Owen ReedBy Owen Reed

Updated November 2026

A dirt bike tire size chart tells you which front and rear tire dimensions fit your wheel rim, so you can buy tires that mount correctly and handle the way you expect. In this guide, you will learn how to read tire markings, measure your current rims, match sizes to common dirt bike wheel diameters, and check that your choice works with your riding style. By the end, you should be able to order a tire with confidence.

How Dirt Bike Tire Sizes Are Written

Most dirt bike tires share a similar marking system, and once you understand it, a size chart becomes much easier to use. A typical front tire might read 80/100-21, and a rear tire might read 120/80-19. Each number has a specific meaning.

Shopping for one? See our guide: Dirt Bike Helmet Size Chart: 10 Best Helmets Compared in 2026.

  • First number (section width): The approximate width of the tire in millimeters when mounted and inflated on the correct rim width.
  • Second number (aspect ratio): The tire’s sidewall height as a percentage of its width. A lower number means a shorter, stiffer sidewall.
  • Number after the dash (rim diameter): The wheel diameter in inches. This is the most important number for fitment, because a tire of the wrong diameter will not mount.

Some tires also carry a letter prefix or suffix, such as “MX” for motocross or “E” for enduro, and a load or speed rating. These indicate the intended use and do not change the basic fitment.

Step-by-Step: Finding Your Correct Tire Size

Step 1: Check the Existing Tire Sidewall

The fastest way to confirm your size is to read the markings on the tire currently mounted on your bike. Look for the numbers molded into the sidewall. Write down the full size for both front and rear, since they are almost always different. If the old tire is worn smooth, the markings may still be readable on the sidewall near the bead.

Step 2: Check the Owner’s Manual or Manufacturer Specifications

Manufacturers specify the original equipment tire sizes for each model year. The owner’s manual or the manufacturer’s website will list the recommended front and rear sizes. This is the safest reference, especially if you are buying for a specific model.

Step 3: Measure Your Rim Diameter

If the tire markings are unreadable or you have changed wheels, measure the rim directly. Measure across the rim from bead seat to bead seat, through the center of the hub. Measure from the inside edge of one bead seat to the inside edge of the opposite bead seat. Most dirt bike rims are 19 inches in the rear and 21 inches in the front, though 18-inch rear and 17-inch rear wheels are common on some models, and youth and pit bikes use smaller diameters.

Step 4: Confirm Rim Width

Rim width matters because a tire’s section width changes slightly depending on the rim it is mounted to. Manufacturers list recommended rim widths for each tire. A tire designed for a 2.15-inch rim will not perform as expected on a much narrower or wider rim. Check the rim width stamped on the wheel or listed in the service manual.

Common Dirt Bike Tire Sizes by Wheel Diameter

The table below shows typical front and rear sizes you will see for common wheel diameters. It is a reference only. Always confirm against your specific bike’s manual before buying.

Wheel Diameter Typical Position Common Tire Size Examples Typical Use
21 inch Front 80/100-21, 90/100-21 Motocross and off-road front
19 inch Rear 100/100-19, 110/90-19, 120/80-19 Motocross and off-road rear
18 inch Rear 120/80-18, 110/100-18 Enduro, trail, and some dual-sport
17 inch Front or Rear 90/90-17, 110/80-17, 140/80-17 Supermoto, dual-sport, and some trail bikes
14 to 12 inch Front or Rear Varies by pit bike and mini model Pit bikes and youth minis

Choosing Between Tire Types for Your Riding

Once the size is confirmed, the tread pattern and compound determine how the tire behaves. Size tells you whether a tire fits. Tread and compound tell you how it grips.

  1. Motocross tires use aggressive, widely spaced knobs for loose dirt and jumps.
  2. Enduro tires use a more mixed tread that balances trail traction with some hard-surface durability.
  3. Dual-sport tires combine street legality with off-road capability and usually have a more road-oriented profile.
  4. Supermoto tires are designed for mixed pavement and dirt riding on smaller wheels.

