Topic: Gear for 35's

[jfrabat]

At any given RPM and tranny gear, lower diff gearing will have more power. When I switched to 33s (still with 4.56) I recall having to get used to shifting at a higher engine RPM.  Is this a lack of power?  It depends on how you look at it.  At a given engine RPM, the Jeep may lack power in 5th but feel fine in 4th.  I really think it is important to be able to save 5th for long flat and downhill stretches.

Here locally, the drive from Monterrey to Saltillo is uphill and mostly free of curves.  This climb is known for causing many big trucks to overheat and for brake failures coming the other way.  My Jeep can climb this section in 4th at a reasonable RPM (actually starting to feel a bit high).  Running 4.88, I would have to rev it even more to go at the same speed or just go a bit slower to avoid the high revving.  To maintain speed and avoid revving so much I'm sometimes tempted to shift into 5th, but I feel the stain on this climb would not be good for the tranny in 5th and the engine would probably not be able to maintain the speed.  Coming down, 5th is great but 4th also works and also allows some compresion braking to avoid heating the brakes. So 4.56 is well suited to this road. Another road into the mountains with many curves always makes me feel a gear right between 3rd and 4th would be great.  It seems 4.88s would provide this (a bit lower 4th).  On other roads and speeds, different gearing may be better. In the end it comes down to the interaction of personal preferences, driving habits, and the types of roads you drive.

In my case, in Miami (does not get much flatter than South FL!), my 5th was a nice decoration after I dropped in the 33's.  When I had 31's, I could cruise at 70mph on the FL Turnpike (that's the speed limit there), and had no problems.  Here in Costa Rica, there is a lot of hills, so, again, 5th is not used much (except when going downhill, which does not count for me because I could easily set the speed on the cruise control and have IT control the speed for me in lower gear)...

[neale_rs]

This helps drive forth my point.  The fact that you don't get to use fifth very much shows you are geared right.  It seems to be a generalized goal to select the diff gearing to allow the use of 5th when going uphill and against the wind.  But 5th on the AX5 is weak and will not hold up for long when used for driving uphill against the wind often.  With your current gearing you could probably use 5th to drive across Texas at 75 mph, right in the powerband.  See http://wahiduddin.net/calc/calc_speed_rpm.htm

Using the info in Sharp's post:

It seems you want a gear between your current 4th and 5th.  The second chart shows you can get that by going to 5.13 and using 5th.  You will get a 5th that is 5% better than what you have now.  Maybe this exactly what you need but by using 5th you also increase the chance of a breakdown.  You can also go with 4.56 gears and get a 4th that is about 20% lower than your current 5th and higher than your current 4th.  You would also avoid overworking 5th gear.  It depends on what you need and/or want: 5% better with greater chance of breakdown or 20% better with lower chance of breakdown and a mostly 4 speed tranny (downside but mostly because of the desire not to waste 5th). Or go with 5.38 and get a 10% better 5th also with increased chance of breakdown.  I really think you at the overall best point already.  5.13 is the best for 70 mph in 5th but where you live now, would you really want to be using 5th on all those hills?

[Jeffy]

I ran 4.56 with 30's for a while.  This is equivalent to 5.016 with 33s or 5.32 with 35s. The power was great but I was shifting into 5th in the city every so often.  This seems too low, it would be more reasonable to use 5th only for highways on long flat stretches and downhill sections and 4th for even mild uphill sections.  5th is too weak on an AX-5 for everyday use. For on-road, 4.88 is probably ideal for 33s and 5.13 for 35s and then if you need lower gears for off-road, get a Tera 4:1 or Atlas TC.

You can't really compare 30's to 33's or 35's as the 30 is much lighter. (unspring weight)  They have a much lower rolling resistance as well.

Phil Howell (Editor of 4WD & SU Magazine) has done a 2.5L build with 5.38's as well as several others with 5.13's and they also had the Tera.  His other projects ran 35's and 5.89's.

