What Rear Tire Size Should Be On My Dirtbike?

 

The most common misconception with dirtbike tires is “bigger is better”. While that may be true with other things, dirtbike tires are not the case. Rear tire size is one of the most important things you can choose on your bike for a solid weekend. Here is just a few helpful hints from us here at The Part Shed. 

 

  • Rear tire size is debatable through all sizes. Big bikes (125, 250, and 450) have a few different sizes you can use. Standard sizes are as follows:

125) 100/90-19

250) 110/90-19

450) 120/90-19

The first number describes width of the tire, the second describes height, and the third describes when diameter. Here are some diagrams to better explain. 

 

                                                         

 

There are obviously different sizes and people will have different arguments of what to use, but these are just the basic sizes.

 

  • On a 125 the most common tire size is a 100/90-19 or a 100/80-19. So a 125 is the least powerful big bike, so you want to run the least amount of weight for your tire. The less tire there is to spin, the less work your bike has to do spin it. Running a 110 or a 120 on a 125 would rob the bike of tons of power.

 

  • On a 250 the most common tire size is a 110/90-19. Some people elect to use a 120/90-19 specifically to gain traction. Although in some instances that’s ok, it still robs the bike of power. Also, it’s a wider tire, meaning it takes more to turn the bike. So while you may be gaining traction on the straights, you’ll be losing cornering capability. A 110 tire width is perfect for the 250 (in most cases).

 

  • On a 450, you definitely want to stay with a 120/90-19. The bike is powerful, so robbing horsepower with a larger tire isn’t really a concern. Realistically it has too much power, so the more traction the better. With the bike being a bit heavier than a 250 cornering is still a little bit compromised by the width, but it may not be noticeable to the common rider.

 

Stick with these tire sizes on your bike if you’re not into the experimenting and money spending. Also as a helpful hint, grease your wheel bearings and axles when changing tires. Check your wheel bearings and seals when the wheel is off. If you need new parts, check out our OEM Parts Finder at www.ThePartShed.com.