Putting BMX cranks on a mountain bike can transform its performance and ride feel. But is it possible, and what do you need to know before swapping out cranksets?
Yes, it’s possible to put BMX cranks on mountain bikes, as long as the mountain bike’s spindle matches the inner diameter of the bottom bracket.
In this all-inclusive, we will overview and discuss everything about installing BMX cranks on a mountain bike.
Essential Things to Know About Putting BMX Cranks on Mountain Bikes
- It is possible to install BMX cranks on a mountain bike in most cases with some compatibility considerations.
- BMX cranks offer increased ground clearance and often a lighter, stiffer, stronger crankset design.
- The downsides are less overall gear range and potential compatibility issues between bottom bracket types.
- The right BMX crankarm length, bottom bracket width, and chainline are crucial for proper MTB fit.
- Splined spindle BMX cranks are easiest since they work with common MTB bottom brackets.
- Some frame and drivetrain modifications may be needed for optimal shifting performance.
Why Put BMX Cranks on a Mountain Bike?
There are a few key potential benefits of using BMX cranks on a mountain bike:
- Increased ground clearance – BMX cranks are more compact and have smaller chainrings, allowing them to sit higher off the ground for better clearance over obstacles, roots, and technical trails.
- Stiffer, stronger cranks – BMX cranks are designed for taking abuse from big jumps and tricks so they are often stiffer and more durable than MTB cranks.
- Lighter weight – Top-end BMX cranks use advanced materials like carbon fiber, aluminum, and titanium to shed weight over stock MTB cranksets.
- Better power transfer – The stiff and direct power transfer of BMX cranks can make pedaling feel more efficient and responsive.
- Cool custom looks – BMX cranks can give a mountain bike a unique style and appearance.
Riders who value snappy power delivery, ruggedness, and tech trail capability are prime candidates for switching to BMX cranks on their MTB.
Potential Drawbacks of BMX Cranks on Mountain Bikes
However, there are also some potential downsides to consider:
- Less overall gear range – BMX cranks often have smaller chainrings with fewer teeth, limiting the gear range compared to MTB triple cranksets.
- Compatibility and fitment issues – Getting the right bottom bracket, spindle interface, chainline, and crankarm length for proper bike fit can require modifications.
- Chain drop – The smaller BMX chainrings and wider Q-factor on some BMX cranks can increase chain drop issues.
- Compromised shifting performance – Optimizing the front derailleur position and shifter cable routing is key for smooth gear changes.
- Higher costs – Aftermarket BMX cranks are more expensive than basic MTB cranksets.
Carefully weighing the pros and cons and setting up BMX cranks properly helps maximize benefits while avoiding drawbacks when installing them on a mountain bike.
BMX Crank Types Compatible with Mountain Bikes
There are two main crank interface spindle types used on BMX cranks:
Splined Spindle Cranks
- Use a spline pattern to interface with the bottom bracket spindle.
- Are the most compatible BMX crank option for mountain bikes.
- Work with common MTB bottom bracket standards like Shimano Hollowtech II, SRAM DUB, etc.
- Examples are Profile Racing, Odyssey, and Subrosa splined BMX cranks.
Euro BB Spindle Cranks
- Have a one piece Euro BB spindle permanently attached to the crankarms.
- Require a dedicated Euro BB bottom bracket and are less compatible.
- May require frame BB shell adaptation to fit the wider Euro BB shell width.
- Examples are Sunday, Bitex, and Tree splined spindle cranks.
Splined spindle BMX cranks are easiest to install on a MTB since they work with modern bottom bracket systems, while Euro BB cranks often require additional frame modifications.
How to Choose the Right BMX Crankset for Your Mountain Bike
Follow these guidelines when selecting a BMX crankset for optimal mountain bike compatibility:
- Match the spindle interface – Choose a splined spindle model that fits your bike’s bottom bracket type, like Hollowtech II or DUB.
- Pick the correct crankarm length – Match your MTB’s stock crankarm length (usually 170mm or 175mm) for proper fit.
- Mind the bottom bracket/spindle width – Match the BB shell width and spindle length specs of your frame’s bottom bracket.
- Consider the chainline – Some BMX cranks use a wider 55-57.5mm chainline vs. MTB’s 49-52mm standard, so this must align.
- Check** chainring clearance** – Ensure the BMX chainrings clear the MTB’s chainstays and have enough frame clearance.
- Account for q-factor – Wider q-factors on some BMX cranks may require re-positioning the front derailleur.
