315's and 5th gear or 295's and 6th gear?

[JMalliet]

I have searched for an hour, and have not come up with an answer myself yet. This weekend i'm going to be towing a 30ft car hauler with 2 offroad rigs on it for 2 hours, GCVW of 20,000 lbs. I have 2 sets of tires/wheels, 315's on 17" wheels, and 295's on stock 16" wheels. The truck is an '01. 5 HO 6speed with 3. 55's, mods in my signature. Towing with the 315's in 5th would put my rpms around 2100-2200 rpm (showing 55mph on speedo actually going 60mph). With the 295's at 60mph in 6th I would be at 1800 rpm. I think that low of rpm would cause my EGT's to be to high. I have towed GCVW of 14,000 lbs in 6th with 315's at 65mph with EGT's staying at 900-1000* pre turbo. Empty cruising at 60mph (55mph on the speedo) i'm at 750* pre turbo, with alittle head wind i'm at 800*. Also that higher then it should be empty? Any input on what I should do?

 

[JMalliet]

Anybody have any input on which tire/gear I should use? Will 2100rpm be better then 1800 rpm?

 

[Rockcrawler]

I'd run the bigger rubber in 6th but that's me. With my 01 mildly bombed 3. 54/285/16's I ran great at 20k with a 5 speed.



My 03 runs the bigger rubber but lower gears and a six speed. My experience has only shown EGt issues at higher elevations and sustained higher RPM (2700+)



wrose case is you'll have to adjust your speed/gear choice to make your EGT happy- it's only a 2 hr trip right?

 

[JMalliet]

Yes, it's a 2 hour trip one way. I'm thinking of leaving the 315's on, run it in 5th for a while until the EGT's cool down from accelerating then try popping it into 6th. Like I said above, when towing just the one rig on a single car trailer the EGT's were between 900-1000* pre-turbo in 6th. I'm afraid with this load being twice the weight as that one, they will be to hot. In 6th gear with the 315's at 60mph (55 on speedo), im only revving at about 1550-1600 rpms. That might be bogging the engine to much.

 

[nps]

I tow my 11k+ 5er at 1600-1650 RPMs all day. No problem. Lugging is when the engine cannot produce power to accelerate the vehicle. I have no problem accelerating at 1600 RPMs even when under a load.

 

[JMalliet]

nps, what are your EGT's at while towing you 5'er?

 

[nps]

nps, what are your EGT's at while towing you 5'er?

Cruising on flat land are about 950-1000*. It takes a 5% grade to downshift to 5th, and I can hold 50mph up any hill. I never tow over 65mph and never allow the EGTs to exceed 1250 - I only need to downshift to keep them in check - I'm EGT limited not power limited.

 

[JMalliet]

Ok, thats what I was wondering. My EGT's limit me also, I have never ran out of power climbng a hill.