Understanding Motocross Tyre Numbers: A Complete Guide for Riders

If you’ve ever shopped for new motocross tyres, you’ve probably noticed a long string of numbers and letters on the sidewall — something like 70/100-19 42M TT NHS. At first glance, it looks like a secret code. But once you know how to read it, you’ll unlock all the essential details about your tyre’s size, load, and performance.

This guide breaks down each part of the code so you can make smarter choices when buying your next set of tyres.

1. Tyre Width: The First Number

Example: 70/100-19

• 70 → The tyre’s width in millimetres.

• A 70 mm tyre is narrower than an 80 mm tyre. Narrower tyres cut into soft terrain better, while wider tyres offer more surface contact for stability on hard-packed ground.

👉 Tip for riders:
Front tyres are usually narrower (e.g., 70 mm or 80 mm), while rears are wider (100–120 mm).

2. Aspect Ratio: The Second Number

Example: 70/100-19

• 100 → The aspect ratio, expressed as a percentage.

• It means the tyre’s height is 100% of its width.

• If the width is 70 mm, then the sidewall height is also 70 mm.

👉 Tip for riders:
A higher aspect ratio (like 100) gives more cushioning and traction, while lower ratios (like 90) give a stiffer, more responsive feel.

3. Rim Diameter: The Third Number

Example: 70/100-19

• 19 → The wheel rim diameter in inches.

• Common sizes: 19" for rear motocross wheels, 21" for front wheels.

👉 Tip for riders:
Front wheels are usually taller (21") for stability, while rears are slightly shorter (19") for better acceleration and control.

4. Load Index & Speed Rating

Example: 42M

• 42 → Load index, which indicates how much weight the tyre can carry.

  • 42 = up to 150 kg (331 lbs).

• M → Speed rating, which shows the maximum safe speed.

  • M = 130 km/h (81 mph).

👉 Tip for riders:
Motocross tyres are built for off-road riding, not top speed. Always check the load rating matches your bike’s requirements.

5. Construction & Service Codes

• TT → Tube Type. The tyre requires an inner tube.

• TL → Tubeless.

• NHS → Not for Highway Service. These tyres are for off-road only and are not street legal.

👉 Tip for riders:
Motocross tyres are usually TT + NHS. If you need road-legal tyres, look for DOT-approved instead.

6. Examples of Common Tyre Sizes

7. How to Choose the Right Tyre

• For soft mud & sand: Narrower tyres like 70/100-19 cut through and find grip.

• For hard-packed tracks: Wider tyres like 110/90-19 give stability and surface contact.

• For general motocross: A balanced setup with an 80/100-21 front and a 100/90-19 rear works well.

8. Brand Examples

• Michelin Starcross 5 Soft → Excels in mud and soft terrain.

• Dunlop Geomax MX33 → Designed for intermediate terrain.

• Pirelli Scorpion MX32 → Great choice for mixed conditions.

Each brand applies the same numbering system, so once you learn how to read it, you can compare across different tyre lines.

Final Thoughts

Tyre codes may look intimidating, but they’re actually your best guide to picking the right tyre for your riding style, bike, and terrain. At eMotoX Sports, we stock a full range of tyres from leading brands like Michelin, Dunlop, and Pirelli — and our team is always here to help you find the perfect fit.

Next time you’re browsing tyres, take a closer look at the sidewall. Those numbers tell a story — and now you know how to read it.