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-   -   axle gearing and towing up hills (https://www.thedieselstop.com/forums/f32/axle-gearing-towing-up-hills-292353/)

SGT JUNK 11-09-2011 07:13 PM

axle gearing and towing up hills
I'm looking for some real world advice on these towing threads I've been reading. I live in FL so 4.10 is all i need for the hills around here, but I'm still having trouble understanding how gearing works as it relates to hills + trailer in tow. I've read tons of google pages on the issue, but I need it explained barney style as it relates to our trucks with trailer in tow
I'm rolling with 4.10 now, but what will 4.88 or 5.13 or 5.88 do to help me make it up the 'hills'? These guys posting are talking about losing speed or not being able to go fast enough up the hills or accelerate very well or EGTs going sky high.
If we swapped our trucks out for these lower gears would that affect/improve our truck's ability to tackle hills/grades with more speed and keep our EGT lower???
I'm trying to understand and combine all the variables that go into towing as it relates to hills. I DO NOT care about gas mileage. It's gonna be terrible so I'm not worried about it. and I don't drive over 65 mph so i'm not worried about top-end or engine noise.
Will the gearing help us tackle the hills and how will it affect EGTs???
My end result would be: the ability to drive up the hills with trailer in tow with EGTs not at dangerous levels and with some speed above 40-45mph.
I'm a great typer so thats why i type so much. Feel free to give short quick answers, I'm a salty trucker but I just don't know it all. so I can put together short answers with the knowledge i have.

Thanks a bunch

PS free free to post pros and cons to lowering the gears to 4.88 I'm open to all opinions and info. i.e. RPMs

here is a link that mimics what i'm saying

DonWarkentin 11-09-2011 10:44 PM

The change from 4.10 to 4.88 is not so much to lower EGT as it is to increase hp at a given speed in a given gear. The 4.88 compared to 4.10 will make the engine run at higher rpm, where it has more hp at a given speed in a given gear. Therefore, with more hp, it will be able to maintain speed for longer as the hill gets steeper. The truck with 4.10 will lose speed and have to downshift sooner, because it was running at lower engine rpm where there was lower hp.

SGT JUNK 11-09-2011 11:03 PM

Good explanation. I'm not necessarily trying to lower EGT, but I want to keep them low or MOD things to help keep them low within reason while towing.

I am under the impression that lower gearing 'compensates' for lack of HP. I won't be adding any hp. I understand your explanation of keeping the truck in the power band of engine, hp-to-rpm. I understand the difference of HP and Torque.
I guess I need to figure out where the peak power of HP and Torque are for my truck and get the gears that will put truck in that operating range.
I'm pretty sure the lowest gears I can get for my truck are 5.13 Maybe that's overkill or too low or will have my truck screaming at 55mph. I know the old F450/ older F-Duty trucks ran 4.88s with the same engine, so 5.13 should not be to bad.

DonWarkentin 11-10-2011 12:06 AM

Here is another way of thinking about it. With the 5.13, the four gears that the transmission has are more closely spaced between 0-55mph, therefore, the transmission is able to keep the engine rpm closer to its ideal rpm more of the time. With the 4.10, the four gears are more widely spaced between 0-80mph; so the transmission isn't able to keep the engine rpm as accurately close to its ideal rpm as much of the time. The advantage, however of the 4.10 is that it keeps the engine turning more slowly at 55-70mph, where fuel efficiency is better, and it doesn't need the extra hp on level ground. Going up hills, however, the more closely spaced gears are an advantage to keep the engine closer to its ideal speed.

1dieselman 11-11-2011 07:12 PM

Also keep in mind that tire size can have an effect on ratio. For example I just recently swapped the 3.54 gears in my 97 to 4.10 gears. I had 285 tires with the 3.54 gears and it was no hot rod but would tow ok. I tried the 285s with the 4.10 gears and if I could keep them hooked up became a great red light to red light racer but I didn't care for the higher rpm's and lower fuel mileage on the highway. I installed a set of 315 tire's which brought the final ratio to exactly what I had with the 3.54 gears and 285 tire's but the torque given from the 4.10 gears allows me to tow with less effort and lower egt's and still get almost 20 mpg. I should also mention that we have some pretty steep terrain here in Arizona. I noticed that your profile doesn't say whether you are turbocharged or not which can make a big difference.

chuckster57 11-11-2011 08:42 PM

My experiences
80 Attachment(s)
Since your running an IDI and it looks like it's N/A from your sig- here's what I have found:

I have the stock 225/75-R16 tires and the E4OD with 4:10 rear end. I tow a Fiver that weighs in at 9,000 Lbs dry. Florida is FLAT compared to my end of the states and I have no real problems with the passes out here. Your being N/A and not turbo'd makes a HUGE difference in the IDI when it comes to pulling weight up a hill. With my mods I am running near 240 HP and 400 Lb/Ft of torque compared to 180 HP for your engine.

