Hey guys! For my first thread I just wanted to share some resources I've found super helpful in researching this "What gear ratio should I run for X setup?" topic.
There's a few variables to be considered here:
- Whats your differential's gear ratio?
- What tire size will you be running?
- ...and of course, How do you plan on using the vehicle? A driver who has a vehicle that sees mostly freeway miles is most likely going to want a very different final drive ratio than someone with a dedicated crawler.
These are (what i understand to be) the basics of answering "What gears should I run", so we won't be getting into things like double T cases or crawl boxes.
Let's take a
255/85r16 (33.1") tires on an automatic 3rd gen T4R with 4.10 gears...
Using the link from the first bullet, we can fill in the information on a gear ratio calculator to find out what driving this vehicle could be like by visiting a gear ratio calculator like this one =>
Gear Ratio Calculator
In the
first attachment you can see that at
70mph the engine will be running at about 2054rpm. At this rate, any slight elevation or need to accelerate will most likely downshift or bog if it doesn't. It also implies that although it's comfortable at 70mph on flat ground, it probably took quite a bit longer to get there as
this gearing loses a lot of torque.
Now let's take that
same T4R and regear it to 5.29. You can see the results in the
second attachment. Notice that at
70mph the engine will be running at 2651rpm. At this rate, you should have
more available torque for climbing hills and passing without downshifting as much. A drawback here is that 2651rpm is quite a bit
noisier than 2054rpm, which could get annoying on longer highway drives. It also implies that although relatively high revving on the freeway,
it will have an easier time accelerating and hauling heavy loads like armor, steel bumpers, gear, or towing. You also have the
option of bumping up your tires to 35's which will again trade off some torque but bring the cruising revs down.
This time, lets
regear the same T4R to 4.88. These results are in the
3rd attachment. At
70mph the engine is at 2445.5rpm.
Finally, lets check out the
same T4R with 4.56. These results are in the
4th attachment. At
70mph the engine is at 2285.4rpm.
TL;DR- IMHO, for this 3rd gen auto 4Runner on 33.1" tires, 4.88 seems like the happy medium in terms of available torque and cruising rpm.
- If you mostly drive big elevation changes, offroad, and/or want the option to eventually get 35's, you might lean more towards 5.29
- If you mostly do long highway drives and/or don't ever plan on going to 35's, you may be happier with 4.56.