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 discussing vehicle handling characteristics in side winds, particularly understeer and oversteer.
| Identifier | ExFiles\Box 170\3\ img094 | |
| Date | 14th July 1936 | |
| CADILLAC MOTOR CAR COMPANY DETROIT, MICHIGAN CADILLAC AND LASALLE MOTOR CARS July 14, 1936. Mr. Grylls, Rolls-Royce, Limited, Derby, England. Dear Grylls: Answering yours of July 6, I think from our experience that the answer is simpler than the sequence of events suggested in your third paragraph. To make a car handle well in a side wind it is necessary to have definite understeer. To prove this try differential tire pressures. 35 fr. 25 r.{Sir Henry Royce} will handle badly, 25 fr. 35 r.{Sir Henry Royce} should begin to handle well (depending to some extent on load distribution and body shape - the more streamlined the worse, since the center of wind pressure shifts more violently). The Chevrolet and Pontiac, with pronounced understeer, handle best in side winds. Twin rear tires on racing cars give better handling because they cause understeer. In other words what happens during the wind gust appears to be less important than the train of events set up by the gust. If these are cumulative (oversteer) the car is unmanageable. If they are "self-damping" (understeer) the car can be made to ignore side winds. Caster should be zero for good handling in side-winds, for obvious reasons. I think you will find interesting results from just playing with differential tire pressure. I agree that no car turns into the wind at the moment of the gust, the reason being that the center of wind pressure is so far forward. I think that if the car tends to run in a curve concave to the wind it is unmanageable; convex to the wind it is stable. Yours, Maurice Olley | ||