Mileage kind of sucks with the 4:10 gears (15 empty and 10.5 with the house on the flats). I just make sure to take it out of O/D when I see a big climb coming and downshift as needed to stay at about 2600-2800 RPM.

If you change your gears to 4:88, I think your gonna be sorry as your truck will be screaming when your towing at 65 MPH ( I am running about 2350 RPM) and your gonna be making lots of fuel stops. A turbo would be so much better than a regear, but $$ can be the driving force.

SGT JUNK 11-14-2011 10:13 AM

Hey Guys sorry for the delay, no internet in Amish Country, Pa.

I will probably play around with the tire size, as I need to get new tread anyway. I don't have a turbo and don't plan on putting one in, i love the simplicity of it even though the turbo is still really basic.
I figured it would scream with 4.88s I don't really want that much noise, but I will tow for another year or so and see about the gear MOD. FL is very flat. Orlando is about as flat as it gets. so I don't need lower gears, but if there was a worth while benefit to doing gears than I'm interested in it.

I haven't done much reading on tire size and gear ratio. I seems odd that changing gears and switching tires around didn't cancel each other out, although you did state the benefits of what you gained by doing so. I will think about that a bit more and probably do what you did.
Thanks again guys great info

nitrogen 11-30-2011 08:05 AM

being 4x4 you will need to regear both ends, you need to factor that into cost as well. I drove a "old" superduty with the 4.88, could not make it past a fuel station(6-8 mpg) and 65 was pretty max rpm. 5.13's if you can 55 you will be doing good. at that point an aftermarket turbo kit will be cheaper,lower maintenance, and much more satisfactory to drive. if you don't believe me just set the cruise at 55 now on the interstate and see how long it takes before you are pissed off at seeing EVERYONE pass you

Kaliburz 12-20-2011 01:59 AM

I have an IDI van and it has 3.54 axles ratio. Just to get up a good incline at 65-70MPH, it usually has to downshift out of OD.

Gears and gearing play an important roll on how fast you slow down on a hill. Look at the semi trucks today and of yester-year. HP today is easily in the 600-700HP range. When you have plenty of power, you can have a 13-15sp tranny to play with. Older semi trucks had their normal transmission and a brownie box (some even with a three speed rear axle- under-direct-over). The brownie box created a multi speed transmission. I have seen a six speed manual transmission with a four speed brownie gear box (that's 24 gears to choose from) and that's with a 350-400HP semi truck (older 70's era).

It's too bad that the old US Gear "under-drive" is no longer being made. You could leave your ratio's alone and the under drive would give you a different ratio (higher number). For example, I think when used with a 3.73, the under drive would give you a 4.10 ratio when activated.

In your case, if you used one, you would be able to switch to the (higher numbered ratio) to tow and when going empty, leave it off (direct) and it would be your normal "as is" ratio.

Or you could try installing a brownie box after your transmission. Someone online did on their truck... not sure which forum I saw that on....

drinkypoo 12-20-2011 06:53 AM


Originally Posted by Kaliburz (Post 2142542)
IWhen you have plenty of power, you can have a 13-15sp tranny to play with.

When you don't have plenty of power is when you need more gears. We don't have room for that much transmission in the pickup.


It's too bad that the old US Gear "under-drive" is no longer being made.
Gear Vendors makes an under/over.

Kaliburz 02-04-2012 06:10 PM


Originally Posted by drinkypoo (Post 2142567)
When you don't have plenty of power is when you need more gears. We don't have room for that much transmission in the pickup.

True.... Most semi's I see now have 10 speed and 13 speed as normal transmission. Hardly see the 15 and the browny box.


Gear Vendors makes an under/over.
Actually, their unit is just an "over drive". They advertise "under/over" because you can split the gears. Like you shift to 2nd gear, but don't want to go to third, you engage the over drive and split second to make a 2nd-over (some hve/could call it a 3rd-under). Speed up, then shift to third and turn off the OD... The options are 1:1 (off) and .78:1 (on)

I have a Gear Vendors on my pickup. It's not like the TRUE underdrive that US Gear offered. The US Gear under drive actually lowered (numerically) your final drive ratio. When it was "off" it would be 1:1 ratio. When you turned it on, it would be like 1:0.78 (sorry for the bad example...). It would turn a 3.55 axle closer to a 4:10. At least that's how I remembered it when I use to read it on their website before they went away.

