Dirt Jumpers: A BMX–Mountain Bike Hybrid For Going Big

Last updated: April 10th, 2024

Key takeaways:

  • Think of a dirt jump (DJ) bike as a BMX–mountain bike hybrid.
  • Most dirt jump bikes are single-speeds hardtails with 26″ wheels, disc brakes, and a suspension fork with 80–100 mm travel.
  • Slopestyle (SS) bikes are basically dirt jumpers with full suspension, designed for the enormous jumps and hard landings of a slopestyle MTB course.
  • DJ/SS bikes are slightly less agile than BMX bikes, but more stable and confidence-inspiring.
  • For singletrack, stick with a regular MTB. Their gearing, seat height, and lightness are more appropriate for trails.

Dirt jump bikes are a hybrid of BMX and mountain bikes. They’re distinct from big-wheel BMX bikes, which use a mix of MTB components and enlarged BMX frames.

Dirt jumpers have the short wheelbase, snappy handling, single-speed drivetrain, and indestructible build of a BMX bike.

Most also inherit the larger wheels (typically 26″), front suspension, and disc brakes of a mountain bike. They typically come in one size, but a few brands offer two.

Over the years, jumps and stunts have gotten ever bigger. Back in the day, it went something like this:

That’s crazy enough, in my book. But today, it’s grown into the completely bonkers Red Bull events we (or at least I) can’t stop watching.

Slopestyle bikes evolved to handle this.

They’re functionally similar, with one key difference: dirt jump bikes are hardtails, but slopestyle bikes are generally full-suspension. Most are still single-speeds, but a few do have multi-speed drivetrains to handle more varied courses.

As an aside, you might also see big-wheel BMX bikes. They’re essentially a novelty. A very fun novelty, to be clear, but neither as agile as a 20″ BMX bike nor as capable as a DJ/SS bike.

What dirt jump bikes are (& aren’t) for

Dirt jumping and slopestyle bikes excel on bigger or rougher jump lines where BMX bikes feel too sketchy.

Full-suspension slopestyle bikes are not optimal for DH or enduro, but they’re plenty burly if you enjoy the occasional lift/shuttle run.

For singletrack riding, a regular mountain bike is the way to go. Conversely, if you stick to skateparks and hit the dirt only occasionally, then a BMX bike gives better bang for the buck.

DJ/SS bikes do this best

Dirt jump bikes are purpose-built for big air. They’re more forgiving than BMX bikes, so you can go bigger on rougher terrain.

That means not only dirt jumps (obviously!) but also massive ramps and drops with less-than-ideal landings…and often rocks strewn about. These conditions push the limits of BMX bikes’ stability and bump absorption.

In light of their hybrid BMX–MTB heritage, dirt jumpers are plenty of fun in traditional BMX settings:

  • Skateparks
  • Freestyle street riding
  • BMX tracks
  • Pump tracks

Slopestyle courses are another ideal setting for DJ and SS bikes. The latter, especially, are made for enormous jumps and drops that need more stability than BMX bikes offer. 

Can you or I go hard enough to actually need that stability?

I can’t speak for you…but count me out.

But for the pros, it’s the key to the mind-boggling stunts that keep us glued to Red Bull competitions.

(My last foray into BMX and dirt jumping ended with cracked ribs and two months of painful breathing, so suffice to say those days are behind me. Turns out I don’t heal as quickly in my 15-year-old downhill racing days!)

When DJ/SS bikes are a struggle

You’re better off with a mountain bike for trail riding, or a BMX bike for highly technical tricks.

It’s possible to ride dirt jump and slopestyle bikes on mountain bike trails, but it’s not very enjoyable.

Their single speed, hefty weight, and smaller wheels are taxing. Descents are fun but sketchy (again, we’re talking 26″ wheels and a short wheelbase) and everything else is just plain hard.

Moreover, they don’t allow proper knee extension while pedaling. They’re built with an extremely short seat tube, which is great at keeping the saddle out of your way during jumps, but not great for actually sitting on.

By modern MTB standards, their short wheelbase may feel twitchy on fast, rough trails.

Sure, they’re technically mountain bikes, but not the kind you’d want for exploring miles of singletrack.

From personal experience, it took exactly one trail ride to cure me of ever wanting to take my Specialized P.Street anywhere near a climb again.

