Axle Ratio

[Sleeplessinpl]

We're getting close to buying our first 5th wheel.  It will most likely be a Doubletree or Escalade.  Before that we need to get a new truck and have settled on a GMC 3500 HD.  One of the options they offer is 3.73 or a 4.10 rear axle ratio.  I have gotten different answers from truck sales people on what this means (surprise, surprise) so I was hoping some of you folks could give me an unbiased explanation/opinion. 

Also, we are leaning towards dual rear wheels to provide better stability.  Wouldn't mind some feedback on this.

Thanks,
David

 

[Alaskansnowbirds]

David,

I can't answer your question but I know that the guys that can will want to know what the GVWR is of the 5th wheel. If you can post that then they can give you a better answer.

 

[BruceinFL]

Usually different GVWR's and GCWRs with different axle ratios. You need to look at the weight chart for the truck you want to buy and the weight of the 5er.

 

[Karl]

David,
While towing weight is certainly a consideration, the terrain you plan to drive is important too. Other things being equal, a higher ratio rear end (the 4.10:1) will pull steep grades easier than a 3.73:1, but at a higher engine rpm. If most of your driving will be on the flat, you may be better off with the lower ratio diff.

If I had to make a choice, I'd go with the 4.10:1 right off the bat and not later regretting not having done so when I'm trying to climb some steep mountain passes. Keep in mind that you may want to upgrade to a larger (heavier) 5th wheel in the future, so having the higher ratio rear end now may keep you from having to buy a new truck later. 

 

[Carl L]

We're getting close to buying our first 5th wheel.  It will most likely be a Doubletree or Escalade.  Before that we need to get a new truck and have settled on a GMC 3500 HD.  One of the options they offer is 3.73 or a 4.10 rear axle ratio.  I have gotten different answers from truck sales people on what this means (surprise, surprise) so I was hoping some of you folks could give me an unbiased explanation/opinion. 

Also, we are leaning towards dual rear wheels to provide better stability.  Wouldn't mind some feedback on this.

The way we evaluate trucks is by knowing the Gross Vehicle Weight Rating of the trailer you wish to pull.  From that, taking into account, a safety factor, you can derive the truck tow rating you need and then the truck that will give that.

So why don't we start with the trailer GVWR?

 

[egdeaile]

I had the option on my new 08 dodge 2500. I took the 4.10 despite the extra cost. My first tow through the mountains justified it completely.... No lugging or problems at all. I know the 3.73 will make it, but it likes it less. My trailer only has an 8000 GVWR, so it's not the heaviest thing out there, either.

The dually lets you handle extra pin weight, but I'm not sure if it give you anything else. I know they track poorly in the snow if the ice builds up between the tires, so if you live somewhere north that might figure in. Just make sure all your weights add up, which is explained in multiple places on the forum.

GOOD LUCK!

 

[Gary RV_Wizard]

The downside of the higher gear ratio (4.10) is that fuel economy suffers when not towing. Maybe when towing too.

As for the dual wheels, stability is not really the issue. Duals increase the carrying capacity of the rear axle, so you need duals if the pin weight of the trailer is higher than what a single wheel (SRW) configuration can comfortably handle. If you don't need duals for weight carrying, you are better off without them. The downside of duals is: a substantially wider rear end (parking space concern), more tire drag (lower fuel economy), and extra tire costs at replacement time. Duals also have reduced traction when there is no weight in the back.

So, the dual vs SRW is also a weight question - need to know what you will be towing.

 

[egdeaile]

I was originally worried about fuel consumption, but it wasn't such a big deal, I drove to Colorado Springs and back yesterday. I averaged 20 MPG for the trip. I'd love to see what a 3.73 gets....

 

[edjunior]

Most of the conversations I've seen between the 4.10 and 3.73 rear-ends as far as MPG differences have all shown to be negligble...from 1 - 3 MPG loss on average.  If you are going to tow the trailer a lot (full-timing or otherwise a lot of towing), go for the 4.10.  Especially if you will be towing in hilly or mountain areas.  You will not regret it.

 

[glen54737]

MPG differences have all shown to be negligble...from 1 - 3 MPG loss on average

I wouldn't call 10% negligible 

 

[Lowell]

Don't forget tire size when comparing axle ratios.  If you have a smaller tire on a 3.73 and a larger tire on a 4.10, there may not be much difference in engine revs. If both trucks have the same size tire, than the axle ratio comments above are true.  If the trucks have different size tires, than maybe...

 

[Vulcaneer]

Assuming your are thinking you'll go with the D/A Diesel.  Would think 3.73 would be OK with the diesel if weight of trailer is in the 12,000# GVWR range.

If you're thinking Vortec Gasser, definately go for 4.10 or more.

 

[tvfrfireguy]

If you choose the diesel engine, it is only offered with the 3:73 gears.  The service manager told me that with 365 hp and 660 ft lbs, of torque, people would be damaging there drive trains if 4:10's were installed.