Originally Posted by JOHN BULL
Correction - On the contrary, SPEED is TOTALLY relevant to GEAR change.
The object of having an engine and gearbox is to transfer the variable load and rpm provided by the power source via a set of gears to achieve Speed in the case of power driven vehicles. Engine load and rpm are completely independent of gearing. THAT is dependent on fuel supply regulated by the throttle control and the force or load exerted by the resistance.
The engine is the INPUT and SPEED is the output. No SPEED, No movement.
I used SPEED and GEARS as layman`s terms for a simple discussion so as to keep precise mechanics out of it. Everybody understands Speed and Gears, everybody does NOT understand the principles of applied engineering mechanics. I am extremely conversant with the relationship between torque, gear ratio, rpm and resulting speed. e.g :-
A transmission or gearbox provides speed and torque conversions from a rotating power source to another device by using gear ratios. Gears are the rotary equivalent of linear leverage.
The energy path is that you utilise a power source to provide the torque needed to overcome a variable resistance through a set of gear ratio`s - speed is a final by-product of this. Crudely, high resistance = low speed, low resistance = high speed and in comes the gearbox.
Please everybody, I do not wish the topic to be diverted to a lecture on Isaac Newton`s wonderful theories.
Are you even listing to what you are saying?
You are telling me you would shift from 1st to 2nd at say 20mph if you 1st gear ratio was 2.5:1 and the same if it was 15:1? the first ratio would be running at 3000rpm, the second would something like 15,000 rpm. Are you still telling me speed is the deciding factor to change gear?
Suppose you are sat in traffic and of course speed is the only factor for which you must shift grears, so you can only shift from 1st to 2nd and say 50mph? no? so would you shift at 10mph? most likely yes. Then suppose you are racing someone off the lights? I guess you would shift up at 10mph too right?
Engine load and rpm decide at what point to shift gears.