We notice the difference in tyres you show, and had corrected our chassis height to agree with actual tyre
  
  


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