I have run into what I believe is a very interesting situation....... 05 RAM 1500 crew cab 2WD 4.7L and 5spd Automatic 245/75/17 tires (30.5 dia) - build and spec sheet for my truck state it should have been built with a 3.55 rear end.... however as I am considering changing the gearing to be able to tow better with this puny motor I put together a spreadsheet with the transmision ratios, tire size and allows me to tweak engine RPM and rear axle ratio to get new calcuated speeds. I found that my calculator wasn't matching up to my real life driving - my baseline reference is 4,000 RMP, 2nd gear = 50 mph - but when using the 3.55 rear ratio the calculator says this should only give me 43 mph. I saw in some forums & spec sheets that a 3.09 axle was put in these trucks at times - so I plugged in the 3.09 ratio & guess what - I get 50 mph calcuated.

Have any of you ran into a similar situation whereby you may not really have the same rear axle ratio as was spec'd in for your truck? If so, has anyone elevated this to the dealer or to Dodge? I consider this potentially a fairly serious issue - with 3.09 gears - no frigg'n wonder we can't tow anything with this little motor - heck - even the guys with big-block trucks run 3.92's or 4.11's - of course it's all dependent upon final drive ratios.... but sample of the excel file below should shed some light on the plight of this little truck.

ps - BTW 4,000 RPM with 4.56 gears will only give 34 mph - whew, quite a drop - 4.11 gears will give 38 mph - details below

final drive final drive final drive final drive
rear end 3.09 3.55 4.11 4.56
1st 4.04 12.48 4.04 14.34 4.04 16.60 4.04 18.42
2nd 2.33 7.20 2.33 8.27 2.33 9.58 2.33 10.62
3rd 1.39 4.30 1.39 4.93 1.39 5.71 1.39 6.34
4th 1.00 3.09 1.00 3.55 1.00 4.11 1.00 4.56
5th 0.73 2.26 0.73 2.59 0.73 3.00 0.73 3.33

RPM 4000
tire dia 30.5 =245/70/17
1st 29.1 25.3 21.9 19.7
2nd 50.4 43.9 37.9 34.2
3rd 84.5 73.6 63.5 57.3
4th 117.5 102.2 88.3 79.6
5th 160.9 140.1 121.0 109.0

 

Hey Green Jeep, you and I have the exact same problem except the camper I pull is a 26' Skamper and weighs better than 5000#'s. I hit some hils bringing it home and thought that poor little engine was going to blow sky high! I'm seriously considering a 4:56 swap but I also found that Yukon makes a 4:88. I'm afraid this will be too tall for the 17" tires under normal non-towing driving though. I sure wish someone would chime in who tows with the 4.7 and 4:56's.....

 

e-mail me at darren@dunetoyz.com if you are interested in the calculator I put together to calculate speeds at given RPM's with the various gear ratio's - it didn't post too neatly as all the text got squished together. You can confirm you have the 3.92 gears.....

I'm actually on business travel this week, but will be headed to the dealer this weekend armed with the data that appears to show I got stuck with a 3.09 gears instead of the 3.55 gears spec'd on the window sticker - although I doubt I'll get them to install 4.56 gears for me... but I'm gonna try..... my poor wife is worried I am going to blow up her truck if we have to continue towing the camper with it.... she's actually wanting me to buy another old beater truck just to pull the camper..... which I might do - if I can find a flatbed truck to carry my jeep & tow the camper behind the flatbed truck.