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Re-gearing on 31" with eye on 33"?

10K views 37 replies 18 participants last post by  mikey 
#1 ·
I've started looking at upgrading my suspension beyond stock.

As my FJ is my daily driver (and I take a lot of highway road trips), I do not expect to go nuts with off-road-specific suspension - 35" tires would probably be pushing it; there is no long-travel in the foreseeable future; a 6" lift will not be happening, etc.

Reading about 33" and 35" tires, the subject of re-gearing comes up. I understand that I will certainly "want" to re-gear if I put 35" tires on.

Other places on the internet suggest a 4.65 (rather than 4.88) ratio for 33"s as a compromise between recouping power and higher RPMs.

My questions are:

  1. Will I suffer adverse mechanical side-effects or damage anything if I re-gear to 4.65 while I still have 31" tires?
  2. My FJ feels a bit sluggish on-road and up steep inclines as-is. In your opinions, will I feel a power boost that justifies the price of re-gearing if I re-gear to 4.65 while I still have 31" tires?
  3. In your opinions, will re-gearing to 4.65 be sufficient for 33" tires? (Internet says "yes," just want to double-check).
  4. If you believe I should skip 4.65 and go straight to 4.88, please answer question #1 for 4.88.

Thanks in advance!
 
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#2 · (Edited)
IMO no need to regear for 33's. It's 4.56 BTW. Regearing for 35's is still based on your preference. Most people with 35's don't. I would think your MPG will drop a fair amount on the 31's if you regear. (running higher RPM's)

My FJ still feels fast on 34's and alot of additional weight, it's all user preference. :)

Edit: Just use more skinny pedal. :grin
 
#3 ·
Reading about 33" and 35" tires, the subject of re-gearing comes up. I understand that I will certainly "want" to re-gear if I put 35" tires on.

Other places on the internet suggest a 4.65 (rather than 4.88) ratio for 33"s as a compromise between recouping power and higher RPMs.

My questions are:

  1. Will I suffer adverse mechanical side-effects or damage anything if I re-gear to 4.65 while I still have 31" tires?
  2. My FJ feels a bit sluggish on-road and up steep inclines as-is. In your opinions, will I feel a power boost that justifies the price of re-gearing if I re-gear to 4.65 while I still have 31" tires?
  3. In your opinions, will re-gearing to 4.65 be sufficient for 33" tires? (Internet says "yes," just want to double-check).
  4. If you believe I should skip 4.65 and go straight to 4.88, please answer question #1 for 4.88.

Thanks in advance!
Up here in Colorado, at elevation so we're losing ~20% of our horsepower over your truck breathing at close to sea level, I've never even heard of a truck on 33's regearing. 35's, yeah regear. But 33's? Nobody does it, and with all due respect our hills are a bit steeper than yours in Texas :)

What year is your truck, how many miles? You should figure out if the sluggishness is something else -- needs new spark plugs etc -- or if it's just the nature of driving a brick at highway speeds. In flat / level down where you live our trucks aren't great highway vehicles anyway. If your truck feels sluggish just with 31's it's either "there's another big problem here" or "that's just how our trucks drive, get used to it". Assume the first one until you prove that's not the case. Go to an FJ meet and have another FJ owner ride with you, or even better, let them drive your truck. My '99 Wrangler had no power but I just thought "it's a Wrangler" until my brother drove it, said something was wrong and we found out the catalytic converter had rusted almost shut.

If your truck is an '07-'09, it was designed to run on premium gas. If you aren't putting premium in it, it's detuning (costing you ~20-30 HP) to keep from knocking. If your truck is a '10+ the stock HP/Torque specs are for regular gas but it can take advantage of premium gas, another 20-30 HP over stock. But again, most of those HP gains are at the top of our RPM range where our trucks don't typically live anyway.

To answer your specific questions: no, regearing for such small tires won't hurt anything, but it will limit your top speed. How much? One of the more technical guys can speak to that. Will regearing give you enough of a power gain feeling to justify the cost? No, because you've got some other problem that isn't being addressed, or the problem is how you think the truck should drive. The only improvement that you can do where you'll feel a big power boost is a supercharger, which are hard to find (the TRD one) for the '07-'09 and the '10+ trucks never got one from Toyota.

