Thanks for all the replies.

So if a sum this up and understand correctly (and I could be way off base) - if I want to cruise comfortable at say 120km/h in final gear (5th), I need to be as close to the optimum torque curve (in the case of the Lexus around 4,000rpm) as possible. There are three main areas to adjust to adjust the rpm - diff ratio's/transfer case gear ratio/tire size.

With my current setup (using the gearing as per Jelo's post) of 1.41 TC, 3.54 diffs, 265/75/16 tire size (80cm or 31.5inch diameter), I would be somewhere around 2,900 rpm at 120km/h.

Given that the smallest gains to be made are in tire size, I will keep tire size constant for purposes of analysis.

- If I change only the diff ratio to 4.7 as has been suggested, the RPM will be very close to spot on at 3,973 [email protected]/h.
- If I had to change only the Transfer Case (as has also been suggested) from 1.4 to 1.2, RPM will be 2,570 [email protected]/h which is lower than it is with my current setup, so I don't believe this is feasible.
- If I changed the diff ratio to 4.7 AND the transfer case to 1.2, RPM will be at 3,412 [email protected]/hr

So it seems to me that my best possible setup is only to change the diffs to 4.7.

I'm assuming weight of vehicle shouldn't be considered in this equation as regardless of the weight, you want to be at your "sweet spot" in the RPM range which, in my case, is 4,000RPM?

Am I on the right track here?

So my big problem seems to be sourcing the correct diffs - I'm struggling to find the 4.7's either online or anywhere in my area (East London)...

## Bookmarks