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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).
Letter from Cadillac Motor Car Company regarding roll-couple distribution and tire wear on the Eyston car.

Identifier  ExFiles\Box 170\3\  img103
Date  31th October 1936
  
CADILLAC MOTOR CAR COMPANY
DETROIT, MICHIGAN

October 31, 1936.

Mr. S. Grylls,
Rolls-Royce, Limited,
Derby, England.

Dear Grylls:

I have been trying to find time to deal properly with yours of September 24th including prints of Eyston car and enclosure from Eyston. Have written Hives my general belief about roll-couple distribution.

I would refer you to my sketch Figure 67 on Page 758 and equation on Page 759 of the latest IAE Journal. Also R.{Sir Henry Royce} D.{John DeLooze - Company Secretary} Evans' paper on tires in SAE Journal of, I believe, March 1935.

Particularly his curve Figure 3 showing the effect of load on cornering power.

I reproduce this roughly in attached sketch.

I notice that the car is front-drive, probably with most of the weight well forward, and is parallel-independent in front and rear. Both ends are stiffly sprung.

The roll axis (Fig 67) will be low and the overturning couple will be carried very largely by the front tires because the springs in front are made stiffer than rear, to carry the heavier load and the track is wider in the front.

Even with springs of equal stiffness front and rear the roll couple distribution will be 55% to the front, due to the track. I find the lateral acceleration on the 10 mile circuit at 175 mph is .244 g or 7.87 ft/sec^2. This corresponds to about 20 mph on our 108 ft radius circle at the Proving Ground - a speed at which roll-couple distribution affects the steering considerably.

In Mr. Eyston's letter when he speaks of wear on the "near-side" of the tread having been transformed into wear all over, does he not mean wear on the inside of the tread?

I seem to see that slight deflation of the tire, or a general
  
  


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