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windsorbill · 10-10-2020, 05:41 PM

I usually run in eco mode and allison shifts into 6th about 62mph. Now if I were to run at 55mph (legal speed in Calif towing) tranny will not shift into 6th, no matter what.

I would like to compare mpg at 55mph in 5th gear VS 62mph in 6th gear. Assuming all level driving of course. 62mph is less rpm, but more wind resistants.

Anyone have a theory?

Crasher · 10-10-2020, 06:43 PM

Quote:

Originally Posted by windsorbill

I usually run in eco mode and allison shifts into 6th about 62mph. Now if I were to run at 55mph (legal speed in Calif towing) tranny will not shift into 6th, no matter what.

I would like to compare mpg at 55mph in 5th gear VS 62mph in 6th gear. Assuming all level driving of course. 62mph is less rpm, but more wind resistants.

Anyone have a theory?

One of the benefits of the eco mode is that mine does shift into 6th near 55 mph. In normal mode it has to be over 60. The other nice thing about eco mode is that it will stay in 6th gear down to 49 or 50, as that is where it is in peak torque rpm. So far, the only reason I can see to run in normal is for cooling if needed. I just like the engine working at it's most efficient rpm. 6th gear at 55 mph should be more efficient than 5th due to a slightly lower rpm. I'm guessing the increased wind resistance at 62 vs 55 would negate any gain from being in a higher gear.

windsorbill · 10-10-2020, 06:57 PM

Quote:

Originally Posted by Crasher

One of the benefits of the eco mode is that mine does shift into 6th near 55 mph. In normal mode it has to be over 60. The other nice thing about eco mode is that it will stay in 6th gear down to 49 or 50, as that is where it is in peak torque rpm. So far, the only reason I can see to run in normal is for cooling if needed. I just like the engine working at it's most efficient rpm. 6th gear at 55 mph should be more efficient than 5th due to a slightly lower rpm. I'm guessing the increased wind resistance at 62 vs 55 would negate any gain from being in a higher gear.

interesting. The only way I can run along at 55 in 6th is to accelerate up to 62+, then let it slow down. If I was even going on a slight downhill, I'm not sure how low I could go before it would down shift to 5th. And that would be in eco mode.

Now you got me thinking. I'm going to have to experiment on the next trip.

Ray,IN · 10-10-2020, 06:58 PM

Quote:

Originally Posted by Crasher

One of the benefits of the eco mode is that mine does shift into 6th near 55 mph. In normal mode it has to be over 60. The other nice thing about eco mode is that it will stay in 6th gear down to 49 or 50, as that is where it is in peak torque rpm. So far, the only reason I can see to run in normal is for cooling if needed. I just like the engine working at it's most efficient rpm. 6th gear at 55 mph should be more efficient than 5th due to a slightly lower rpm. I'm guessing the increased wind resistance at 62 vs 55 would negate any gain from being in a higher gear.

I agree with your last sentence.
It says in that article to leave in eco-mode and manually downshift one gear. i have no idea which is best, or if it actually makes a difference for RVers. personally I let the Allison TCM do the thinking.

96 Wideglide · 10-10-2020, 07:00 PM

Quote:

Originally Posted by windsorbill

I usually run in eco mode and allison shifts into 6th about 62mph. Now if I were to run at 55mph (legal speed in Calif towing) tranny will not shift into 6th, no matter what.

I would like to compare mpg at 55mph in 5th gear VS 62mph in 6th gear. Assuming all level driving of course. 62mph is less rpm, but more wind resistants.

Anyone have a theory?

Bill, we likely have the same drive axle gear ratio.
In eco mode, mine will stay in 6th on small rises like overpasses at 61mph. Thats where I set the cruise control driving in Cal.

Never tried it because I don't want semi's slowly passing me,(ie running along side me) but I would think you would get a little better mileage in 5th, at 55mph, for the reason you mentioned.

Crasher · 10-10-2020, 07:08 PM

Quote:

Originally Posted by windsorbill

interesting. The only way I can run along at 55 in 6th is to accelerate up to 62+, then let it slow down. If I was even going on a slight downhill, I'm not sure how low I could go before it would down shift to 5th. And that would be in eco mode.

Now you got me thinking. I'm going to have to experiment on the next trip.