Specialized P-Street dirt jump bike, equipped with 24" wheels and rim brakes.
This single-speed 24″ DJ bike was fun at the pump track, but rooty hills were another story.

On the other end of the spectrum, dirt jumper and slopestyle bikes are too cumbersome for flatland tricks or extremely tight, steep jumps (including some skatepark features).

With a longer wheelbase and bigger wheels, steep transitions feel even steeper, and there’s altogether more size and mass to throw around.

DJ bikes just aren’t as “flickable” as their BMX counterparts.

Dirt jump, BMX & mountain bike design comparison

Dirt jump/slopestyle, BMX, and mountain bikes have major differences in design, component choice, and ride quality.

Understanding these differences is key to choosing a bike that’ll be exciting—not a struggle—to ride.

(These comparisons will focus on freestyle BMX bikes. Race bikes are another matter.)

Dirt Jump / SlopestyleFreestyle BMXMountain
Frame materialGenerally aluminum; sometimes steelSteelGenerally aluminum or carbon; steel also available
Wheel sizeGenerally 26″20″ (other sizes are uncommon but available)27.5″ or 29″ (but 26″ on older bikes)
Front suspension~80–100 mmNone~80–200 mm depending on discipline (rigid forks also available)
Rear suspensionNone (DJ) or ~100 mm (SS)None~100–200 mm depending on discipline (hardtails also common)
DrivetrainGenerally single-speed; occasionally multi-speed with derailleurSingle-speedMulti-speed with derailleur
BrakesFront & rear mechanical/hydraulic discsRear rim brake; sometimes no brakesFront & rear mechanical/hydraulic discs
Riding positionStanding only (very low saddle)Standing only (very low saddle)Sitting & standing (dropper posts are common)
GeometryModerate top tube, short chainstays, moderate head & seat tube anglesShort top tube, very short chainstays, steep head & seat tube anglesTrending toward long top tube, short chainstays, very slack head & seat tube angles

Frame material

Freestyle BMX bikes use steel frames and forks. They need to withstand repeated drops from high up, often onto concrete. Weight is a distant second priority—at most.

Today’s top-tier MTBs are replete with featherweight carbon, but their low- to mid-range siblings stick with various aluminum alloys. Aluminum lacks the lightness and vibration dampening of carbon fiber, but can be made plenty strong for a fraction of the price.

Aluminum frames are also standard in the DJ/SS world, although steel frames do exist.

Carbon DJ bikes are vanishingly rare. They’re basically relegated to one-off experiments like this prototype from dirt jumping legend John Cowan. A bombproof carbon frame is simply too expensive to produce for the minuscule number of dirt jumpers who actually care about weight.

Wheel size

Nearly all BMX bikes use 20″ wheels for maneuverability. (You’ll see plenty of 16″ children’s bikes and 24″ cruisers, among other sizes, but these aren’t standard for freestyle riding.)

Dirt jumpers are noticeably larger at 26″, or 24″ in a few cases.

In the mountain bike world, 27.5″ and 29″ have prevailed since the late 2000s–early 2010s. Twenty-six inches was the previous standard; it’s still used on some very small sizes, but mostly appears on older, secondhand MTBs.

Larger wheels sacrifice nimbleness for smoothness and stability. Standard, 20″ BMX wheels are more responsive on tight, steep jumps, but they’re a handful on rough or rocky ground.

All else being equal, 20″ wheels are stiffer and stronger. With a small radius, horizontal forces don’t create as much leverage on the rim. Pragmatically, manufacturers simply compensate by beefing up 26″ rims. You might need to true your 26″ rims a little more often, but you shouldn’t need to worry about their strength.

Suspension

All BMX bikes are rigid, meaning they don’t have suspension.

There have been a few rigid dirt jumpers over the years, but the industry has settled on a suspension fork with about 80–100 mm of travel. Slopestyle bikes often have full suspension, with roughly the same amount of travel.

Unlike on other mountain bikes, DJ suspension is set up with extremely stiff preload (spring resistance). That reduces the chance of bottoming out on a harsh landing. 

For other aggressive MTBs—like trail and enduro models—the standard is 130–160+ mm of front travel (and often rear travel) with softer preload. It still helps with hard landing, but the real goal is suppleness to dampen rocky, rooty chatter at high speeds.

