18x9.50-8 Grass Master Wheel Assembly

What It Is

The 18x9.50-8 Grass Master Wheel Assembly is a replacement drive wheel and tire combo designed for zero-turn mowers, lawn tractors, and commercial walk-behinds that use an 18-inch tall, 9.5-inch wide tire on an 8-inch rim. It’s built for heavy-duty turf or gravel surfaces, not for front caster wheels.

Fitment & Compatibility

Before buying, verify these three things:

• Tire size: Must be exactly 18x9.50-8 (height x width – rim diameter). Measure your current tire’s sidewall markings—don’t rely on mower model alone.
• Bolt pattern & axle size: This assembly uses a 4-bolt hub with a 4-inch bolt circle (common on many Gravely, Scag, and Husqvarna zero-turns). Measure center-to-center across opposite bolts. Axle hole diameter is typically 5/8" or 3/4"—check yours with a caliper.
• Offset & clearance: The Grass Master wheel has a 2-inch offset (center of tire to mounting face). Compare to your existing wheel to avoid rubbing the deck or frame. Measure from the mounting flange to the inside edge of your current tire.

This is an aftermarket part, not an OEM Grass Master (if your mower brand is Grass Master, confirm OEM part number). It fits most residential zero-turns with 18x9.50-8 tires, but not all.

Key Things to Know

• Quality: Rated 5.0 stars (2 reviews) – likely a solid aftermarket option, but limited feedback means few real-world reports. Expect decent tread life for homeowner use, not commercial abuse.
• Installation: Moderate difficulty. You’ll need a jack, socket set, and possibly a torque wrench (lug nuts typically require 50-70 ft-lbs). No tire mounting needed—it’s a pre-assembled wheel/tire unit.
• Common gotchas: The hub may use metric or SAE lug nuts—verify thread pitch (usually 1/2"-20 or M12x1.5). Also, the tire’s tread pattern might be more aggressive than OEM, which can leave marks on delicate lawns.
• Weight: About 25 lbs – heavy enough to require care during installation, but manageable for one person.

Should You Buy It

Buy this if you need a direct-fit 18x9.50-8 drive wheel for a zero-turn or lawn tractor, your current wheel is damaged or worn out, and you’re comfortable with basic mechanical work. Skip it if you have a non-standard bolt pattern, need OEM-specific parts for warranty reasons, or operate in very muddy conditions where a deeper tread is required. At $114.95, it’s a fair price for a pre-assembled replacement.