Maybe I'm a bit of a purist, but the only highway miles I like on my FJ are when it's taking me to / from a trail. If you're putting a lot of highway miles on your FJ, and you love your FJ and want to keep it forever, stop doing that. Go buy a cheap efficient highway car, the MPG savings will pay for the car in a couple of years. My highway car is an '11 Lexus GS460 that gets 30 MPG highway, it's like riding in a sporty couch with a great sound system that can do triple-digit speeds all day long. But you can start at used Civic / Corolla and work your way up from there based on your price range.
 
#5 · (Edited)
Very helpful, thanks!

It's a 2013 FJ, bought certified pre-owned from a Toyota dealer with 30k miles, passed my trusted mechanic's inspection (whole family fleet has been going there for 10+ years; all their managers and most of the techs know us by name). I'm up to 52k now. I just recently learned (since my last fill-up!) that the FJ's engine actually can benefit from premium gas; I'm going to try that first. That and more skinny pedal :D

However,

If you're putting a lot of highway miles on your FJ, and you love your FJ and want to keep it forever, stop doing that.
No! I like driving my FJ. I have a Camry (all 20 years of its life in the family, 12 years with me) that gets more than double the mileage of the FJ but I don't daily drive it anymore 'cause it's not the wonderful FJ! :D Camry made it 20 years of daily driving and still goin' strong; ain' no reason the FJ can't do the same. Especially since it's getting pampered from day 1 (whereas the poor Camry had a rough stretch of years in the middle).


@Jimmy-buffet if I had more money than sense, though, I could just find a supercharger that'd fit in the engine compartment, combine that with some willing techs in search of an adventure, and everything'd work out well, though, right?
 
#6 · (Edited)
Using my FJC as an example, the stock tire size 265/75R16 is 31.6" on average (these numbers will vary some with tire manufacturer), so a little closer to 32" than 31". The 33s most people run (such as 285/75R16) are 32.8".

So the difference between the stock tire size and "33s" is only 3.7%. Not worth the substantial cost of regearing, IMO.

My other off-roader went from 29.5" tires to 35". That was an 18.6% difference, which was worth regearing...again IMO.
 
#10 ·
You also have to take into account the spinning weight differential created by going up in size. Even the lightest 33" MT takes a significant amount more horsepower to achieve the same centrifugal force as the stock unit, for instance I believe my Toyo 33's weigh in at over 70 pounds compared to the stock tire that's about double.

Now add the weight difference to the size differential and the percentage goes way up.
 
#12 ·
So ill chime in.. I have 33's with 4.88 gears (bought it like this unbeknownst). The torque she has is tremendous but once you get past the initial influx of power and get to cruising speed she suffers. At 60+ MPH the RPMs are pretty high, I think 2k RPMs, but it just isn't ideal for highway cruising. If I had the chance to swap 4.88 for 4.56 Id do it just based on what I drive on a daily basis. Gas mileage really isn't that bad to be honest, depending on how heavy my foot is. One thing I've noticed is the sound she makes due to the K&N CAI, magnaflow muffler and 4.88s allowing for higher RPMs is the sound of perfect harmony.
 
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#15 · (Edited)
Mainly running around town but I'll do some long distance travel here and there. Most of my driving includes a lot of idling due to stop and go traffic and I'll keep it running with the AC on if the dog is in the truck. I'll use my Cressida for long distance driving and sometimes the 4runner. When I was breaking in my diff, I did a nice 400 mile drive with cruise set on 65-70 and the truck returned 22+mpg. Now I just drive it like I stole it because the torque is fun. Here's some figures:
 

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#18 ·
Re-gearing on 31" with eye on 33"?

I am running Goodyear MTR 33" with 4.56 gears and very happy with this set up. Also keep in mind that "FINAL" gear ration which is in the diff will dictate your low range gear in the transfer case. Which means if you keep going taller in tire size, your Low range becomes less effective and when you are on the trails you will have less "torque". Here is a link how to choose a proper gearing for your truck and at the same time keeping your MPG in a decent range.

https://youtu.be/oDVpyhKEbaw


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#21 ·
Re: Re-gearing on 31" with eye on 33"?