Drivetrain

BMX bikes and dirt jumpers generally use a single-speed drivetrain with roughly 55″ gearing.

That’s low enough to accelerate quickly, but high enough to build up speed to clear large jumps.

That points to a gear ratio of about 2:1 on most 26″ DJ bikes. For instance, 32:16 is a popular combination. The exact gear ratio also depends on tire width, so you’ll want to plug the numbers into a gear inches calculator.

That same 55″ gear is also a good starting point for slopestyle. Big slopestyle courses need more speed than typical dirt jumps, so higher gears are also common.

Some slopestyle bikes even use a 7-speed derailleur drivetrain. That way, there’s no need to swap gears to suit wildly different courses or to hit faster trails at a lift-access bike park.

Mountain bikes have far wider gearing to make steep climbs and descents possible. You’ll usually find a 10- to 12-speed rear derailleur with a wide-range cassette.

Brakes

BMX bikes have minimal braking power. Most have only a rear brake, since riders don’t want a front brake cable/line to interfere with barspins.

What’s more, freestyle BMX bikes only use rim brakes, which are especially weak and inconsistent in wet weather.

Some dirt jumpers use that same, rear-only configuration, but with a disc brake for somewhat greater power (in all conditions).

Rear-only braking is not suitable for demanding trails. You need dual brakes for unexpected descents, obstacles, and generally adequate speed control.

To that end, front + rear disc brakes are the industry standard for all regular MTBs, slopestyle bikes, and many dirt jump bikes as well. That’s a genuinely trail-worthy set-up that provides terrific power in all conditions.

Riding position

BMX, dirt jump, and slopestyle bikes are only intended to be ridden standing up. They have saddles, but they’re for safety and rest—not for extended use.

The reason is frame size.

For stunt-oriented riding, the frame needs to stay out of the way. In practice, that means a low top tube and therefore a short seat tube. By the time the seatpost is short enough to slide all the way into the seat tube, it’s too short for good knee extension when sitting.

Regular mountain bikes use conventional seat tube lengths that allow full knee extension when seated. Telescopic “dropper” posts are a common upgrade these days. They provide on-the-fly adjustment between full saddle height (for seated pedaling) and lower saddle height (for jumps or technical descents).

Geometry

BMX and dirt jump bikes aim for the shortest possible wheelbase that won’t cramp the rider. The shorter the bike, the easier it is to whip around.

Slopestyle wheelbases may be an inch or two longer to accommodate rear suspension travel, but they remain as compact as can be.

BMX head tube angles are extremely steep: around 75°, give or take 1. Such a steep angle makes for incredibly quick, light steering. That’s a good thing for precise, technical tricks at lower speeds, but unnerving at high speeds on rough ground.

DJ/SS bikes are somewhat slacker, often in the 68–70° range. They don’t feel as responsive when weaving through skateparks with hair’s-breadth precision, but they’re much more predictable on trails and bigger jumps.

In recent years, mountain bikes have gone slacker still. For now, they’ve settled at around 65–67° for trail and enduro bikes. Combined with low bottom brackets and long top tubes, the result is incredible stability at speed, but a bit of a handful in tight, steep dirt jumps.

(It’s a little more complex in reality, since fork travel and rear suspension travel—if any—can make the same head tube angle feel different. But that’s a topic for another day.)

BMX and DJ/SS sizing is limited. Brands and models vary a bit in geometry—10 mm longer top tube here, 1° steeper head tube there—but there are only one or two sizes for adult riders. 

When you ride standing up, your body moves and shifts continually, so sizing differences largely fall off your radar. And with super-low top tubes across the board, standover clearance is seldom an issue in the first place.

MTBs need to accommodate extended seated riding, so they typically come in four or five sizes per model. Your body position is fixed, so even small changes in the handlebars–cranks–saddle relationship can feel huge (for better or worse).

Common questions about dirt jump bikes

Can I just ride dirt jumps on a regular mountain bike?

Absolutely! This was common in the 1990s and early 2000s, before dedicated DJ bikes were widely available. I have the scars to prove it!

However, those older MTBs used 26″ wheels and front (or no) suspension. Some weren’t as burly as dedicated dirt jumpers, but they weren’t entirely different, either.

