[300SLR]

If the excess shaft is fouling something then that has to be fixed (either by cutting off the shaft or removing the something its fouling.)

If the motor is ever going to be reused with a pinion on the other end, enough shaft has to be left that end.

If the motor is going to be stripped an rebuilt there are sometimes practical considerations to what shaft length is convenient (Probably not applicable as you seem to be talking about the sorts of motor that aren't usually stripped an rebuilt.)

There's a slight weight saving by cutting off the unused shaft (how much does that matter?)

If none of those are an issue it cannot matter much if the shaft is left full length or shortened.

 

[300SLR]

Hollow axles will give a small weight saving.
A weight saving can also be achieved by using smaller diameter axles. (These can also reduce bearing friction.)
For example with a 55mm long axle, there's a saving of about 1 gram going from 3mm down to 3/32" diameter.

Do that at both ends and you've reduced the mass by 2 grams - around 3% off a 70gm car. Not a major differance but for those who are convinced weight savings help it might be worthwhile.

Independently rotating fronts can change the chassis performance on some cars, and make absolutely no difference on others. If there is a differance independent is usually better and the advantage is mostly pretty small.
If you are just adding independent fronts to a solid front axle, the change in weight will be insignificant. (If you scratch build parts of the car that's another question)

QUOTE (rick1776 @ 28 Jan 2012, 22:35) <{POST_SNAPBACK}>You would be hard pressed saving 0.1g in weight. Probably closer to 0.05g. The weight you are taking off would have an absolute minimal impact on reducing rotational inertia. I did some calculations once on the benefit of using hollow 3/32 axles. Assuming that the weigth saving was 1g you could achieve the same reduction in rotational inertia by removing 0.001g off the tyre. There are better ways of achieving a performance gain.

cheers
rick1776
I agree the saving is very small, but the numbers don't quite stack up.
Saving 0.1g from the weight of a normal (2mm) motor shaft means shortening it by just under 5mm, so rather more than that would be saved by removing the unused shaft.
The reduction in rotational inertia is indeed small, but in a moving car the linear inertia has to be considered as well.