re-gearing for 35's

[AVILES]

hi, i was wondering what would be a good gear ratio to go with 35's. i've been running my 97 jeep wrangler with 35's for a while now and i havent seen 5th since then. i was wondering what would be a good gear ratio to run the 35's and gain a little more speed on the highway and hopefully use 5th. i mainly use this as a daily driver but every now and then i do go offroading. also i was wondering if it was easier/cheaper to swap the whole axle or to actually change the gears inside the differential? thanks in advance

 

[ralavoie_417]

For 35s your looking at 4.56 gear ratios for the axles. 4.88s if you're looking for some power. The cost is about 600 bux per axle. An axle swap will end up costing more and be more work. I currently run 4.88 on my 37 inch tires and cruise at 70-80 mpg at about 2200 rpm.

 

[xjmarc]

Depends on what transmission you're running. Autos tend to need lower gears than manuals. Depending on what you have you might be able to find a set with lower gears at a decent price but prob would be easier to swap them out. Unless you are familiar with ring and pinion set ups pay someone. It isn't cheap but then you only have to buy the gears once.

 

[Bounty__Hunter]

Also depends on which engine you have. It's often best to find out what your stock axle ratio is and go from there. For example, the recommendation to use 4.56 gears wouldn't be very wise if you had a 2.5L 5spd with stock 4.10 gears, you wouldn't notice much difference and be out the money and time involved.

Give us more info about your rig.

 

[AVILES]

Thanks abt , right now I have the Mercedes om617 3,0l turbo diesel mated with an ax15. As of right now I think it feels very similar to the 2,5l when on the highway at around 60 , so idk I was thinking of 4.88 gears . As to how hard it is to swap the gears, I did most of the engine swap my self with out knowing either, so I thought I could figure out the axles aswell, but idk I need to research before I start messing with them.

 

[clemtiger8]

I have 4.11 front and rear with the 4.0 six cylinder. I push my 35s well with no problems. Running in 5th gear 1800 rpm at 62 MPH.

 

[xjmarc]

Engine swaps have a lot bigger margin for error than gears. Gears are either dead on the first time or you'll trash them.

 

[jps4jeep]

With the diesel, I am absolutely surprised your having issues with maintaining speed in 5th with even 3.07 gears (not sure what you have)

Generally with a diesel, due to the red line being very low, I think the E300's tached out at about 2300 rpm, you want to keep your gearing a little higher (numerically lower) I would suggest looking for a 4.11 8.8 and regear your front. you should be able to get the rear, plus new brakes, pads, seals etc for about $500. gear the front to 4.10, gears and master install kit vary in price but let ball park $300. I think this would be an Ideal gear selection for that motor.


EDIT if you plan on highway driving, 4.88 gears are not at all ideal with a E300 TD. you will hit about 60mph in 5th and bounce off the revlimiter

 

[orangecrush06]

i have an 06 tj 4"suspension running 35's and was going to go from a dana 35 with 3.07 gears to 4:10's. any opinions or suggestions much appreciated

 

[Bounty__Hunter]

Welcome to the Z.

You will find that 4.56 gears will bring your RPM's back close to stock at highway speeds. While 4.56 gears will help
account for the increase in tire height, it doesn't really help
for the added rotating mass and increased wind resistance.

I'd run 4.88 for the best all-around performance.

 

[cali_92]

i dont understand how re-gearing "gives you more power".... are you talking in a sense of bring the power range of ones rpms into different gears. going from stock 4.10 to say 4.88 mean the gears are "shorter">? so one would shift through their gears faster.? i have a 2.5 with 33x12.5 help would be appreciated.
srry dont mean to steal the thread. mostly interested in how this helps

 

[Bounty__Hunter]

You won't shift through the gears faster because the larger tires already lowered your 'final gear ratio'. Regearing 'lower' in the axles just compensates for the addition of larger tires and brings the RPM range back to where it was in stock form, and you shift through the gears at a similar pace as when stock.

 

[cali_92]

You won't shift through the gears faster because the larger tires already lowered your 'final gear ratio'. Regearing 'lower' in the axles just compensates for the addition of larger tires and brings the RPM range back to where it was in stock form, and you shift through the gears at a similar pace as when stock.

so i'll just be in higher rpms in the same gear after regearing... wont that just cause my mpgs to drop?

 

[cali_92]

ooo! after re-reading what bounty hunter said,
so it will fix the problem of my slow acceleration from take off and so on?

 

[Bounty__Hunter]

Yes, it will improve acceleration off the line.

You will be at higher RPM's in the same gear at a given speed after regearing, but theoretically regearing should return your RPM's back to where they were with stock size tires at a given speed.

Installing larger tires drops your RPM's at a given speed. Regearing just brings your RPM's back up and allows your engine to operate in it's optimal power band instead of lugging.

I run 5.38 axle gears with 35" tires beneath my 2.5L 5spd and I can get anywhere from 15-21mpg as the engine is operating in it's optimal power range the majority of the time.

