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).
Analysis of the effects of increasing caster angle on vehicle handling, understeer, and cornering power.
| Identifier | ExFiles\Box 98\3\ scan0076 | |
| Date | 3rd February 1939 | |
| GRY{Shadwell Grylls} - Any comments Rm{William Robotham - Chief Engineer} To Rm.{William Robotham - Chief Engineer}.. from Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions} c. By.{R.W. Bailey - Chief Engineer} Da.{Bernard Day - Chassis Design} Rm{William Robotham - Chief Engineer}/AFM.{Anthony F. Martindale} c. Rm{William Robotham - Chief Engineer}/FJH.{Fred J. Hardy - Chief Dev. Engineer} Ev.{Ivan Evernden - coachwork} Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions}26/N.3.2.39. Increased Caster Angle Without Increased Caster Offset, B.V. /406 With regard to Rm{William Robotham - Chief Engineer}/AFM.{Anthony F. Martindale}5/MH.{M. Huckerby}23.1.39, in which it was stated that Rm.{William Robotham - Chief Engineer} wished to try the effect of increased caster angle without increased caster offset, this would imply the handing of two major components, the pivot forgings and the brake carrier plates, and before being committed to this, I thought it would be a good thing to investigate the effect of this increased caster angle. The advantage claimed for it was the reduced outward lean of the front wheels on corners and hence the improved cornering power of those wheels. In order to decide accurately the importance of this effect, the front and rear slip angles and hence the under or oversteer were calculated by a method described by Olley, but with slight modifications to allow for our front roll centre being above the ground. The resulting curves are plotted in Fig.1. together with some actually obtained on our skid pan for the same conditions and it will be seen that the agreement is very close indeed. The final breakaway, front or rear, depends on a number of factors not allowed for in the calculation, such as rubber buffers, etc. The effect of giving 6° caster, instead of 3° on the inclination of the front wheels during cornering, is shown in Fig.2. the angles shown being such that an outward angle means that the top of the wheel is further from the car centre line, than the bottom. Outward inclination of the outer wheel in relation to the car is also outward in relation to the corner, but on the inside wheel outward inclination in relation the car is inward in relation to the corner; this should be borne in mind in studying Fig.2. In Fig.3. is shown the effect on the basic understeer curve of this 6° caster. The first case considered is with the 5° lock angle ( corresponding to approx. 120 ft. radius curve) and it will be seen that the effect is small but reduces the understeer tendency. Cont'd..... | ||