Dirt Bike Tire Guide
Size markings, terrain tires, official off-road pressures, Bib Mousse facts, tire changing and replacement, from Dunlop, Michelin and NHTSA.
Statements on this page come from Dunlop Motorcycle Tires, Michelin and NHTSA, as named. Always verify sizes and pressures with your motorcycle's owner's manual and the tire maker's data for your tire. TireCalculatorHub is not liable for damages arising from use of this information.
Quick Reference
Common dirt bike tire questions answered from the makers' own pages.
Decode 80/100-21
80 = section width in mm, 100 = aspect ratio (the height is 100% of 80 mm), 21 = rim diameter in inches. Dunlop explains that motocross sizes now follow the same standard as street tires, with the width measured at the sidewall.
What pressure?
Dunlop gives 12.5 to 13.5 psi front for hard, intermediate and soft conditions, and Michelin gives 13.1 psi front and rear for the Starcross 6. Check the maker's figure for your tire, measured cold.
Which terrain tire?
Dunlop: choose from the dominant condition; MX34 for varied hard-packed to loose loam, MX53 for hard terrain, MX14 for soft terrain, mud or sand.
Bib Mousse?
Michelin: the Bib Mousse eliminates the risk of a flat, is rated NHS (Not for Highway Service) with a maximum speed of 130 km/h (80 mph), and can be used for a maximum of 6 months after fitting.
When to replace?
Dunlop: replace at 2/32 inch of tread remaining, have tires of 5 years or more inspected by a specialist at least annually, and replace tires 10 years or older from the date of manufacture as a precaution.
How Dirt Bike Tire Sizes Work
A metric size such as 80/100-21 gives the section width in millimetres (80), the aspect ratio as a percentage of that width (100, so the height is 100% of 80 mm), and the rim diameter in inches (21).
Dunlop says that when motorcycle tire standards for width, diameter and load capacity were introduced they did not include motocross tires, so motocross tires varied in dimensions from one maker to another and most were marked by tread width. Under current standards the width is the section width measured at the sidewall. An off-road machine that previously fitted a 4.50-18 or 130/80-18 now fits a 110/100-18, which has the same actual dimensions.
With 19-inch motocross sizes the aspect ratio was reduced to keep the same outside diameter: a 250cc machine going from 110/100-18 to 110/90-19. Dunlop also describes wider, lower-profile rears (110/80-19 and 120/80-19) and a wider 90/100-21 front that fit on existing standard-size rims.
Michelin warns there are two classifications for the same tire dimension. The old Enduro and Desert ranges are sized by the width at tread level; the Starcross, AC10, Trial Light and Xlight ranges are sized by the width at sidewall level. A 130/70-19 Cross Competition S12XC corresponds to a 110/90-19 Starcross 5.
For the sizes your motorcycle takes, use the owner's manual. Dunlop says to consult the motorcycle manufacturer if you intend to mount sizes other than those in the manual, and to keep adequate clearance of fenders and swingarm. We do not list sizes by model because we have no manufacturer source for them.
Choosing a Terrain Tire
Dunlop says to determine the overall track conditions, including the starting line, and let the dominant condition dictate the choice. It also says not to be afraid to mix off-road tire patterns front and rear to feel more comfortable.
Varied conditions: hard-packed to loose loam
A versatile intermediate tire such as the MX34 (Dunlop).
Dunlop: front 12.5–13.5 psi, rear 14 psi
Hard terrain
The MX53 is Dunlop's choice for hard terrain; a combination of hard front and intermediate rear (MX53F and MX34) is also suggested.
Dunlop: front 12.5–13.5 psi, rear 14 psi
Soft terrain, mud or sand
For cushioned, rutted ground with soft berms Dunlop suggests a soft terrain tire such as the MX34; for strictly deep sand or mud, a specialty tire such as the MX14.
Dunlop: front 12.5–13.5 psi, rear 11–12 psi
Tire Pressure: What Dunlop and Michelin Publish
Measure pressure cold. NHTSA says cold means the vehicle has not been driven for at least three hours, and Dunlop says checking tire pressure is the most important tire maintenance function. Dunlop says underinflation may cause wheel damage on rocky, rough terrain and let the motorcycle squirm or wander on smooth, hard terrain; overinflation may damage the tires and cause an unnecessarily harsh ride.
Dunlop off-road inflation pressure (psi)
| Conditions | Front (psi) | Rear (psi) |
|---|---|---|
| Hard | 12.5 – 13.5 | 14 |
| Intermediate | 12.5 – 13.5 | 14 |
| Soft | 12.5 – 13.5 | 11 – 12 |
| Minis | 13 – 14 | 13 – 14 |
Source: Dunlop Motorcycle Tires, Off Road Facts.
Michelin off-road cold pressure with inner tube (psi)
| Tire | Front | Rear | Min. front | Min. rear |
|---|---|---|---|---|
| Starcross 6 | 13.1 | 13.1 | 11.6 | 11.6 |
| Starcross 5 Mini | 17.4 | 17.4 | 14.5 | 14.5 |
| Enduro Medium | 14.5 | 14.5 | 11.6 | 8.7 |
| Enduro Xtrem (rear) | — | 11.6 | — | 8.7 |
| Desert Race | 17.4 | 21.8 | 14.5 | 14.5 |
| Desert Race Baja (rear) | — | 17.4 | — | 14.5 |
| Trial Light | 6 | 5.8 | 5.8 | 5 |
| Trial Competition | 6 | 5.8 | 5.8 | 5 |
Source: Michelin motorcycle off-road tire pressure page. Michelin says this is the pressure recommended depending on the terrain, the weather conditions, the power of the bike and the type of control.
