EQUUS - - Contents - Tom Scheve South­ern Pines, North Carolina

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.

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