Trucking 101: Governed Trucks

[Tobin S.]

A lot of people don't know that the speed of most trucks is limited. I'd guess that is the case with about 80% of trucks. There is a truck part called a governor where a mechanic can set the top speed of a truck. The big trucking companies usually set their trucks somewhere between 65 and 70 mph. Most trucks don't go faster than 70. There are companies that set their top speeds lower and others a little higher. I know of a carrier that sets their trucks at 61. I know of another that sets them at 75, but they run out west a lot where the speed limits are higher. But your average truck is pretty slow. Mine is governed at 68 mph.

This is why it takes trucks a long time to pass sometimes. It's also why it's not a good idea to speed up when a truck is trying to pass you unless you plan on going faster than the truck. Chances are the driver is already going as fast as he or she can. And, to be fair, it's also a good idea that governed trucks should stay put of the hammer lane most of the time. Most drivers are pretty good about staying to the right and only using the hammer lane to pass, but I know some aren't.

It is possible for some big trucks to go well over 100 mph, but there aren't too many like that out on the road. The trucks that can go that fast are usually owned by independent owner/operators.

[kentauros]

1. I wish they were all governed.

That wouldn't stop the ones that know how to remove the governors, but it would bump that 80% a bit higher. But it might also stop the handful of asshole truckers out there, or make them think more about their driving behaviors.

I respect the good truckers and help them out where I can (like "blocking" the inconsiderate car traffic when the truck is trying to change lanes.) I know most of them are good to great drivers; it's just the handful of bad ones that ruin it for all of you and the rest of us on the road around them. And I do recognize that some of them may seem bad due to having to react to even worse car/truck drivers, but I'm talking more about tailgating, not being able to remain in their lane, especially on gentle highway curves, and so on.

Most of my driving is in-city, but as this is Houston, most of that driving is also on freeways ;)

So, your truck is governed at 120kph? :D

[Tobin S.]

2. I'd be a speed demon in Canada. :)

Truckers do appreciate your help especially with that lane changing in heavy traffic deal. :thumbsup:

[Orsino]

6. I would like them all governed...

...so that the demands and stress wouldn't so easily turn them into assholes.

[madrchsod]

3. walmart is up to 60.

i`ve been driving I-39 from rochelle il to janesville wisc and most trucks are pushing 70-75. average speed for autos is 75-80. it is really scary out there because of the margin of error and reaction times.

my dad worked as a dispatcher for 35 years so i`m aware of the etiquette of the road.

[A HERETIC I AM]

4. Since almost every heavy truck on the road has electronic engine controls these days....

the "governor" is actually a rev/fuel limiter. The electronic engine controls (often called the "Electronic {or Engine} Control Module" or ECM) on modern diesels can allow the top speed to be set virtually anywhere along the speed curve the truck is capable of, and when the truck reaches that speed, the ECM simply stops adding fuel. The ECM is taking data from a wheel speed sensor and using that to shut fuel flow down. As a result, they can't really be "removed" so much as altered. That alteration is a simple as hooking up a computer/interface device to the trucks ECM and setting the limit higher or lower. In the days of mechanical fuel injection systems, the governor was merely an RPM limiter set by a screw and was in no way associated with wheel speed.

All trucks also become "gear bound" at some point. That has to do with the upper limit of RPM's the engine is capable of (which in large truck diesels is rarely more than 2200 RPM's), coupled with the rear end ratio and the tire size. If the ECM has no top speed set into it, there comes a point where the gearing, available horsepower, RPM's and tire size allow the truck to go no faster on flat ground. Some trucks are geared such that they can run faster but lack the horsepower to push the truck through the air.

I've driven trucks with big horsepower and no speed limiter set at all, but became gear bound at about 115 MPH.

This one, in fact;


And no, I didn't run that fast all the time. I did a flying mile once in Middle of Nowhere Nevada on I-80 and ran through the mile averaging 107 MPH. The truck was accelerating the entire time and I still had about 450 RPM's to go before I lifted.

[Tobin S.]

5. I appreciate the technical info, Heretic

The fastest truck I've driven so far was an old JB Hunt reject cabover I used to own. When I bought it I told them to turn the governor off. The RPM topped out at 1800 and it had a 9 speed transmission with overdrive and I think a 3.73 rear end ratio. It would do 80 with a good tail wind. I was just happy to be able to do the speed limit everywhere I went.

[A HERETIC I AM]

7. LOL @ "80 with a good tail wind"

Yeah, that and downhill with a following wave! I've been there, so I know what you're talking about.

The Pete in the picture above had a 13 speed, 3.55 rears and a Series 60 Detroit that had been modified several times. We kept that truck at the Detroit Diesel plant in Redford Michigan and it was often in their experimental lab. By the time we got rid of it, it was pushing almost 500 HP to the ground and it had a Gen III flywheel but a Gen II ECM which made things difficult for the subsequent owner. I saw it about 6 months after we got rid of it and chased the guy down to talk to him about my "baby"! After talking to him, he said "well, I'm glad I got some history about this thing because every time I take it to a DD shop, the mechanics have no idea what they're dealing with".

I drove that truck from June of 1989 to the end of the 1994 season. We replaced it with this Freightliner;


I had the luxury of spec'ing that truck out from the tires up. It had 3:33 rears, one of the strongest Series 60's built up to that time (1995) at 525 HP and would run like like a scalded dog. That's the same trailer BTW, just repainted and modified.

Ahhhhh...the good ol' days!

[gmoney]

8. I guess that explains...

the phenomena of when the truck doing 58.0 is being passed by the one doing 58.1 and it backs up everybody else for a quarter mile until the pass is completed and the 58.1 gets back in the right lane.

Or is that sometimes done deliberately by the truckers to slow everyone down or what?

[hobbit709]

9. I'd say that 75% of the trucks that pass me on the highway

are going over 75 since I usually drive just over 70 and they pass me up in no time.

[flvegan]

10. "Always let the lorry go first." - Richard Hammond

Top Gear, Season 12, Episode 1

I learned quite a little bit about how hard it is to drive a truck from that episode. I had never even heard of a "crawler gear" until then.

I've always given the big rigs extra space and greater warning with my turn signals, etc. Have to respect people operating mass like that at speed.

[Roon]

11. I drove for Werner 20 years ago..

and the trucks were governed to 62-miles-an-hour. The highest speed limit at the time was 65.

[trof]

12. I rented a governed truck some years ago.

It was HUGE, for me.
Biggest box truck Ryder would lease without you having a commercial license.
We were moving household from B'ham, AL to Merrimack, NH.
Speed limit was 55 back then (Arab oil embargo) and that's what the rig did, pedal to the metal.
No cruise control, but didn't need it. Just kept the pedal on the floor all the way.
55 on level stretches, 50 going uphill, maybe 60 downhill.

I'll never do that again.
whew