Trying to figure out what dirt bike tire size you have or which is best for your specific bike? Whether you’re struggling to decipher the numbers or just want a step-by-step guide on understanding dirt bike tires, you’ve found the right article!
Choosing the right tire can make a HUGE difference in your confidence while dirt bike riding off-road because traction is so important – it’s easy to install the wrong tire for the type of riding that you’re doing, making you slide out more quickly, which is scary!
In this article, you’ll learn:
- Tire size – how to identify what you have or need
- Tube size – An simple conversion chart
- Type of tire – Choosing the best tire for your specific needs
How to know what size your dirt bike tires are
The easiest way to find out is to look at the tire’s sidewall- it shows its diameter, height, and width. For example, if it says “80/100X21”, that means it’s a 21” inch diameter tire.
What do the numbers and letters on dirt bike tires mean?
For off-road use only tires, you usually see numbers, such as 80/100×21 with no letters. A street legal dirt bike requires DOT-legal tires, so you should see DOT letters on the tire.
Here’s what each number means on a dirt bike tire, such as (120/90 – 17):
- 120 (First number) – Tire width in millimeters (120mm).
- 90 (Second number) – Tire sidewall height as a percentage of the width [90% of 120 = 108mm sidewall height]
- 17 (Third number) – Tire diameter in Inches that goes on the rim/wheel
What does the arrow on a dirt bike tire mean?
An arrow on a dirt bike tire simply means that’s the intended installation direction. You want the arrow to be rolling forward when it’s on the bike moving forward if you want it to work properly.
For example, the knobbies are placed in a pattern that works best in a certain direction if the front or rear tire has an arrow on the sidewall. If you install it backward, you won’t have as much control because the tire won’t grip or track as well.
On a knobby tire – if the width is 120mm, does that include the entire part of the knobs?
It really depends on the brand of dirt bike tire you buy. For example, you might have a Metzeler 130/90/18 rear tire that measures 140mm including the width of the knobs, but the tire carcass width is only about 115mm.
My recommendation is to buy the exact tire size that came on your dirt bike from the manufacturer.
Most common dirt bike tire sizes
While this list doesn’t include all of the variations of tire sizes (widths, sidewall, etc), these are the most common size tires and rims based on the size and type of dirt bike:
|Dirt Bike Size||Tire & Wheel Size (Front/Rear)|
|50cc 4-stroke trail bike||2.50-10” / 2.50-10”|
|50cc 2-stroke MX bike (mini)||2.50X10” / 2.75X10”|
|50cc 2-stroke MX bike||60/100×12” / 2.75X10”|
|65cc 2-stroke MX bike||60/100-14” / 80/100-12”|
|110cc 4-stroke trail bike||2.50X14” / 3.00X12”|
|85cc 2-stroke/125cc 4-stroke (Small wheel)||70/100×17” / 90/100×14”|
|85cc 2-stroke/125cc 4-stroke (Big wheel)||70/100×19” / 90/100×16”|
|200-250cc 4-stroke trail bike||80/100X21” / 100/100X18″|
|125 2-stroke/250 4-stroke MX bike||80/100X21” / 100/90X19”|
|250cc 2-stroke MX bike||80/100X21” / 110/90X19”|
|250cc+ Enduro bike||80/100X21” / 110/100X18”|
|350-450cc 4-stroke Enduro bike||80/100X21” / 110/100X18″|
|450cc 4-stroke MX bike||80/100X21” / 110/90X19″|
Dirt bike tire & tube conversion size chart
It’s confusing if you’re trying to figure out what size tube you need for your tire size, which is why I made this simple chart. Tube sizes are often shown in inches, so there’s a simple conversion needed when going from a metric tire size to a U.S. standard tube size.
The simple equation is “X (tire width) / 25.4 = tube size/width”. 1-inch = 25.4 millimeters, which is why the width is divided by 25.4.
So if you have an “80mm” wide tire, then the equation is (80 / 25.4 = 3.15). That’s why you would use the 3.00/3.25 wide tube.
Front tire to tube size conversion:
|Front tire size||Correct tube size|
Rear tire to tube size conversion:
|Rear tire size||Correct tube size|
Do you need a new tube when replacing the tire?
If you’re unsure, it’s better to be safe and buy a new tube to replace the old one when you’re installing a new tire – it’s a pain to install most tires, so you don’t want to have to remove it twice in case the old tube fails with the new tire.
With that said, I don’t always replace my dirt bike’s tube every time I put on a new tire. If the tube has never leaked and it still looks good, especially if I just replaced it within the last year, I’ll try and keep using it.
