Misused & confused bicycle terms
Commonly confused bicycle terms - the bike mechanic's dictionary
Is dishing a wheel the same as truing?
What’s trimming?
Does my bike really have a clutch?
Each industry has its own terminology and jargon, and sometimes these phrases can sound like complete gibberish to others. The bike industry is definitely no exception. Throw in technical language, synonyms, abbreviations and slang, and you can end up wondering what the hell your bike mechanic is actually talking about.
But fear not! We are here to de-baffle terms you might not know, and clarify some others, including things they get incorrectly confused with.
In addressing the processes and components that we're most commonly asked about, we found that there are so many terms that need explaining that this post is part one of a two-parter. (We'll link to it here once it's up.)
After all, there’s no shame in admitting that you don’t know something, and we’re here to help.
Facing
Sometimes called: machining, milling
Sometimes confused with: reaming
What is facing?
Facing is the process of removing material from a frame or component in order to achieve a perfectly flat and parallel surface.
Facing is usually done on bottom bracket shells, head tubes and disc mounts, but can also be done on components such as head stems and spacers.
When you make a surface completely flat and parallel, components will contact it without gaps or rough edges. This eliminates many annoying creaks and squeaks that can plague frames which haven’t been properly finished. In addition, when it comes to bearings, parallel frame faces will also always result in better bearing alignment.
As most bike shops tend to ignore the benefits of facing, it’s not a well-known process, even for seasoned bike riders. In fact, often the first time a new customer has even heard of the term is when they receive our general service notes upon completion of their bike.
Terminology-wise, facing frequently gets confused with reaming, but they’re not the same thing.
Reaming
Sometimes called: finishing
Sometimes confused with: facing
What is reaming?
Reaming is the process of cleaning up and sometimes enlarging an existing pre-drilled hole or frame area. This process ensures that things such as headsets and bottom brackets fit precisely and spin freely.
The most commonly reamed areas on a bike are the head tube, seat tube, bottom bracket shell and cable entry/exit holes.
A section of frame that’s not properly reamed can lead to poor alignment, not to mention difficulty with fitting components (and not damaging them or the frame in the process). An unreamed seat tube means that a seat post won’t slide in smoothly, and then can’t be adjusted or clamped correctly. A head tube that’s not correctly reamed can result in headset cups not sitting squarely, or getting crushed while they’re being pressed in. We’ve seen several cases where an undersized bore has lead to the head tube cracking or splitting as the headset cups were installed.
Like facing work, reaming tackles alignment and component fit, but how exactly do the processes differ?
While facing makes a surface completely flat and parallel, reaming smooths out an existing hole, ensuring that it’s perfectly round and also exactly the correct diameter.
Here's a quick illustration of facing versus reaming on a headtube. The top (and bottom) surfaces of the headtube get faced. The headset bearing seat and walls (inside the headtube), where the bearings sit, get reamed.
Bottom bracket
Sometimes written as: BB
Sometimes confused with: BB shell, cranks
What is a bottom bracket?
A bottom bracket connects your crankset to your bike, and lets it spin. Some people use the term ‘bottom bracket’ interchangeably with ‘crankset’; while they do work together, they’re separate components.
There are technically lots of different types of bottom bracket, so we'll keep it simple and distil it down to the four basic types or systems:
- Threaded, which screw into the BB shell;
- Press-fit, which are pressed in;
- External, where the bearings sit outside the BB shell; and
- Internal, where the bearings sit inside the BB shell.
We won’t get into the ‘which bottom bracket is better’ debate here (otherwise this post will be 10,000 words long); all you need to remember is that they’re not interchangeable – your choice of bottom bracket depends on the frame and the cranks it’s being bolted to.
(Remember: despite what the internet says, not everything bolts to everything else.)
Bottom brackets contain bearings and—like the rest of your bike—need maintenance. Worn or damaged bearings not only feel horrible to ride on but can end up damaging or destroying the frame and/or cranks.
Ideally, a bottom bracket should spin freely, feel smooth, and fit precisely in the frame (especially if that frame has been faced and/or reamed correctly).
The BB is a crucial component – after all, if your cranks don’t turn, you ain’t goin’ nowhere.
Bottom bracket shell
Sometimes written as: BB shell
Sometimes confused with: bottom bracket
What is a bottom bracket shell?
The bottom bracket shell is the section of frame which houses the bottom bracket.
As the BB shell is a structural part of the frame, and has to cope with pedalling load and forces, it commonly suffers from clicks and creaks. These noises can often be due to the bottom bracket/bearings not fitting correctly, hence the importance of machining/facing this section of the frame. In fact, it's probably the most common area of the frame that we do facing work on, but also one of the least-known reference terms.
