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).
Proposed measures to address excessive 'jellying' and body boom issues by testing modifications to engine feet, springs, and tyres.
| Identifier | Morton\M19\ img139 | |
| Date | 2nd April 1931 | |
| ORIGINAL. To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} c. to Sg.{Arthur F. Sidgreaves - MD} Nor. c. to K.{Mr Kilner} Ds. c. to Wy. Fn. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}/7/KT.2.4.31. x634. x457: BODY BOOMS P.II. with reference to R4/M.25.3.31. (1) Proposed Palliative Measures. We note that on 18-EX you have experienced excessive jellying with your rear engine feet removed. We have carried out this alteration on five experimental cars and three Sales cars. On our experimental cars we have made careful comparative tests of jellying and road shocks with and without the rear engine feet. The tests were conducted on main roads at speeds up to 80 MPH. We have no bad surface near Derby where we can do very high speeds. Briefly the results we obtained were as follows. (a) Cars with standard road springs and shock absorbers. Provided the front tyre pressures were not allowed to fall below 35 lbs/sq.in. the jellying and steering shocks were not more than 10 - 15% worse on reasonable good road surfaces when the rear feet were removed. On very bad surfaces at moderate road speeds the "jellying" difference was slightly accentuated. Our general impression is that four feet give "nibbles" on the steering on good surfaces, but do not permit big kicks on the wheel over a pot hole, two front feet only smooth out the nibbles but allow worse shocks over pot holes and would permit of high speed wobbles building up more easily should the wheels be out of balance. They also reduce the directional stability of the steering at maximum speeds. We can say roughly that the difference between two and four engine feet is generally not so great as (1) The difference between cars fitted with various types of bodies. (2) The difference between low rating and standard road springs. (3) The difference between tyres at 30 lbs/sq.in. and 45 lbs/sq.in. Your car 18-EX is fitted with low rating road springs and we believe that if you are running with very low tyre | ||