A Rookie Mistake That Future Dirt Jump Owners Could Be Making… 

from Rookie’s Keyboard

Hello, friends

Yesterday I overheard a conversation between two parents who were observing a group of kids making tricks on dirt jumpers. Their exchange made me realize that regular people don’t know the difference between a dirt jumper and an MTB. And how can you blame them? Dirt jumpers (DJs) are extremely similar to a hardtail (HT).

But there are MASSIVE dissimilarities nonetheless that make dirt jumpers close to unusable on regular trails. 

DJs are 24 or 26-inch hardtail bikes engineered specifically for skate parks and jumping.

You can think of them as a mix between a BMX and an MTB. They are pretty good for street riding too, albeit not as capable as a BMX due to the longer wheelbase and larger size. 

The Differences Between a DJ and a HT

  • Head Tube Angle

The head tube angle (HTA) of a frame greatly influences a bike’s handling.

There are two HTA types – slack and steep.

А slack HTA positions the front wheel further away from the bike whilst a steep HTA brings the front wheel closer to the rider.

Most dirt jumpers come with a steep head angle(e.g., 69°) by the standards of modern MTBs.

The steep HTA improves the maneuverability of the bike at low speeds and positions the rider’s weight closer to the front wheel. This engineering makes it a lot easier to lift the front wheel for tricks.

Meanwhile, modern MTBs have slacker HTAs (e.g., 66.5°).

The table below contains the HTA of popular hardtails and dirt jumpers.

Head Тube Angle Comparison

HardtailHTADirt JumperHTA
Rockhopper Expert 2969.8°DMR Sect 69º
Canyon Exceed 7.069.5°Scott Voltage YZ 0.168.5°
Trek Stache 9.767.8°Marin Alcatraz69º
Fuse Comp 2966.5°Commencal Absolut Dirt69°
Giant XTC Advanced69.5°Santa Cruz Jackal68.7°
Santa Cruz Chameleon67.3°Canyon Stitched 720 Pro69°
Rocky Mountain Growler 2067°NS Movement 169°
Merida BIG.TRAIL 40067.5Specialized P369.5°
Kona Mahuna68°Pivot Point68°
Saracen Zenith Pro67°Mongoose Fireball SS69°

So, the average HTA of hardtails is about 0.88° slacker.

The benefits of a slacker HTA are:

1. Additional stability when descending

2. Lower chances of going over the bars due to the increased wheelbase 

3. Compatibility with forks of greater travel.

Note: When a suspension fork compresses, the HTA of the bike gets steeper. For that reason, bikes with a steep HTA cannot operate with long travel forks as the HTA will get too steep upon compression.

This is one of the reasons why a dirt jumper is not as safe to ride downhill. The chance of going over the bars is just too high when the terrain is demanding.

Seat Tube Length  

Dirt jumpers are built for tricks rather than comfortable pedaling and have a very short seat tube. The goal is to get the saddle out of the way.

This property makes DJs awful climbers and commuters as you are always pedaling outside of the saddle. Strong riders may cover fairly long distances like that, but their efficiency will still be quite low due to the additional drag and the high energy expenditure per 1 crank spin.

MTBs (apart from downhill models), on the other hand,allow you to climb forever in a fairly comfortable position. 

The next table below compares the seat tube lengths of some hardtails and dirt jumpers:

HardtailSeat TubeDirt JumperSeat Tube
Rockhopper Expert370-560mmDMR Sect 330mm
Canyon Exceed 7.0375-535mmScott Voltage YZ 0.1315mm
Trek Stache 9.7394-521mmMarin Alcatraz320mm
Fuse Comp 29340-505mmCommencal Absolut Dirt310mm
Giant XTC Advanced350-520mmSanta Cruz Jackal340mm
Santa Cruz Chameleon390-420mmCanyon Stitched 720 Pro326mm
Rocky Mountain Growler 20380-480mmNS Movement 1335mm
Merida BIG.TRAIL 400390-540mmSpecialized P3312mm
Kona Mahuna370-530mmPivot Point285.7mm
Saracen Zenith Pro393-533mmMongoose Fireball SS292mm

Conclusion: The seat tubes of dirt jumpers are much shorter than those of hardtail MTBs. (what a “surprise”!?)

  • Seat Tube Angle(STA)

The seat tube angle STA (image below) is important too.

A slack STA puts the rider closer to the rear wheel; a steep one pushes the rider forward.

MTBs have steeper seat tube angles as a way to compensate for the slack head tube geometry.

Dirt jumpers, however, have slacker STAs as otherwise there will be no room for the rider.

When you install a long seat post on a dirt jumper, the seat goes behind the bottom bracket by a mile and makes pedaling in a seated position uncomfortable.

The table below compares the STAs of popular hardtails and dirt jumpers.