I would question whether your Allison is actually going into economy mode if you have to run up over 60 for the shift. That's the shift point for normal position.

96 Wideglide · 10-10-2020, 07:13 PM

Quote:

Originally Posted by Crasher

I would question whether your Allison is actually going into economy mode if you have to run up over 60 for the shift. That's the shift point for normal position.

That's going to depend on your differential gear ratio.

windsorbill · 10-10-2020, 07:26 PM

Quote:

Originally Posted by Crasher

I would question whether your Allison is actually going into economy mode if you have to run up over 60 for the shift. That's the shift point for normal position.

That's a good question. I don't know. We're headed out late next week. My wife is going to be asking why are you speeding up and slowing down so much.

windsorbill · 10-10-2020, 07:37 PM

Quote:

Originally Posted by 96 Wideglide

Bill, we likely have the same drive axle gear ratio.
In eco mode, mine will stay in 6th on small rises like overpasses at 61mph. Thats where I set the cruise control driving in Cal.

Never tried it because I don't want semi's slowly passing me,(ie running along side me) but I would think you would get a little better mileage in 5th, at 55mph, for the reason you mentioned.

Mine is exactly the same way. 61 on cruise and as long as it's rolling gentle inclines, it will stay in 6th. But I nearly always push the eco mode button.

I've never had an issue running at 61-62 towing in CA. Semi's are often doing 60+ too. CHiP are going after the guys doing 90+ or darting in and out between traffic.

Wrascal · 10-10-2020, 08:01 PM

I have ZERO knowledge / Zero experience in a motorhome, but I do know this has been argued extensively on many automotive forums. My belief is the design engineers know more about it than I do.

In my private vehicles this grand-pa driver uses Econ mode and has no qualms about it. Same-same for the now standard engine auto stop/ start systems that have many owners complaining.

windsorbill · 10-10-2020, 08:31 PM

Quote:

Originally Posted by Wrascal

I have ZERO knowledge / Zero experience in a motorhome, but I do know this has been argued extensively on many automotive forums. My belief is the design engineers know more about it than I do.

In my private vehicles this grand-pa driver uses Econ mode and has no qualms about it. Same-same for the now standard engine auto stop/ start systems that have many owners complaining.

Sorry, but I'm confused. If you have no experience in motorhomes, why is your signature a 2010 Tiffin?

Crasher · 10-10-2020, 09:57 PM

Quote:

Originally Posted by windsorbill

interesting. The only way I can run along at 55 in 6th is to accelerate up to 62+, then let it slow down. If I was even going on a slight downhill, I'm not sure how low I could go before it would down shift to 5th. And that would be in eco mode.

Now you got me thinking. I'm going to have to experiment on the next trip.

If you have to get above 60 for it to shift into 6th when in eco mode, how fast do you have to go to shift into 6th when in normal mode??

On a recent long incline, we started up at 65 mph in eco mode and was down to 50 at the top and it was still in 6th gear @1400 rpm, peak torque.

asuperheat · 10-11-2020, 04:48 AM

Quote:

Originally Posted by Crasher

I think it climbed long inclines better when pulling in or near the peak torque rpm. My silverleaf showed a maximum of 1175# of torque @1400 (rated at 1250), and only 390hp (rated for 450) @2000-2200 rpm. Of course as the rpm's go above 1400 , the torque level goes down. If the Silverleaf is accurate, the engine is not developing maximum power. I could have it tweaked up, but where it's at leaves a safety margin for EGT and load on the transmission rated for 1250# torque.

That is TQ at the crank shaft you are seeing but you loose TQ to the wheels every time the transmission up shifts. The TQ to the wheels is multiplied by the drivetrain. As the gear ratio increases the TQ decreases to the drive wheels. So shifting sooner would actually hurt your performance under heavy load and work the engine harder. Shifting sooner will increase your EGT's and engine temp.

windsorbill · 10-11-2020, 05:22 AM

Quote:

Originally Posted by Crasher

If you have to get above 60 for it to shift into 6th when in eco mode, how fast do you have to go to shift into 6th when in normal mode??

On a recent long incline, we started up at 65 mph in eco mode and was down to 50 at the top and it was still in 6th gear @1400 rpm, peak torque.

Crasher,
I always just hit the eco mode when I start, so to answer your question about how fast in normal mode to shift, I don't remember. It's on my list to do this coming trip.