I can't drive 55

[Full-Timers]

We traveled today and I thought I would travel at 55 MPH to see what the mileage results would be. I haven't checked my mileage yet but what I did observe is that my 2002 workhorse W22 chassis with Allison Transmission does not like running at 55 MPH. The transmission normally upshifts to overdrive at 55 so it stands to reason that you can lug the engine very easy on an incline at 55. The transmission wants to downshift into 4th on any moderate incline so it appears to be shifting more often. At 63 MPH where I usually travel, the engine and transmission love it. I am going to continue to drive 55 until the next fill up. At that point I will calculate my mileage. If the results are not significant I am going to continue driving in my 63 MPH comfort zone.

[Full-Timers]

We traveled today and I thought I would travel at 55 MPH to see what the mileage results would be. I haven't checked my mileage yet but what I did observe is that my 2002 workhorse W22 chassis with Allison Transmission does not like running at 55 MPH. The transmission normally upshifts to overdrive at 55 so it stands to reason that you can lug the engine very easy on an incline at 55. The transmission wants to downshift into 4th on any moderate incline so it appears to be shifting more often. At 63 MPH where I usually travel, the engine and transmission love it. I am going to continue to drive 55 until the next fill up. At that point I will calculate my mileage. If the results are not significant I am going to continue driving in my 63 MPH comfort zone.

[BigSkyBob]

After a year of travels I have determined my most optimum speed is 65 MPH. My transmission won't down shift on moderate grades plus with my gearing, which I feel is a huge contributor, my torque sweet spot is at 65 MPH. My last round trip was 775 miles and I pumped 74.9 gallons of fuel at a Flying J. Next week I have to go through about 300 miles of the Republic of California so 55 MPH will not help me but oh well.

[John-D]

Every vehicle has a "Sweet spot" when it comes to speed.. Mine is right around 60 mph

The only way to find it is to do what the O/P is doing.. Fill up, drive xx mph, fill up, computer MPG, Drive yy mph, fill up, compute MPG

The dash computer will give you a hint, but accuracy there leaves a bit to be desired

Of course.. you need to fill up at either the same station or a station you know to be honest... Several stations in the south were seling 120 ounce gallons. (A gallon is 128 ounces) or smaller.

[RamblinFever]

We have a similar experience. I drive 55 on the level but boost it to 60 on rolling hills.

If you think 55 is hard, try driving at 50, the posted max on the Natchez Trace. I drove mostly in 4th but occasionally if no one was around I'd run it up to 55 to shift and then drop back. Sure was a pretty drive.

[dieselclacker]

[QUOTE]Originally posted by BigSkyBob:



Next week I have to go through about 300 miles of the Republic of California so 55 MPH will not help me but oh well.

Bob even tho the tow speed limit is 55 in California, you can safely get by with 60-62 on the interstates without offending the CHP. Just drive in the two slow lanes that trucks and vehicles towing are restricted to, and you should have no problems.

Just returned from your neck of the woods in "Big Sky Country". Absoloutly beautiful!!

Dieselclacker

[rvten]

My old W-20 did not shift to 5th gear until you went of 55. Like 57.

[al koffman]

I used to drive at 63, now at 55-56. Mileage went from 7,3-7.5 to 8.3-8.4. sometimes even better or worse mainly depending on the wind. My rig shifts into overdrive at 52-53 on level road and no head wind. It will stay in overdrive at 55-56 on slight upgrades.

[DriVer]

At the Workhorse Rally we heard a number of seminars and in both the Allison and Workhorse seminar we heard both of the lecturers present the same information.

Workhorse's Alan Stegich told us to drive it like you stole it. Alan told us that you're essentially driving a truck and as such the vehicle is so heavy duty that it needs to be exercised. This includes all systems whether it be brakes, downshifting, acceleration or cruising. The vehicle needs to be brought into a zone where the torque curve and HP almost cross one another. If you run too fast you'll burn too much fuel. If you run too slow you'll be lugging your engine and it'll be playing catch-up a lot of the time requiring premature downshifts and more coal to achieve an efficient speed. Alan suggested that a speed in between 60 to 63 MPH is just about right.

Alan told us what we already know regarding grades that we should be in the same gear going down the grade and we would be in climbing the grade. Alan told us not to be concerned if your engine pulls revs in holding back your vehicle. We were also told to be proactive and early-on the throttle in coming on a grade. Keep your energy level high under a load and you can indeed climb mountains. The use of cruise in climbing is not recommended because the coals don't come on as early as if the driver were to get into the throttle a bit more early and get the RPM climbing. Once your energy is spun up the motorhome will negotiate grades with relative ease.

Paul DeWitt from Allison Transmission presented a seminar on our beloved Allison MH and LCT series transmissions. We have seen demonstrated where gear ratios and speed and essential to be managed by the driver by bringing in engine compression on descending grades by the use of select shifting and or the "Grade Brake". Paul also told us that getting into the throttle early brings all the resources of the transmission on line at an efficient speed where everything internally in the box spins and clutches up efficiently. Paul suggested that a speed in between 60 to 63 MPH is just about where the transmission performs both efficiently and optimally. Let there be no doubt that the transmission will operate well at most all forward speeds however its sweet spot is calibrated to run co-jointly with the sweet spot of the engine.

The consensus of opinion between your vehicle's National Director and the transmissions OEM Account Manager is that a range in between 60 to 63 MPH is going to provide the best in climbing power and cruise efficiency. The question is most likely can you get better MPG at lower speeds - most likely BUT in regards to running your vehicle within its optimal performance envelope it is recommended that you consider forward speeds where the engine are transmission are optionally configured.

[Full-Timers]

OK, I picked up 1.1 MPG at 55 MPH as opposed to 63 MPH. In other words I went from an average of 7.8 to 8.9 MPG. This test has another bias though, on this trip I left the toad behind. I did a test a while back without the toad and only picked up .5 MPG. So I guess we could say 55 MPH shows a gain of .6 MPG. Not hardly worth the effort. It's back to 63 for me.

[Dave from MN]

I try to keep my speed at about the same range of 62 to 64. The big factor is the wind! It is hard to get 2 days in a row with wind in the same direction & speed. I have had a 35 mph head wind & got around 5 mpg. I also have had a 35+ tail wind & got over 9 mpg. Also leaving MN for the west or southwest, I start out at 1300 elevation & it is up hill all the way. But down hill coming back. All I can hope for is a tail wind or no wind at all. It is hard to stay at 62 with a strong headwind or even coming in at an angle.