Need advice on tire size and regear

Should I regear?

  • Keep 285/70/17 tires and run stock gears

    Votes: 5 100.0%
  • Regear to 4.88s and keep 285/70/17s

    Votes: 0 0.0%

  • Total voters
    5
Joined
Oct 12, 2019
Messages
184
Location
Atlanta, GA
A couple questions upfront: how much does weight affect the decision to regear to 4.88s? If I do regear on my current tire size 285/70/17 will I be able to drive 80-85 mph on the highway?

Since Ive been doing quite a bit of wheeling Ive developed a need and desire to at least add rear locker. I've decided to go with an ARB air locker and I'll be sending my diff(s) out to ECGS to do the locker install. In my quote from ECGS they are going to put in and setup new ring and pinion gears. So there is no additional cost to go to 4.88 gears. Of course the next logical question after choosing elocker or air locker is the question of whether or not to regear. I'm leaning to just biting the bullet and sending in both diffs which really puts pressure on me to make a decision as to what I want to do, go 4.88s or keep the stock 4.30s.

Heres some info on my truck: 99 LX470, rear LSD and 4 speed trans, 4.30 stock gear ratio. Current tires are Nitto Ridge Grapplers in 285/70/17, so I think thats a 32.8" tire, on 17" Icon wheels with 25mm offset. Stock AHC suspension. I'm carrying quite a bit of extra weight in the form of front bumper with winch, rear bumper with dual swingouts, skids, sliders and roof rack.

In terms of the use of the truck, its not a daily driver, but it does see a bit of use on road trips so highway driving usually around 80-85 mph. I have not paid enough attention to the rpms when at that speed but I do not that my speedo is 5 mph lower than actual speed. Offroad I'm not a fan of rock gardens, I'd prefer mud. The truck is built more for overlanding so I dont think I need 35s but as I'm doing more upgrades like the lockers I dont want to be limited by tire size.

I've done quite a bit of searching and reading various post, not only in the 100 forum but the 200 and 80 forum as well and from what I can tell if you have 35s definitely do the 4.88s. Where it gets kinda muddy is if you're not running 35s. I've seen people say regear with 33s and the 4 speed. Does it matter than I dont have true 33s? Should I still regear? If I do what rpm will I be seeing at 80mph with the 4 speed trans?

I just brought the 285/70/17 Ridge Grapplers so I dont want to get new tires but if I were to go bigger what size should I get on the 17" wheels? Can I go 35x12.50x17 with the 25mm offset Icons? Or do I need to do like a 315/70/17?

I apologize for the long post, feel like I'm kinda rumbling but I'm on the cusp if dropping a good bit of coin and want to make sure I'm making a good decision.
 

GTV

Joined
Jan 31, 2019
Messages
1,581
Location
Where Crosstreks aren’t
The decision whether or not to regear is totally subjective, it depends on how you use the vehicle and what you want/need it to do. Some will say it isn’t necessary and others will swear you must do it. If you feel like you’re lacking power now then it is something you should definitely consider.

4.88’s will correct your gearing when going to 35’s- it puts things right back to where the factory gearing was. 4.88’s on 33’s will make for more agressive gearing than factory. There are plenty of gearing calculators online that will show what happens when you make changes, find one and play around with it so you can understand what happens when you make a change. Then you can decide what makes sense for how you use the vehicle.
 

suprarx7nut

YotaMD | ADGU
Supporting Vendor
Joined
Sep 28, 2010
Messages
4,947
Location
Colorado
Website
www.YotaMD.com
Personally, I view a re-gear as means to get back to near-stock speed/RPMs. Doing 4k RPM and going 70 mph on a cross country road-trip would get old real quick.

If the break point is 35's as @GTV suggests and you're rocking 33.X tires, then I'd embrace the slow roll and stick with factory gearing.
 
Joined
Oct 18, 2020
Messages
147
Location
Vancouver
I'm one of the guys running 35x12.5 with stock 4.30 gears. It's slow but that doesn't bother me most of the time.
4.88 with 33s would be turning a lot of rpm on the highway, especially with the 4spd.
35s aren't plug and play but +25 offset is totally workable.
 
Joined
Oct 12, 2019
Messages
184
Location
Atlanta, GA
The decision whether or not to regear is totally subjective, it depends on how you use the vehicle and what you want/need it to do. Some will say it isn’t necessary and others will swear you must do it. If you feel like you’re lacking power now then it is something you should definitely consider.

4.88’s will correct your gearing when going to 35’s- it puts things right back to where the factory gearing was. 4.88’s on 33’s will make for more agressive gearing than factory. There are plenty of gearing calculators online that will show what happens when you make changes, find one and play around with it so you can understand what happens when you make a change. Then you can decide what makes sense for how you use the vehicle.

