Regearing Questions (1 Viewer)

[Red Beard]

From other users, it sounds like highway driving improves when 4.88's are put in and running 33's. On stock gears and 30"s, its okay on the highway, but it almost sounds with the 4.88's and 33's it runs better?

 

[Beowulf]

Typically, people install a lower gear ratio (higher numerically) to improve off-the-line performance. Lower gears will give you a little better ratio when going up hills at highway speed but the same thing can be accomplished by turning off OD (on trannys with this feature) or shifting to a lower gear.

When you throw on taller tyres you effectively change the final drive ratio so instead of the optimum 4.10:1 and 30" tyres that Mr T designed for your truck, you now have 3.80:1 (or something). By selecting 4:88 gears and taller tyres, you will get back to an effective 4.30:1 (or something)

Find a wiki on automotive final gear ratios and do some reading.
-B-

 

[Larry Haun]

Totally appropriate gearing for everything from 30" grocery getters, right up to 38" boggers. It's true. 4.88s have actually been determined to be perfect in all ways. Clears dandruff, halts premature muffler bearing failure, eliminates driver fatigue and makes girls in the passenger seat giggle.

Unfortunately for me, I'm still running 4.11 w/ my h151 because I like to be able to use both 1st *AND* 5th and I've only got 31's on there now.

Seriously, though--- stock diffs are 4.11. If you do 4.88/4.11= 1.187, or about a 19% change in gearing.

If you are running 33" tires, that's about a 10% increase over stock size.

So if you want slighly lower gearing than stock--- 4.88 will give it to you. If you want about stock, 4.56 will give it to you. If you want to run 35" tires with "like stock" gearing, then 4.88 also works.
Then do similar math for other

Man you sound like you know what you’re talking about so I’m going to ask you this. I have a stock 1997 FJ80 and I am about to put a 2”OME lift on it, primarily for looks (don’t hate me). I’m not an off-road guy- I use 4-wheel drive out of necessity when I go hunting, but that’s it. The rest of the time I’m on pavement (it’s my everyday driver). I’m wanting to put 315/75R16 tires on the stock wheels and somebody told me I need to regear it or I’ll have issues with that size tire. Is that true? Can you confirm the stock gearing ratio for the 80? I basically want it to drive as stock as possible and I don’t want to have to spend an extra $1500 to regear it after the lift and tires. Thanks in advance for any insight you can give me.

 

[Letsgomoreplaces]

Man you sound like you know what you’re talking about so I’m going to ask you this. I have a stock 1997 FJ80 and I am about to put a 2”OME lift on it, primarily for looks (don’t hate me). I’m not an off-road guy- I use 4-wheel drive out of necessity when I go hunting, but that’s it. The rest of the time I’m on pavement (it’s my everyday driver). I’m wanting to put 315/75R16 tires on the stock wheels and somebody told me I need to regear it or I’ll have issues with that size tire. Is that true? Can you confirm the stock gearing ratio for the 80? I basically want it to drive as stock as possible and I don’t want to have to spend an extra $1500 to regear it after the lift and tires. Thanks in advance for any insight you can give me.

Your factory gearing is 4.10. with 315's 4.88 is most ideal. Some go lower (5.29) if the truck is really heavy or not a ton of highway. With 4.10 and 315's the RPM's will be low enough that OD is no longer useful and MPG, drivability and off the line performance suffer quite a bit.

 

[Railwelder93]

@Larry Haun
4.88s make a big difference.

If your not sure on regearing but you are sure about fitting 315s, then just put tires on first and see what you think.

 

[Road Apple]

There is also the option of installing high range 10% under-drive gears in the transfer case. This will give you the equivalent of 4.56 differential gearing. Just right for 33” tires. Many people also install low range 25% gear reduction in the transfer case at the same time, for more control off road. Transfer case gears are easier to install than diff gears.

Here’s a video explaining the install.