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).
Comparison of steering and ride characteristics using Dunlop 6.75' and Michelin 6.2' tyres at various pressures.
| Identifier | WestWitteringFiles\P\2July1926-September1926\ Scan188 | |
| Date | 1st September 1926 guessed | |
| contd :- -3- (a) 6.75" traction tread 'Dunlop'. These tyres at 35 lbs/sq.in. with 5 - 6 lbs. friction in the ball ends, and 1500 lbs. springs in standard side steering tube, give quite satisfactory steering if accurately balanced with front shock dampers at 40 and 80 lbs. The badly worn examples we have shew no signs of wobbling under these conditions, though small joggles are transmitted to the wheel at high speeds. These joggles are less than we have experienced on a standard axle low geared steering with high pressure tyres. The tyre pressures should not be less than 35 lbs/sq.in. in front, or the steering is liable to be spoilt. 40 lbs/sq.in. would provide a factor of safety and does not spoil the riding. Pressures should be measured in the garage as they increase 3 - 4 lbs/sq.in. on the road in hot weather. General feeling of the steering is solid, and gives confidence. Absence of rattles, and suspension on bad roads (rear 35 lbs/sq.in.) very good. Steering is reasonably light under these conditions for shunting and town work. (b) 6.2" Michelin. These tyres have not quite the riding attributes of the 6.75" and are slightly more susceptible to wobbles and shocks. Nevertheless, if run at 40 lbs/sq.in. and accurately balanced, on the front, they give a good steering, and much better riding (rear 35 lbs/sq.in.) than the standard high pressure tyres. We have no badly worn examples, but do not anticipate high speed wobbles from their general behaviour. Accurate balancing is an absolute necessity. contd :- | ||