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Gear swap

Benefits of swapping gear

Gear swap

Postby aaronK9 [OP] » Dec 29 2020, 11:12am

Hi guys,
New to SSforums.
Planning on purchasing a new Travel Trailer soon. The GVWR of the trailer is approx 7500#.

I've got a 2013 GMC Sierra 1500 crew cab short box 4x4, 5.3L, 3.42 gear ratio (Code GU6). Everything I've read (including the owners manual) shows my truck is rated at about 9400# towing capacity. I have the HD towing package (Z85) including the trans cooler, oil cooler and an AFE cold air intake and I just replaced the old worn out stock shocks to new Bilstein 5100 series Shocks all the way around. I also plan on adding air bags and a weight distribution hitch.

My question is what are the benefits of changing my gearing from 3.42 to either a 3.73 or a 4.10?

Yes, I've read a lot of other threads in here, and haven't really found a definitive answer. I've read it helps with towing, but in what ways exactly? I realize it may or may not increase the amount I can tow. I'm not interested in that so much as I don't plan on going over the vehicle rating of 9400#.

Basically what I'm looking for is better towing capabilities. I live in the foothills of Northern California and most of the towing that I'll be doing will be mountainous roads.

If it's not going to make that much of a difference I won't go through the trouble. Thanks for your guys advice and opinons.
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Re: Gear swap

Postby GBSierraSLE » Dec 29 2020, 4:31pm

I'm sure others will chime-in, too.

Changing gear ratios will make it easier to tow but it will not increase the amount you can tow. You run out of payload capacity long before reaching your tow limit anyway. That won't change with a gear change. I would not tow more than 6,000 to 6,500 # with a 1500 truck regardless of what GM claims you can tow. If you want to tow 9,000 #, get a 2500.

Switching from 3.42 to 3.73 you won't even notice the difference. Changing to 4.10 would be a sweet spot with stock tires. I don't tow but wish I had 4.10 instead of 3.42 on my '13 with 33" tires.

Speaking of tires, if you're going to be towing a lot, I would switch to E rated tires. Much more stable for towing.
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Re: Gear swap

Postby 19trax9519trax95 is online! » Dec 29 2020, 6:22pm

That camper is right on the ragged edge for a 1500 to tow comfortably in my opinion. You will get pushed around quite a bit in any sort of wind.

But as far as the gear ratio goes, essentially, the lower ratios(higher numerically) will help to keep the motor in its power band more. This is done several ways, with the transmissions, and with gearing. The 6 speed transmission, while much better than the older 4 speed transmissions, still don't have the gear choices like the newer 8 and 10 speed transmissions do, which means that a change I'm gear ratio will help more for towing performance, but could hurt your fuel mileage when not towing due to the higher rpm while cruising.

That's where the newer 8 and 10 speed transmissions shine. You can have a relatively tall gear ratio in the diff, but the trans can make up for that, so you get good performance off the line, yet lower rpms while cruising.

However, 4.10 is about perfect for stock size to 33" tires with the 6 speed trans.
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Re: Gear swap

Postby 00pooterSS » Dec 29 2020, 6:32pm

The gears will help get the weight of the trailer moving with less strain on the truck.

Don't forget you need to stop that trailer, make emergency maneuvers etc..

The whole truck needs to be considered when towing.

I would be really uncomfortable towing 7500 with a half ton truck, and lets be honest, that trailer is going to get loaded down with more and more stuff as time goes on, and the truck will get heavier with equipment etc you take with you.

If you won't go to a bigger truck, at minimum do the above and upgrade the tires to to E rated LT tires preferably.
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Re: Gear swap

Postby CritterGitter » Dec 29 2020, 6:37pm

It sounds like you'd like to understand the concept of final drive ratio a little better. You don't need to look any further than some of the knowledgeable fellas online that do a pretty darn good job of explaining it. (youtube) Spend a few minutes and watch a couple of them.

Without delving into the math part, I'll give you a very simplistic explanation of what you'll get from changing your gear set (changing your final drive ratio). You will achieve greater torque to the wheels in each gear. As it applies to the towing, you'll notice the truck pulls your load easier because your getting more of your engines torque in every gear when going to a 4.10 from 3.42 final drive. It is absolutely a noticeable difference in your towing experience but you want to jump up more than a 3.42 to a 3.73 ratio. It just doesn't make sense to spend the amount of money you'll spend for this only making a minor change in final drive ratio.

A couple drawbacks will be decreased fuel mileage on the highway because your truck will sit at a higher RPM after jumping to a 4.10 gear set. You'll also have a lower top speed in every gear. The trade off can still be worth it if your gonna tow frequently. You just have to way the pros and cons. Your gonna have at least a couple thousand in a job like this changing your gear set in a 4wd. (unless you do the work yourself or know willing/able experienced mechanic)

Hope this helps and remember to do some research if you want a more "scientific" explanation of final drive ratio.
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Re: Gear swap

Postby 00pooterSS » Dec 29 2020, 7:31pm

A tune will be needed too, to correct the speedo and shift points etc
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Re: Gear swap

Postby roorancher » Dec 29 2020, 8:21pm

Do yourself a favor.....If you're going to be towing 7500+ pounds, especially thru the foothills and mountainous roads, invest in a 3/4 ton truck.
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Re: Gear swap

Postby aaronK9 [OP] » Dec 29 2020, 9:59pm

CritterGitter wrote:It sounds like you'd like to understand the concept of final drive ratio a little better. You don't need to look any further than some of the knowledgeable fellas online that do a pretty darn good job of explaining it. (youtube) Spend a few minutes and watch a couple of them.

Without delving into the math part, I'll give you a very simplistic explanation of what you'll get from changing your gear set (changing your final drive ratio).


Thats perfect. Thank you.

As for getting a new truck? Right now its not feasible do plan on getting a tune if I do this. I also plan on getting a chip and set it for towing when towing and economy when not towing. I do know a guy who could help me with this project. I meant to add that the 7500# weight was a fully loaded trailer. Dry it weighs appropriate 5700#. I know totally understand that fully loaded it would be a lot, but I don't plan on dry camping very often. I like some of the conveniences of having hook-ups. Haha
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Re: Gear swap

Postby 19trax9519trax95 is online! » Dec 29 2020, 10:04pm

Get with Lew for a tune. No need for different tunes on a stock gasser. One good tune will do everything well.

Lew is THE man for tuning these trucks, both engine and trans. https://www.diablewtune.com/
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Re: Gear swap

Postby MacQ » Dec 29 2020, 11:40pm

GBSierraSLE wrote:You run out of payload capacity long before reaching your tow limit anyway. That won't change with a gear change. I would not tow more than 6,000 to 6,500 # with a 1500 truck regardless of what GM claims you can tow.


Great advice and so true! I tow a 3820 lbs (dry weight) camper with my 1500. Even then, the "dry" tongue weight eats up 28% of my 1624 lb. payload capacity. However, that dry weight does not include things like propane tanks sitting on that tongue, gear in the trailer, food, water, etc. Add my fat ass, mama, the dog, and camping gear to the mix and the payload reserve diminishes quickly!

I rule of thumb I was told to follow is to tow no more than 66-70% of your rated tow capacity (that would be about 6200-6580 in your case).
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