Signs of an old dirt bike tube that needs replacing:
- Pin-hole leak when filled with air – duh!
- Bubbling – if one section of the tube is “swollen/enlarged”, it’s likely to fail soon
- Corroded valve stem – The valve stem area can start leaking just from old age and corrosion
- Dry cracking – Rubber deteriorates over time
Tire size comparison – what is the effect of different sizes?
While it’s generally best to stick with what tires came on your dirt bike from the manufacturer, you can get some positive effects by switching to a slightly different size. However, there is usually some compromise when going bigger or smaller…
Here is what you will generally feel when changing the tire size on your dirt bike:
- Wider is better traction
- Narrow is better handling and less likely to get caught in a narrow rut
- Taller is more plush
- Shorter is quicker steering
- More weight = more stable
- Slower handling
Why do enduro bikes have an 18-inch rear wheel?
An 18” rear tire for an off-road enduro motorcycle has the same outer diameter as a 19” rear tire for an MX bike – the main difference is that the diameter of the tire that goes on the rim and the sidewall height is different. This means the sidewall height is quite a bit taller on an 18” enduro tire compared to a 19” MX rear tire.
The main benefits of an 18-inch rear wheel are:
- More plush (acts as extra suspension) – Softer sidewall
- Better traction – softer sidewall compresses more for more contact surface
In comparison, the benefits of a 19-inch MX rear wheel are:
- Can handle big jumps without feeling “mushy”, which can affect the handling – Stiffer sidewall
- Better high-speed cornering/stability – the tire is less likely to “roll” due to a stiffer carcass/sidewall
Which is better for trail riding?
For most types of trail riding, an 18-inch rear wheel and tire setup is better for a number of reasons. This is why virtually all full-size trail and enduro bikes come with an 18” tire from the factory, but that doesn’t mean it’s always the best.
A 19” rear tire is better for trail riding when:
- Riding at high speed
- The trails have jumps and big obstacles at moderate to high speed
An 18” rear tire is better for trail riding when:
- Riding at low speeds
- Traction is limited (wet rocks, roots, mud, etc)
Pros & Cons of a 21/18 vs 19/16 Setup (Full-size vs Mid-size)
Going from a mid-size big wheel 125cc 4-stroke or 85cc 2-stroke with 19”16” wheels to a full-size trail bike with 21/18” wheels and tires is a big step up in size, height, and performance in most cases.
The 19/16” midsize wheel combo is definitely lighter, lower to the ground, and has better handling when it comes to easier and flatter trails. However, they don’t handle obstacles, such as roots, logs, and rocks as well due to simple physics (a 21” wheel rolls over a 10” log with less effort than a 19” wheel).
The 21/18” wheels are heavier, which slows the handling down, but they are more stable and handle moderate to aggressive and technical trail riding better because they roll over obstacles more easily.
Dirt bike rim width – should you change it?
There aren’t many reasons you should change the width of your dirt bike rim. For example, going from a 1.85 to a 2.15 18” rear rim on a YZ250FX enduro bike will allow you to run a wider rear tire, but there are drawbacks.
Yes, the wider tire can give you more traction, but it will also slow you down.
Pros & cons of wider rims
Think about it, you’re adding considerably more weight with more rim, tube, and tire material – these act as more flywheel weight and unsprung weight.
The extra flywheel weight cause the engine to rev slower and feel like there’s less power (which could actually help in conditions with low traction). The wider tire and unsprung weight significantly affect handling, making your dirt bike harder to lean & turn, and handle slower but have slightly more stability.
Types of dirt bike tires – the deciding factor
Okay, so you’ve figured out what size tires you need, but there’s a big difference when it comes to the type of tire you need as well. It mainly depends on the terrain you’re riding, but some people get these types confused based on their name, so I’ll break it down.
Soft – no, the tire isn’t soft, per se
A “soft terrain tire” is made for soft terrain, such as sand. Some people see the word “Soft” when searching for a tire and think the rubber compound is soft, which is generally best for rocky and slippery conditions, but that’s not the case.
A soft terrain tire is often slightly harder, but more importantly, the tread pattern works best in soft sand/terrain. For example, a soft terrain tire might have bigger “knobbies” in a pattern similar to a paddle tire, giving you better traction.
Intermediate – the great compromise?
An “Intermediate terrain tire” is usually a good compromise between soft and hard because it will give you the best overall traction and control if you’re riding in all kinds of conditions, such as sand, rocks, hardpack, and loamy dirt all in one day.
For example, my favorite rear tire for trail riding in all conditions is the IRC VE33 (Amazon) because it gets good traction if the terrain is dry, wet, rocky, or sandy.
