gear changes for better towing

lancekeys wrote:

I am thinking of possibly changing the gears to raise my RPM so that I will have more power at a slower speed. My truck has the factory original 3.55 gears and I was thinking that switching to 3.73 or 4.11 would help.

As others have said, you cannot increase power by changing your gears. But you're not trying to increase power, you're trying to make more available at a slower speed.

If you're happy with the power you currently have at 70mph, but want that same power at 60mph, you need to re-gear such that the RPMs you now have at 70mph will be what you get at 60mph. 70 / 60 ~= 1.17, so you need about a 17% increase in RPM, and therefore a 17% change in gear ratio, to make that happen.

If you're currently running 3.55s, you'll need 3.55 * 1.17 ~= 4.15. In other words, 4.10s will give you pretty close to what you want.

-- Rob

If you're re-gearing (assume it's a 2wd or cost will be about what the truck is worth!), try to find a junk yard or used axle to swap out. Cheaper and easier than having it re-geared and then you cna likely sell the old axle for about what the new one cost. I see lotsa people parting out Older Dodge diesels. You could actually get a better/heavier axle that would bolt right in and maybe research it, but with a simple master cylinder switch you may be able to bolt in an 01.5 and up rear end with factory rear disk brakes!

Yes I misread the 3rd vs 4th. 3rd does calculate 55.1 at 3428 :)

4.56 gear will put you 60mph, 2873, 4th gear :B
Should be a sweet spot cruising and much easier accelerating from a stop.

With a 5 speed transmission the 5th gear is an overdrive gear. When towing you will want the gas engine in the RPM range where it produces its peak torque while in 4th gear at 65 MPH. If your engine produces max torgue is at 4200 RPM as with the current Chevy V-8 and the truck in 4th gear is at 3300 RPM at 65 MPH you have too tall a gearing setup.

Having 3.55 gears you were already in trouble and going to bigger tires was exactly what you should not have done. With GM trucks the 4.10 rear end with the gas engines increases the tow rating by 25% over the identical trucks with the 3.73 rear end. But for your situation check the RPM's at 65 MPH and see how much of a change is needed overall and then see how much you might gain from changing the tires and how much from changing the gears.

Going from 3.50:1 to 4.11:1 will increase engine RPM's by about 14% and going from 3.50:1 to 4.57:1 will increase engine RPM's by about 20%. A shop that specializes in gear swaps should be able to help you check the math.

It may be possible to change only the gears and not the oversized tires presently on the truck which would save you some money.

Of course it does not add up. When figuring gears you need to multiply not add!

In third gear like I stated, I run 3428.2 rpm at 55miles an hour

third gear in my standard transmission 5 speed, two wheel drive is 1.67:1
fourth gear is 1.00:1
Fifth gear is 0.75:1

I can do the math, but math does not make up for real world experience, which is what I was looking for (and found) when I asked the question.

lancekeys wrote:
I am driving in direct. 4th on the 5 speed is 1.00:1 in third I turn 3500 at 55 mph, so going down another gear is out of the question.

3500 rpm, 32" tire, transmission 1:1 direct, 3.55 ratio = 94 mph

www.4lo.com

Something does not add up. Even 4.56 you should be going 73 mph.

mooky stinks wrote:
What the OP needs is an upgrade. He's pulling a 28' 5er with a 245hp engine. No offense but it's 15 years old and the technology has produced another 100 HP out of the same size engine. Gearing is nothing more than a band-aid, and a very exspensive one at that. I didn't see if it's 4WD, if it is, double the price of the gear change. You would be better off putting the stock size tires on it until you can upgrade to something with more power.

And that 28' 5'vr weighs in around 10,000#(+)

I'd try and attitude adjustment first. you're towing a heavy object driving a heavy object. If you can rationalize being OK with slowing down a little bit, while also visualizing the cash saved (and thus available for other purposes) you'd be golden.

Otherwise ... tough call to throw more money at your current rig. I have a 1999 F150 and I go through this every now and then, for now I haven't messed with it. Newer trucks have more powerful engines but more importantly 6 or 8sp transmissions to work with. An 8 speed transmission would make a huge difference just on its own.

I took the band-aid remark to be referring to the too small of the engine for that load and not the gearing per say. Climbing larger hills that engine is going to be at or near the 4000 RPM to handle that rig and on the level OD will be geared too high when towing I expect. 2nd gear will be required climbing steeper grades (over 3-4). Gas engines when climbing must be in the 3500-4500 RPM range depending on the engine/load to protect the engine and automatic transmission.

4.10/4.11s for sure and I would consider 4.30s possibly. There are lots of RPM calculators out there. Make a spread sheet for each transmission gear and the respective RPMs you'd be towing at. True the key to look at is your Over drive and Direct drive RPMs at highway towing speed. If you get those where you want them the rest will likely fall in place. FYI, gearing is the furthest thing from a band aid that I can think of, that's a ridiculous statement!