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).
Calculation for the required weight reduction to maintain acceleration performance when changing an axle pinion.
| Identifier | ExFiles\Box 70\1\ scan0112 | |
| Date | 8th September 1927 | |
| EV{Ivan Evernden - coachwork}3/8.9.27. cont. It there are to be a number of these built all somewhat similar, it would appear advisable for us to supervise the design and to make tests before construction is started or the coachwork may easily spoil the success of the venture. We suggest that Hs.{Lord Ernest Hives - Chair} should measure the acceleration of 10.EX. at certain speeds, in its present condition, and then reduce the weight by 32# lbs. by removing the passenger, the spare wheel and tools and other suitable pieces, before making exactly similar tests with a 17 tooth axle. If M is the mass of the car. F is the propelling force at the road. a is the instantaneous acceleration at a given speed. t is the co-eff. of total tractive resistance at that speed. F = Ma + Mt or M = F / (a+t) M & F when a & t are const. If we assume a constant M.E.P. over the small range of speeds concerned, and consider the instantaneous acceleration at a given speed to be constant with pinions of 16 and 17 teeth, F₁₆ = F₁₇ * 17/16 therefore, for the same performance in acceleration with a 17 tooth axle, the weight must be reduced in the ratio of 16 to 17 The total weight of the car under test was 5,500 lbs. The reduction would therefore be. M₁₆ - M₁₇ = M₁₆ - M₁₆ . F₁₇/F₁₆ = M₁₆ - M₁₆ . 16/17 = 1/17 M₁₆ = 1/17 . 5,500 lbs = 324 lbs | ||