View Full Version : About Truck Governed Speed

Barry Morris
07-21-2010, 01:27 PM
I'm just wondering if trucks don't actually go FASTER with the law governing them at 105 KMPH.

Here's what I'm thinking. Trucks now have 5 and 6 hundred horesepower engines. I'm thinking they may have been de-tuned so they wouldn't go 120 - 130, which is hard on the equipment. Consequently, when they came to a hill, they would slow down.

NOW that big engine is NOT messed with, since the truck is controlled at 105, and so they climb the hills at 105 easily, and barrel down the other side as fast as she'll go.

Seems to me another Ontario law has been shown to be just politiking.

Any mechanics out there??

Jack Butler
07-21-2010, 02:01 PM
I'm not a mechcanic but, limiters or governers can be based on kph rather than rpm.
The newer pickups are a prime example.

Jack Butler
07-21-2010, 02:07 PM
The electronis on the new 200hp Yamaha VMax motorcycle governs the top speed to about 140mph.
It runs a 1/4 mile in the 9's!

07-21-2010, 05:15 PM
The last highway tractor I owned was controlled through a fuel limiter that held me below 110 in high (18th) gear. If I dropped down a gear I could go faster as it by passed the fuel limiter and I could hit 2400 RPM and let her breath freer. Where there is a will there is a way.

07-21-2010, 05:28 PM
Seems to me another Ontario law has been shown to be just politiking.
That's usually the case. More friendly to the environment, lol.

Reducing the speed of a vehicle will result in lower fuel consumption that helps reduce greenhouse gas emissions and saves money on fuel purchases.

Setting truck speed limiters at 105 km/h on all heavy trucks in Ontario would save about 100 million litres of fuel a year - the equivalent of 280,000 tonnes of greenhouse gas emissions according to the results of the 2007 Transport Canada study.

07-21-2010, 05:47 PM
Speed limiters on big rigs are usually set by km/h. You can be in 18th gear doing 700 rpm, or in 12th gear doing 3500rpm. The speed will not go higher than 105, while the tractor maintains full power in the lower speeds for the hill. As anapeg described there are other less popular models that do have backdoors. The main reason most companies do this is to save big money on insurance.

Miles From Nowhere
07-21-2010, 05:52 PM
With modern trucks being controlled by an ECM (electronic control module), you can set parameters for just about anything. Governed speed can be controlled by applying rev limiters to each gear but can also be set based on speed. My truck has been locked out at 95 km/hr on the cruise and 97 km/hr on the pedal. My engine is a 475 Cummins ISX and has the power opened up on each gear, I hold pretty good on hills even with 40 tons in my tanks. It's also a fallacy that limiting speed will damage an engine, what will damage that engine is running head on into another transport in the middle of the night like what happened the other night on 69 north of Nobel. As far as the top speed laws, you can certainly let it go down hill faster than 105, if your truck is set properly, jakes will kick in at 108 and hold you back somewhat...just hope that the cops aren't at the bottom of the hill. It definitely is political, AFAIC because with top speed now at 105, big trucks are more of a rolling roadblock and passenger car drivers are taking more and more aggressive actions to get around us. It has nothing to do with safety and everything to do with public perception that the government thinks they know how to cut down on highway fatalities.