Exhibit A: an Evil D.O.C. custom build from 2007-ish. It was an all-around aggressive hardtail, but awfully similar to today’s DJ machines.

Custom Evil D.O.C. freeride hardtail, with 26" wheels and single-speed drivetrain.

Modern mountain bikes are less conducive to dirt jumping. Wheels are larger, tires are fatter, wheelbases are multiple inches longer, geometry is slack, and full suspension is ubiquitous.

A modern trail or enduro mountain bike with long, slack geometry.

Those features help tear up trails, but make BMX-style dirt jumps feel cramped.

Are dirt jump bikes good on trails?

Dirt jump and slopestyle bikes are capable but not fun to ride on MTB trails. They get extremely tiring, since there’s no shifting gears and no pedaling while seated.

Their 26″ wheels aren’t a limitation per se, but they’re not as smooth as larger, modern MTB wheels, either.

If you still want to try your DJ/SS bike on singletrack, then stick with shuttled or lift-accessed trails, and don’t plan to race your buddies on trail or enduro bikes!

Should I get a dirt jumper or a BMX bike?

They’re very similar, and both are excellent for dirt jumping. The decision depends on what else you want to do.

If you plan on bigger/rougher dirt jumps, slopestyle courses, and some limited singletrack, then get a dirt jump or slopestyle bike. 

They’re also smoother and more forgiving, which inspires confidence in new riders. However, that makes it easier to get away with sloppy technique when riding at the edge of your abilities.

If you plan to stick with smoother dirt jumps and skateparks, then a BMX bike is the way to go. They’re more affordable and nimble. They’re also less forgiving, which tends to reinforce good technique and knowing your limits.

Ultimately, your skill matters far more. A good BMX rider can do things that a newbie on a dirt jumper couldn’t dream of. A pro on a slopestyle bike can find creative skatepark lines that BMX newbies won’t even see.

Time on the bike will help you progress more than time researching it. So, for the moment, grab whatever you’ve got and see how far you can (reasonably) push it!

Key takeaways:

  • A BMX mountain bike hybrid is called a dirt jump (DJ) bike.
  • Most dirt jump bikes are single-speeds hardtails with 26″ wheels, disc brakes, and a suspension fork with 80–100 mm travel.
  • Slopestyle (SS) bikes are basically dirt jumpers with full suspension, designed for the enormous jumps and hard landings of a slopestyle MTB course.
  • DJ/SS bikes are slightly less agile than BMX bikes, but more stable and confidence-inspiring.
  • For singletrack, stick with a regular MTB. They have the necessary gearing, seat height, and lightness that trails demand.

Ever wonder if there’s a BMX–mountain bike hybrid?

Something that’s easy to flick around in the air, compact enough for the skatepark, and still able to hold its own over rocks and roots?

Enter the dirt jump (DJ) bike and its bigger sibling, the slopestyle (SS) bike.

The BMX–mountain bike hybrid

Dirt jump bikes are a hybrid of BMX and mountain bikes. There are also big-wheel BMX bikes, which use a mix of MTB components and enlarged BMX frames.

Dirt jumpers have the short wheelbase, snappy handling, single-speed drivetrain, and indestructible build of a BMX bike.

Most also inherit the larger wheels (typically 26″), front suspension, and disc brakes of a mountain bike. They typically come in one size, but a few brands offer two.

Over the years, jumps and stunts have gotten ever bigger. Back in the day, it went something like this:

That’s crazy enough, in my book. But today, it’s grown into the completely bonkers Red Bull events we (or at least I) can’t stop watching.

Slopestyle bikes evolved to handle this.

They’re functionally similar, with one key difference: dirt jump bikes are hardtails, but slopestyle bikes are generally full-suspension. Most are still single-speeds, but a few do have multi-speed drivetrains to handle more varied courses.

As an aside, you might also see big-wheel BMX bikes. They’re essentially a novelty. A very fun novelty, to be clear, but neither as agile as a 20″ BMX bike nor as capable as a DJ/SS bike.

What dirt jump bikes are (& aren’t) for

Dirt jumping and slopestyle bikes excel on bigger or rougher jump lines where BMX bikes feel too sketchy.

