When you're shifting while towing a trailer, proper gear selection is critical to reduce the amount of strain placed on the tow vehicle. This applies to manual transmission-equipped vehicles as well as those with an automatic transmission. Now, you may be thinking, "Proper gear selection in an automatic?" In recent years, some auto manufacturers have included a tow/haul mode on some cars and trucks equipped with an automatic transmission. The tow/haul mode reduces an automatic transmission's constant search to find the proper gear to suit the terrain. On vehicles equipped with an overdrive off feature, locking out the overdrive gear will have a similar effect [source: Job].
Manual transmission gear selection, as you would expect, is in the hands of the driver. One of the most important things to remember when you're shifting while towing with a manual transmission-equipped vehicle is to be conscious of the terrain. Being prepared to shift at just the right moment as you're climbing a hill can mean the difference between making it to the top nearly effortlessly and straining and coaxing your vehicle every inch of the way.
Gear selection when descending a hill while towing is equally important with a manual transmission-equipped vehicle. The added weight of a trailer can cause a vehicle to go down a hill a little (or a lot) faster than you might expect, and the extra weight may prove too much for the brakes to handle. What's the solution? How can you maintain control? The answer is the same as when you're not towing -- engine braking, or using the engine rather than the brakes to slow down. To do this, you simply remove your foot from the gas and downshift into a lower gear. The engine's RPMs go up, but the vehicle slows down as the engine acts as a compressor to reduce the speed. This reduces brake wear and keeps the vehicle limited to the speed that you feel comfortable with based on your gear selection.
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