Confused again about rear end ratio

I am looking for a truck and want optimum fuel economy . I will be hauling campers . I will be stretching the frame so that one camper will be on the bed and then I will be pulling one behind . I need to have 22.5 LP for height requirements . Because of the length of bed , I can not have more than a 66" sleeper which limits my choices . It seems that every truck that I find with a 60 - 66" condo sleeper , Detroit 12.7 and LP tires have a high number rear end ratio . I usually drive between 62 & 66 mph . I found a 2000 Freightliner with a 12.7 Detroit , 13 speed but it has a 3.73 rear end . Plus , I would have to change the tires from 22.5 to 22.5 LP which to my understanding would raise the rpms even higher . With my application ( very light loads ) , would this rear end be unwise ? Does the higher the number usually equate to a heavier load application ? In camper moving , if you don't have excellent fuel economy , you won't last too long . Am I making a mountain out of a mole hill ?

 

Your over thinking this way too much. The 13 speed will take care of any issues you may think you have, you have control of this with gear selection and rpm. That light of load really does not dictate anything special gearing at all. Hauling campers is virtually hauling empty trailers... no worry.

 

HUGE mountain out of a tiny mole hill. To go from 22's to lo-pros will make very little difference in rpm's.If you run at mid 60's for speed, it all seems about right. Main question is the truck in good shape ?

 

yes, your tire size WILL matter.

http://www.csgnetwork.com/multirpmcalc.html

I looked at this just this morning as I was trying to figure out, "LP 22.5 or 11R22.5?" for my next set of tires.

It means the difference of running 65 MPH at 1378 RPM or 67-68 MPH at 1378 RPM.

May not seem like a difference, but that's 2.5 mph difference. Just driving across IA, that means you'd record an 8 mile difference in your odometer. (discussed that with a friend that went from LP 24.5 to tall 24.5 tires on his Pete. That's just ONE state, ONE time without correcting his computer setting.

Go that way, it would appear to help your IFTA out. Go the other way, you'll pay more in your IFTA. Just one of the areas it will effect. Changes your final overall gear ratios as well.

 

HUGE mountain is what I was hopeing for !! I have been looking for months and always come back to this one . Looks good in pics and content but haven't seen in person yet . Haven't done the ECM or dyno check yet either . THANK YOU to both of you .

 

I will be going from a 11R22 .5 to a 255/70R . 22.5 LP . I will have to have the speedo and odometer reset .

 

Correct me if I am wrong but I thought that a 255/70 R 22.5 is a LP

 

I had a 99" FLD120 with a 12.7 DET, 10spd and 3.90 rears. I got 7-8mpg going 63mph pulling a van trailer and it was a flat-top truck.

The 12.7 engine requires higher ratio rear-ends for optimum performance. It is not like the 14L or 15L that do not need the higher rpm's.

You will be fine with the 3.70's..... and a question about the 225LP's, how tall is the campers you will be pulling??? They can't be over 8' in height I am thinking or you will be running over the legal 13'6" requirements.