Road use.Dunlop says the minimum pressure for dual-sport and adventure off-highway use is 22 psi front and 22 psi rear, and that pressures must be increased to those the motorcycle manufacturer specifies for highway use. Michelin says to reinflate to the manufacturer's recommended road pressure before riding on tarmac.
For road-going motorcycles the motorcycle tire dimensions calculator and the sport bike tire guide apply, and four-wheel off-road sizes are on the ATV tire size calculator.
Inner Tube vs. Bib Mousse
Michelin says the Bib Mousse, which it invented, is intended for cross country, rally, enduro and MX use and eliminates the risk of a flat. It is designed to fit inside Michelin off-road tires and has a pressure equivalence of 0.8 to 1.0 bar (11.6 to 14.5 psi).
- Rated NHS (Not for Highway Service), with a maximum speed of 130 km/h (80 mph); it should not be used on the public highway.
- Can be used for a maximum of 6 months after fitting; the lifespan varies considerably with the intensity of use and is much shorter for motocross than for enduro.
- Should not be kept long term at temperatures above 30°C, and it is best to avoid temperatures above 40°C altogether.
- Before a fast stage, warm up the tire and the Bib Mousse progressively at a moderate speed.
- Apply Michelin gel every time you fit or remove a Bib Mousse, new or used, to prolong its life and avoid excessive overheating.
We have no official source comparing mousse, tubes and other systems by weight, cost or lifespan, so this page does not.
How to Change a Dirt Bike Tire (Dunlop's Steps)
Removal
- Lay the rear wheel sprocket side down and the front wheel brake side up.
- Remove the valve core and loosen the rim locks.
- Stand the wheel up and use the flat side of a tire iron to push the rim locks down, breaking them loose from the tire bead.
- Lay the wheel down again and stand on the tire sidewalls with your feet pushing to break the beads loose from the rim. A little soapy water at the tire and rim junction helps loosen the beads.
- With the brake side of the wheel up, insert two tire irons between the bead and rim, one on each side of the valve stem. Lever one at a time, working around the tire in small increments.
- After the first side is removed, push the valve stem into the rim and pull the tube all the way out.
- If your wheel has rim locks, remove them before beginning removal of the second bead.
- Remove the second bead by inserting a tire iron under the bead on the brake side of the wheel, then lever the bead over the rim and push it off.
- Clean the bead area of the rim. Check the rim locks, rubber rim strip or tape covering the spoke nipples for damage.
Installation
- Install one rim lock and lubricate one bead of the tire. Push down on the top of the tire, insert one side of the wheel and the rim lock into the bottom part of the tire, and begin levering the first bead on.
- Insert the second rim lock if your wheel uses two. Before installing the tube, inflate it to make sure no damage was done during removal. Check the nut at the stem area for tightness and look for cracks in the stem. Leave just enough air in the tube for installing, so it holds its shape.
- Apply baby powder to the outside of the tube and inside the tire to prevent chafing in use.
- Install the tube carefully, starting at the valve stem hole, and make sure it is not bunched up or caught under the rim locks.
- Lubricate the bead with a mild soap and water solution and push a small section under the rim near the stem area. Insert one tire iron and start levering the bead on, taking very small bites and being careful not to catch the tube.
- With each bite, check that the bead on both sides of the tire is as far down in the well of the rim as possible.
- After the final bead area is installed, be sure the rim locks and valve stem move freely.
- Inflate the tire and seat both beads. If the beads do not seat properly, do not over-inflate: re-lubricate the bead areas and re-inflate until seated.
- After the tire is fully inflated, let the air out and re-inflate so the tube can settle inside the tire. Tighten the rim locks and adjust the tire pressure.
Before every ride (Dunlop)
- Check air pressure prior to every ride.
- Make sure the valve stem has not spun; if it has, deflate the tire and reset it.
- If riding in a rocky area or track, look between the knobs for cracks or cuts to the tire carcass.
- Check the spokes and make sure the rim lock is securely tightened.
When to Replace Your Tires
Tread at 2/32 inch or at the tread-wear indicator
Dunlop: remove tires from service before they reach the tread-wear indicator bars; Dunlop recommends replacing a tire worn to 2/32 of an inch.
Cuts, gouges, missing knobs, excessively worn tread
Dunlop off-road safety tips: check for cuts and gouges that may cause air leakage, and for missing knobs and excessively worn tread.
Tire age
Dunlop: tires in use for 5 years or more should be inspected by a specialist at least annually; replace tires 10 years or older from the date of manufacture, including spares, as a precaution.
Pressure loss
Dunlop: loss of pressure may come from worn-out or badly seated valve cores; check them, and use a metal or hard-plastic valve cap with an inner gasket.
Reading the date code. NHTSA says the last four digits of the tire identification number give the week and year the tire was made (0308 is the third week of 2008), and that the number may not be on both sides of the tire.
Storage. Dunlop says to store tires where the area is clean, dry, well ventilated and temperate, and not where they are exposed to direct sunlight, extreme hot or cold temperatures, ozone-generating sources such as electric motors, battery chargers, generators or welding equipment, or petroleum-based products or solvents.
Run-in. Dunlop says new tires should not be subjected to maximum power, abrupt lean-over or hard cornering until approximately 100 miles have been covered.
Frequently Asked Questions
Try the Dirt Bike Tire Size Calculator
Convert between metric and inch sizes and compare overall dimensions of two tire sizes.