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Hills pose risks for some riders
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This article was featured in the May 2009 issue of Consumer Reports magazine.

Hills pose risks for some riding mowers

Last reviewed: May 2009
Illustration of what would happen when trying to make a downhill turn with a zero-turn-radius mower
All of the zero-turn-radius mowers we tested lost steering control when we tried to make a hard turn downhill.
Illustration by Jason Lee

This article is the archived version of a report that appeared in May 2009 Consumer Reports Magazine. Visit our lawn mowers and tractors page to see the very latest information on lawn mowers and tractors.

Zero-turn-radius mowers can outsteer most tractors and zoom back to the shed much faster when you're done. But those attributes also make the machines riskier if there's a wall, pond, road, or other potential hazard at the bottom of a slope.

We've long found those machines hard to steer downhill because, unlike tractors, they steer with their rear wheels. The front wheels are merely casters that can flop around like those on shopping carts. A general rise in deaths for riding mowers appears to track with the growth in market share for zero-turn models, prompting us to take a closer look at steering control on hills. Indeed, loss of control is a factor in many injuries and deaths, based on our analysis of Consumer Product Safety Commission (CPSC) data.

What we tested, what we found

We compared several zero-turn-radius riding mowers marketed to consumers with a lawn tractor on slopes ranging from roughly 5 to 20 degrees. We used a typical 4.5 mph mowing speed over both dry and wet grass, going up and down as you should with most ride-on machines. So far, so good.

The trouble began when we made a hard turn down 10- to 15-degree slopes. The zero-turn riders lost most of their steering control, skidding straight into our simulated hazards. All could stop in time when the brake was applied, though stopping entails manipulating two levers that also do the steering. That's less intuitive than a tractor's foot brake. And while the zero-turn models steered controllably at slower speeds, time savings is a major selling point for zero-turn machines.

The rollover risk

Rollovers are another concern with all ride-on mowers, contributing to the more than 15,000 injuries and 61 deaths associated with those machines for 2007, according to estimates based on CPSC data. Commercial tractors and riding mowers often include a roll bar, called a rollover protective structure (ROPS), and a safety belt. Both are supposed to work together to protect and confine the operator if there's a rollover. But even that approach leaves lots of room for error.

"If you forget to buckle the belt, you can be injured by being crushed by the ROPS itself," says Carol Pollack-Nelson, Ph.D., a human-factors safety consultant formerly with the CPSC. Such systems also raise a tractor's or riding mower's center of gravity, which could increase the chance of a rollover on a hill, adds Pollack-Nelson. Nonetheless, she believes a roll bar and safety belt should be on all tractors and riding mowers because users don't always read the owner's manual and might not be able to accurately gauge the risks that can lead to a rollover.

Rollovers are apparently on manufacturers' radar. Proposed revisions to standards for consumer and commercial tractors and riding mowers will include rollover discussions, according to the Outdoor Power Equipment Institute, an industry trade group. Consumers Union, the nonprofit publisher of Consumer Reports, believes all tractors and riding mowers should meet strict safety requirements that address rollovers, which aren't covered under the current voluntary standard. We also believe a system that warns when a tractor or riding mower is tilted 10 degrees or more would be another critical safety improvement.

Safety steps

  • Choose a front-steering tractor over a zero-turn-radius rider if you're mowing slopes 10 to 15 degrees or greater. (A 10-degree slope rises roughly 20 inches over every 10 feet.) If you already own a zero-turn-radius riding mower, be sure to mow slowly on hills. And mow only on dry grass to maximize traction.
  • Give yourself time to learn the controls on any ride-on mower, especially a zero-turn mower's levers for steering and speed.
  • Mow straight up and down slopes with a tractor or rider unless the manual says otherwise. And mow side-to-side with walk-behind mowers, especially uphill.