The numbers and letters that you see on the tires of your dirt bike might seem Greek to you if you do not know what they mean. Things were easy in the past when you could understand everything of width and diameter from the inches. You would easily estimate that you require 4.50-5.00″ x 18″ tire if you own a dirt bike featuring 250cc to 500cc and 3.50-3.75″ x 18″ for 125cc 2-stroke.
But, when as soon the manufacturers turned their face to the metric system for describing their dirt bike tire sizes, things became complex like programming languages. However, it might not still be as tough as you might think it now. Deciphering the dirt bike tires will be easy if you can read this post till the end.
In this article, we are going to decode the numbers you see on the side of the tire to let you know what they mean. We will also help you with tire categories, dirt bike tire conversion chart. And how to choose the right-sized tire for your dirt bike. Let’s go ahead.
Decoding the Numbers and Letters
A good understanding of the aspect ratio is the key to finding the right dirt bike tire. If you have a closer look at the side edge or wall of the tire, you will see some numbers separated by a slash (/) and dash (–). These express the tire size and rim diameter of the tire.
Let’s see it by example. If you look at the sidewall of a typical rear tire of a dirt bike, you might see 120/80-19 or 110/90-19 in it. You will see the same for the front tires with a little bit increase in the diameter. So, which one of these do you need? It might be the first one or the second, or maybe neither of these. What dirt bike tire size you need depends on a variety of factors. We are going to talk more about this issue below.
One of the most common measurements that you see on the sidewall of the tire is the widest distance between the tire sidewalls. It is generally measured and expressed in millimeters (mm). So, if you see 120 or 110 written on a tire sidewall, you have to understand that it is the width of the tire in the millimeters.
However, if you are interested, you can also calculate the millimeters of width into inches. What you need to do is to divide the millimeters by 25.4. In this way, a tire of 110 mm will be 4.330 inches in width while a tire of 120mm will be 4.724 inches.
The number that sits next to the width is the aspect ratio of the sidewall. Generally, a slash is used to separates the aspect ratio from the width. However, millimeter measurement is not a standard for aspect ratio. Instead, a percentage measurement approach is used here. By aspect ratio, the height of the tire’s sidewall is indicated.
So, when you see 80 or 90 written on the sidewall of the tire after the width of 120, you have to understand that the height of the sidewall from tread to the rim is 80 or 90 percent of the width of 120mm. Usually, under the same width, the larger the aspect ratio is, the taller a tire will be. However, though a 110mm tire might seem narrow, it is tall too.
When it comes to the rim diameter, most of the rear rims have a size of 18 to 21 inches. It sits next to the aspect ratio with a dash in front of it. Off-road bikes, with a higher aspect ratio, usually come with 18-inch rear rims.
Apart from the width, aspect ratio, and rim diameter of the dirt bike tire, you might also find load or speed ratings, date code, tire model number, and direction of rotation on the sidewall of some tires.
Dirt Bike Tire Categories
Tires for dirt bike can be categorized into the following classes by their terrain:
Sand Tires: If you love beaches and deserts to explore, the sand tire is a perfect choice. It runs smoothly in the desert trails and on the sand of the beaches.
Soft Dirt Bike Tires: When you drive in loose and muddy conditions of powdery surfaces, you need to go for soft dirt bike tires.
Intermediate or Medium Dirt Bike Tires: For packed ground along with some rock surfaces, intermediate dirt bike tires are suitable.
Hard Dirt Bike Tires: In case you are an extreme racer who explores the rocky terrain, trails, routes with many obstacles like tree debris, hard dirt bike tires are made for you.
Hybrid Dirt Bike Tires: Apart from the tires mentioned above, manufacturers also intermediate-hard, soft-intermediate, and other variations for the local terrains or routes.
Dirt Bike Tire Conversion Chart
If you are confused about the metric system of the tire size, you can convert them into inches. Here are some of the common metric measurement of dirt bike tires into inches:
How to Choose The Dirt Bike Tire Size
Dirt bike tire size is important because it influences the performance. When you choose the right dirt bike rear tire and front tire, you have to consider the dirt conditions, load factor, tire pressure as well. That’s the very reason why you will see that manufacturers offer various models with distinguished patterns to choose from.
The compound variation can be divided into soft, intermediate, and hard, and choosing the middle one is great if you want the do-it-all type of tires.
If you buy a wrong tire, e.g., a wider tire for a 125cc two-stroke, you will end up hurting the acceleration of engine and performance as well. It happens due to the added traction and excessive weight.
Power output and engine size are two of the most important factors that you should not ignore when you go for buying the tire for your dirt bike. If a bike of 125cc two-stroke uses a 120mm tire, it will consume more power and will affect the efficiency and life of the engine. On the other hand, a skinny tire of 90mm for 450cc 4-stroke will be worn prematurely and will be affected by low traction.
Here’s how to determine the best tire sizez for your dirt bike:
- Consult the user manual to find out the dirt bike tire size chart. Follow the recommendations mentioned there.
- Contact and ask from the manufacturer of the brand from which you are going to buy the tire. They can honestly give you the best advice or suggestions regarding their dirt bike tire sizes.
- Also, see the optimum compound of the dirt bike tire you have chosen to buy.
- Go and have a look at the local off-road race or motocross competition to find what brand, model, and tire size the racers are choosing for their dirt bikes.
Frequently Asked Questions
How do I know what size dirt bike tire I have?
Just look at the sidewall to find the width, aspect ratio, and rim diameter of your dirt bike tire. You can also convert the metric system into inches.
Why are dirt bike tires different sizes?
Dirt bike tires come to different sizes due to the difference of trails, routes, and purpose they are made for. The tire size that works great for beaches might not work well in the rocky mountains.
What size tire will fit my motorcycle Rim?
It depends on the rim measurement of your motorcycle. Here is a chart that can help you determine the size that will fit perfectly to your motorcycle rim.
How wide is a 180 motorcycle tire in Inches?
A motorcycle or dirt bike of 180mm has a width of 7.09 inches.
How wide is a 150 motorcycle tire?
A tire of 150 mm usually has a width of about 6 inches.
How to find the tire width?
The tire width is generally the first number that sits before the aspect ratio and the rim diameter. So, in 120/90×19, 120mm is the width of the dirt bike tire.
What do R and B denote in the dirt bike tire?
R stands to mean the radial tire and B stands to mean the bias-ply tire. However, if there is no mention of R, you can think that as a bias-ply tire by default.
Where can I get cheap dirt bike tires?
Visit your nearest dirt bike tire shop, compare the prices and models to find the cheaper one for you within your budget. You can do the same online.
So, have you got a clear understanding of dirt bike tire sizes? We hope the answer would be ‘yes’. Choosing the right dirt bike tire sizes is important for a smooth ride and durability of the tire.