Posts about rpm's and gearing come up all the time and I searched through many of them before making the call on my current gearing. In order to find out which was best for me, I broke down all the rpm's for each of the gears. I get asked the question all the time so I though this might be useful to some who are contemplating regearing their 1500 like I did, or use a base line to recalculate tire sizes etc. Now I realize that some trucks may vary in #'s due to overall tire size or fluctuations in speedos and I'm not looking at arguing numbers with anyone but these are the actual #'s with the stock 245/70-R17's on my 2004 with the 5spd Auto and 5.7 engine

Now I'm sure many wonder why I want the 4.56's with those 'little training wheels' but for me it comes down to 2 things. Since the '04 doesn't allow the 4th gear to be locked out, I found it annoying while towing bouncing between 4th and 3rd and loosing 5th completely. Second, who wouldn't want to get to the next red light a little faster. And the look on those kids' faces when they try to get around me in their rice rockets is pretty priceless too! lol.

Row for each gear (3rd-5th)
Column for each gearing
3.55 3.90 4.1 4.56

140km/h or 87mph
d 3617 3973 4177 4646
od1 2625 2884 3032 3372
od2 2333 2563 2695 2997

120km/h or 75mph
d 3100 3406 3580 3982
od1 2250 2472 2599 2890
od2 2000 2197 2310 2569

110km/h or 68mph
d 2842 3122 3282 3650
od1 2063 2266 2382 2649
od2 1833 2014 2117 2355

100km/h or 62mph
d 2583 2838 2984 3318
od1 1875 2060 2165 2408
od2 1667 1831 1925 2141

 

Good write-up. With 35" tires, my RPMs are a good bit lower than yours. For example, at 70 mph with my 4.56 gears I'm at about 2100 RPM...

 

Thanks and at least we know the numbers work out... your tires are about 15% bigger than my 30.5" so if you add that 15% to your 2100, you're just over my 68mph #. It might not be 100% accurate but it should serve as a pretty good guideline.

 

With 34" tires and 3.92s at 60 im at 1600 RPMs, 70=1750 and 75=1900. These are all in 5th gear and with SC Performance tune

 

Nice.

I just used this as a guide in .67 (Final Drive Ratio)
mph x gear ratio x 336
__________________ x gear ratio trans
Tire diameter

I run 4.56's with 28" tires and its a great medium for me even though i miss the axle slapping hole shots of my 4.88's.

 

Here is the my calculations based on tire sizes and gear ratios in 5th gear.
RPM at 60MPH
5th Gear 30 31 32 33 34 35
3.55 1599 1547 1499 1454 1411 1371
3.92 1766 1709 1655 1605 1558 1513
4.1 1847 1787 1731 1679 1629 1583
4.56 2054 1988 1926 1867 1812 1761
4.88 2198 2127 2061 1998 1939 1884