I am running Goodyear MTR 33" with 4.56 gears and very happy with this set up.

https://youtu.be/oDVpyhKEbaw
This ratio sucks according to the video. :grin
You should have 4.03. I still jump over the gears with 35", I can't see any other point than the low crawler gear you have.
 
#19 ·
Don't regear on 33's/285's. There is no need, you'd just be wasting money. Try traveling as light as you can and give it some beans before you start going uphill, not during. Also with your upcoming tires - 33" tires are 12.5" wide, while 285's are 11.2" Width is where the weight is and rubbing problems occur, so run a lightweight 285 AT tire.
 
#27 ·
Re-Gearing:

The Ring & Pinion is the main set of Gears inside the Axle. Four wheel drives have 2 (1 front 1 back). Vehicle manufacturers choose particular gear ratios based on a number of factors, that all revolve around a bone stock vehicle's weight, tire size, horsepower, torque range, etc. They choose ratios to offer a mix of good performance and economy. This day and age Economy is generally favored. Even small alterations in tire size and added weight can drastically affect a vehicles drivability, performance, and economy.

This is especially important for off-road / overland type vehicles. These vehicles tend to be heavily loaded with expedition and offroad enhancing gear like tents, fridges, bumpers, sliders, skidplates, winches, etc. Most of these vehicles also are running larger tires than stock. Also, most see a great deal of highway miles, making correct gearing even more important

It is a common misconception that Re-Gearing a vehicle is only for Hardcore Off-roaders or for huge oversized tires. In fact, most of the late model vehicles we produce aftermarket ratio's for are daily driven vehicles with slightly oversized tires. In an effort to improve fuel economy, Late model overdrive transmissions are geared very high which means RPM's are very low on the highway. When even a slightly taller tire is installed the RPM's are reduced below acceptable levels that the engine was designed to run. This causes constant shifting out of overdrive, sluggish acceleration, poor economy and rapid wear on the transmission and other components.

By changing the Ring & Pinions in your vehicles differentials, you can match the ratio to the tire size to bring the RPM's back to where the manufacturer intended. Typically it is recommended to select a ratio slightly lower (higher numerically) than what the math will tell you. This will help accommodate increased rolling resistance, wind drag, and added weight of aftermarket accessories and gear.

For Example:
2007 Toyota FJ Cruiser Automatic.
Stock:
3.73 & 31" tires 65 mph 1839 rpm
3.73 & 34" tires 65 mph 1607 rpm
4.10 & 34" tires 65 mph 1817 rpm *close to stock, but not enough for other factors
4.56 & 34" tires 65 mph 2021 rpm *ideal
4.88 & 34" tires 65 mph 2194 rpm *ideal for especially hilly area or heavy vehicle.
 
#28 ·
Re-gearing on 31" with eye on 33"?

Thank you justdifferentials. Well said and I rest my case.
Cheers


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#31 ·
Late to participate and it's a rant I've had often, so cliff notes:

I feel that a stock FJ is GROSSLY under powered off the showroom floor

Adding a lift and E rated 33's made it worse

Adding a ton of armor and gear worse still

Going 4.56 gears made it livable

Went up a couple MPG around town due to not trying to KEEP the skinny pedal pushed through the floor

Highway around 75-80 lost a few MPG (Texas HWY speed limits 70-85 as posted)

Went to 35's and now trying to push the pedal through the floor again

Don't want to do 4.88s on this rear axle, maybe an 8.2 but not the "8.0"
 
#33 ·
Late to participate and it's a rant I've had often, so cliff notes:

I feel that a stock FJ is GROSSLY under powered off the showroom floor

Adding a lift and E rated 33's made it worse

Adding a ton of armor and gear worse still

Going 4.56 gears made it livable
Meh, you guys are spoiled. My other rig only has 175 hp running 35s, bumpers, armor, etc., and you're complaining about 258 hp (what my 2010 has anyway)?

OTOH, I think you guys are too worried about higher rpm. Given the same load, higher rpm has only a minor effect on mpg, and in some cases it can actually improve mpg if the transmission can stay in the same gear with the torque converter locked, as opposed to shifting all the time.
 
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