Full-suspension slopestyle bikes are not optimal for DH or enduro, but they’re plenty burly if you enjoy the occasional lift/shuttle run.

For singletrack riding, a regular mountain bike is the way to go. Conversely, if you stick to skateparks and hit the dirt only occasionally, then a BMX bike gives better bang for the buck.

DJ/SS bikes do this best

Dirt jump bikes are purpose-built for big air. They’re more forgiving than BMX bikes, so you can go bigger on rougher terrain.

That means not only dirt jumps (obviously!) but also massive ramps and drops with less-than-ideal landings…and often rocks strewn about. These conditions push the limits of BMX bikes’ stability and bump absorption.

In light of their hybrid BMX–MTB heritage, dirt jumpers are plenty of fun in traditional BMX settings:

  • Skateparks
  • Freestyle street riding
  • BMX tracks
  • Pump tracks

Naturally, DJ and SS bikes are also ideal for slopestyle courses. The latter, especially, are made for enormous jumps and drops that need more stability than BMX bikes offer. 

Can you or I go hard enough to actually need that stability?

I can’t speak for you…but count me out.

But for the pros, it’s the key to the mind-boggling stunts that keep us glued to Red Bull competitions.

(My last foray into BMX and dirt jumping ended with cracked ribs and two months of painful breathing, so suffice to say those days are behind me. Turns out I don’t heal as quickly in my 15-year-old downhill racing days!)

When DJ/SS bikes are a struggle

You’re better off with a mountain bike for trail riding, or a BMX bike for highly technical tricks.

It’s possible to ride dirt jump and slopestyle bikes on mountain bike trails, but it’s not very enjoyable.

Their single speed, hefty weight, and smaller wheels are taxing. Descents are fun but sketchy (again, we’re talking 26″ wheels and a short wheelbase) and everything else is just plain hard.

Moreover, they don’t allow proper knee extension while pedaling. They’re built with an extremely short seat tube, which is great at keeping the saddle out of your way during jumps, but not great for actually sitting on.

By modern MTB standards, their short wheelbase may feel twitchy on fast, rough trails.

Sure, they’re technically mountain bikes, but not the kind you’d want for exploring miles of singletrack.

From personal experience, it took exactly one trail ride to cure me of ever wanting to take my Specialized P.Street anywhere near a climb again.

Specialized P-Street dirt jump bike, equipped with 24" wheels and rim brakes.
This single-speed 24″ DJ bike was fun at the pump track, but rooty hills were another story.

On the other end of the spectrum, dirt jumper and slopestyle bikes are too cumbersome for flatland tricks or extremely tight, steep jumps (including some skatepark features).

With a longer wheelbase and bigger wheels, steep transitions feel even steeper, and there’s altogether more size and mass to throw around.

DJ bikes just aren’t as “flickable” as their BMX counterparts.

Dirt jump, BMX & mountain bike design comparison

Dirt jump/slopestyle, BMX, and mountain bikes have major differences in design, component choice, and ride quality.

Understanding these differences is key to choosing a bike that’ll be exciting—not a struggle—to ride.

(These comparisons will focus on freestyle BMX bikes. Race bikes are another matter.)

Dirt Jump / SlopestyleFreestyle BMXMountain
Frame materialGenerally aluminum; sometimes steelSteelGenerally aluminum or carbon; steel also available
Wheel sizeGenerally 26″20″ (other sizes are uncommon but available)27.5″ or 29″ (but 26″ on older bikes)
Front suspension~80–100 mmNone~80–200 mm depending on discipline (rigid forks also available)
Rear suspensionNone (DJ) or ~100 mm (SS)None~100–200 mm depending on discipline (hardtails also common)
DrivetrainGenerally single-speed; occasionally multi-speed with derailleurSingle-speedMulti-speed with derailleur
BrakesFront & rear mechanical/hydraulic discsRear rim brake; sometimes no brakesFront & rear mechanical/hydraulic discs
Riding positionStanding only (very low saddle)Standing only (very low saddle)Sitting & standing (dropper posts are common)
GeometryModerate top tube, short chainstays, moderate head & seat tube anglesShort top tube, very short chainstays, steep head & seat tube anglesTrending toward long top tube, short chainstays, very slack head & seat tube angles

Frame material

Freestyle BMX bikes use steel frames and forks. They need to withstand repeated drops from high up, often onto concrete. Weight is a distant second priority—at most.

