100 series Diff gear/change

If your only looking for a small change, larger tires will do the same thing and will be a lot cheaper.
Cheers Dave...

I understand what you are trying to achieve, but If you get the revs below 2400 you are starting to drop out of the torque band (i assume it's a 1HZ) and may end up using more fuel. Also the higher speed will cause you to use more fuel anyway, because of wind resistance.
Cheers
Dave

G/day,Gdad.I have an 80s with 285/75/16 ATs, I don`t save much fuel but I do get excellent wear from the bigger tyres,110,000 from the last set, and looking about the same for these.I have found the need to change to a lower gear uphills,eg., 4th instead of 5th, but it is much better at cruising speed.I think it may also make it easier on the car,less rpm, it didn`t make much difference to the speedo,maybe try tyres before changing the diff.

Regards Keith C

If you have a naturally aspirated 1HZ then I believe you will use more fuel with the bigger diffs and cost will be quite high for what you are trying to achieve.

You would be better going to 85 profile tyres in a wider tyre but I still believe you will have no gain in fuel consumption.

My old girl has a 6.5l chev diesel in her and I still have the original diff ratios, when climbing and descending steep terrain I find the low gearing great, even with all the torque she has at idle,it is nice to apply a little hand throttle and let the old dear have her head up steep inclines.