What gear to use when towing?
 

I'm going to be pulling a trailer (with trailer brakes) with my '09 Tahoe Hybrid in less thank a month. It'll be about 4000-4500 pounds of weight (tongue weight's not bad though - trailer is double axle and the weight's fairly well balanced over the wheels). I've already had a Tekonsha P3 Proportional controller installed by the dealer. In my old truck, I would keep it out of overdrive. Now, no overdrive. Does it matter? Do I need to move it down to Manual range (M4 I guess)?

Re: What gear to use when towing?
 

The 2 Mode will use gears when it can and modes when it must. It has NO torque converter so the excessive heat from constant stall (converter) while in OD is not a problem. Run in drive. Your vehicle will easily tow at up to 12,000 lbs COMBINED total weight. Again NO torque converter that just makes heat.

You can monitor the transmission temperature if you want. You probably will not exceede 185 F. If you ever hit 200 F back off a little. (see below) I tow a 5000 lb Sea Ray as shown in my vehicle photo gallery. The day of that photo I was a little over at 12,601 for the whole rig, family, and dog on the scales. It's real easy to get up to that even with a 4500 lb camper or boat. All the extra stuff...

If you want to maximize FE while towing don't use cruise control. Let the vehicle slow down on grades up and allow the V4 fuel off to help while going down hill. Your instant FE may worry you on up hill but coming back down it will work out well.

"M" will keep the engine running on ALL 8 and deprive you of V4. M also will use the engine as a drag/brake on steeper grades down. Keep it in drive unless you need the M3, M2, M1 for engine braking on down grades.

If you want to make time you can stick your foot in it on up grades. It will shift to Mode 1 and if floored keep the engine at about 5100. Then the electrically variable ratio of the two motors will maintain peak horsepower to the wheels. Without overheating.

I have done this "drive it like you stole it" but I also dropped to 8 mpg doing it. But I can run posted speed on every grade I have ever encountered. I paid for it too at the pump.

So drive on flat and going up. M if you want to keep the brakes cool. The hybrid battery is not that big. Re-Gen braking down hill it fills up fast. Especially with the extra mass.

Keep the fluids full, watch the temperatures, and have fun.

Re: What gear to use when towing?
 

with that statement, does it mean that the gm hybrid is more than 4 speed because of the 2 mode CVT? that is comparing it with the X6 hybrid and ML450 hybrid with advertised variable 7 speed CVT tranny?

Re: What gear to use when towing?
 

The GM 2 Mode system has the four (4) fixed gear ratios and two (2) electrically, continuously variable modes. I can't remember first and second but third gear is 1:1 and fourth is overdrive at about 0.71:1. The modes are electrically variable or EVT.

In mode 1 the rear of B motor is coupled to the output shaft and in mode 2 the forward or A motor is. The planetary gear arrangement forces the following equation always true.

Engine Speed = (A speed + B speed)/2 This math is true in gear and in mode. In fixed third engine = A = B. The math holds. In fourth or overdrive gear the B motor is held at zero by a clutch. Therefore A speed is twice engine speed.

If it were tuned to act like a step gear transmission, the modes could provide many more than 7 speeds.

Re: What gear to use when towing?
 

Thanks Marty for the great advise/info! I knew the tranny was full of "special" enginnering, but - wow, that is quite a beast!! :angel:

Re: What gear to use when towing?
 

Just drive in Drive like you normally do. I tow a BMW race car on a steel trailer with no problem. Have a soft foot, watch the MPG gauge, watch the efficiency gauge on the dash. I can drive around parking lots etc with electric only. I get 15 mpg towing about 6000 pounds. Watch your tranny temp as well.

Re: What gear to use when towing?
 

some good info here by hybrid_hillbilly.

on my first tow with mine, 2k miles with about 5500 or so on the back total. I spent some time towing in m4 mode and leaving it in just normal drive. drive is much better and the tip about not using cruise is very helpful when it gets hilly. I found letting it run down the hill helped a ton keeping it in high gear on the way up. using cruise it shifts, well not really shifts since it's all modes. bit it increases rpm very often like a down shift in a normal tranny.

watching tq app, having the throttle peddle and the actual throttle body % up is interesting. you can get it to about 50% throttle body opening before it kicks down to a higher rpm mode. i averaged 13mpg over the 2k. which might not sound great, but my diesel friends get about the same in the real world, and I was running 3$ 87 not 4.50 diesel. turbo still makes for a more comfortable drive towing, but I only do it once every year or so, so no buggie. happy with the mileage for what it is.

if you have the self leveling air shocks, be careful with tongue weight, the specs I found where max 80psi shocks and 120psi compressor for them to be happy. one guy reported about 150psi it blew a line off. not what you wanna deal with away from home. the unloaded psi is around 20psi. I set my car on the trailer where it was at 80psi and it rolled nicely, no sway even thru the worst construction jumps. 140k original air shocks too. which have a bad rep for failure.

anyway, what I really wanted to add to this thread besides it saves fuel to not run cruise control is that I sent out a tranny fluid sample to black stone labs, along with my car stuff I normally do after track days. and got the results back. shows pretty good, no extra wear from running in drive or anything and steady 167deg tranny Temps. never above it, like it's got a thermostat in the tranny cooler or something. I had just changed the fluid and filter when I got it about 9k ago, was thinking of maybe changing it again after the trip, but after the test results, I'll probably let it ride.

just thought it was interesting, since the tranny is kinda the whole truck. when the tranny goes, high chance they end up in the junk yard at this point.


edit, let me edit that better

https://cimg0.ibsrv.net/gimg/www.gre...7b207e66ab.png

Re: What gear to use when towing?
 

you set the bar