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Speed Governor

I drive a couple different vehicles, almost all new, Freightliner M2’s, Cascasias, International Durastars, MCI D4500s, to name a few. They are all governed to 110kph (about 70mph) via rpm limit (2100). The operation of governors are beyond me, but i was told to stay below the speed to ensure control for blowouts or other problems. The question, if i did run at the limited speed, is there some problem, damage or increased wear from this? A short piece on the governors would be appreciated as well.

If our workforce is any example, there are no issues with running it to the limit. It was interesting to me many truck tires have a 70 mph speed rating. I can ask one of our mechanics about the specific operations of the governor on Monday if you wish,

I used to rent Penske trucks years ago and before that…U-Haul trucks. We were told that governing the trucks was the only way to prevent over-revving of the engines and causing engine damage. The reason was that most commercial trucks were geared so low because they hauled heavy loads. They could be geared higher but customers wanted the trucks to “get up and go” even while hauling heavy loads.

The short answer is nope, there is absolutely totally completely no problem, damage or increased wear from operating at the governor limits. The speed is limited by the engine computer, and it actually protects the engine rather than stressing it.

Can’t believe there would be any problem. Gotta be just the computer limiting the injector pulse width. Interesting on our Olds, the normal governed speed is something like 110 mph. Computer won’t let the car go any faster than that I’m told. Except if you had the “autobahn option” which it has. That option took the governor off so it could run up to 135 or so mph. It hasn’t gone over 40 for the last 8 years and even in its prime never went over 80 so its all according to the book.

I think my Dakota is limited to 106 ,but with the V6 engine I have never had it above a grudging 102 mph(that was fast enough in that ride.)The governor wont protect a truck going downhill unless the engine brake kicks in which will help sometimes ,please note some of these heavy carcass tires are rated for only 65 mph.The Boss’s son had a front tire come off the rim going over 80 mph ,someone must have been looking out for him.Its probably a good thing most trucks are limited to 65 or 70 mph,hard to stop at high speeds (like a train )
Some modern trucks dont like to run 2000 rpms or above because the reciprocating mass is so high,these engines are large displacement wise and have high torque rise(accelerates under load better )Due to the highway gearing these engines are electronically controlled to turn less RPMs in top gears,with steel pistons a Cat 3406 is a case in point ,these torque monsters are probably governed to around 1750 RPMs ,they are there for the long haul ,the older mechanical governed engines had a sweet spot of max torque ,with the governors slowly cutting the fuel back as the engine rpm increased ,the modern ones probably just signal the injectors to stop injecting fuel above a certain point(I think the injectors are piezoelectric or something like that ,to make the fuel inject ,could be something else ,but I do know you can get a nasty shock when the engine is running.( dont think think many Diesels would stand “Fury Road” 4000 rpms .)

Running at the Governed limit…is ok… Because that limit was set and is no indicator of the remainder of rpm or power that is blocked off from your use. The limit was set so you do not tread into the danger zone of RPM or power …so you can run at the set limit with not much concearn.

If you removed the governor…that is where you will run into cause for worry. But as is you really cannot hurt it. It was set there to prevent any damage to engine or wheels etc…


My car is allegedly “limited” to 127mph… but I don’t intend to ever find out if it’s true. Not ever. :smiley:

The way I read the starting post is that the OP was told to drive below a certain speed and he wants to know if the governor activating will cause damage making it apparent that he did not do as told.

I interpreted it as it was written. I understood the question as would constantly running the vehicle at the governed limit cause undue wear or damage to anything. I saw no hint that he/she was concerned about “getting caught”, but only about possible wear or damage.

Every U-Haul truck I’ve rented had a,governors. My first wife’s father drove for a feed company. He owned his own trucks. He had his own trucks fitted with a governor. He would always,start in second and accelerate until he felt the governor limir the engine rpm then shift to the next gear. I used his technique when I rented the U-Hauls with manual transmissions. In my opinion, it isn’t good for an engine to lug it in a gear that is too high for the conditions. With a governor to limit the rpms, running the engine up to the governor limit doesn’t hurt the engine, particularly when the truck is loaded. It’s certainly better than lugging the engine. Automatic transmissions calibrated to shift at the correct point.