[FourbangerYJ]

Phil Howell (Editor of 4WD & SU Magazine) has done a 2.5L build with 5.38's as well as several others with 5.13's and they also had the Tera.  His other projects ran 35's and 5.89's.

But were they drivers or trailer queens?
I think 5.89's and 35's is geared to low. 5.38's would be good maybe a tad high but would work.

[Torch_Ind]

But were they drivers or trailer queens?
I think 5.89's and 35's is geared to low. 5.38's would be good maybe a tad high but would work.

who does up there jeep on 35-37's with a 4cld to highway drive??  I would rather have the bigger gears like 5.38's and 5.89's and have good off road then jack up my jeep with 35's and highway drive it and wear it out doing that?  also you have to factor in the mass and even worse aerodynamics with more air under the vehicle then over top with highway on lifted and big tires trucks so you have to add more power for that fact or bigger gears and you will have to run a little higher then norm rpm's to keep it rolling vs stock

this kinda goes with the fuel economy aspect!!


Whats the primary motive of the jeep? 

highway or off-road town top down cruiser?   

 If your going for highway and mpg's and less brake down stay stock..

 if your building a rig build a rig.

[Jeffy]

But were they drivers or trailer queens?
I think 5.89's and 35's is geared to low. 5.38's would be good maybe a tad high but would work.

No he drove all of them.  He's one of the few guy's I know in publication who likes 4bangers.

[FourbangerYJ]

http://www.novak-adapt.com/knowledge/gearing.htm

Looking at this gearing calculator 5.38's would be ideal for 35's. I used 70 MPH and .85 for the final gear. I know Jeffy said in the past to use 1:1 for the final gear.

For me the 5.89's would be best. I thought it might be to low, but it seems it would be just about right. If I win lotto and get D60's I'd do 6.17's. 

who does up there jeep on 35-37's with a 4cld to highway drive??  I would rather have the bigger gears like 5.38's and 5.89's and have good off road then jack up my jeep with 35's and highway drive it and wear it out doing that?  also you have to factor in the mass and even worse aerodynamics with more air under the vehicle then over top with highway on lifted and big tires trucks so you have to add more power for that fact or bigger gears and you will have to run a little higher then norm rpm's to keep it rolling vs stock
this kinda goes with the fuel economy aspect!!
Whats the primary motive of the jeep? 
highway or off-road town top down cruiser?   
 If your going for highway and mpg's and less brake down stay stock..
 if your building a rig build a rig.

I don't have a trailer or truck to tow, so mine gets driven everywhere. If you add large tires then you need to gear the axles accordingly. When in doubt gear a bit lower if you can.
If you think your gonna get good mileage with a lifted Jeep your gonna be pretty sad. Weather its a 2.5L or 4.0L
I feel mine is a pretty built rig. Not much more I really want to do to it. I built it to go everywhere easy-hard type trails. I enjoy all the aspects of getting off the pavement. I enjoy driving mine each and every time I do. 

[sharpxmen]

http://www.novak-adapt.com/knowledge/gearing.htm

Looking at this gearing calculator 5.38's would be ideal for 35's. I used 70 MPH and .85 for the final gear. I know Jeffy said in the past to use 1:1 for the final gear.

i used that calculator to verify my charts and it's dead on for the speed based on rpm, the rpm based on speed is off by 3 rpm but since we're talking over 2000 is really not much at all, so the formulas are good.

[Mozman68]

Since I actually run 35's (and a lot of extra weight), I'll chime in.

I went with 4.88's in my D60's because I didn't want to re-gear when I drop in a V8 (yes...someday I will... )

It's pretty flat here, but I drive the highway everyday...and I use 5th gear everyday.

I usually drop down to 4th at 2500 rpm...regularly cruise at 70-75 mph in 5th....

Would 5.13 be fine, even better? Sure, but with my engine, lift, tires, etc. 4.88's are great....and I wouldn't be buzzing at 5,000 rpm when I drop in a bigger engine.   

