Why Should I Regear?

nitro-gear

Supporting Sponsor - Differential & Axle Parts
Overlanding.


I don't need to regear, my tires are only a little bigger than stock.


It's a common statement and one we enjoy addressing when the opportunity presents itself. Overland preparation tends to add weight to the base vehicle. Bumpers, winches, skidplates and tire carriers can add a tremendous amount of weight from stock. Add a rooftop tent or rack assembly up high and aerodynamic drag is greatly increased as well further reducing performance both on and off-road.


Beyond increased weight, vehicle manufacturers almost always opt for a borderline gear ratio from the factory to optimize unloaded fuel economy. This means that even running near stock size tires, a heavily loaded, taller than stock and factory undergeared Overland 4x4 is a very poor performing machine both in terms of acceleration and fuel economy. This reduces cross country fuel range, on road responsiveness and off-road control all at the same time.


The solution is regearing. Proper gear ratios put the engine at optimum RPM for performance and fuel economy and give you the opportunity to add traction aiding differentials during gear installation greatly enhancing the capability of your backcountry 4x4 in the field, on the highway and around town.


Just Differentials is the leader with gear packages available for all the common Overlanding platforms. These kits include ring and pinions, full master setup parts and everything your mechanic needs to regear your rig and make it function as it should instead of gasping every time you climb a mild grade.



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Happy Joe

Apprentice Geezer
Regearing is very vehicle use, drivetrain and driver dependent.
I am a big fan of regearing (its cheap since I do it myself); but finding a shop that is willing to take the time to do it right (this includes minor changes to optimize the gear contact pattern) is sometimes tough, and expensive.

A little clarification; gearing is much more critical for manual transmissions; (becoming ever more rare) slippage in automatics can effectively lower the gear ratio at very slow speeds as much as 2 times.
For more extreme off roading it can be a good idea to optimize the axle gearing for street and highway then gear the transfer case for off road/low range use, IMO; note this is not typically necessary for basic travel.
Small, low torque engines sometimes need lower axle gearing to compensate for simple mods (tire size) or heavier loads just to regain some drivability.
I am a big fan of selectable lockers on antique 4WD vehicles however they are not, typically, necessary on vehicles with electronic traction control (as long as it keeps working).

Enjoy!
 
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nitro-gear

Supporting Sponsor - Differential & Axle Parts
Regearing

Agreed @Happy Joe, it can be noted also that we've found an even greater need in regearing late model vehicles with Automotic transmissions. The overdrives are very tall and the vehicle manufacturer's gear ratios are very tall. Basically, most of today's vehicles are geared to run unloaded on flat highway, and barely stay in overdrive without down shifting. This makes them very sensative to any changes such as increased weight of accessories, and even more so a slightly taller tire. While your average overlander isnt running huge tires, I could say that most are running larger than stock, and when asked about performance will have complaints if running stock gearing. Recently at FJ Summit we talked to several hundred FJ Cruiser owners. The typical conversation would start with "well I only am running 285's" litterally heard this a hundred times, but all but one or two complained that overdrive was useless and performance was not up to par. The other group said "well I am only running 285's, and performance was but, but I put your gears in now it is great." It was nice to get feedback from numerous vehicle owners who have regeared, they would even hang out to share their excitement with others. Ive often said that the only people that will say you do not need to reagear with larger tires are those that have not regeared...



Regearing is very vehicle use, drivetrain and driver dependent.
I am a big fan of regearing (its cheap since I do it myself); but finding a shop that is willing to take the time to do it right (this includes minor changes to optimize the gear contact pattern) is sometimes tough, and expensive.

A little clarification; gearing is much more critical for manual transmissions; (becoming ever more rare) slippage in automatics can effectively lower the gear ratio at very slow speeds as much as 2 times.
For more extreme off roading it can be a good idea to optimize the axle gearing for street and highway then gear the transfer case for off road/low range use, IMO; note this is not typically necessary for basic travel.
Small, low torque engines sometimes need lower axle gearing to compensate for simple mods (tire size) or heavier loads just to regain some drivability.
I am a big fan of selectable lockers on antique 4WD vehicles however they are not, typically, necessary on vehicles with electronic traction control (as long as it keeps working).

