RPMs while towing

[Radshooter]

Just wondering what RPMs y'all run while towing heavy loads. Our fiver is a 38 footer triple axle, and weighs around 17k, and I don't like to tow much over 65 mph. On a flat stretch of road, I am usually in 5th gear running 2500-2600 RPMs. If I shift to 6th, the RPMs drop to 1600-1700 RPM range. In fifth gear, I have no problem topping small hills without loosing speed. In sixth, I am downshifting a lot to keep from lugging the engine, so I decided to just leave it in fifth most of the time. It just seems like the 1600 RPM range is a bit low and lugs the engine a lot. If I push it up to 75 mph, the RPMs come up to around 2200 in sixth, but I don't like to run that fast with the fiver. All my guages say normal when towing, so I haven't been too worried, and I can still accelerate in fifth if I have to.



Is 2600 too close to redline for all day towing?



Thanks for your input...

Steve

 

[ndurbin]

No 2600 is fine. I've been around several of these motors in AG. uses and they run at or near the redline all day long year after year. And those are in poor conditions and sometimes poor maintence.



Nathan

 

[Radshooter]

Thanks Nathan..... I figured it was better to run higher RPMs than to lug the engine all day.



Steve

 

[jelag]

I run my 04 all the time at 55-60 mph in 5th... ... if I get much higher than 60 I go to 6th..... the truck now has 90K and pulls the trailer about 80% of the time



Jim

 

[klenger]

Given your weight and 3. 73 gears, your are doing the right thing by staying in 5th gear. If you had the 4. 10's, you should be able to run at 2100 RPM at 66 MPH, which would probably work. I'm not suggesting you switch axle gears, only pointing out that with the 3. 73's and that much weight, downshifting is a good idea.

 

[Radshooter]

Thanks jelag and klenger. It is hard to explain, but the truck just seems happy at that rpm. I looked at a few charts from links on klenger's web site, and from the looks of things, horsepower and torque both peak around 2800 rpm if I read the graphs correctly. If I run 2600, that still gives me room to accelerate some, or pour it on for a hill without having to downshift to 4th. I remember back in grade school and high school when working fields with Dad's big tractor and being told over and over "Downshift if you have to, but NEVER EVER lug a diesel. " I guess my old man wasn't so dumb after all Thanks Dad. . The older I get, the smarter you were!



Steve

 

[d.miner]

Mileage?

Radshooter,



Just curious what kind of fuel mileage you're getting running a steady 2500 - 2600 RPM?

 

[mhenon]

Radshooter, I cruise all day long in 6 gear and 1700rpm. This is somewhere around 63 mph. I don't think this is lugging the engine as you're right there in the torque curve.

I agree. . the steeper hills can't be pulled without down-shifting in high gear. . but driving through Nebraska this fall. . I never took it out of cruise.

As far as running at 2600rpm... the Cummins should do that all day long too. What an engine!

Mike

 

[Radshooter]

d. miner... When we moved from Idaho Falls to Yuma, we averaged around 8. 5 to 9 mpg with the trailer. The truck barely had 2k miles on it though, so still getting broke in. Now, at 6k, I am getting 18 highway empty.



mhenon... are you pulling a trailer at 1700 rpms? I run empty around 1700 no problems, but was wondering about heavy haulin.



I guess a new twist to my question is... Does running empty or hauling heavy have any bearing on what rpms we should be running?



Thanks guys.

 

[mhenon]

Radshooter, I didn't make that very clear. Yes, I tow a 10k lb TT mostly through through the western US and Mexico. The hills and passes do force me out of cruise and high gear... but for the most part I'm in 6th gear... running under 65 mph (about 1750rpm).

Mike

 

[RustyJC]

With the 4. 10's, I run 2350 RPM @ 70 MPH in 6th. I only come out of 6th gear when required by traffic or curves. It'll hold 6th gear on a 6% grade just fine with my engine mods. If I get much under 2000 RPM, I'll downshift primarily to keep EGTs in check. (5ver is 16,000 GVWR)



Rusty

 

[y-knot]

We have a 36' tri-axle trailer that weighs in at close to 16,000lbs, I pull it in OD and generally travel in the 65-75 mph range. My RPMs average in the 2100 area.

 

[CTA]

Just wondering what RPMs y'all run while towing heavy loads. Our fiver is a 38 footer triple axle, and weighs around 17k, and I don't like to tow much over 65 mph. On a flat stretch of road, I am usually in 5th gear running 2500-2600 RPMs. If I shift to 6th, the RPMs drop to 1600-1700 RPM range. In fifth gear, I have no problem topping small hills without loosing speed. In sixth, I am downshifting a lot to keep from lugging the engine, so I decided to just leave it in fifth most of the time. It just seems like the 1600 RPM range is a bit low and lugs the engine a lot. If I push it up to 75 mph, the RPMs come up to around 2200 in sixth, but I don't like to run that fast with the fiver. All my guages say normal when towing, so I haven't been too worried, and I can still accelerate in fifth if I have to.



