Easier/quicker gear changes

[Bob Culver]

Those with just a casual interest in all this may be interested to note that the 4.9 cars in 2nd pull about the same rpm as the 5.25 cars in 3rd of the synchro boxes. The latter corresponds to 50 mph in top which many owners of ordinary cars may consider a resonable sustained maximum. 
The 4 speed crash box is considerably lower geared in 3rd.

[austin]

I wonder how much extra power you need to squeeze out of an RP saloon to get it to go at 75mph? I can get mine to run up to 55mph (on the speedo) on the flat on a good day but anything faster than that I think I'd bottle it - it sounds like it's in imminent risk of self destruction which usually makes me back off. Engine is standard apart from 37 head and 1 1/8th SU. Wind resistance must be a huge limiting factor, as it's as aerodynamic as a house brick.

Quite a bit!

My father used to race his with a Shorrock supercharger attached, went rather well...

[Bob Culver]

Hi RR

At higher speeds power is vaguely related to the cube of speed, so would need an engine of some 50 bhp, about what larger cross section, heavier, but more streamlined cars required for this top speed.

[Colin Morgan]

If the air resistance goes up with the square of the speed, the air resistance would increase by 1.9 times from 55mph to 75mph, and if rolling resistance (tyre and frictional power consumption etc) increase is linear, then the total power required at 75mph would be 2.5 times that at 55mph. However, the Wikipedia article on rolling resistance says: "Rolling resistance greatly increases with applied torque. At high torques, which apply a tangential force to the road of about half the weight of the vehicle, the rolling resistance may triple (a 200% increase). This is in part due to a slip of about 5%. The rolling resistance increase with applied torque is not linear, but increases at a faster rate as the torque becomes higher." Therefore, a power of more than 2.5 times might be required to reach 75mph?

Colin