Topic: Gear for 35's

[redneck97]

I am currently running the stock drivetrain with 33" tires but I would like to upgrade to 35's.  What gear ratio would be optimal for this.  I know anything over 4.88's I would have to change axles.  With this in mind what gear ratio can the ford 8.8 and the d44 accept.

[FourbangerYJ]

http://www.4wheelerssupply.com/catalog/index.php/cPath/470_496_23_498

5.13's would be your best bet. Not sure if there is any other brands of gears on the market. I just did a quick search and posted the first thing I found.
I didn't know the 8.8 could be geared to 5.71 or 6.14 

[jfrabat]

I would go deeper; 5.35 if you can.  I run 33's with 4.88 and I wish I could go to 5.13 for the 33's I have.  I think BountyHunter runs 5.35 (D44 on both ends, though) and he's always reported he's happy with the setup...  Now, from a quick search online, it seems the 8.8 only gets to 5.13 so you may be stock on that gear (which is not terrible).

[neale_rs]

A friend of mine got 5.89s in his Dana 44s and now can't keep up on the highway!  I think this is as low as you can go on the Dana 44.

[Jeffy]

Well since the 8.8" is the limiting factor, you'll probably want 5.13's.  Really though, you'd want 5.38's but 5.13's will work.

[Torch_Ind]

Well since the 8.8" is the limiting factor, you'll probably want 5.13's.  Really though, you'd want 5.38's but 5.13's will work.

5.38'S Would be nice I would do that if you could at least.  I would go 5.38's with 33's if I could

[jfrabat]

5.38'S Would be nice I would do that if you could at least.  I would go 5.38's with 33's if I could

5.38 would be too much for 33's IMHO; but 5.13 with 33's or 5.35 with 35's would be SWEEEEEEET!

[neale_rs]

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.

[FourbangerYJ]

I am pretty happy with the 5.38's and 37's. It could be a tad lower but they don't make a ratio that would work. Besides 5.38's is as low as I can go with the HP front end.

[jfrabat]

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.

I dont know; I ran with 31's and 4.88 for a while and loved it.  When I switched to 33's, I felt the Jeep lacking a bit of power, which is why I wish I could go to 5.13 with 33's...

[neale_rs]

I dont know; I ran with 31's and 4.88 for a while and loved it.  When I switched to 33's, I felt the Jeep lacking a bit of power, which is why I wish I could go to 5.13 with 33's...

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.

[redneck97]

So I think I want to go 5.13's but I am still unsure whether or not the d30 can be geared for it.  From what everyone has wrote I now know the 8.8 can but have gotten some mixed infor from this board and another popular board on the D30.

[neale_rs]

The d30 will only go to 4.88.

[sharpxmen]

I'm trying to get some excel spreadsheets to calculate the speed/rpm based on R&P, Gearbox (tranny) ratios and tire diameter - i can share the spreadsheet with whoever wants it, not sure if i can upload it to the site (i don't think i can). The idea is that you can change the tire diam, rpm or speed or tranny ratios and you'll get the results calculated like you can see below

Would be great if someone can verify this for me so i can make sure they're accurate

here are the formulas i used
speed in MPH = PI*<Tire_Diam_inches>*<RPM>*60/(<Gear_Ratio>*<RP_Axle_Ratio>*63360)
RPM =<Speed_MPH>*<Gear_Ratio>*<RP_Axle_Ratio>*63360/(PI*<Tire_Diam_inches>*60)

where 63360 is how many inches are in 1 mile
60 is for converting the time from minutes to hours and viceversa (since we have rpm in rotations per minute and speed in miles per hour).

I know can't be exact since a 33 inch tireis not exactly 33/2 inches from the center of the axle to the ground due to deflection under load and wear and also not being exactly 33'' in diameter anyway, I'm looking to find out if it is at least close.

   Speed in MPH at RPM for NV3550   

tire diameter	rpm			R&P Ratio
33	3000		Gear Ratios	5.36	5.13	4.88	4.56	4.1	3.73
		1st	4.01	14	14	15	16	18	20
		2nd	2.33	24	25	26	28	31	34
		3rd	1.39	40	41	43	46	52	57
		4th	1	55	57	60	65	72	79
		5th	0.78	70	74	77	83	92	101

     Engine RPM at Speed for NV3550   

tire diameter	speed (mph)			R&P Ratio
33	60		Gear Ratios	5.36	5.13	4.88	4.56	4.11	3.73
		1st	4.01	13143	12579	11966	11181	10078	9146
		2nd	2.33	7636	7309	6953	6497	5856	5314
		3rd	1.39	4556	4360	4148	3876	3493	3170
		4th	1	3277	3137	2984	2788	2513	2281
		5th	0.78	2556	2447	2327	2175	1960	1779

[Torch_Ind]

5.38'S Would be nice I would do that if you could at least.  I would go 5.38's with 33's if I could

going from 4.88's to 5.13's would only raise about 100-150 rpm.  If I could I would run 5.38's.  I can use 5th when I get it up to speed but can't do hills and wind very well in 5th and hold a decent speed