I have a 2007 Dodge 1500 Hemi 4X4 with 37 12.50 20s. What gears should I get for it if I want a better fuel efficiency and I wont be offroading? This is my primary daily driver. Thanks for the help. Pics will be coming soon. It looks pretty good. Also, where can I buy the gears from?

Thanks
Black Mamba

 

4:56 hands down. 4:10 with 37's and you will only notice a hole in your wallet.

Worth every penny! Gears and DTT are the two best things I have done yet.

 

+1 on the 4.56's and here's an idea of what you're looking for:
http://moesperformance.com/index.php...oducts_id=1163

Later on down the road I'm looking to get a DTT diff. So if you can spare the bit extra $, get one (or even a different LSD or locker even) and have it installed at the same time.

Good luck.

 

i have 4.56's and im running 35's, drives better than it did with the factory setup, get the 4.56

 

Well it looks like 4.56 is the way to go! Thanks guys...but what is at DTT or LSD??? I was told to just get the whole drive shaft replaced. Is that basically what you guys are telling me? I will post some pics as soon as the weather cooperates long enough to get it cleaned up!

 

Why in the world would you get the driveshaft replaced? The weak link is the CV axles up front NOT the driveshaft or the 9.25" solid rear!

A DTT is a Detroit Tru Trac LSD, that or an Auburn Gear LSD would be your best choices. LSD as in Limited Slip Differential.




Oh, and you do know on a 4x4 you have to replace the ring and pinion in both the front AND the rear, right???

 

Here's a helpful link.

 

Gear Ratio & Tire Size Chart


Good "rule of thumb" calculation is to mutiply .12 by your tire diameter. (.12 X 38" = 4.56)
) The below table can be used to get a rough idea on gear ratios. The colors represent ideal RPM's at highway speeds (65). For highway cruising and best fuel economy stay towards the yellow (2600 rpm), around town daily driving is color coded green (2800 rpm), and for better towing power or just more 4-low power use the ratios near the red (3100 rpm). These calculations are assuming a manual transmission with a 1:1 ratio. If you drive an automatic your RPMs will be slightly higher, and the opposite is true if you have overdrive (your RPMs will be slightly lower).

Better Gas Mileage Near Factory Ratio More Power




http://www.4lo.com/calc/geartable.htm

 

I've found that this chart is a bit outdated. I first saw this chart in a magazine years before there was even an internet and MOST trucks had manual transmissions. So the numbers are skewed quite a bit high, especially in our trucks with the 545re tranny that essentially has two overdrives. But it gives a good general idea.

If you went by the true numbers on that chart, then by my calculations you'd need 6.17 gears to be in that "ideal" range with 35" tires and that would be crazy (not too mention they don't exist). Something around 2100 rpms would be a good number to shoot for for maximum efficiency at 65 mph.
For comparative purposes, I was around 1600 after I installed the lift and 35s with the stock 3.92 gears and am just a hair under 2000 rpm with the 4.56s, so 4.88s would probably be ideal for 35's with our truck/tranny combo. Only problem is, 4.88s don't exist for the front of our trucks...

 

Thanks fellas! I really appreciate it.