What Gear Do You Drive On Interstate?

Topic: What Gear Do You Drive On Interstate? (Read 1823 times) previous topic - next topic

What Gear Do You Drive On Interstate?

September 14, 2019, 08:54:54 pm

If you're travel along a relatively flat U.S. highway or interstate - what gear do you typically drive?

I find 6th gear totally useless for our style traveling. The previous owner of our 42' 2002 U320 told me that the coach had a 'sweet spot' at 62 mph. Of course, I didn't believe him (he was older than me - wouldn't have believed him if he was younger than me either). After a couple of thousand miles, I found out that he was absolutely correct. My wife set that speed (62 mph) as the limit for my abilities, so if the road is relatively smooth, we drive 62. That means the ISM is turning 1500 rpm - so one might as well paraphrase that the previous owner meant to keep the ISM at 1500 (or little above). That mandates 5th gear for us. To run the engine 1500+ rpm in 6th gear is NOT a consideration.

Consequently, if we're on a 55 mph road, whether to be legal or to keep from beating the coach to death, means 4th gear in order to maintain 1500 rpm. At 1350 rpm and 55 mph, engine performance is dreary. At 1200 rpm, it's kind of like beating a dead mule.

My 36' U295, with a C8.3, never had these issues. With 5.13 gearing, it ran along spryly, at whatever RPM seemed to fit the scenario.

I sure would be interested hearing about your experience.

Larry

Re: What Gear Do You Drive On Interstate?

Reply #1 – September 14, 2019, 09:10:06 pm

Which engine is in the U295? The torque curve of my 5.9L in-line 6 Cummins really does feel the same as the 251 Cu.In. inline-6 my Chrysler had, maximum torque at 1600 RPM.

Re: What Gear Do You Drive On Interstate?

Reply #2 – September 14, 2019, 09:16:19 pm

Mechanical 8.3.

Re: What Gear Do You Drive On Interstate?

Reply #3 – September 14, 2019, 09:16:56 pm

Check out the torque curve for your engine and run in what ever gear will keep you in the flat portion of the curve and at the speed you want. I have a CAT 3208T with an Allison 4 speed trany and my best cruising speed is 67 mph @ about 2300 rpm. I run this speed even if the speed limit is 80. For other speed limits, I run about 5mph under the limit for various reasons. Have a great day ---- Fritz

Re: What Gear Do You Drive On Interstate?

Reply #4 – September 14, 2019, 09:43:49 pm

Torque curve peaks at 1200 rpm, but the engine can barely accelerate going down hill at that rpm. Anything below 1350 rpm is abysmal.

Re: What Gear Do You Drive On Interstate?

Reply #5 – September 14, 2019, 09:54:34 pm

Cat 3176B here.....1500-1600 is the sweet spot...oh and that's 70mph

Re: What Gear Do You Drive On Interstate?

Reply #6 – September 14, 2019, 09:57:21 pm

My 96 U295 cruises happily at 1750 rpm which is 63 mph in 6th gear in the Allison 3060R tranny (I think that's the model number). It is very happy at that pace, will climb hills effectively and ranges from 8.2 mpg up to 9 mpg depending upon topography while towing the Subaru.

Re: What Gear Do You Drive On Interstate?

Reply #7 – September 14, 2019, 10:02:19 pm

Our 1995 U320 (400 hp/1350 lb-ft M11) seems to be happy in 6th gear on the freeway. I typically downshift manually only when descending steep grades. Otherwise I just let the Allison decide which gear it likes and I'm happy.

Re: What Gear Do You Drive On Interstate?

Reply #8 – September 14, 2019, 10:06:30 pm

At what speed, David? And rpm?

Re: What Gear Do You Drive On Interstate?

Reply #9 – September 14, 2019, 10:18:13 pm

Quote from: U295 Owner – September 14, 2019, 10:06:30 pm

At what speed, David? And rpm?

At 70 MPH it's just over 1500 RPM. I haven't paid close attention at other speeds

Re: What Gear Do You Drive On Interstate?

Reply #10 – September 14, 2019, 11:21:04 pm

My ISC 8.3 is happy at a 17-1800 you pick the gear 5th 58-60 or so 6th 65-68 or so.

Re: What Gear Do You Drive On Interstate?

Reply #11 – September 14, 2019, 11:24:15 pm

Our Detroit turns 1700 rpm at 65.4 mph in 4th gear out of 4. Unless boring countryside, we usually cruise at 1600+ for a little better mileage. 4th gear is too short for the absolute best fuel mileage and would love to have the 6 speed and turn about 1500 at 65. No reason to spin it that fast but no 6 speeds were available for the torque in '93.

Pierce

Re: What Gear Do You Drive On Interstate?

