04-04-2020, 04:02 AM
(This post was last modified: 04-04-2020, 04:06 AM by Bob Culver.)
Intuitively, with the rear wheels acting as anchor, it is hard to figure why 2WB cars are neverthelss prone to spin. (A locked wheel is just a rectangle of lubricated rubber with little or no directional preference so is free to go sideways.) Many quite expensive cars had relativley primitive cable and pulley systems little better than the Seven (Riley, Bugatti). He mentions but not very clearly many cars including Model A, Ford Y, had a pushrod through the centre of the kingpin.
On the occasional narrow unsealed winding road with blind corners as common in the 1920s, can get a mighty surpise in a "modern". I have encountered cattle in the roadway, stationary trucks, but worst of all is the city type in a 4WD. With 2WB there must have been many exciting moments. Perhaps it is why so many cars ended in ditches. it was a requirement here to sound the horn.
Comparison is easier if expressed as % of 1G stop, about the limit for older tyres on smooth surface. 1G is 32 ft per sec per sec.
decel=speed squared /2xdistance in feet. 30 mph is 44 fps. Hence the limit around 31ft from 30 mph. Until very recently 50% was considered reasonable, and any better dangerous for buses!! It is the legal requirement for laden 40/50 ton outfits which tailgate cars. The Seven road tests acheived a wide range, but the pre girling often less than 50%. The Girling 70% and better. The 21ft from 30mph is an error unless on a surface like a gear cog.
On the occasional narrow unsealed winding road with blind corners as common in the 1920s, can get a mighty surpise in a "modern". I have encountered cattle in the roadway, stationary trucks, but worst of all is the city type in a 4WD. With 2WB there must have been many exciting moments. Perhaps it is why so many cars ended in ditches. it was a requirement here to sound the horn.
Comparison is easier if expressed as % of 1G stop, about the limit for older tyres on smooth surface. 1G is 32 ft per sec per sec.
decel=speed squared /2xdistance in feet. 30 mph is 44 fps. Hence the limit around 31ft from 30 mph. Until very recently 50% was considered reasonable, and any better dangerous for buses!! It is the legal requirement for laden 40/50 ton outfits which tailgate cars. The Seven road tests acheived a wide range, but the pre girling often less than 50%. The Girling 70% and better. The 21ft from 30mph is an error unless on a surface like a gear cog.