others who drive my 126 tend to change down to first gear towards junctions and get a bit of a crunch.
I'm glad your friends don't drive *my* car !!! And if they change down into first whilst moving, don't worry, you're not the only one who doesn't understand gearboxes !!
I don't know whether or not your particular gearbox has synchromesh on first gear, many early synchro boxes only had it on the upper "driving" gears - reason being that for most cars first is far too low a gear for anything but starting from rest - but your view of first as a "starting off" gear is entirely correct.
Modern full syncho boxes *can* be moved into first on the move, but any experienced driver will shudder as much the gearbox at the very thought of it
If you look at the physics of gearboxes, changing from one moving gear, say 3rd, to another, say 4th, involves changing the gear ratio for driving at one speed - say 30mph - to another. Say, 40 mph. In physics terms, the moving body (the car) has to accelerate from one finite velocity to another, in this case by just over 30%. In crude terms (ignoring all sorts of practical issues like friction, air resistance etc) this means the engine has to transmit an extra 30% of its energy thought the gearbox.
However, when starting from rest, the initial velocity of the body is zero. To go from zero mph to even 0.5mph takes a HUGE amount of energy - in theoretical physics/maths terms, the initial change from zero veleocity to the tiniest non-zero velocity takes an infinite anount of energy. Now obviously the fuel tank isn't *that* big, and even if it were the carburettor would in theory have to deliver an infinite amount of fuel in zero time to provide enough energy to get the car to move at all.
Fortunately, in the real world these theoretical limits are not met, but even so the principle still applies - to accelerate the vehicle from rest to moving takes a huge amount of effort, even though it's only for a first tiny fraction of a second. So how is this achieved?
The answer is by setting up the engineering to deliver all that energy as quickly as possible. So, the engine spins at a high rate and delivers power through a slipping clutch. The carburettor delivers higher than usual amounts of fuel through extra jets and by-pass tubes etc, and the gearbox transmits the power through the lowest gear that is practiacable.
So you are very much correct that first is a starting off gear. Never in my nearly 50 years of driving have I ever encountered it being used for engine braking, and I am astonished that anyone would ever think of it like that. Is that what they teach at driving school these days?
Please, don't EVER let anyone drive your car if they use first as a braking gear !!