In this instance we arent talking about “electronically speed limited”…we are talking about a proper governor for large equipment. They are widely used…as you dont want any knucklehead trying to do smoky burnouts in a backhoe nor let him rev its engine to its full potential.

There are lots of reasons behind the use of a governor on large equipment…they are devices to prevent rampant idiocy basically. In this case he can run this up to its governed limit as it was set for the no damage range and to prevent you from getting into the damage range.


I think Blackbird has the right nomenclature.

Limiters work differently than governors. Governors are meant to be used all the time. Run it up to 70 and hold it there.

Limiters are not usually pleasant when they are reached. My truck has a speed limiter at 99 mph. It stutters the engine, probably from dropping spark, when you hit the limiter. It is a less than gentle reminder to Stop That! Same for RPM limiters.

In my 55 year driving class 8 trucks and buses almost everything I drove had a governor, Some were mechanical arms that stopped the throttle when were were driving gasoline engines, then for many years after we switched to diesels, the governor was in the fuel pump. Later they changed to governors that only worked when the transmission was in top gear, signaled by an air port in the tranny and an air supply to the governor. That one was easy to defeat (No I am not going to tell you how).

Just before I retired they changed to Drive by wire, computer controlled throttles with the computer doing the governing. I don’t know if drivers have found a way to defeat those but I have some ideas about how it could be done.

As long as drivers are paid by the mile, they will be trying to defeat governors.

Reminds me of the Phrase “Running Balls Out”… This may not be what you would imagine at first and has nothing to do with Anatomy class…nor those swinging appendages added to a trucks tow hitch.

“Balls Out” comes from the use of speed governors on all manner of things but mostly the Steam Age. It looks like a wind measuring device sort of… It is triangular with linkages…at the end of the spinning arms were brass Balls…or weights. Increase the speed and they would spin and throw outward from centrifugal force…and simultaneously move a rod and then a mechanical valve…a steam pressure valve usually. So when you reached certain RPM…it cut the feed of steam to prevent runaways.

So forget Anatomy class whenever you say…“I was running the thing Balls Out” LOL


I think it is time for GPS governors on vehicles that have to try to make it up steep grades wothout impeding traffic flows so much and it is time for reasonable speed limits a crash at 60mph is not as catastrophic as one at 85 mph,When you are working on Interstate and those doubles are passing you at close to 80 mph ,you know death is inches away .

On the down grades there’s always Georgia Overdrive, aka neutral on a diesel.

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A true governor is an automatic throttle that opens and closes by itself to hold a constant rpm. Your lawn mower has one, push through thick grass and the throttle automatically opens in response to the engine slowing down, then it automatically closes when you go over a bare spot to keep the engine from running away.
Farm tractors and industrial machinery are also governed. The guy using a backhoe has enough to do without also having to constantly ride the throttle as the load on the engine increases and goes away.

Just to gripe a little, I had my old lawn mower from 78 with a throttle speed control, now I would run at lower speed, and only ramp up the rpm as needed. Well nice guy I am mowing elderly ladies lawn, for $5, as she would not let me refuse the payment, after in a thick polish accent Hey neighbor, can you mow my lawn for me? Now she always used to cut her own grass with a push rotary lawnmower, no problem I say. Sure I did lawn and sidewalk snow for her for years, but after I busted my mower hitting a stump in her yard, got a new craftsman with a honda engine, no throttle speed control.

Emission standards they say, wtf how can a lawnmower be more efficient running at max, instead of a lower rpm. engineer explanation please.

That lawn mower has a throttle, it’s just not controlled by you. I had an old Lawnboy like that, a one speed engine, but that speed was maintained by a centrifugal governor that automatically opened or closed the throttle to maintain that set speed, sort of like cruise control.
On your old mower, you only opened and closed the throttle indirectly. That “throttle” lever actually just tightened the spring that the centrifugal weights had to compress in order to close the throttle. This adjusted the speed that the governor was set to.
Some of the simple Briggs & Stratton engines used an air vane to govern the engine. There was an air flap in the fan shroud, as the engine sped up, the flywheel fan blew more air over the engine and that air would move the air flap which was connected to the throttle. A tug of war between the air flap and a spring that you tightened by “opening the throttle” determined the engine’s governed rpm.