Turning off OD when towing
Lead Driver
Joined: Jan 2006
Posts: 7,308
Likes: 250
From: Hartford, WI
Originally Posted by Clubwagon
There is some truth to that. On level ground, aerodynamic drag is a bigger concern than weight. The answer comes down to the same thing; load and gearing. If you can pull OD comfortably, then tow in OD.
My van doesn't have a big motor (its just a 5 liter) but I use it to tow my racecar (on an open trailer) all over the US. I have 200,000+ miles towing it since '97. When climbing mountains I cancel OD at the bottom and use the power from the additional rpm to climb.
I once had to tow an enclosed car hauler (a 22 ft Pace) when a friend had the transmission (in his Chevy truck) take a dump 250 miles from home. My van could handle the weight but the aero drag meant I had to tow in 3rd gear. It wouldn't pull OD on level ground. 3rd gear worked fine but because of the shorter gear, I had to drop my speed back rather than run the motor at an rpm that was higher than I was comfortable with. I knocked my cruise speed back about 10 mph and it did just fine.
So yes, aero drag is an issue. I have seen some travel trailers that are very tall, like towing a barn, I know the drag is enormous. But if the motor will pull it the transmission should be OK. Now there are limits. If you do a bunch of power adders and don't upgrade the transmission too, then you can overpower it.
My van doesn't have a big motor (its just a 5 liter) but I use it to tow my racecar (on an open trailer) all over the US. I have 200,000+ miles towing it since '97. When climbing mountains I cancel OD at the bottom and use the power from the additional rpm to climb.
I once had to tow an enclosed car hauler (a 22 ft Pace) when a friend had the transmission (in his Chevy truck) take a dump 250 miles from home. My van could handle the weight but the aero drag meant I had to tow in 3rd gear. It wouldn't pull OD on level ground. 3rd gear worked fine but because of the shorter gear, I had to drop my speed back rather than run the motor at an rpm that was higher than I was comfortable with. I knocked my cruise speed back about 10 mph and it did just fine.
So yes, aero drag is an issue. I have seen some travel trailers that are very tall, like towing a barn, I know the drag is enormous. But if the motor will pull it the transmission should be OK. Now there are limits. If you do a bunch of power adders and don't upgrade the transmission too, then you can overpower it.
Anyways, BTS said that with my tranny, I can tow in OD without a second thought unless the tranny is hunting. Of course, that is a built 4R100 not a stock version.
Lead Driver
Joined: Jan 2006
Posts: 7,308
Likes: 250
From: Hartford, WI
Talked to Brian at BTS and he said it should be able to tow in OD unless you get some huge grade. However he said I could leave his tranny in OD and forget about it. I can tell you that his tranny is all I could want in a tranny, bar none. Well, if it was free it would be better. 