Installing BMX cranks can be straightforward with the right crank specs matched to your MTB’s bottom bracket and drivetrain. Test fitting parts and measurements ahead of time ensures optimal compatibility and performance.
The Step-By-Step Process for Installing BMX Cranks
Once you have the right compatible BMX crankset, here are the key steps for removing your stock MTB crankarms and installing the new BMX cranks:
Remove Existing Crankset
- Shift chain onto the smallest rear cog for chain slack.
- Remove crank bolts and extract crankarms using an 8mm hex wrench.
- Unthread and remove the bottom bracket spindle.
- Thoroughly clean BB shell and apply fresh grease.
Install BMX Bottom Bracket
- For splined BMX cranks, press in the matching new bottom bracket according to the specs.
- For Euro BB spindles, adapt the BB shell if needed and press in the dedicated Euro BB.
- Torque bottom bracket to manufacturer specs – usually 35-50Nm range.
Mount BMX Crankarms
- Apply thin layer of grease to the spline or spindle interface.
- Orient non-drive crankarm and firmly press onto the spindle.
- Install 8mm crank bolts and torque evenly to specs.
- Repeat the process for the drive-side crankarm.
Final Setup and Adjustments
- Reinstall chainring bolts, pedals, and chains.
- Spin cranks to ensure smooth rotation and check for rub.
- Fine-tune front derailleur height and position over smaller BMX chainrings.
- Shorten the chain if needed to eliminate slack from smaller rings.
Take it for a test spin to dial in shifting performance and make any final tweaks for optimal clearance and drivetrain function.
3 Crucial Compatibility Tips for BMX Cranks on a Mountain Bike
Follow these top 3 tips when choosing and installing BMX cranks on a mountain bike:
- Match the spindle interface – Choose a splined BMX crank that fits your bottom bracket type like Shimano Hollowtech or SRAM DUB.
- Mind the chainline – Ensure the BMX crankset chainline aligns closely with your MTB’s standard chainline.
- Fine tune the front derailleur – Expect to adjust the front shifter height and limit screws to accommodate the smaller BMX chainrings.
Getting the right spindle interface fit while optimizing chainline and drivetrain setup will ensure maximum performance from your new BMX crankset on a mountain bike.
Frequently Asked Questions About BMX Cranks on Mountain Bikes
What bottom bracket do I need for BMX cranks on a mountain bike?
For splined spindle BMX cranks, you can reuse your current MTB bottom bracket like Shimano Hollowtech II or SRAM DUB. Euro BB spindle cranks require a dedicated Euro BB bottom bracket and sometimes frame shell width adapters.
Will BMX cranks work with my mountain bike shifters and derailleurs?
Most likely, yes, but the front derailleur position and limit screws will need to be adjusted to accommodate the smaller BMX chainring sizes. The rear derailleur just needs proper chain length.
Do I need a chain guide if I put BMX cranks on my MTB?
It’s a good idea to add a top-mounted chain guide to prevent potential chain drop issues from the smaller BMX chainrings. A tensioner can also help manage the chain slack.
Can I leave my MTB triple crankset on and just use the middle ring with BMX cranks?
This is not recommended, as the redundant outer rings can interfere and strike the chain in certain gear combinations. Remove all three rings and just run the proper BMX single, double or triple crankset.
What’s the best BMX crankarm length for converting a mountain bike?
For proper fit, choose a BMX crankarm length that matches your MTB’s original crankarm length, usually 170mm or 175mm. Don’t size down or go shorter.
Summary: The Benefits and Drawbacks of BMX Cranks on Mountain Bikes
Installing BMX cranks on a mountain bike can provide increased ground clearance, a stiffer and stronger crankset, snappier power transfer, and a unique style when done properly. Just be aware of the potential downsides like less gear range, compatibility challenges, and drivetrain tuning required.
Overall, BMX cranks are a cool way to boost the performance and appearance of a mountain bike for certain riding styles. By matching the spindle interface, choosing the right crank length, considering how chainline and q-factor impact derailleur setup, and fine tuning the drivetrain, you can unlock the full benefits of these durable, responsive cranks on a mountain bike.
Mahin Abrar is a passionate writer and outdoor enthusiast. As a regular contributor to Bikepics.net, Mahin shares his knowledge and experiences in the fields of biking, cycling, hiking, and camping. With a deep understanding of these activities and a keen eye for detail, he offers valuable insights and practical advice to help readers get the most out of their adventures. Whether you're a seasoned pro or just starting out, Mahin's writing is sure to inspire you and guide you on your journey.