Speed Governor for Trucks: Engine Setting or Aftermarket Governor?

A speed governor caps a truck’s road speed. In the US the words governor and limiter mean the same thing for road vehicles. A truck can be governed in two ways: through a road speed setting in the engine computer, or with a separate aftermarket governor that the fleet seals and controls. Both save fuel. They differ in who controls them, which vehicles they cover and what proof they give you.

What does a speed governor actually do?

It stops the engine giving more power once the truck reaches the set speed. Below that speed, the truck drives normally. At the cap, pressing harder on the pedal does nothing, and the truck holds its speed. Brakes and steering are untouched.

It is not the same as an engine RPM governor, the kind fitted to generators and pumps. A road speed governor works on vehicle speed, not engine revs.

Engine setting or aftermarket governor: which is better?

	Engine (ECM) road speed setting	Aftermarket governor
Fitted to	Most modern heavy trucks	Trucks, vans, pickups and buses, old and new
Who changes it	Anyone with the maker’s service software	The fleet owner; the unit is sealed
Mixed fleet	One method per make	One policy across every vehicle type
Proof of speed	Only what the truck’s own data shows	GPS evidence with TrackSpeed
Zone limits	No	Yes, with GeoKontrol 2

If your fleet is all modern heavy trucks, the engine setting is in place, and nobody changes it at service, use it. An aftermarket governor pays off where any of that is not true: the fleet includes vans and pickups, the vehicles are serviced by different shops, or you need to show a customer or insurer that the cap was in force.

What speed should a truck be governed at?

That is the fleet’s decision. There is no federal rule setting it. Posted limits vary by state, and Texas, for example, allows up to 85 mph on roads designed for it. Your cap does not have to follow the highest posted limit.

What the fuel figures say:

• The EPA’s SmartWay program says a heavy truck driving at 65 mph instead of 55 mph can use up to 20% more fuel.
• The Department of Energy says gas mileage usually drops quickly above 50 mph.

Many fleets settle on a cap a few mph under the highway limits their trucks see most. Set it too low and drivers lose time on long legs, set it too high and you save little. If you send us your routes, we can talk through the trade-off.

What does governing save at today’s diesel price?

The EIA’s weekly on-highway diesel average was $6.35 a gallon in the week of October 26, 2026, after a record $6.53 in September. At the start of the year it was $3.48.

A truck covering 100,000 miles a year at 6 mpg burns about 16,670 gallons, roughly $105,900 a year. An independent one-year trial of 177 vans and 30 trucks measured an average fleet saving of 5% after speed limiters were fitted (CE Delft for Novem, 2009). On this truck, 5% is about 830 gallons, or $5,290 a year. Across 20 trucks, that is roughly one whole truck’s fuel bill saved every year.

The saving is bigger for trucks that spend long stretches above the cap, and smaller for local work. Our speed and fuel data shows the shape of the curve.

Do governed trucks crash less?

Speed is in a large share of fatal crashes. NHTSA’s Speeding: 2024 Data counts 11,288 deaths in speeding-related crashes in 2024, 29% of all US road deaths. The same report found 8% of large-truck drivers in fatal crashes were speeding.

NHTSA also notes that stopping distance grows four times over each time speed doubles. A governor does not make a truck stop faster, but it limits how fast the truck can be going when something goes wrong.

Which AutoKontrol governor fits which truck?

Vehicle	Unit
Electronic throttle (drive-by-wire)	DBW speed limiter
SENT throttle sensors	SENT speed limiter
Mechanical fuel control	System 80
Governor plus GPS tracking	TrackSpeed
Lower limits in yards and sites	GeoKontrol 2

The choice depends on how the engine controls fuel, not on the make or model: an electronic (drive-by-wire) throttle takes the DBW unit, a mechanical fuel system takes System 80. Vans and pickups are covered too, see truck and van speed limiters.

Frequently Asked Questions

What is a speed governor on a truck?

A device or engine setting that caps the truck’s road speed. Once the truck reaches the set speed, extra throttle does nothing, so it holds that speed.

Is a speed governor the same as a speed limiter?

For road vehicles, yes. Governor is the usual US word and limiter the usual word in Europe. Both cap road speed. An engine RPM governor on a generator is a different thing.

Are speed governors required on trucks in the US?

No federal rule requires them. FMCSA and NHTSA withdrew their heavy-truck speed limiter proposal on July 24, 2025, and said carriers can still choose to limit their own trucks. See truck speed limiter law in the US.

Can a mechanic change the governed speed?

An engine setting can usually be changed with the maker’s service software. An aftermarket governor is sealed and set by the fleet owner, which is one reason fleets add one.

How much fuel does a speed governor save?

An independent trial of 177 vans and 30 trucks measured an average 5% across the fleet. For a truck covering 100,000 miles at 6 mpg, that is about $5,290 a year at $6.35 diesel.

How do US fleets buy AutoKontrol governors?

Through Scorpion, our parent group’s US team. Start with the quote form and fitting is agreed per job, by your own technicians or our engineers and partners.

Put a cap on fuel and risk

Every truck you govern takes the top end off its fuel bill and its risk, on every shift. Tell us what you run and we will match a governor to each vehicle and price it. Get a quote or book a free consultation. How US fleets buy is set out on our US speed limiters page.

AutoKontrol has made speed limiters in Britain since 1985 and supplies fleets in more than 50 countries, with approvals including ISO 9001, UTAC, TÜV and VCA.