Reply #12 – September 14, 2019, 11:26:28 pm

My isl400 is happy in 6th at any speed 55 and above. I keep it in 6th except 5th in rolling hills.

Re: What Gear Do You Drive On Interstate?

Reply #13 – September 15, 2019, 12:48:39 am

My '99 won't go into 6th. until 62 mph makes towing in Cal. a pita.

Re: What Gear Do You Drive On Interstate?

Reply #14 – September 15, 2019, 07:48:46 am

my 96 is happy around 1650 and 70 ish mph. I keep it on cruise otherwise she wants to keep getting faster.

Larry

Re: What Gear Do You Drive On Interstate?

Reply #15 – September 15, 2019, 08:14:07 am

95' U280, C8..3 / 6 speed running Michelin 275 80 22.5 XZE - LRH......... 75 psi front ....85 psi rear (cold)
6th gear @ 1700-1800 rpm ........ 60 - 65 mph verified by Garmin ....... using cruise control and "Mode On" in the non-hill country.
Average 10 - 10.5 mpg on our 3 trips out west from our home state of Florida (and I let it idle alot).

Using the "Mode" selection makes a big difference in the driving experience on our coach when traveling in flat country or rolling hills and interstate overpasses. The downshifting from 6th to 5th on overpasses and gentle hills was annoying while driving at speeds of less than 65 while in the default performance mode.

To answer the OP's question, always 6th gear unless mountain grades dictate otherwise.........

Re: What Gear Do You Drive On Interstate?

Reply #16 – September 15, 2019, 08:45:07 am

Our '93 coach runs just like Justin's (above). Cruising on the highway, the sweet spot is 6th gear at 65 mph which is about 1800 rpm on the tach. Our transmission also defauts to "performance", so I turn "mode" on when driving in the flatlands and let engine torque do it's thing.

Unlike Justin, I actually like letting the Allison get a little exercise, so I take it out of "mode" when driving in the rolling hills. I like to feel the trans make the smooth down and up shifts as it sees fit, and I like the sound of the engine and turbo spinning up to 2300 rpm (we have a resonator). I also like keeping the revs up when climbing even moderate grades in the summertime, because it helps the engine run cooler.

Yes, I know...all the extra shifting burns a bit more diesel. I didn't buy a motorhome to go hypermiling.

Re: What Gear Do You Drive On Interstate?

Reply #17 – September 15, 2019, 09:15:34 am

Quote from: U295 Owner – September 14, 2019, 08:54:54 pm

If you're travel along a relatively flat U.S. highway or interstate - what gear do you typically drive?

My 36' U295, with a C8.3, never had these issues. With 5.13 gearing, it ran along spryly, at whatever RPM seemed to fit the scenario.

I sure would be interested hearing about your experience.

Larry

I'm a retired toolmaker and one of the ways I annoyed my employers was questioning their orders. Why? Because sometimes they hadn't asked the correct question.

Larry, I wonder if you as a U295 Owner appreciate the difference between a 2-stroke and a 4-stroke engine.

A 2-stroke engine always gives you its best at higher rpms, whereas a 4-stroke engine can be designed either way, but 4-stroke diesels always develop their maximum torque at low rpms.

3-cylinder, 2-stroke Saab being flogged for all she's worth.

Saab 96 2-stroke singing - YouTube

So. What is the operational difference between a 2-stroke Detroit Diesel and all the others?

Re: What Gear Do You Drive On Interstate?

Reply #18 – September 15, 2019, 09:42:40 am

My little U-240 has a Cat 3116 250hp with Allison MD3060R. It runs best at 2200rpm 6th gear doing 68mph. My limiting factor is the towing of the 11 chevy HHR is 65mph and we always tow it. So we cruise in 6th gear at 2000rpm doing 64mph on flat level ground getting 9.5 mpg.

Re: What Gear Do You Drive On Interstate?

Reply #19 – September 15, 2019, 10:38:41 am

Quote from: Old Toolmaker – September 15, 2019, 09:15:34 am

I'm a retired toolmaker and one of the ways I annoyed my employers was questioning their orders. Why? Because sometimes they hadn't asked the correct question.

So. What is the operational difference between a 2-stroke Detroit Diesel and all the others?

I've read that the best way to drive a Detroit 2-stroke is to "drive it like you stole it." That high-RPM operation seemed to work well with the 8V-71 engine in the MC-5 coach I used to drive for our church. Our Cummins M11 is much different in that it's quite happy at lower RPM as I let the Allison decide which gear it prefers.

Re: What Gear Do You Drive On Interstate?

