Do you want to try dirt jumping but don’t know which bike size to get? Are you confused about the size you should buy?
Maybe you tried asking other dirt bikers, but they said conflicting things about dirt jumper sizing. You tried searching on the internet but got information overload.
You’re not alone in this dilemma. New bikers often need the correct information to make buying decisions.
Fortunately, you’ll learn about the right bike from this article. So kindly read on to understand how you can choose the right-sized dirt bicycle for your needs.
Dirt Jumper Size Chart
| Frame Size | Height (in feet and inches) | Height (in cm) | Effective Top Tube (in feet and inches) | Effective Top Tube (in mm) |
| Small | 4’7″ – 5’7″ | 140 – 170 | 21.5″ – 22″ | 546 – 558 |
| Medium | 5’7″ – 6’1″ | 170 – 185 | 22″ – 23″ | 558 – 584 |
| Large | More than 6’1” | At least 180 | At least 23” | At least 584 |
This dirt jumper size chart serves as a guideline only.
What Factors Influence Dirt Jumper Sizing
Contact Points
A rider considers the bike’s pedals and handlebars when riding a BMX or dirt bike.
The top influencer in deciding the frame size is the distance between the head tube and the bottom bracket.
To measure the distance, you may consider the down tube’s length or the frame’s reach.
The reach is the horizontal distance between the middle of the head tube’s upper portion and the center of the bottom bracket.
If you want an excellent way of measuring the dirt jumper, you should refer to the reach or cockpit room.
Unfortunately, some bike manufacturers don’t offer the reach number with their models.
Top Tube Length
Dirt jumpers have a frame size based on the top tube’s length, which is the horizontal distance between the seat and head tubes.
Bike makers often offer information about a bicycle’s adequate top tube size instead of the actual length of the top tube.
Unfortunately, these values differ between manufacturers.
Which Is a Better Indication of Frame Size: Reach or Top Tube Length?
Generally, the length of the top tube determines the frame size, but it’s not an accurate measure.
The seat tube angle changes the top tube length without affecting the setup.
Two bike frames may have the same reach but non-matching lengths of the top tube because of the difference in seat tube angles.
Therefore, you should use the reach to measure the frame size because the seat tube angle doesn’t affect it.
Seat Tube
Cyclists can’t use the seat tube length in sizing a BMX bike or dirt jumper because these dirt bikes are for stunts; therefore, they’re for out-of-the-saddle riding.
It would help to consider the top tube’s length because the seat post isn’t a contact point when you ride.
You use the seat to rest between jumps and tricks and not when pedaling in a seated position.
Sizing
Many dirt jumpers are in one size to fit cyclists of average height. Generally, they have a 600mm effective top tube and 400mm of reach.
Frames
Many dirt bikers use smaller bike frames because they can quickly manipulate them. Smaller sizes are also lighter; therefore, most riders choose them even if they’re tall.
Adjusted Fit
The stem length is also significant because a short stem shortens the reach, and a long stem increases it.
Many dirt jump bicycles have a shorter stem for snappier handling. Moreover, it makes the bikes more stable.
Unfortunately, a short stem limits the weight on the front wheel; thus, climbing becomes harder.
Dirt jump bikes aren’t for climbing, so short stems work best. You can find stems from 30 to 50cm.
The handlebar elevation also affects the fit and geometry. If you’re tall, use handlebars with more rise to boost the perfect bike height and create a roomier frame.
You also maintain a more vertical back angle if you use handlebars with more rise.
Riding Style
You can have a more stable jump using a large frame with an extended wheelbase. On the other hand, a structure with a short chainstay is the standard if you’re after technical riding.
Rider’s Anthropometry
Height is essential in dirt bike sizing; however, your proportions or anthropometry is also vital.
For instance, if you have short or long arms or legs, you may find it uncomfortable to ride a bike that’s suitable for your height.
Top Considerations in Buying a Dirt Jump Bike
Robust Fork
Get a strong fork for a dirt jumper because it can withstand abuse. Pinch the wheel from the front and between your legs.
Then, grab the handlebars and turn them from side to side several times. If you see the fork twisting, you shouldn’t get it.
Chain Retention
If you have a single-speed bike, you should also consider chain retention. Ensure that it has a chain guide on the sprocket’s front if the bike has gears.
These factors will ensure you don’t lose a chain when dirt jumping.
Wheels
The wheels should be sturdy, especially when you’re training. Get a bike with 36-spoke wheel size and maintain the tires at 45psi.
Frames
Check the manufacturer’s sizing chart if you want to get the perfect size for you. For example, an aluminum frame is affordable but stiff.
On the other hand, a Chromoly steel frame is lighter because it combines carbon, titanium, and aluminum.
FAQs
Which is Better: a 24-inch or 26-inch Bike Dirt Jumper?
A 24-inch dirt jumper is nimbler and accelerates faster because of its small tire size. It also works with a petite frame; therefore, it suits cyclists with short stature.
On the other hand, a 24-inch dirt jumper doesn’t absorb bumps, unlike a 26-inch bike.
Get a 24-inch dirt bike if you prefer technical tricks and the 26-inch bicycle is too big for you. If you have a BMX background, you’ll be familiar with a 24-inch bike.
Conversely, a 26-inch dirt bike is more suitable if you want to rid big trail jumps.
What Size Should I Use if I’m a Growing Teenager?
If you have the budget, you should buy a dirt jumper that fits you now; then buy another one once you outgrow it.
However, if money is a problem, get a standard-sized dirt bike. You may also buy a second-hand bike and a high-quality, high-end model as you reach adulthood.
