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).
Performance issues, including lack of low-speed power and steering wobble, with proposed solutions and competitor comparisons.
| Identifier | ExFiles\Box 19\4\ Scan318 | |
| Date | 25th May 1931 guessed | |
| - 3 - Rolls Royce chassis and it was thought had been lost, and this without any appreciable impairment to the high speed performance. We do notice a tendency to roll, both on chassis and finished car, which brings a reaction on the steering and caused the car to zig-zag slightly - this is a very low frequency effect, and while it is noticeable, we do not think yet it is sufficiently objectionable to register as a complaint. On this point we must await the verdict of our owners. The almost universal comment on these jobs, both as chassis and this finished car, is the lack of power at low speeds. We see no improvement in this respect over the earlier PII chassis that we complained about, and 202-AJS in this respect seemed quite inferior to what we are turning out now. I say seemed because possibly this is more apparent than real, although all our acceleration tests so far, show very slightly in favor of our PI, yet what I believe makes it so noticeable is that the difference in power at low and high speeds is so very much greater with the increased high speed power of the PII, and as such becomes more noticeable to the driver. We also believe that it is in the power of an expert driver to make this very noticeable to the passengers or imperceptible, according to as he may operate the car. Caswell puts this down to the late closing of the inlet valve, which is about 10° later than we are using, and would be expected to give increased high speed power at the expense of the low speed. He claims that some power is definitely lost between 750 and 1500 revolutions, and it is not in the carburetor since changing the mixture strength does not affect this feature. We are afraid this will bring out the worst criticism we have to face. As regards the steering, we find it very sensitive to maladjustments, when right it is very nice, but if it gets a little bit too free there is a tendency to snatch. We noticed this on a chassis where we got a definite wobble at 65 m.p.h. (5300 lbs. load), but the wheels were out of balance. Even then when the wheels were balanced, the steering was nothing like so smooth as another chassis we tried about the same time. Measurements of steering friction on these two chassis showed that in every respect the friction in the good steering job was just a little bit higher than in the one that was not so good. However, so far we have had only one finished job in which the steering was on the whole excellent, and feel that we cannot reasonably judge steering snatch from results obtained from a chassis, so we should withhold comment on this point. Here we should like to bring up again the question of wheels. In the revised specifications of our contract, it was agreed that the 20" wheels would be replaced by 19" wheels at an early date. Can you give us now any prospect of getting 19" wheels at an early date? I think at this stage we want to go still further and ask for 18" wheels, feeling that this would be in line with other cars in our class at the present time and would, by giving a 10% increase in gear ratio help us very appreciably in getting over this dead spot in the power curve. I give below some tire sizes now being used by various models: Engine Revs. per mile. Cadillac 12 - 7" x 18 2950 Cadillac 16 - 7" x 19 (Sedan 7" x 18") 2760 Chrysler Imperial- 7" x 18 (Sedan 7.50 x 17") 2520 Lincoln - 7" x 19 2951 Marmon 16- 7" x 18 2312 | ||