Reply #20 – September 15, 2019, 11:06:18 am

Quote from: D.J. Osborn – September 15, 2019, 10:38:41 am

I've read that the best way to drive a Detroit 2-stroke is to "drive it like you stole it." That high-RPM operation seemed to work well with the 8V-71 engine in the MC-5 coach I used to drive for our church. Our Cummins M11 is much different in that it's quite happy at lower RPM as I let the Allison decide which gear it prefers.

D.J. Osborn? I still don't know if U295 owner's rig is a Detroit or some other engine. I was suggesting the question that Larry should have asked in my humble opinion.

Vintage Saab Two Stroke Race Car with Crazy Swede Driving. - YouTube

Re: What Gear Do You Drive On Interstate?

Reply #21 – September 15, 2019, 11:56:30 am

Quote from: Old Toolmaker – September 15, 2019, 11:06:18 am

D.J. Osborn? I still don't know if U295 owner's rig is a Detroit or some other engine. I was suggesting the question that Larry should have asked in my humble opinion.

Vintage Saab Two Stroke Race Car with Crazy Swede Driving. - YouTube

Actually had a Saab 96 back in the day, shocked a lot people at gas stations, when I poured a quart of two stroke oil into the gas tank.

Re: What Gear Do You Drive On Interstate?

Reply #22 – September 15, 2019, 12:06:03 pm

Thank Pierce. I've always been fascinated with 2-strokes, and our U225 is probably our forever home so I won't experience the Detroit. That being said I went back to the beginning, and remember why I don't trust my memory or as Lynn puts it to me "The mind is the last to know."

Larry wrote "That means the ISM is turning 1500 rpm - so one might as well paraphrase that the previous owner meant to keep the ISM at 1500 (or little above). That mandates 5th gear for us. To run the engine 1500+ rpm in 6th gear is NOT a consideration."

So he's driving a 4-stroke. So my answer to U295 Owner Larry is to remind him why trucks have all of those gear ratios to choose from: to be able to run the engine at it's best speed. Larry? Run in the gear that gives you the engine speed you want.

I enjoy your writing on the Detroit 2-stroke Pierce. Many of them travel the highway here bringing farm good to market. Then WalMart truck goes by with the driver hypermiling.

"A video of a walk around the running Sulzer/Wärtsilä 12RTA96C main engine on board the Maersk Kimi, currently at 70 revolutions per minute. It is the world's most powerful reciprocating engine to date."

"Wärtsilä-Sulzer RTA96-C. The Wärtsilä RT-flex96C is a two-stroke turbocharged low-speed diesel engine designed by the Finnish manufacturer Wärtsilä. ... The design is similar to the older RTA96C engine, but with common rail technology (in place of traditional camshaft, chain gear, fuel pump and hydraulic actuator systems)."

Sulzer 12RTA96C: a walk around world's most powerful reciprocating engine,...

Art

P.S. Waiting for my back to recover and enough enforced rest so that I can install the last three bolts in the Siata's new exhaust system.

Re: What Gear Do You Drive On Interstate?

Reply #23 – September 15, 2019, 12:09:18 pm

Quote from: jcus – September 15, 2019, 11:56:30 am

Actually had a Saab 96 back in the day, shocked a lot people at gas stations, when I poured a quart of two stroke oil into the gas tank.

That's what helped discourage people from owning the 2-strokes in New England: the availability of 2-stroke oil. People would pour in regular motor oil, as a substitute, in the winter time and it would just sit on the bottom of the tank.

Re: What Gear Do You Drive On Interstate?

Reply #24 – September 15, 2019, 12:49:42 pm

This thread is very off-putting. In a previous thread, OP, U295OWNER stated that he has not changed his user name, even though he has sold his U295 and currently owns a 2002 42' U320 with ISM power.

So, if the original question asks what gear do you drive on the interstate in your 2002 U320, earlier answers won't help you much.

But on freeways, 95% of the time, I drive my 2001 U320, ISM, in 6th gear, econ mode, at 65-67mph, around 1450RPM, in the peak of the torque curve, and get 8.4mpg pulling a toad. Faster/headwind=lower MPG due to parasite drag mostly. With a tailwind, I will go 70ish.

You need to be above 60mph without full pedal for the Allison to shift to 6th gear. If you drive at PO's 62 sweet spot, in 6th gear, RPM will be lower and not at peak torque, but you'll have better fuel economy as long as the turbo isn't screaming (turbo pressure is what I use to approximate MPG...high turbo pressue = low MPG). Any RPM above 1450 will give you more horsepower and burn more fuel. In hilly terrain, I deselect Econ mode for quicker downshifts, and that keeps the speed up on the uphill pulls and increases cooling to engine and transmission.

U295OWNER, to avoid confusion, you really need to change your user name, or add a signature line to your profile stating what model coach you have.

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