Today’s top-tier MTBs are replete with featherweight carbon, but their low- to mid-range siblings stick with various aluminum alloys. Aluminum lacks the lightness and vibration dampening of carbon fiber, but can be made plenty strong for a fraction of the price.

Aluminum frames are also standard in the DJ/SS world, although steel frames do exist.

Carbon DJ bikes are vanishingly rare. They’re basically relegated to one-off experiments like this prototype from dirt jumping legend John Cowan. A bombproof carbon frame is simply too expensive to produce for the minuscule number of dirt jumpers who actually care about weight.

Wheel size

Nearly all BMX bikes use 20″ wheels for maneuverability. (You’ll see plenty of 16″ children’s bikes and 24″ cruisers, among other sizes, but these aren’t standard for freestyle riding.)

Dirt jumpers are noticeably larger at 26″, or 24″ in a few cases.

In the mountain bike world, 27.5″ and 29″ have prevailed since the late 2000s–early 2010s. Twenty-six inches was the previous standard; it’s still used on some very small sizes, but mostly appears on older, secondhand MTBs.

Larger wheels sacrifice nimbleness for smoothness and stability. Standard, 20″ BMX wheels are more responsive on tight, steep jumps, but they’re a handful on rough or rocky ground.

All else being equal, 20″ wheels are stiffer and stronger. With a small radius, horizontal forces don’t create as much leverage on the rim. Pragmatically, manufacturers simply compensate by beefing up 26″ rims. You might need to true your 26″ rims a little more often, but you shouldn’t need to worry about their strength.

Suspension

All BMX bikes are rigid, meaning they don’t have suspension.

There have been a few rigid dirt jumpers over the years, but the industry has settled on a suspension fork with about 80–100 mm of travel. Slopestyle bikes often have full suspension, with roughly the same amount of travel.

Unlike on other mountain bikes, DJ suspension is set up with extremely stiff preload (spring resistance). That reduces the chance of bottoming out on a harsh landing. 

For other aggressive MTBs—like trail and enduro models—the standard is 130–160+ mm of front travel (and often rear travel) with softer preload. It still helps with hard landing, but the real goal is suppleness to dampen rocky, rooty chatter at high speeds.

Drivetrain

BMX bikes and dirt jumpers generally use a single-speed drivetrain with roughly 55″ gearing.

That’s low enough to accelerate quickly, but high enough to build up speed to clear large jumps.

That points to a gear ratio of about 2:1 on most 26″ DJ bikes. For instance, 32:16 is a popular combination. The exact gear ratio also depends on tire width, so you’ll want to plug the numbers into a gear inches calculator.

That same 55″ gear is also a good starting point for slopestyle. Big slopestyle courses need more speed than typical dirt jumps, so higher gears are also common.

Some slopestyle bikes even use a 7-speed derailleur drivetrain. That way, there’s no need to swap gears to suit wildly different courses or to hit faster trails at a lift-access bike park.

Mountain bikes have far wider gearing to make steep climbs and descents possible. You’ll usually find a 10- to 12-speed rear derailleur with a wide-range cassette.

Brakes

BMX bikes have minimal braking power. Most have only a rear brake, since riders don’t want a front brake cable/line to interfere with barspins.

What’s more, freestyle BMX bikes only use rim brakes, which are especially weak and inconsistent in wet weather.

Some dirt jumpers use that same, rear-only configuration, but with a disc brake for somewhat greater power (in all conditions).

Rear-only braking is not suitable for demanding trails. You need dual brakes for unexpected descents, obstacles, and generally adequate speed control.

To that end, front + rear disc brakes are the industry standard for all regular MTBs, slopestyle bikes, and many dirt jump bikes as well. That’s a genuinely trail-worthy set-up that provides terrific power in all conditions.

Riding position

BMX, dirt jump, and slopestyle bikes are only intended to be ridden standing up. They have saddles, but they’re for safety and rest—not for extended use.

The reason is frame size.

For stunt-oriented riding, the frame needs to stay out of the way. In practice, that means a low top tube and therefore a short seat tube. By the time the seatpost is short enough to slide all the way into the seat tube, it’s too short for good knee extension when sitting.