Enjoy!
 

gwittman

Adventurer
I have a situation that is both good and bad with regearing. I regeared from 4.10 to 4.56 when I went to 33" off-road tires. They work great with the 33" tires but when I am not going off-road I put the stock size 31" highway tires back on. The low gearing doesn't allow me to run the speeds I like on highways. The engine and drivetrain rpms are higher than its intended design. I also get at least 1 mpg less than I did with the 4.10 gears and 31" tires. One thing I do like about the 4.56 gears and 31"tires is it accelerates very well.
.
Before I switched to 33" tires, I ran 32" tires off-road. This worked OK with the 4.10 gears but was at the limit of being usable, especially with some medium rock crawling while loaded down. It was slower to accelerate than I like also.
.
When my 31" tires wear out I will probably just run my 33" off-road tires all the time. They are not as road worthy but are better matched with the 4.56 gears. I will just put up with the increased road noise, take it easier in the corners and may go to an AT tire eventually.
 

Happy Joe

Apprentice Geezer
Re: overdrive transmissions; I agree, I am of the belief that the overdrive will often tell you if you got the gearing close. If the axle gearing is too tall the overdrive won't work well.

One of the minor dissatisfactions that I have heard from a few people is the "excessive" highway rpm with smaller (cheaper) tires. Its why I recommend that they settle firmly on a tire size before doing the regear. A side benefit of determining the tire size up front is that the existing axles can be evaluated for strength/compatibility.

One friend (with a 5.0 HO and T-5) had the 33" tire axle ratio pretty well optimized, for the highway, with 4.27 gearing (he had them on the shelf); when he went to 35s he found that his overdrive was effectively unusable.
On the other hand, I went to 35s to reduce the rpm on the interstate, OD can be entered at 45mph and it is happy puling most hills, lightly loaded. When hauling the gear (~800 lbs.) I regularly have to down shift for hills. The medium traction BFG mud terrains also helped my front axle shaft longevity.
Having a deep reduction gear in the transfer case essentially lowers the first gear by one step (I typically off road in 3rd gear) in low range giving an optional lower crawl ratio for the rare times that I wan to sneak up on an obstacle.
Enjoy!
 

sargeek

Adventurer
One of the biggest regrets I had was not re-gearing a 99 Jeep TJ. I migrated over time from the OEM 205/75R15, to a 30x9.5x15, to a 31x10.5x15. The TJ has 215K on the odometer. These are pretty mild tire size increases, but the effect on the Jeep is significant, especially at altitude of Denver. Most drivers just compensate and adapt their driving to the new performance of the vehicle. I had the differential fail, and replaced it with a OEM out of a 4 cylnder Jeep. It was like driving a new vehicle. I could actually use 5th gear again, acceleration improved, fuel mileage improved, and general performance returned, and the Jeep could tow much better. After the re-gear - it was amazing the improvement in daily operations, and the shifts drivability were back in the power band. Prior to the gear change the 4.0 could barely maintain highway speeds in 5th gear, a small hill or head wind, and you would have to downshift and rev the engine to maintain speeds.. I wish I would of done it 100,000 miles earlier. The Jeep will never be able to run 205/75R15 tire again, but I can use the 31 year round, on and off road.

I don't know how Jeeper run 33"-35" tires on the OEM gearing - the must lose 4th & 5th gears unless they are going down hill. . I also have a 06 Tacoma, and I tow a relatively large travel trailer with it. I could not tow the trailer if I changed the tire size diameter from the OEM sizing without changing the gearing.

IMHO axle gear is one of the most critical decisions you can make for a vehicle.
 

Happy Joe

Apprentice Geezer
...Just got a junker '95 XJ (jeep Cherokee) for a winter street vehicle (it will likely never go more than 50 feet off road) and never haul the camping load (~800lbs); it has the stock 3.07/3.08 gearing and OEM tire size was P 225/70 R 15 (27.4 inches in diameter).
This is the typical "too tall" OEM tire/gearing design. Since it is a street only, very light load, vehicle the performance is adequate. The tires that it will get will be 235s (leftovers from the last XJ).
The roughly 2.2% increase (per the internet, I didn't bother to get out the calculator) in diameter, is not worth re-gearing.
However, if I happen on some 3.73 geared axles, they may migrate underneath; its easier to change out axles than to re-gear..
Enjoy!
 
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