 

[cali_92]

Yes, it will improve acceleration off the line.

You will be at higher RPM's in the same gear at a given speed after regearing, but theoretically regearing should return your RPM's back to where they were with stock size tires at a given speed.

Installing larger tires drops your RPM's at a given speed. Regearing just brings your RPM's back up and allows your engine to operate in it's optimal power band instead of lugging.

I run 5.38 axle gears with 35" tires beneath my 2.5L 5spd and I can get anywhere from 15-21mpg as the engine is operating in it's optimal power range the majority of the time.

Thats what im talking about! i like it. i run 33s with my 2.5 what gears do u suggest i run? i do alot of on road driving hoping my top speed will improve.
...5.38! thats kinda extreme isnt it?

 

[jfrabat]

so i'll just be in higher rpms in the same gear after regearing... wont that just cause my mpgs to drop?

Not necessarily. The mpg's do not increase by reducing RPM's (not always, anyway). You get the best MPG by driving where the engine is the most efficient (typically, where it produces the best torque), and this is rarely low in the RPM range (or at the high end, for that matter; it tends to be somewhere in the middle).

i run 33s with my 2.5 what gears do u suggest i run? i do alot of on road driving hoping my top speed will improve.
...5.38! thats kinda extreme isnt it?

I have run 31's on 4.10, 31's on 4.88 and 33's on 4.88. The best MPG's I got while driving the 31's on 4.88. For 33's, I think the best gear ratio is 5.13's (assuming a manual transmission and 2.5L engine!). Of course, the stock axles only go to 4.88, which is why I am still running that setup. It is OK, but not as good as 5.13's could be.

In bounty's case, since he runs 35's and 36's, 5.38 is the right gear. Keep in mind the charts usually tell you how to compensate for the extra size, but not the extra mass, air resistance, etc... This is why running higher gears (higher number, but really LOWER gears) than what most charts say you should run tend to work a bit better in the real world.

hope this helps!

 

[cali_92]

Not necessarily. The mpg's do not increase by reducing RPM's (not always, anyway). You get the best MPG by driving where the engine is the most efficient (typically, where it produces the best torque), and this is rarely low in the RPM range (or at the high end, for that matter; it tends to be somewhere in the middle).

I have run 31's on 4.10, 31's on 4.88 and 33's on 4.88. The best MPG's I got while driving the 31's on 4.88. For 33's, I think the best gear ratio is 5.13's (assuming a manual transmission and 2.5L engine!). Of course, the stock axles only go to 4.88, which is why I am still running that setup. It is OK, but not as good as 5.13's could be.

In bounty's case, since he runs 35's and 36's, 5.38 is the right gear. Keep in mind the charts usually tell you how to compensate for the extra size, but not the extra mass, air resistance, etc... This is why running higher gears (higher number, but really LOWER gears) than what most charts say you should run tend to work a bit better in the real world.

hope this helps!

yes that helps. thank you. i didnt know stock axles only allow you to re-gear to 4.88, i guess thats as far as i will be going. hopefully i can get this done this weekened. appreciate it bounty hunter and jfrabat

i just read this on some other site

Your engine operates more effeciently within a certain powerband. When you add larger tires and leave the gear ratio the same you throw off the drivetrains optimum operating range. Regearing brings it back into spec so the engine and transmission operate effeciently and don't have to work as hard to do the work. You will lose top end speed up to a point, but getting there is easier.

the part that i am concerned with still is the losing top end speed.. that is mainly what im trying to get. but am i really losing that much or any at all. because if their talking about like 70-80 mph i dont even care because i cant even get my jeep going that fast.

 

[jfrabat]

i didnt know stock axles only allow you to re-gear to 4.88, i guess thats as far as i will be going.

Yeah, only the Rubicon comes with both D44's (which can take you higher) and SOME Saharas came with a D44 rear (IIRC, but not 100% sure on that last one)

the part that i am concerned with still is the losing top end speed.. that is mainly what im trying to get. but am i really losing that much or any at all. because if their talking about like 70-80 mph i dont even care because i cant even get my jeep going that fast.

With 31's and 4.88, I used to run at 75 down the FL Turnpike on 5th with the cruise control (aftermarket) on (as in not having to downshift). I could have probably taken it to 80, but I never bothered to try (hey, it's a Jeep, not a Ferrari, after all!). I can still do 70 with the 33's, but unless it is DEAD flat and no headwind, I have to keep it in 4th.

 

[cali_92]

With 31's and 4.88, I used to run at 75 down the FL Turnpike on 5th with the cruise control (aftermarket) on (as in not having to downshift). I could have probably taken it to 80, but I never bothered to try (hey, it's a Jeep, not a Ferrari, after all!). I can still do 70 with the 33's, but unless it is DEAD flat and no headwind, I have to keep it in 4th.

thats still not bad! you basically are a Ferrari in jeep 2.5 terms going that fast haha. i believe im going to re-gear.. i think its the best upgrade that i can do right now.