When I am driving on smooth straight road at say 100 km/hr and I realize I want to stop at say 1 km ahead (assume that there is no other vehicle ahead or behind). I can continue at same speed or little less speed, and later apply break when I want to stop. But that means I waste some fuel.
To avoid that, when I realize that I want to stop 1 km ahead, I can take off my foot from accelerator, and
1. Fully press the clutch. As speed decreases, car will gradually stop (and I may apply break to bring is to complete rest at right spot). Change gear from top to neutral position after complete stop.
In this case, if car looses speed too early, when speed need to be increased, put gear in appropriate level and release clutch, apply accelerator to gain speed, and then again fully press clutch to repeat the process.
2. Fully press the clutch, and as the speed decreases, keep lowering gears. Finally change gear to neutral position after complete stop. In this case, although I have to keep lowering the gears, if need arises to increase speed, I am already in right gear.
3. Fully press the clutch and move to neutral gear and fully release the clutch. As speed decreases, car will gradually stop.
In this case, if car looses speed too early, when speed need to be increased, press the clutch, put gear in appropriate level and release clutch, apply accelerator to gain some speed, and then repeat the process
4. Press clutch, move to lover gear, release clutch and repeat these steps as speed decreased. Finally change gear to neutral position after complete stop. In this case, car is likely to stop sooner, since car in lower gear will have effect of breaking.
Now, if idea is to save fuel (by lifting foot off accelerator 1 km before stop), how these effect the car (wear & tear of clutch, gears)?
Options 1 and 2 are almost same, only difference is convenience of increasing speed if required. So I guess, comparison is of first two with third & fourth. (In 4th option, since gears help in breaking, they have wear and tear, and I therefore would rather avoid this option.)
And secondly, how exactly ‘riding with clutch’ (foot on clutch but clutch not pressed while at high speed) damage the clutch?