3:73 or 4:10 gears

THE BIGPUNN · January 27, 2003

i understand what 3:73 and 4:10 gears do as far as driveshaft turns to wheel turns. what i dont understand is why with 4:10's you can tow so much more. and is there a difference in mpg between the two? and do gears have a lot to do with torque? ???

Shaners · January 27, 2003

The gears have alot to do with torque. The engine is in it's powerband sooner, and stays there longer. My truck at 70 mph turns 2400 RPM with 4.10 gears, which is about 400-500 RPM more than 3.73 gears.

MPG's will probably be a little less in most cases, but I have heard of alot of people getting better MPG's under certain conditions because the motor is making power and not "lugging" as much.

Threejaws · January 27, 2003

I agree with Shaners, you get alot more torque.Lifted 2003, 2500HD

Beaux Duke · January 27, 2003

A lower gear ratio (higher numerically) doesn't necessarily equate to higher towing capacity. The type of towing (5th wheel or goosneck versus ball) plays a big factor.

03HD 5th wheel towing specs for 8.1 engine

3.73 = 13,600 lbs

4.10 = 15,600 lbs

03HD ball hitch towing specs for 8.1 engine

3.73 = 12,000 lbs

4.10 = 12,000 lbs

I got these figures from the GMC website. Load placement along with bearing size is a key factor in determining load capacity.

Now to try and answer your question. Gears maximize/multiply the torque an engine produces by multiplying the available torque to move a load. Here's an example:

Lets suppose an engine is making 350 ft/lbs of torque at 3000 RPM, and our 1st gear ratio is 3.36:1 and a final drive of 3.73:1.

350 X 3.36 X 3.73 gives us 4,386 lb ft of torque at the rear wheels.

That same engine with a 4.10 rear produces 4,822 lb ft of torque at the rear wheels. 436 more lb ft of torque to move the same load.

Of course there are parasitic losses from friction but you get the basic idea.

As far as MPG goes since the difference between 3.73 and 4.10 is approximately 10% you can assume that the engine will turn 10% higher RPM's consuming approximately 10% more fuel to cover the same distance. This is a rough approximation though and will vary by driver, tire size, road conditions and vehicle modifications.

Hope this helps.

CMNTMXR81 · January 27, 2003

It's a simple matter of physics in relation to leverage.

A 10 speed bike is a perfect example.

If you are lifting a heavy object using a wedge. The closer you place the fulcrum point and/or the longer the length of the wedge you use, the easier it'll be to lift the object.

Same applies to gearing.

In a 3.73 gearset, the driveshaft/input shaft will spin 3.73 times for each one turn of the ring gear (wheel). IN a 4.10 gearset, the driveshaft/input shaft spins 4.10 times for each turn of the ring gear (wheel). I.E., more leverage.

That's the simplest that I think I can explain it.

Mortgage Paul · January 30, 2003

I wish they had a 4.56 or a 4.88 gear option.

When youre towing 10,000 lbs up a 26% grade at 9,500 feet, you almost need 4W Low.

Now Lift it up on 35's or 37's and its more important. If Top speed WFO Redlined in my Truck was 90 thats enough. I want pure towing power. I could care less if I get 4 gallons to the mile when towing.

Cruiser2500HD · January 30, 2003

In regard to the 12K to 12K comparison (3.73 vs 4.10) for the 03HD Ball Hitch.... I would think that the weight limit there is more a function of what the hitch will handle rather than a reflection of the gearing.... a truck w/ 4.10s is simply going to get a load moving better than a truck with 3.73s... and it'll keep it moving better because, as was mentioned earlier, you are closer to the peak of the torque curve (higher RPM at speed) at any given moment....