If you ride mostly trails with some pavement, an enduro or dual-sport tire is usually a better fit than a pure motocross knob. Your local terrain and how often you ride on pavement should guide the choice.

Factors That Affect Fit Beyond the Size Chart

Tube Type and Valve Stem

Most dirt bike tires use a tube, but some rims are tubeless-compatible. Make sure you buy the correct tube size for the tire, and confirm the valve stem length works with your rim’s valve hole, especially on deeper rims.

Brake Rotor and Fender Clearance

A taller or wider tire can rub the swingarm, fender, or brake caliper. If you are moving up in tire size, check clearance by rotating the wheel by hand with the bike on a stand and watching for contact.

Tire Pressure

Pressure changes how the tire’s section width and profile behave. Off-road riders typically run much lower pressures than street riders. Always follow the pressure range in your owner’s manual and the tire manufacturer’s guidance.

Common Mistakes to Avoid

  • Assuming front and rear sizes match. They almost never do on dirt bikes.
  • Ignoring rim width. A correct diameter can still perform poorly on the wrong rim width.
  • Buying by the brand name alone. Two tires from the same brand can have different sizes and purposes.
  • Forgetting tube size. Tubes are sized to the tire, so verify the tube matches before installing.
  • Skipping clearance checks. Oversized tires can rub on the swingarm or fender at full compression.

Tips for Ordering the Right Tire

  • Photograph the existing tire sidewall before you shop so you have the markings on hand.
  • Measure rim diameter if you have modified or replaced wheels.
  • Keep your owner’s manual handy for the original equipment specification.
  • If you are unsure, ask a motorcycle shop to confirm the size from your bike’s VIN or model year.

A few supplies make tire changes and fitment checks much easier. These are general-purpose tools that help with the process described above.

  • Tire levers for motorcycles: Sturdy plastic or metal levers protect the rim and make bead removal manageable. View on Amazon
  • Tire pressure gauge: A dial or digital gauge lets you set low off-road pressures accurately. View on Amazon
  • Tire bead lubricant: Helps the bead slide onto the rim without damage during mounting. View on Amazon
  • Dirt bike stand: Lifts the bike so you can spin the wheel and check clearance safely. View on Amazon

FAQ

What does 80/100-21 mean on a dirt bike tire?

The 80 is the approximate section width in millimeters, the 100 is the aspect ratio as a percentage of width, and the 21 is the rim diameter in inches. This is a common front motocross tire size.

Can I use a different tire size than the manufacturer recommends?

Sometimes, but only with careful checks. The new tire must match the rim diameter, be within the rim width range, and clear the swingarm, fender, and brake components. Ask a qualified motorcycle technician if you are unsure.

Are front and rear dirt bike tires the same size?

Usually not. Most dirt bikes use a larger diameter front wheel and a different rear size. Always check each position separately.

Do I need a different tube for a different tire size?

Yes. Tubes are sized to match a specific tire width and rim diameter. Buy a tube labeled for your exact size.

How do I measure my dirt bike rim?

Measure bead seat to bead seat across the center of the rim for diameter, and check the stamped rim width or service manual for width. Measure carefully, since small errors can lead to fitment problems.

Does tire brand affect size?

The size markings are standardized, so a 120/80-19 from one brand should fit the same rim as a 120/80-19 from another. Real-world fit and profile can still differ slightly, so check the manufacturer’s rim width recommendations.

Should I consult a professional before changing tire size?

Yes, if you are considering a significant change in size or wheel setup. A motorcycle shop or qualified technician can confirm clearances, suspension effects, and braking considerations for your specific bike.

Conclusion

A dirt bike tire size chart is most useful when you pair it with the markings on your current tire, the manufacturer’s specifications, and a measurement of your rim. Confirm both the front and rear sizes separately, check rim width, and verify clearance before you install. Once the size is right, choose the tread and compound that match your terrain. Taking these steps will help you buy tires that fit, perform, and stay safe on the trail.

Ready to choose one?

Owen Reed

About Owen Reed

Owen writes about cycling for beginners. Each guide starts with research into how products are built and what owners report after months of use, and is revised when better options appear.