How Fast Can A Car Go In Reverse

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Cars

Thursday, 29 October 2009 10:32

By josh max-auto.aol

Pity poor reverse; modern cars typically have 4, 5, 6 or even 7 forward gears, but reverse gets a measly 1. So I was pleased to accept the challenge of discovering how fast a ride can go backwards, and decided to use a 2010 Audi S5 loaned to me as my guinea pig.

I wasn’t arrogant enough to think my little test was going to provide the definitive answer, though, so first I consulted Mike Allen, senior editor at Popular Mechanics, who builds, works on and races cars and who was dubious about getting any sort of speed going in reverse.

“Cars have front suspensions that are meant to go forward, not back,” Allen said. “That prevents any driver from getting any serious speed going. Couple that with the fact you’re driving looking over your shoulder, and top speed runs in reverse usually terminate in a spectacular spinout. It’s very difficult to go in a straight line while driving backwards.”

My own test happened spontaneously; I had scoured my surrounding towns looking for an abandoned airfield or other safe test spot when I came upon a deserted avenue in my neighborhood on a lazy sunny Sunday. All streets but one had been cordoned off by authorities to provide space for a bike race, the competition had just finished and the street was completely devoid of people, cars and anyone but the police.

The only way for me to get to an artery leading to a street where I could pick up a highway out of town was to back up one-way, which I was given permission to do by a friendly officer.

“Keep an eye on the speedometer,” I said to my passenger and I threw my S5 into “R”, turned my head to look out the back windshield and accelerated backward in a straight line, keeping the wheel straight with some effort and I continued until I could go no further. “Twelve miles per hour!” said my passenger. Not the Indianapolis speedway by any means, and I would have stopped at 15 MPH, anyway.

I reported my results to Rick Roso, a 16-year racer and media liason for Limerock Racepark, who said, “Usually reverse gears are based on what first gear is, so you’ll be RPM limited. I’m pretty sure you can go faster than 12, but you need the gear and the skill and the room. And do you really want to take your own car to engine redline?”

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Of course, no manufacturer would ever sanction such tomfoolery. We asked General Motors if they kept top speed numbers on their reverse gears. Not surprisingly, they peered down at us over their reading glasses like we had asked to swing the family cat around the living room.

"We don't recommend going fast in reverse," said Jim Lanzon, Executive Director of Transmission Engineering at GM. "We put a lot of attention, in terms of design and analysis, toward the reverse gear - as much importance on that gear as the forward drive gears. Each vehicle application regarding reverse gear is somewhat unique and engineered accordingly.

Specifically, gear ratios for gradeability, so you can back up a steep incline, is something we design for."

Lesson Learned: Don’t try this at home.

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