Yeah I agree that its subjective which I'm not a fan of. I love when things are more clear cut. The thing with vehicle use is that I do love offroading, not hardcore but you know decent trails and I find myself doing more and more of it. For right now I dont think that tire size and gearing on the trail is a problem BUT it could just be my inexperience as this is my first offroading/4x4 vehicle. As I continue to get experience, to get braver on what I'm willing to do that very well may change. I guess at that point I'll regear? I think what I'm doing is trying to future proof the truck. I hate investing time and money into something only to turn around later and say man I should have did went 4.88s when I did the lockers.
 

a_traut_man

SILVER Star
Joined
Feb 28, 2016
Messages
560
Location
Austin, TX
I've been running a tire slightly larger than 285 75 r17 for about 110k miles on the stock gearing without any complaints. I usually make the "well I'm in there anyway might as well" call for most things but on gearing I don't think you need it if that is all the tire you are going to run. Sure acceleration isn't as snappy as it was before (if you can call it that) but I also don't mind going a bit slower.
I thought through the same thing when I went e-locker front and rear a few months back and stuck with stock gearing... but I also didn't think I would make the jump to 35s (but now a set is sitting in my garage).
 
Joined
Oct 18, 2020
Messages
147
Location
Vancouver
You could always do the transfer case gearing later if you feel you need more umph, and no need to open up both the pumpkins again
 
Joined
Oct 12, 2019
Messages
184
Location
Atlanta, GA
I've been running a tire slightly larger than 285 75 r17 for about 110k miles on the stock gearing without any complaints. I usually make the "well I'm in there anyway might as well" call for most things but on gearing I don't think you need it if that is all the tire you are going to run. Sure acceleration isn't as snappy as it was before (if you can call it that) but I also don't mind going a bit slower.
I thought through the same thing when I went e-locker front and rear a few months back and stuck with stock gearing... but I also didn't think I would make the jump to 35s (but now a set is sitting in my garage).

What size tire are you running?

In hindsight I think I should have gotten the 285/75/17s
 

hoser

SILVER Star
Joined
Dec 21, 2003
Messages
10,651
Location
Bay Area, CA
For 33's, I'd just stay with stock gearing. I ran that 32.x"/4.88/4sp combo for a short time and I didn't like it at 80+ mph but
@trdcorolla did just do that same combo and is down in SoCal where everyone drives 85 mph (when traffic permits) and he said he is happy with it.

*You could actually run 4.56 ratio if you really wanted to (80 series). Rear requires some extra parts. The front R&P is a drop in. I've been running the 80 series rear R&P for over 15 years w/o issue. Reason, there were no 100 series gears back then. (Only OE 4.3, 4.1 and 3.9)

The t-case gears is also a good suggestion... but only if you are in there for another reason. Otherwise, cost is high.

Take a look at the chart... if you are cruising along at 2800 rpm now, it'll jump almost 400 rpm to 3186 rpm.
4.88/4.3= 13.5% increase. So, your rpm will be 13.5% higher across the board.

Screen Shot 2022-11-21 at 9.00.29 AM.png

 
Joined
Oct 12, 2019
Messages
184
Location
Atlanta, GA
For 33's, I'd just stay with stock gearing. I ran that 32.x"/4.88/4sp combo for a short time and I didn't like it at 80+ mph but
@trdcorolla did just do that same combo and is down in SoCal where everyone drives 85 mph (when traffic permits) and he said he is happy with it.

*You could actually run 4.56 ratio if you really wanted to (80 series). Rear requires some extra parts. The front R&P is a drop in. I've been running the 80 series rear R&P for over 15 years w/o issue. Reason, there were no 100 series gears back then. (Only OE 4.3, 4.1 and 3.9)

The t-case gears is also a good suggestion... but only if you are in there for another reason. Otherwise, cost is high.

Take a look at the chart... if you are cruising along at 2800 rpm now, it'll jump almost 400 rpm to 3186 rpm.
4.88/4.3= 13.5% increase. So, your rpm will be 13.5% higher across the board.

View attachment 3174306

Thanks. Whats the downside of running say 315/70/17s with the stock 4.30s? Just that its slow off the line? Also is it true that just because the engine is at a higher rpm that its actually working less?

I know the t-case gears are an option but there is the risk of some whine from what I've read in some previous posts, not a fan of that.
 

hoser

SILVER Star
Joined
Dec 21, 2003
Messages
10,651
Location
Bay Area, CA
Yes, 315/70R17 will be slower off the line. Transmission will be fine as long as you aren't towing heavy trailers, all the time. The 2UZ-FE engine has a broad power band and will be happy with any of your proposed combinations. If you were really wanted to reduce the workload, you wouldn't drive so fast. ;) Wind resistance is a greater factor.

Stock for stock, the 5sp get slightly better fuel mileage than the 4sp as their final gearing is slightly higher (numerically lower) 3.24 vs 2.94:1
new_gear_chart.jpg
 

Users who are viewing this thread

Top Bottom