Towing with cruise control?
Q:Years ago [EQUUS Medical Editor] Matthew MacKaySmith, DVM, wrote about how he used his cruise control traveling from Virginia to California for the Tevis Cup and that as a result he saved a lot of money on gas. Several of my friends are now telling me that I shouldn’t use cruise control when hauling my trailer even though I’ve been doing it all this time, and there seem to have been no ill effects. What is the current thinking on this? Robby Vizard Lewisberry, Pennsylvania
A:The forerunner to modern cruise control was invented in 1948 by mechanical engineer Ralph Teetor after he grew frustrated riding in a car driven by his lawyer, who kept speeding up and slowing down as he talked.
Today, cruise control is designed for two main functions: to improve driver comfort on longer trips, by allowing you to shift in your seat and move your legs around, and to reduce fuel consumption, by maintaining a steady speed.
However, keep in mind that when driving with cruise control engaged, it may take a few moments longer to get your foot onto the brake. That means this feature is not well suited for some kinds of roads and driving conditions. In general, you want to use cruise control only on roadways that do not require frequent stops and turns, such as flat, straight highways without too much traffic. You won’t want to use it when towing in heavier traffic, on winding or hilly roads, around towns, or on roads that are wet, icy, bumpy or otherwise treacherous.
How much benefit you will get from using cruise control to reduce fuel consumption depends on the towing capacity of your vehicle compared to the total weight of the trailer you are pulling. For example, a vehicle with a towing capacity of 14,000 pounds pulling a 6,500-pound trailer can maintain the speed setting much more easily than could a vehicle with a towing capacity of only 7,500 pounds pulling the same trailer.
This difference would become more obvious on hills and uneven terrain. On steeper upgrades, the transmission may start downshifting, which will increase fuel use. It is best to turn off the cruise control and drive manually up steeper hills while maintaining a speed that will prevent the transmission from “hunting”---shifting back and forth between gears. Coming down hills, cruise control will not keep the speed from exceeding the set point, so for safety, it is best to drive manually.
In addition, I would advise extra caution using cruise control with a tow vehicle that has an automatic braking system. If you are on an interstate and your automatic braking is set to react to obstacles a fair distance in front of you, a slower car moving into your lane up ahead could trigger a sudden braking surge. With cruise control engaged, you may not be able to react in time to mitigate the effects; without it, you might have enough distance to manually slow your rig at a more even pace.
Finally, a word about speed. Posted speed limits on U.S. highways can reach 70 to 85 mph. However, many trailer tires are rated for maximum speeds of 65 mph---maintaining speeds faster than a tire’s speed limit over long distances may cause the tires to overheat, which can lead to a blowout.
Check your owner’s manual for more specific instructions and recommendations for using cruise control with your vehicle.
SAFETY FIRST: In general, you want to use cruise control only on roadways that do not require frequent stops and turns, such as flat, straight highways without too much traffic.