JESSE 1 02-10-2012 03:44 AM

We bought a new '88 F-SuperDuty (450) diesel and the only gears offered were the 5.13. The truck would run 70 mph but you'd be pushing 3000 rpm if I remember correctly. Just not a lot of power in the N/A 7.3. I had a '94 F-350 dually with the N/A 7.3 Turbo (factory) and was really surprised how much more power the turbo provided. That was still a simple engine but quite a bit more power than the non-turbo 7.3.

burlhall 03-05-2012 09:50 PM

I bought a new 92 ford F250 with the 7.3. It did alright but I wanted a little more performance out of it. So, I put a Banks sidewinder turbocharger on it and did it ever make a difference. I made several trips over Mount Eagle pulling a trailer that weighed about 10,000 pounds. Before I added the turbo the truck would pull down to about 35-40 mph going over the mountain and at the top I think the E40D was in 2nd gear. After adding the turbo I had no trouble pulling the mountain at the 50 mph speed limit. The truck could maintain that speed in 4th gear but I would shift it down to 3rd to keep the egt's down.

montibank 01-03-2019 04:12 PM

1989 F350 7.3
Banks Sidewinder
ZF5s manual
stock tires were 285
now 315
stock gearing 4.10
installing now 5.13

Before gearing would lose speed uphill at 55 in fourth but on the same hill would hold 65 mph fine under ambient temps of 90 degrees F pulling my trailer.

My goal ... like OP is to be able to hold 55 in fourth vs. any hill when pulling my rig.

On flat ground 5 gear is stupid tall... I have no business doing 85 mph in a 30 year old truck.

Fingers crossed 65mph (actual) is around 2500 rpm if in 5th and 4th @ 55mph is around 2800 rpm.

montibank 01-03-2019 04:51 PM

Side note my truck is NOT a daily driver. It just tows my junk from place to place and pulls tree stumps.

Randy 4614 01-03-2019 08:58 PM

I have a 93 dually with factory turbo , 4.10 and ZF5 trany. 215 tires , factory size. When first got the truck , used, it had a wide ratio transmission it. I pull close to 18000 to 20000 # behind it. Had to be really careful starting or backing up on much of a grade. Had transmission problem so rebuilt it to a close ratio. Lost about 10 mph on top end , but now it will pull. We have some pretty good hills and mountains here in Montana. Yes it pulls down on the hills , but still gets me there. Get around 15 empty and 8- 10 loaded , still run down the highway 65 -70 pretty easy. this is what I pull with mine.

wpetko 01-05-2019 10:05 AM

Regearing a 4x4 truck is a big red flag for me because you would have to regear the front axle as well. I would first research auxiliary transmissions like Gear Vendors before I got into the differentials. Also, unless you are towing WAY too heavy & your truck is overloaded a 4.10 gear should be completely adaquate for any hills that you find in Florida. If the truck is having a hard time towing with your present ratios then maybe you should consider adding a turbocharger or other engine upgrades.

DENNY 01-05-2019 12:42 PM

So when you are towing at say 60 mph and you come up to a hill and start to slow down does you truck tranny shift out of overdrive? Simply dropping a gear lower in tranny will give you higher rpm and more power. What are your EGT temps and what is the location of the probe.

montibank 01-13-2019 03:07 PM

"Towing waaay to much weight" yes likely.

Shop goofed and put 4.88 in it, thank god they did. Gearing is spot on for what I wanted rpm at 55 in fourth and 65 in 5th with 315s on it. In break in now so can't pull my trailer to test. Kinda wish I did have them put positraction in it. They called halfway through the job and I said no. Regeetting that choice already... Had to put it in 4wd to get up my buddies driveway the other day. His driveway is dirt, it was raining, and it is a really steep climb.

montibank 01-13-2019 03:10 PM

Oh ... it already has a factory turbo. Not that it wouldnt do the job... it did just fine if I was willing to go 35 mph. 120 miles at 35 vs 120 miles at 55 mph is a huge difference in time.

montibank 01-13-2019 03:11 PM

zf5 ... manual not automatic

montibank 04-12-2019 10:43 PM

So ... long story short ended up with 4.88 gearing. A little bummed I didn't have to go up to 37" tires to 'fix' my mistake but 4.88 with ~34" tires is pretty *****in for towing. Fuel mileage not so much but that was not a problem I am worried about. Next up... get the speedo fixed so I can figure out my range on a fill up.

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