Equipment Focus: May 1997, Getting The Right Tires

As technology directing mower design continues to yield more complex and productive walk-behind and riding machines, tires are also spending plenty of time in engineers’ hands and on the testing grounds.

DESIGN LINES. "The key to tire design is minimizing the turf damage they cause, yet still letting them be able to hug the hills," according to Brian Mas-terson, marketing manager, Toro Landscape Contractor Group, Bloomington, Minn.

Tires have either straight or curved edges. "The straight shoulder tires are usually more suited to mowers that will be driven on roads or hard surfaces," explained Dane Scag, president, Great Dane Power Equipment, Elm Grove, Wis. "Curved shoulders don’t hold up or move as well on surfaces like asphalt, but they are better than straight shoulders on turf."

Tire treads vary from no tread to intricate swirl and diamond shaped designs. "Different treads are used for how well they hug and hold the turf," Masterson explained. "We use swirl designs because we think these designs offer more traction than straight line treads."

"Too aggressive tread designs - such as those with really sharp lines - can cut divots in the turf, although they do offer some traction advantages," added Rick Curlett, director of marketing, Exmark Mfg., Beatrice, Neb.

Scag commented that tire design has really been emphasized by manufacturers since zero-turn mowers began accumulating market share. "Zero-turn machines with square treads or treads with sharp angles can really dig or scuff the lawn," he said. "When the mower turns, the inside of the tire is not moving as rapidly as the outside of the tire, and this is where the tread lines can catch and tear turf."

Manufacturers generally put as little traction as possible on the front caster wheels of walk-behind mowers since these tires aren’t expected to provide much traction or maneuverability.

APPLY THE PRESSURE. A variety of cutting maladies can be traced to tires with too much or too little air pressure. "Some hydro walk-behinds have the tendency to drift left or right, and that’s a real nuisance for the operator," said Curlett. "But we’ve found that a big cause of this is having drive tires at different pressures. When this happens, contractors should measure the tires’ circumference to make sure they’re equal. If they’re not equal, then the pressure is off on one tire."

"If a tire is rated at 20 psi, we recommend running the tire at 12 to 14 psi to create more surface area on the ground and improve traction," directed Todd Wanie, design engineer, Scag Power Equipment, Mayville, Wis. "Tires inflated to the maximum pressure have less surface contact and are more likely to slip in the turns.

"If contractors are getting an uneven cut, this may be due to the tires’ pressure levels," Wanie continued. "Different pressure levels could cause the machine to sit at an angle and affect the mower’s performance."

Having the proper pressure level inside the tire maintains the optimum size footprint for the tire on the turf. "Bigger footprints put less pressure per square inch on the turf so the blades of grass aren’t overly compressed," noted Scag. "It’s important not to compress the turf too much or else it won’t get cut on the next pass-by."

In terms of tire composition, more manufacturers are embracing the advantages of foam filled tires for wider applications, despite the added 5 to 10 pounds per wheel.

"Foam filled tires don’t have an inner tube or air in them, so they’re less likely to be damaged," said Curlett. "This makes them good tires for front caster wheels because those wheels get so abused. They’re also good for use in areas with a lot of pine needles or puncture threats to the tires."