Roadies describe BMX bikes as tough and bombproof durable with adjustable driveline.
And given the frequent use and abuse BMX sports fanatics like myself put such bikes through, it’s hard not to imagine whether their cranks can fit any type of bike.
But can you put BMX cranks on a mountain bike? If so, how do you do it?
You can put a BMX crank on a mountain bike with a Euro bottom bracket whose inner diameter corresponds to either a 19 or 22mm spindle of the MTB. Get a 7 or 8-inch axle if you intend to use a chain guide, or a 6-inch spindle depending on the alignment and size of the mountain bike’s chainring.
The problem with BMX crank is weight.
The setup with the British bottom bracket weight about 2.5 pounds, which is much heavier than mountain bike cranks.
But in a setup where strength is everything, the weight may not be deal breaker after all.
Can You Put BMX Cranks on a Mountain Bike? (Into Details)
It’s not the first time I’ve read this question in popular bike forums.
And the short answer is yes, you can put BMX cranks on a mountain bike to save some bucks during the build.
Keep in mind that the chainline of a BMX is different from that of a MTB, so you’ll need to shim accordingly for the best fit.
That means adjusting the chainline between the bottom bracket bearing and the chainwheel crank of the BMX.
You’ll find fitting a BMX three-piece crank on a MTB easier than a two-piece. The 22mm and 3/4-inch spindle with Euro BB would be the most appropriate to use.
What Bottom Bracket Should I Get?
The first step to putting a BMX crank on a mountain bike is to get the right bottom bracket.
Just to be clear, and especially if you’re new to switching cranks between bikes, a bottom bracket is a combo of axle and bearings that holds the crank in place.
It’s in the middle a bike’s frame, right where the chain stays, seat tube, and down tube meet.
A bottom bracket ideal for putting BMX cranks on mountain bike must meet the following conditions:
- It should work well with either a 19mm or 22mm spindle. Rarely will you find a 20mm spindles (axles)
- The bottom bracket should match the shell of the mountain bike frame
From what I understand, there’s only one BMX bottom bracket that meets these two conditions.
It’s called the Euro bottom bracket.
There are a few, well-rated bottom brackets that you might want to consider, so I’ll put the links to them down below:
You will love these recommendations because they are not only cheap but also well made.
It’s important to understand that many mountain bike frames have 63 or 73mm wide bottom bracket shells, with some being even wider than the standard options.
As such, you need to make sure that the bottom bracket you choose will fit the shell of your MTB’s frame.
How Should I Install The Euro/British Bottom Bracket?
Now that you’ve selected the Euro bottom bracket that can fit your mountain bike’s shell, it’s time to install the bracket.
Here’s exactly how to do that:
Step 1: Check The Spacing Of The Bottom Bracket
This is important because it’s the only way to determine if the bottom bracket you picked will fit the frame of your mountain bike.
You don’t want the bearing to bind or the crank to feel unstable, so it’s necessary to check to be sure that the BB isn’t too wide or too narrow.
- Slide the axle through one cup and a sleeve onto the axle.
- Add at most two washers and then put the other cup on the axle.
- With your bike positioned upside down, place the axle parallel to the wider section of the BB shell
Note how the cups fit.
You’ll need a longer sleeve or an additional washer if the cups are close to each other.
If they’re far apart, consider using a shorter sleeve or removing a washer.
The objective here is to ensure that the cups rest well on the lip of the BB shell.
Step 2: Cleaning The BB And Shell
Skip this step if the bottom bracket shell is clean.
Otherwise clean, degrease, wipe with a cotton rag and allow it to dry.
Lube the outer ring and threads of the BB bracket to keep it from making a squeaky noise.
Step 3: Installation
Use your fingers to attach one cup into the frame thread it slowly until it gets down to the outer ring and follow this by pushing the axle (spindle) through the cup.
Now slide the sleeve and one or two washers onto the spindle.
Can I Put BMX Crank on MTB If The Frame Doesn’t Have Threading?
You can still put a BMX crank on a mountain bike even if its frame doesn’t have a threading.
To be clear, a bike without threading on its frame can’t support Euro bottom brackets.
But there are a few ways to get around this.
1. Use an Adapter
If your MTB’s frame features a press fit BB30 bottom bracket, use FSA BB30 to BSA Adapter to convert to Euro bottom bracket.
You will first need to install the bottom bracket. Then, apply Loctite 609 or similar retaining compound to both the bottom bracket and the adapter.
Complete the process by pressing the adapter into the bottom bracket.
2. Get a Bottom Bracket Reducer Adapter
The work of a reducer adapter is to make the select bottom bracket compatible with smaller spindles.
Note that BB reducer adapters are available for PF30 and BB30 bottom brackets.
Yes, you can put BMX cranks on a mountain bike and enjoy the convenience, strength, and performance optimization that they bring. All you have do to is to follow the steps we’ve shared above.