Regular mountain bikes use conventional seat tube lengths that allow full knee extension when seated. Telescopic “dropper” posts are a common upgrade these days. They provide on-the-fly adjustment between full saddle height (for seated pedaling) and lower saddle height (for jumps or technical descents).

Geometry

BMX and dirt jump bikes aim for the shortest possible wheelbase that won’t cramp the rider. The shorter the bike, the easier it is to whip around.

Slopestyle wheelbases may be an inch or two longer to accommodate rear suspension travel, but they remain as compact as can be.

BMX head tube angles are extremely steep: around 75°, give or take 1. Such a steep angle makes for incredibly quick, light steering. That’s a good thing for precise, technical tricks at lower speeds, but unnerving at high speeds on rough ground.

DJ/SS bikes are somewhat slacker, often in the 68–70° range. They don’t feel as responsive when weaving through skateparks with hair’s-breadth precision, but they’re much more predictable on trails and bigger jumps.

In recent years, mountain bikes have gone slacker still. For now, they’ve settled at around 65–67° for trail and enduro bikes. Combined with low bottom brackets and long top tubes, the result is incredible stability at speed, but a bit of a handful in tight, steep dirt jumps.

(It’s a little more complex in reality, since fork travel and rear suspension travel—if any—can make the same head tube angle feel different. But that’s a topic for another day.)

BMX and DJ/SS sizing is limited. Brands and models vary a bit in geometry—10 mm longer top tube here, 1° steeper head tube there—but there are only one or two sizes for adult riders. 

When you ride standing up, your body moves and shifts continually, so sizing differences largely fall off your radar. And with super-low top tubes across the board, standover clearance is seldom an issue in the first place.

MTBs need to accommodate extended seated riding, so they typically come in four or five sizes per model. Your body position is fixed, so even small changes in the handlebars–cranks–saddle relationship can feel huge (for better or worse).

Common questions about dirt jump bikes

Can I just ride dirt jumps on a regular mountain bike?

Absolutely! This was common in the 1990s and early 2000s, before dedicated DJ bikes were widely available. I have the scars to prove it!

However, those older MTBs used 26″ wheels and front (or no) suspension. Some weren’t as burly as dedicated dirt jumpers, but they weren’t entirely different, either.

Exhibit A: an Evil D.O.C. custom build from 2007-ish. It was an all-around aggressive hardtail, but awfully similar to today’s DJ machines.

Custom Evil D.O.C. freeride hardtail, with 26" wheels and single-speed drivetrain.

Modern mountain bikes are less conducive to dirt jumping. Wheels are larger, tires are fatter, wheelbases are multiple inches longer, geometry is slack, and full suspension is ubiquitous.

A modern trail or enduro mountain bike with long, slack geometry.

Those features help tear up trails, but make BMX-style dirt jumps feel cramped.

Are dirt jump bikes good on trails?

Dirt jump and slopestyle bikes are capable but not fun to ride on MTB trails. They get extremely tiring, since there’s no shifting gears and no pedaling while seated.

Their 26″ wheels aren’t a limitation per se, but they’re not as smooth as larger, modern MTB wheels, either.

If you still want to try your DJ/SS bike on singletrack, then stick with shuttled or lift-accessed trails, and don’t plan to race your buddies on trail or enduro bikes!

Should I get a dirt jumper or a BMX bike?

They’re very similar, and both are excellent for dirt jumping. The decision depends on what else you want to do.

If you plan on bigger/rougher dirt jumps, slopestyle courses, and some limited singletrack, then get a dirt jump or slopestyle bike. 

They’re also smoother and more forgiving, which inspires confidence in new riders. However, that makes it easier to get away with sloppy technique when riding at the edge of your abilities.

If you plan to stick with smoother dirt jumps and skateparks, then a BMX bike is the way to go. They’re more affordable and nimble. They’re also less forgiving, which tends to reinforce good technique and knowing your limits.

Ultimately, your skill matters far more. A good BMX rider can do things that a newbie on a dirt jumper couldn’t dream of. A pro on a slopestyle bike can find creative skatepark lines that BMX newbies won’t even see.

Time on the bike will help you progress more than time researching it. So, for the moment, grab whatever you’ve got and see how far you can (reasonably) push it!