It's all a mathematical formula. You have to take entire drivetrain into consideration......and what you plan to do with it. Engine RPM (HP/TQ), transmission ratios, differential, tire size, etc...

There are ratio calculators on the web you can use to figure it out.

Fwiw, I think 4:30 is perfect for the 5.7L N/A. With the Supercharger, I have considered a 4:10 swap.

 

No, stay with the factory options. Gearing in the Tundra's transmission is designed for lower differential gears, especially overdrive. Whenever looking at differential gears, you need to consider how the transmission is setup.

Take Ford F150 for example...it comes with 3.55 gears, BUT 4th gear is 1.14:1 ratio. Tundra has 1:1 ratio, thus requiring lower gears.

 

I agree, you have to look at the drive train completely.

This is the F-150 6 speed

4.17Transmission gear ratio (1st)
2.34Transmission gear ratio (2nd)
1.52Transmission gear ratio (3rd)
1.14Transmission gear ratio (4th)
.86Transmission gear ratio (5th)
.69Transmission gear ratio (6th)

Gear selections 3.31, 3.55, 3.73 (depending on which motor)

Tundra 6 speed

3.520
2.042
1.400
1.000
0.716
0.586

Gear selections for the 5.7 4.30

What your looking for is overall driving performance. For instance, my 2003 Jeep Wrangler came with 4.10 with 31" tires. I am now running 5.38 gears and 40" tires. With that gear ratio it is as close to factory as possible for performance. Do you thing it feels like that? Nope, I'm looking at a Chevy LS V8 swap sometime soon.

Here is a good website to calculate what your looking for and the performance differences you can expect. Hope this helps.

http://www.grimmjeeper.com/gears.html

 

What are you using it for? Although I agree that the overall setup has to be considered (transmission will just downshift as necessary), if you are towing you probably want deeper gearing (4.30:1) and if you are after mpg then you want higher gearing (4.10:1 or even taller, albeit not an option). Pretty generic truth right there. Only modification is, tall gearing and hilly terrain might be annoying, if the transmission keeps downshifting--a deeper rear gear may be better. Same goes for city driving.

Don't know about the newest ones, but is the 5.7 only available with tow package, and thus 4.30:1? Is it just the 4.6 which can be tow/non-two, and thus with 3.90:1 / 4.10:1? IMO, tow package adds a bit of value (it's a truck!), and, at least on my 4.6, while I wouldn't mind the 3.90:1 on flat ground while not towing, the truck downshifts enough in the hills with its 4.10:1.

In some ways I wish it had my 4.6 had 4.30:1; seems like the 5.7 would be quite happy with 4.10 unless if towing at the limit. I wonder why Toyota didn't make it an option, like the Big 3, so as to let consumers chase mpg vs towing. Whatever. But eh, I'd rather have the tallest gear while unloaded, and I can easily drive in a lower gear while towing. Regardless of rear end ratio, getting a load moving isn't the problem.

 

Thanks, guys! Right now, I'm not using it for anything - don't have one yet! I'm like old (actually new member) MustGo, researching all makes of trucks still, and just wondered about Tundra's differential. Think I understand now, I didn't think about transmission ratio too. For my needs, towing a 6,000 lb. trailer, I think the 4:10 will be good.

 

For my needs, towing a 6,000 lb. trailer, I think the 4:10 will be good.

Then you will be getting the 4.6L, as the 4.6 w/tow pkg comes with 4.10 gears, correct?
The 5.7 w/tow pkg comes with 4.30 gears.
They come like this from the factory and you won't find a 5.7 with 4.10 gears unless it doesn't have the tow pkg.
I guess you could get a 5.7 without the tow pkg and 4.10 gears and then install an aftermarket tow pkg. but that's a lot of work just to have 4.10 gears.
The tow pkg comes with wiring for a trailer brake and extra engine and tranny oil coolers. It also comes with "TOW" mode, which I believe is different computer programming/shift points for the tranny. Like I said, kinda silly to forgo an entire factory installed system and all it's components, just to get the rear end gears that you think might be better.
Toyota decided that 4.30 would be better for towing a 6000 lb trailer with the 5.7, so I trust they did the math. Besides that, if they gave more options, they would have to deal with people ordering all different configs and then complaining about mpg or lack of power when towing, etc. They're better off just picking the best overall gearing and not dealing with all that.
Unless you want the 4.6 V8 with tow pkg and 4.10 gears, then disregard what I said.
Just trying to save you some frustration, if you were thinking you could order different configs.

 

My wife's Land Cruiser 200 Series (same drive train as the Tundra 5.7, but has the same rear axle as the 4.6) has 3.90 gears. We live in the mountains of western Massachusetts.... I already have 4.30 differentials on the shelf, and will be swapping them in asap. For flat land the 3.90 ratio is probably excellent.

 

Good information! Thanks!