Jim’s Tech Talk
By Jim Langley
Recently I discovered that some roadies are struggling to remove cranksets. And that the cranksets that are giving them trouble are actually designed to be easily removed. I know because I work at a company that makes some of these cranks, Praxis. Another company making cranks like this is SRAM.
Our sets are spec’d by several major makers, such as Specialized. And Specialized also specs SRAM cranksets.
The defining feature designed to make these cranks easy to remove is something I still call a One-Key-Release, which I believe is a term Shimano coined circa 1980. But the basic mechanism has been around even longer so it could have been named otherwise at one point. Today, it’s also called a self-extracting crank – which is a bit confusing since a wrench is required, removal doesn’t happen on its own. So here, I’ll stick with One-Key Release or OKR to simplify.
Why Remove Cranks?
First, in case you’ve never removed your crank, a reason to do it is to check the bottom bracket, which is the assembly inside the frame that the crank spins on. With the crank removed you can reach the bearings and other components and feel them to make sure everything’s tight, clean and the bearings still turn smoothly.
With some cranksets – and certain Praxis cranks use this design, another reason to remove the crank is to swap the chainring size or type (single to double). That’s something riders do more often now with bikes that work great on different terrain. The gearing for hanging on fast group rides tends to be a lot higher than for gravel grinding, for example.
In the case of removing cranks to change the gearing, that’s something you’d want to be able to do in a hurry. That way if your ride plans changed suddenly, you’d always be able to have the best gearing. And that’s one of the reasons cranks like this are designed to be easily removed.
How It Works
The way the OKR mechanism works is that the bolt that is tightened to fasten the crankarm (or both of them in older systems) is held captive inside the arm. Typically there’s a cap threaded into the arm on top of the bolt. The cap has a hole in it allowing access to the bolt.
This cap that’s threaded into the crankarm gives the head of the bolt something to push against. But only when the bolt is unscrewed (turned counterclockwise). Backing out the bolt like this makes its head bump into the cap and as you keep turning, the bolt pushes the crankarm off the bottom bracket axle (also called a “spindle”).
Cranks Are Press Fit On
You might wonder why you can’t simply loosen the bolt and pull the arm off with your hand? That’s because crankarms are pressed onto the axle/spindle.
This press fit on the SRAM and Praxis cranks involves a mating spline, male on the spindle and female inside the crankarm. When fully tightened, the spline and press fit ensure that even if the bolt loosens the crankarm will remain tight for some time.
“One-Key” As In Only One Hex Key
With early One-Key Releases, you used a 6 or 7mm hex wrench for the bolt. Newer ones such as these I’ve been getting questions about removing, use an 8mm. The key thing to know is that only a single tool is required. That’s part of what makes it so easy.
However, in terms of the effort to loosen and remove these crankarms, it can take a massive amount of force. They’re tightened to over 50 newton meters, which is a lot.
That’s what threw these home mechanics off. They tried using the allen because they saw that there’s a place for it in the crankarm – and also no wrench hole in the other arm. But, when they tried to loosen the bolt with the wrench it would not turn, no matter how hard they tried.
Which naturally caused them to deduce that removing the arm requires some special disassembly and tool that they needed to get.
Tips for Tight Cranks
Actually, the OKR system works easily if 1) you realize it can be super hard to loosen the bolt; and 2) if you’re prepared for battle with the right weapon and/or help! Here are a couple of suggestions:
For Praxis cranks with the system I made a video showing how to use a simple trick to loosen the bolt. Be sure to insert the 8mm allen wrench all the way into the bolt first. I go over this in the video so have a look.
For the SRAM Red DUB crank I recently did battle with, I could not use the simple trick I show in the video. Because their One-Key Release bolt is on the right crankarm. This means that the crank turns as you try to loosen the bolt.
It makes you want to strap the crankarm to the chainstay, or an old trick is to put something solid across and through the chainstays to block the crank moving. However, with frame walls so thin on fine road bikes, that’s asking for trouble – and the bike in my repair stand was a $10K spankin’ new Specialized Roubaix. I didn’t even want to leave fingerprints on the paint.
Outsmarting the Crank Design
So, first I broke out a cheater bar to be able to gain leverage. I have one that works well and was only $10. To go with it, I also have an 8mm socket that was less than $5. Here’s that bar: https://www.harborfreight.com/38-in-drive-17-in-breaker-bar-67931.html. And here’s the socket: https://amzn.to/2Wytdq0.
Of course, if you want to use a length of pipe, that can work, too. I prefer the positive connection the cheater bar gives you.
With the cheater bar and socket in place, I stood over the bike, held the other-side pedal as tightly as possible and put all my weight on the handle of the bar to break the bolt loose. Right. Nothing happened. I kept trying, even bouncing on the wrench, and still the bolt would not budge.
I considered removing the left pedal and slipping a pipe over the non-drive crankarm to give me the leverage to resist the force from the cheater bar. But, I decided against that worried it might scratch the brand new crankarm. Also, trying to apply enough force on one side and resist it on the other myself wasn’t working.
Time to Get Help
I hate not being able to get a job done myself, but I know when I’m licked. And I also know that as far as upper body strength goes I’m as weak as a kitten. So, my next idea was to recruit Scott who runs our shipping department at Praxis.
With the two of us, he could push on the cheater bar while I held the left pedal to prevent the crank from turning under the force. It took a few tries to figure out how to best hold onto the cheater bar and pedal while stabilizing the bike to protect it.
We did finally break the bolt loose. That’s what it sounded like, too – a loud crack. But it was just the bolt freeing up, nothing breaking. And once it did, it was cake turning the bolt and extracting the SRAM crankarm.
Be Smarter than Your Tight Crank
I’ve only described two scenarios in this Tech Talk. The OKR crank you’re trying to remove could be different. If you run into one that’s difficult to remove, start by looking for instructions on proper removal.
Unfortunately, it’s getting more difficult to locate instructions on manufacturer websites. I still try there first since they’re the experts, however, if I can’t find anything in a few minutes, I give up and search youtube. It’s rare that I don’t find someone showing how to do what I’m about to try. If you have a trick for removing a tight OKR crank that will help your fellow roadies, please leave a comment explaining.
Ride total: 9,709
Was this article helpful?
Jim Langley is RBR’s Technical Editor. He has been a pro mechanic and cycling writer for more than 40 years. He’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Check out his “cycling aficionado” website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim’s streak of consecutive cycling days has reached more than 8,000. Click to read Jim’s full bio.