[TahoeYJ]

4:88's and 35's works well for me, but with all the highway driving I do I wish it was a little lower. Stuck with what I got until I replace the Dana 30 though. I can hold 70 in 5th all day long, if I'm cruising down the interstate for long drives I can pull a draft off the car ahead of me and cruise 75+. I do downshift on grades, but I usually only need to drop down to 4th. When I get my new tires next week I know I'll see a change in the way it runs, my current 35's measure out less than 33" with the weight of the jeep on them.

I looked around and I found that Motive gear makes 5:29's for both the D44 and Ford 9", if I ever slap a d44 up front then I'll probably rehear to that ratio. I think 5:38's and 35's would be a bit high for all the street driving I do.

I think I could actually live with 4:88's for quite a while if I had a 6 speed... I know Art said 4:56's and 35's with the 6 speed was actually not bad... But with what I've seen it takes a loooot of work to get the newer 6 speed to mate with the 2.5. I'd rather swap in a 4L with that tranny at that point

[neale_rs]

But were they drivers or trailer queens?
I think 5.89's and 35's is geared to low. 5.38's would be good maybe a tad high but would work.

I have a friend who runs 5.89 and 35s.  He doesn't keep up on the highway anymore.  Not due to lack of power but due to not wanting to run at such high RPM for extended periods.  He wanted to maximize the off-road capability and was willing to sacrifice the on-road speed.

[jfrabat]

When I ran 31's and 4.88, I would be around 3,500RPM's (I think it was actually a bit less, but I dont remember, to be honest) when driving at 70mph.  I would drive all the way North to West Palm Beach or all the way South to the Keys (or even to Naples on the other side of the FL penninsula), and never had problems.

At that RPM, the 4 banger can go all day.  That SHOULD be more or less the same RPM you would get with 5.13 and 33's or 5.38 and 35's...  But lower (like 5.89 and 35's) WOULD be too high an RPM for my taste!

[Jeffy]

http://www.novak-adapt.com/knowledge/gearing.htm

Looking at this gearing calculator 5.38's would be ideal for 35's. I used 70 MPH and .85 for the final gear. I know Jeffy said in the past to use 1:1 for the final gear.

The reasoning is that you're not passing in 5th  It's an OD gear and isn't as strong as 4th.  All of the charts you usually see have this in mind.

I've driven from SD to SF at 34-3700RPM and held it there for all 7 hours.  I've only done +4000 RPM for maybe 30 minute or so climbing the Grapevine.  No problems what so ever.  As long as your temps and oil pressure are OK the engine will be fine.  I know most people baby their 2.5L's too much and rarely get them into the sweet spot of the power band.

Even with an engine swap, you're not going to be screaming with lower gears.  The RPM's will be about the same except you'll have a lot more torque and HP so that will keep the speed up.  Also considering that most transmissions for V8 swaps have a higher OD, it won't be a issue really.  Then you have to consider how long the time period between getting the gears and actually doing the swap.  If it's a long period then it would make sense to go lower then regear if you have to later.  I would have definitely went with 5.13's as that's a good compromise.

[Torch_Ind]

I have a friend who runs 5.89 and 35s.  He doesn't keep up on the highway anymore.  Not due to lack of power but due to not wanting to run at such high RPM for extended periods.  He wanted to maximize the off-road capability and was willing to sacrifice the on-road speed.

this would be me as well. 

I checked my jeep today and at 70mph I was running roughly 27-2800rpm and I'm only runny 33's  I wouldn't want to run it any lower then that or you will loose speed on the highway. I would run 5.13-5.38's with 33's and would love it!!

I don't care if I even run 70 I would run 60-65mph and cruise were ever were going with tires that big. not to mention you get better fuel econo at the lower speeds.

[Bounty Hunter]

I run 5.38 and 35" tires with my 5spd and it's awesome onroad, cruise down the interstate just fine.  Drove 2:30 hours Wednesday to the lake and got 17.75mpg, not bad for this setup.