HardtailSTA*Dirt jumperSTA
Rockhopper Expert 2973.8°DMR Sect 71º
Canyon Exceed 7.072.7°Scott Voltage YZ 0.171°
Trek Stache 9.767.8°Marin Alcatraz71°
Fuse Comp 2974°Commencal Absolut Dirt72°
Giant XTC Advanced73.5°Santa Cruz Jackal72.7°
Santa Cruz Chameleon72.8°Canyon Stitched 720 Pro72.5°
Rocky Mountain Growler 2073°NS Movement 172°
Merida BIG.TRAIL 40073.5°Specialized P370°
Kona Mahuna75°Pivot Point70.2°
Saracen Zenith Pro74°Mongoose Fireball SS70°

Conclusion: The average STA of modern hardtails 1.77° steeper than that of the dirt jumpers.

  • Chainstays

For easier execution of bunny hops and manuals, dirt jumpers have shorter chainstays than regular MTBs.

Shorter chainstays make front wheel lifts almost effortless because the rider doesn’t have to move much to get their weight behind the rear axle.

Meanwhile, hardtails come with longer chainstays for extra stability during descending and climbing.

The notably short chainstays on dirt jumpers are dangerous when covering demanding terrain as the bike may jump out in front of you.

  • Bottom Bracket Drop 

The bottom bracket drop represents the vertical distance between the center of the bottom bracket and an imaginary horizontal line between the axles.

Dirt jumpers have a shorter bottom bracket drop than hardtails.

Why? A small bottom bracket drop facilitates manuals and hops whilst a big bottom bracket drop increases stability.

  • Frame Size

Trail bikes come in a variety of sizes designed to accommodate most riders. Meanwhile, most dirt jumpers are uni-size.

Frame Weight

Dirt jumpers have heavy frames and could end up weighing as much as a geared hardtail. Why? Because the extra strength that the frame needs to handle the impact comes with more material and more weight.

No Accessories

Dirt jump frames don’t have eyelets for fenders, racks, or water bottles. I don’t know about you, but that doesn’t sound like a fun bike to cover high distances…

The next table shows the frame differences between hardtails and dirt jumpers in a compact form.

Hardtail MTBDirt Jumpers
Slack head tube angleSteep head tube angle
Steep seat tube angleSlack seat tube angle
Long seat tubeShort seat tube
Various sizesOne or a few sizes
Large Bottom Bracket DropSmall Bottom Bracket Drop
Bottle cage mounts (occasionally rack and fender eyelets too)No eyelets
  • Suspension 

The travel of dirt jumps forks is quite short between 80 and 100mm. 


  1. To keep the HTA steep(reasons are explained above)
  1. Stiffness

DJ forks are designed to absorb hard but relatively infrequent landings. Thus, they are kept stiff. Short travel helps with that too.

Meanwhile, the fork travel of modern hardtails often is between 120-140mm…sometimes more. 

The extra travel is nice for difficult off-road terrain, but it’s not needed for dirt jumping.

The next table contains the fork travel of the models from the previous tables.

HardtailFork TravelDirt JumperFork Travel
Rockhopper Expert 2980-100mmDMR Sect 100mm
Canyon Exceed 7.0100mmScott Voltage YZ 0.1100mm
Trek Stache 9.7120mmMarin Alcatraz100mm
Fuse Comp 29100-150mmCommencal Absolut Dirt100mm
Giant XTC Advanced100mmSanta Cruz Jackal80-100mm
Santa Cruz Chameleon120mmCanyon Stitched 720 Pro100mm
Rocky Mountain Growler 20130-140mmNS Movement 1100mm
Merida BIG.TRAIL 400140mmSpecialized P3100mm
Kona Mahuna100mmPivot Point100-120mm
Saracen Zenith Pro120mmMongoose Fireball SS100mm

Ironically, since DJ frames are massively overbuilt, many can take forks with ultra-long travel. But the geometry of the bike isn’t engineered for such forks.

  • Wheel Sizes

Most MTBs use 29-inch wheels. 27.5″ are also available but are becoming rarer. Meanwhile, dirt jumpers are equipped with 26-inch wheels and occasionally 24-inch.


29″ wheels are good for speed as each revolution covers a greater distance. They also have great “roll-over-ability” or in other words pass over obstacles easily.

But they aren’t as strong and as maneuverable as 26″.

  • Transmission

DJs are single-speed for simplicity and weight reduction. Therefore, they are super inefficient commuters.

In different, MTBs offer a fairly wide gearing range allowing them to cover all sorts of terrain. 


Standard DJs typically come with a rear brake to make the execution of tricks such as bar spins possible. 

A rear brake is not enough for trail riding. The front brake that DJs are missing provides more stopping power.

“Hybrid Dirt Jumpers”

Some DJs have a bit of “hardtail bone” in them and can work as multi-purpose bicycles:

Example models:

  • NS Clash
  • Kona Shred
  • Dartmoor Shine
  • Santa Cruz Chameleon
  • Chromag Stylus
  • Dartmoor Hornet
  • NS Eccentric
  • Marin San Quentin
  • …etc.

That said, those still aren’t as good as the real thing when it comes to trail shredding. 

Until next time,

– Rookie





Leave a Reply

Your email address will not be published. Required fields are marked *