Differential question

[Sluttypatton]

Here's my question, I understand gear ratios, differentials and why it is nescessary to have both. But, why have a gear reduction in the differential (rather than 1:1) when this could be accomplished by adjusting the transmissions gearing to compensate. The only reason I can think of, being the need to keep a transmission more compact, and doing so by inserting a gear reduction that will effect all gears so the gearing in the transmission need not be as severe (and space consuming). Opinions? Again, I understand how all this works, I am only asking why we need a reduction in the diff.

[texan]

That, plus the ability to quickly change overall gearing by replacing one ring and pinion. Gearing, ideally, should be optimized for each individual application, and it'd be very expensive to generate that many different gearsets for a transmission.

[FYRHWK1]

Size as well, having the overall ratio for 1st gear solely inside the transmission would increase the size of the unit, plus since you need a rear differential, why not make use of it?

[SaabJohan]

Also, if the gear ratio in the differential was 1:1, the torque transfer from the gearbox must be higher since the same power should be transfered (and the driveshaft will now rotate slower). Because of this the gearbox and drive shaft must be made stronger and therefore heavier and bigger.