Driving Lessons in the Derby Area
with a Professional Derby Driving Instructor
Gears explained
On this see-saw, a person (called effort) sitting on the long end of the see-saw could raise a heavier person sitting on the short end of the see-saw a short distance.
On this see-saw, the same person (effort) is now sitting on the short end of the see-saw. He can't raise a heavy person at all, but can raise a light person a long distance.
Gears work on the same principle, but they are in the form of round cogs, so instead of just raising a load a certain distance, they keep turning.
A low gear can quite easily move your heavy car, but like the see-saw above that can only move the heavy load a short way, a low gear doesn't move the car very much - but as the cogs are round the car can keep going. That means that a low gear can easily move a car, but only at low speeds.
A high gear wouldn't be able to move the car at all unless the car was lighter, so we have to use the low gears to get the car moving until it's easy for the high gears to take over, then the car can be driven at high speeds. (The see-saw above can move the light load a long way using the same effort that only just manages to move a heavy load a short way).
When to change up through the gears

The diagrams above show the approximate gear ranges of an average car.

The blue diagram shows a driver starting off in 1st gear, then progressively changing to the higher gears at an early opportunity until reaching a speed of 70mph. This driving style doesn't give great acceleration, but is very good for saving fuel.

The red diagram shows a driver starting off in 1st gear, then accelerating hard until he has no choice but to change up. He accelerates to 70mph in 3rd gear, and as he cannot go any faster without breaking the speed limit changes directly to 5th gear to cruise along. This driving style gives rapid acceleration but uses lots of fuel and wears the engine.

Cars have quite a flexible gear range, and when to change up depends entirely on what demands are placed on your car at the time - are you comfortable to 'potter along', or do you need a lot of speed in a hurry? Changing up into a gear before you are in it's range will result in the car labouring (struggling) and possibly stalling. (For example, this would happen if an attempt was made to change into 4th gear at 15mph).

 

Peter Jackson Dip.DI

www.peterjackson.org.uk