Is 2600 too close to redline for all day towing?



Thanks for your input...

Steve

Radshooter ... Wow, that is quite a 5th wheel! I have the SRW, SB version of your truck. I haul "less" then 1/3 of the load you do and unlike you I don't mind running between 70 - 75 mph, which is done 99% of the time in 6th gear at around 2100 - 2200 rpm. The "other" guy I travel/camp with has a need for speed and I generally end up following him. I prefer a solid 70 but I try not to rock the boat.



No problems so far but my truck is barely broken in at around 28k. If I recall correctly, the peak HP will be at around 2800 but the peak Torque is around 1400 - 1600, isn't it?



Hope you run synthetic!



Safe hauling.

 

[rweis]

I have the 3. 54 ETC (DTT) and run out of O/D 60 mph at 2200 rpm. Has good torque, easy tow (13k 5er), get about 11 real mpg (console shows 14).



OD lugs (1600 rpm) the engine with the 3. 54.



I run DD2's KSB1-B and a Comp (no VP wire) and EGT's etc all stay well in check. My wife and I split the driving as I know she is not going to able to overtemp anything or go out of limits on anything.



Bob Weis

 

[Radshooter]

Thanks everybody for all the info. I think I will try 6th gear a little more often when we pull out of Phoenix after this contract just to see what happens. It certainly won't hurt the MPG factor.



CTA... . if our trailer only weighed 1/3 of what it does, I think I would be in 6th at 70+mph too. I am too paranoid however about having to stop 25,000 pounds of rolling steel and aluminum in a hurry when someone stupid in front of me does something idiotic. I have had the trailer up to 80 mph for a short run on interstates in 6th gear just to see how it feels. Solid like a rock (wait,,, that is cheby... ) and no problems. There was nobody around for 3 miles either direction, but I wouldn't want to have to do a panic stop from that speed. It pulls great, it is the stopping that worries me. That is why I don't like to get much above 60-65. We are full-timers, and everything we have is hooked to the truck. If we had a major wreck, we would be homeless.



Thanks again guys. I have a couple pics in my reader's rigs if anyone wants to see "the beast" Nothing spectacular, but at least it will give you an idea about why I like the 60 mph thing.



Steve

 

[rweis]

I am researching puting air over or electric over hydraulic disc brakes on my 5er to combat the "ok, now I have it going, what's it going to take to STOP it" syndrome. I only run at 60mph to keep the E=mv*v equation to something reasonable and controlable.



Less to no fade, shorter stopping distance, better peace of mind.





Still does nothing for stupidity on the road though.



Bob Weis

 

[RustyJC]

I am researching puting air over or electric over hydraulic disc brakes on my 5er to combat the "ok, now I have it going, what's it going to take to STOP it" syndrome. I only run at 60mph to keep the E=mv*v equation to something reasonable and controlable.

Bob,



I was considering this (although the electric brakes on the Mobile Suites are much better than the ones on the Jayco Designer XL were). I've dropped it, however, as some of the users are reporting a 2-3 second lag in trailer braking caused by the necessity for the electric pump to start and build up pressure before any trailer braking takes place. Not what I want in an "omigod!!!" emergency stopping situation!



Rusty

 

[Gary - K7GLD]

"On a flat stretch of road, I am usually in 5th gear running 2500-2600 RPMs. If I shift to 6th, the RPMs drop to 1600-1700 RPM range. "



You're saying your RPM increases nearly *1000 rpm* from OD back into direct?



That's unreal! On my 6-speed, the RPM definitely change from direct into OD - but I seriously doubt it's close to 1000 RPM!



Our 5er is much lighter than yours at around 6500 lbs loaded, and we usually tow even 7% Sierra grades in OD, as long as I can keep the speed up to 60+ MPH - RPM in OD with my 3. 55 diferential is right around 1800 RPM at that speed, and no lugging is evident - still good accelleration if needed. Naturally, out in the flatland, we loaf along in OD.



Guess I'll have to pay more attention to the RPM difference between direct and OD to see exactly what ours does...

 

[jeepit]

Am I not correct in thinking that anywhere in the torque curve while towing 7,000 lbs is not lugging the motor? I know I may downshift to pass but motor just chugs along at 1500 to 1700 rpm's just fine.