My truck is a 10 speed and at 55 mph, it's running right at 1200 rpm in 10th. At 65 mph, it's running 1475 rpm. That's where MY truck gets its best fuel economy. "Utter horseshit"? "most trucks have 13 speeds"? What planet do you come from? Interstate has over 3,000 trucks on the road and maybe, just maybe, 2 percent of them are 13 speeds.

 

Heeeeeeeeeeeere we go again.. physics do not apply to the BBR.. those silly laws are for everyone else...

SSDD...

I can hardly wait to see 55 MPH for everyone again..

 

There's no way a truck gets best fuel mileage "at 1475 rpms" it doesn't happen buddy. Sweet spots are always a compromise between performance and fuel economy.

What engine do you have?

I wasn't talking about interstate, but most trucks on the road. I'm sorry if your employer couldn't afford you a 13 speed.

Do you have an instant MPG readout?

 

allan5oh
The days of ALL companies running over a 10 speed are gone.
MOST companies uses 10 speeds for the simple fact that MOST drivers have a hard time driving anything over that. Sweet spots depends on the engines and how the manufacturer sets the cpus up.

 

But here's the problem:

The RPM where the engine is most efficient is ALWAYS lower then the "sweet spot". The sweet spot is always the best compromise between performance and efficiency.

The most efficient spot is the torque peak.

Look at cats c15, sweet spot is 1325 rpms, yet peak torque is 1200 rpms.

ISX? Kind of vague on the sweet spot, but they say basically 1450 rpms, not going below 1400 rpms. Yet peak torque is 1200 rpms.

 

Most "instant MPG readout" really are not accurate. The only true measurement is to take the average over an extended distance vs fuel consumption.

I do agree most trucks are equipped with a 10 speed. In fact the 13 speed is not found that often. Most have either a 10 speed or 15 speed.

kc0iv

 

They maybe be out, but I find they're out the same amount every time.

Not only that, they're best for instant readout. That's what matters in this situation. As you slow down, and the speed settles, the MPG goes up every time.

 

I agree that most fleets today are using 10 speeds. I don't know for sure that is because most drivers can't find more gears than that though. I think the biggest reason is that most fleets don't need more than 10 speeds.

I will also agree with Allan on the fuel efficiency. You can gear it however you want, but I've never seen any truck (or 4 wheeler, for that matter) that gets better mpg at 65 over 55. It just flat doesn't happen. Some will do much better than others at 65 than others, but that same truck will still do better at 55.

 

I heard about a month ago on Bill Mack that Transport America was offering their drivers a 1 cpm increase if they would allow them to turn their truck back to 62 or something like that. They were talking about another company doing the same thing on the radio today, but I didn't catch the company name. I think you'll see more and more companies doing this in the coming weeks.

Fuel must not be that big of an issue with a lot of people because I don't notice too many people out here slowing down whether we're talking big trucks or POV's. It must not be hurting my company too much either because they're talking about turning our trucks up from 65 to 70. They claim that freight isn't delivered fast enough. They can turn it up to 85 if they want, I run 60 when it's governed at 65, I'll run 60 when it's governed at 70 also. Turning it up or down makes little difference to me.

 

I gonna drop out of this bs session for the pure fact that there's too many "expert" witnesses here. Some people like to make "fact" based statements on what they perceive to be facts, when in my opinion, they're really limited on their experiences apparently.
And to set the record staight, my 05 Columbia is one of many on the road in the same company and fuel consumption on the Detroits in our trucks was determined a long time ago by real experts in the company. My truck has only 550k on it and where I got my info was from the onboard computer. I've ran I-5 a ton of times and I've been east too where I can open it up to 68. My fact based statement is based on those facts delivered to me thru the onboard computer. Believe what you want, but I know for a fact.

p.s. I used the fact word 6 times. There was no cow manure used in this statement anywhere.