Hard – is it actually hard?
A “Hard terrain tire” is often soft or called a “gummy” tire in the off-road enduro world today. The softer rubber, such as the Bridgestone Battlecross X40 (Amazon) “grips” the hard dirt or rocks better than a harder compound tire.
However, some hard terrain tires also have a hard carcass (rubber), making them last longer, but the knobby tread pattern works well in hard terrain.
What if there’s a combination tire (e.g. soft/intermediate)?
You’ll often see a tire that says Intermediate/soft or Intermediate/Hard terrain, such as the Dunlop Geomax MX53 tire (Amazon) or even a Multi-terrain tire. This just means that the tread pattern and rubber compound is a mixture of the two.
It won’t work quite as well as a hard terrain tire in the rocks and hardpack, but it will work a little bit better in the dirt and slightly softer terrain.
What’s the best dirt bike tire for you?
Best front tire for casual trail riding:
- Bridgestone Battlecross X40 (Intermediate/Hard) – Amazon
- Bridgestone Battlecross X30 (Intermediate) – Amazon
- Shinko F546 (Soft/Intermediate) – Amazon
Best rear tire for casual trail riding:
Best front tire for hard enduro riding:
- Bridgestone Battlecross X31 (Soft/Intermediate) – Motosport
Best rear tire for hard enduro riding:
Cheapest dirt bike tires:
- Pirelli Scorpion Extra X Dirt Bike MX Tires (Full-size 80/100-21 F 110/90-19 R) – Amazon
- WIG Racing MX Tires W/ Inner Tubes (Full-size 110/90-19 &80/100-21) – Amazon
- Tusk EMEX T-35 Soft/Intermediate Tire Set (Choose your sizes) – Amazon
Tire Pressure – How to get the most traction without getting a flat tire
There’s a fine line between getting more traction and getting a flat when it comes to the “right dirt bike tire pressure”. However, it’s not always the same number for everyone, and it also depends on where you’re riding.
For example, 11-13 PSI of pressure is a good starting point, but it also depends on:
- Bike weight
- Rider weight
- The tires you choose
- The tubes you choose
- Type of terrain
- The speed you’re riding
How long do dirt bike tires usually last?
You can usually get 20-50 hours on a set of dirt bike tires because they start losing significant traction, but there are many variables that affect how long they’ll last for you.
For example, if you’re racing a hard enduro course with lots of rocks and you’re on a 300cc 2-stroke or 450 4-stroke, you might only get 3-5 hours before the knobs start ripping off.
These factors affect how long your tires will last:
- Bike power – more power = less tire life
- Terrain – Harder terrain = less life
- Tire selection – Softer rubber = less life
- Bike+rider weight = more weight = less life
- Riding style – aggressive throttle (spinning) = less life
When you have 120/70-17 front and rear is there a difference in width? (4.25-4.5 vs 4.5-4.75)
If the tires show the same size with the three numbers (120/70-17), then they’re the same size whether you use them on the front or back. For the tube size, you just use the simple conversion of (120 / 25.4 = 4.72).
This means you would want to use a 4.5-4.75 tube with a 120mm wide tire, but a 4.25-4.5 tube will work if that’s all you have and you need to get home or back to camp.
Tube vs Tubliss vs Mousse Bibs
There is no “perfect choice” when it comes to what you should use for dirt bike tire inflation – they all have pros and cons.
Conventional Inner tubes (pros & cons):
- Cheapest option
- Easiest to replace
- Different thickness tubes offer better or worse flat prevention
- Can slightly change tire pressure for different feel & traction
- Most likely to get a “pinch flat”
- Generally require the least maintenance
Tubliss (pros & cons):
- No conventional inner tube to “pinch”
- Can run very low PSI for better traction (good for hard enduro/slow speeds)
- Less weight (unsprung weight)
- Require high PSI for high-pressure inner tube (seals to the rim)
- More expensive
Mousse bibs (pros & cons):
- Virtually 100% flat-free due to complete foam construction
- Most difficult to install
- Cannot change “tire pressure”
- Wears out quicker at higher speeds
- Should be replaced every 1-2 years due to foam deterioration
- Most expensive
How to have more control while trail riding
A fresh set of dirt bike tires is one of the best ways to have more confidence, but if you’re trying to teach yourself how to ride then you might be forming habits that are causing you to slide out or lose balance and fall over.
I want to show you how to build your confidence 5X faster by forming positive riding habits. As a thank you for reading this far, I want to give it to you as a gift – download it here for FREE today!