MTB Bolt Checks – Simple but Critical To Your Safety
Consistent MTB Bolt Checks are critical to your bike’s reliability and safety. While components should be checked throughout their service life, it is particularly important to check new fittings. Stem, handlebar, grip and brake assemblies are especially important.
Why You Need to Bolt Check
Light weight, minimal contact and leverage.
With the exception of WTB’s Padloc grips, everything that attaches to your handlebar requires radial clamping force to keep it positioned radially (around the circle of the bar) and laterally (left and right).
If the fastener is appropriately tight the radial assembly produces more “bite” than the loads encountered and nothing moves.
So you torque it and it’s good forever? No. Nope. No.
In fact, you torque it – stress it – re-torque it – and then occasionally check it.
MTB Bolt Checks
What causes a torqued bolt to come loose? Man that’s a fun google / text your engineer friends rabbit hole.
For the purposes of this write up – Loss of bolt pre-load from: vibration, material yield, and material stretch.
Pre-load
Pre-load, in regards to bolts, is the amount of clamping force the bolt applies through the thread interfaces.
This pre-load pulls your stem bits together (C clamp), applies pressure to the hinge clamp or closes the gap on your handle bar ends. It creates the force to keep the components located radially in relation to the handlebar.
When pre-load is compromised your radial clamping force is in jeopardy. With less clamping force to resist movement you are more likely spin a component.
On a sport level mountain bike we’re working with a variety of dis-similar materials, designed to be as light as possible, with relatively small fasteners. The difference between the right torque and something spinning around isn’t very much.
Vibration / Force / Leverage
One of the things that compromises bolt pre-load is movement between the bolt and the threaded assembly. In a mountain bike handlebar this is usually due to the forces between the trail and you, the rider. Adding to these forces are the increased leverage ratios between your hands and the clamp points.
Material Yield and Material Stretch
Working with such small fasteners it doesn’t take much for the threads to lose some bite and create issues.
Material stretch can affect bolts as they slightly elongate. Looking at stems however, most the bolts are steel while the assembly is aluminum.
This leads me to think that material yield is a more likely culprit if the female threads were to “give” slightly. Carbon fiber handlebars and particularly some of their finishes are also likely points to have slight amounts of material yield. It doesn’t take much to have a system slightly loosen up.
The area highlighted green is the torqued, pre-loaded, surface area of your stem bolt. That minute amount of metal produces the clamping force to support your most aggressive riding…
The Reasons, then the Actions
Alright we’ve looked at “why” your torqued assembly will loosen. And I do say will. So what do you do about it?
Bolt checks. My personal bike has a Race Face Turbine-R stem and Renthal Fatbar Carbon bars. Some of the best on the market. I check the torque at build. And again before the first descent on my first ride. And again before the second ride. It is very typical for me to find fasteners that are slightly loose at one of these points. In fact, much like a hub break, in I’m waiting for the cockpit to slightly loosen at first to know it’s mated up.
After the initial stress and re-torque I do bolt checks with tune ups or if I have any noise or feel that leads me to suspect a loose interface.
Is it that easy?
Yes and no.
Yes, doing a bolt check is relatively quick and easy. Certainly easier than dealing with a spun bar on the trail.
However doing a bolt check incorrectly is no good either.
Some common issues:
Bolt checks aren’t an opportunity to ‘put a quarter turn on everything’. Welcome to over torqued and possibly broken bolts.
False torque is a thing.
We used to see this with the early SRAM XD cassettes. The rotating interface was rough, or tight, and when you “torqued” the system down it had a false bottom out and was still actually loose.
I suggest a tab of appropriate loctite even if the bolts have pre-applied thread locker. The fresh, liquid drop or two you put on will help lubricate the threads for a more accurate torque.
Use a clicker wrench and watch the bolt. Pedro’s has a great line of single setting, one way clickers. They’re perfect for your toolbox to ensure the right stem torque.
Whether you use one of those or a more standard clicker when you bolt check watch the fastener. If there is much movement as you bring it to torque consider pulling it out, reapplying loctite and reinstalling. This is because not all thread lockers are effective after they’ve been “broke” free.
Disclaimer, remember ‘you do you’, If you’re headed out for a ride and do a bolt check and see movement you’re probably fine without reapplying thread locker for the ride. Maybe something to think about at the next tune, etc.
More Disclaimers
If you doubt your mechanical abilities you should always refer to a trusted resource.
That said, to truly enjoy the sport learning some very basic skills such as mtb bolt checks, headset adjustments, basic suspension setup, changing tires – these are skills that will get you back on the trail rather than headed to the shop. Find a competent friend and learn these skills. BikeCo’s Tips & Tricks are a great place to see videos and blogs for common issues.
Why isn’t a schedule for bolt check provided with directions? Well, I reached out to several stem manufacturers looking for published details on torque check timelines and procedures. However as of initial publication none have responded beyond the torque spec’s printed on the stems. I will publish any data provided on this page in the future if provided. I imagine many manufacturers stay out of the conversation to minimize any potential issues or liability. Update: One cockpit manufacturer responded that while they didn’t have a torque schedule it should always be checked during scheduled service… But no one comes out with “this bolt size, with this bolt finish, integrated to these threads should be reviewed at X, Y & Z”.
The cynical part of me attributes this to engineers unable to fully calculate loads encountered , which is somewhat understandable with off road applications, or liability experts trying to muddy the waters. (similar concept to why helmet manufacturers don’t acknowledge that foam ages and your helmet should be replaced on a timeline whether crashed on or not. another story for another day.) But neither of these help me as a rider. So I check my torques more frequently when things are first installed.
Torque Wrenches
In fact even quality torque wrenches have some interesting steps you might miss if you don’t read the directions. Click the image for full size to read – but here’s a photo of my personal Pedro’s Demi Torque Wrench instructions. This wrench is in my home tool box and I do use it. It’s interesting that it requires “before first use or after extended storage adjust wrench to highest torque setting and operate click mechanism 5-10 times to redistribute the factory applied lubricant”. Since this maxs at 15NM it’s not a big deal, I just put a bolt in a vice and click it a few times.
It also talks about calibrating the tool. Since my personal wrench isn’t used too much I simply check it against the Pedro’s single click tool (which I keep in my car tool box) now and then.
What’s my point? Well, learning how tight something should be and being able to replicate it, or understand if it feels way off is important with or without a torque wrench.
I’m not qualified to give you a hard bolt check timeline. I am certainly experienced enough to know MTB bolt checks are critical!
Many of my motorcycle upgrades, automotive as well, call out a full bolt check at 50 or 100 miles. So maybe an hour or so of use for those larger fasteners. This timeline does somewhat line up with my personal experience on the smaller fasteners associated with your mountain bike. As I said I tend to do a quick bolt check of new components at the top of the first climb and before the second ride – probably in that 45 minute to 3 hour range.
Looking for more about MTB bolt checks? Below are some links if you’re interested in some of the rabbit holes of fasteners (note all of these links open in new windows):
Why do bolts loosen – Nord-lock.com
Loosening of prevailing torque – BoltScience.com
Self loosening of threaded fasteners – BoltScience.com
RaceFace Top Lock stem installation
RaceFace Handlebar installation