Bleeding
Sometimes called: flushing
Sometimes confused with: replacing brake cables
What is bleeding?
Bleeding a brake involves pushing fresh brake fluid through the brake line (also called a brake hose) to replace the old fluid, which degrades over time and can become contaminated.
The aim of brake bleeding is to evacuate any air from the hydraulic components, while simultaneously flushing out as much of the old fluid as possible.
Like brakes, dropper posts which use a hydraulic line—such as the RockShox Reverb—also need to be bled at regular intervals.
Why do we want to remove any contaminants or air bubbles?
An hydraulic brake relies on fluid to work, so air in a brake line is a problem. Unlike fluid, air compresses under pressure, which can then stop the brake working properly.
Brake fluid also breaks down over time and can become contaminated by heat as well as moisture from the air. (While brake systems are sealed against leaks, they aren’t air-tight.)
Your brakes then start feeling squishy or spongy, or begin performing unreliably. If they get really bad, they can stop working altogether, leading to injury or death.
Bleeding is a tricky process to get right, and requires a mechanic with skill and experience. It should be done regularly as part of your bike’s general maintenance – don't wait until your levers pull back to the bars before booking them in to get serviced.
Keeping on top of it means you’ll be able to rely on safe and effective braking, rather than screaming down a descent and discovering you can’t actually stop.
Same with dropper posts – it’s hard to enjoy an afternoon on the trails if your saddle gets stuck at a height you don’t want.
Fun fact: sometimes customers ask us to bleed their mechanical or cable-actuated brakes, which is technically impossible. You can’t get fluid out of a steel cable.
(Or, if you can, you have bigger problems on your hands.)
Truing
Sometimes called: straightening
Sometimes confused with: dishing
What is truing?
Truing a wheel makes sure that it’s perfectly straight and round when it spins. The process focuses on correcting lateral (side-to-side) and radial (up-and-down) deviations, and adjusting spoke tensions to correct any misalignment or unevenness.
Truing is required when a wheel becomes misaligned. This can happen through impact—and an impact will also throw the spoke tensions off—or just through general use. While you ride, your wheels are under constant variations in load and tension, which can eventually cause spokes to stretch. This issue is exacerbated if you’re riding with a lot of load or in rough conditions (which is why we custom-build a lot of wheels for off-road touring bikes).
Truing is also done after a wheel has been built or respoked, to ensure that the spoke tensions are correct and the wheel is reliable and durable.
Truing is a precise balancing act—each spoke’s tension affects the others. Have you ever broken a spoke and then noticed your wheel wobbling around like a jelly? All you need is one loose or incorrectly tensioned spoke to throw the whole wheel out of true.
Dishing
Sometimes called: centering
Sometimes confused with: straightening, truing
What is dishing?
Dishing a wheel means to ensure that it’s centred between the hub’s contact points with the frame/forks.
Tightening the spokes pulls the rim towards that side of the wheel, and loosening does the opposite. By manipulating the spoke tensions on both sides, the rim can be centred correctly.
It’s pretty obvious why you want a wheel to run straight, but what does it matter if it’s centred between the hub contact points?
Firstly, a wheel that’s sitting unevenly in the frame can potentially create stability issues and affect the way the bike handles.
Secondly, if you have rim brakes, it’s critical in terms of proper brake alignment – it’s pretty hard for your brakes to work correctly if the pads aren’t fully touching the rim.
Thirdly, if your rim or tyre is hitting the frame, it can actually wear a hole in it. We’ve seen multiple frames eaten in spots by tyre rub, and the owner is usually blissfully unaware of it. (At least, until the frame cracks.)
Overall, dishing and truing are crucial to wheel maintenance, and are often done in tandem to confirm that the wheel is aligned and centred correctly for maximum performance and longevity.
Jockey wheels
Sometimes called: derailleur pulleys, rear derailleur pulleys, derailleur wheels, pulley wheels, guide pulleys, tension pulleys, pretty much any combination of these words that you can imagine
Sometimes confused with: derailleurs, derailleur cages
What are jockey wheels?
Jockey wheels are the two wheels that make up part of the rear derailleur. They sit inside a rear derailleur cage (which itself is part of the rear derailleur, but often confused for being the same thing).
Jockey wheels ensure that your shifting is smooth and accurate by keeping your chain correctly tensioned and in the right position when changing gears. The top jockey wheel guides the chain as it switches between different cassette cogs, and the lower one helps take up any chain slack.
Like all wear and tear parts, jockey wheels require replacing and servicing. They contain bearings, which (sing it with us!) wear out with use. Because the chain runs over the jockey wheels thousands of times, their teeth also get worn down. Riding on worn, chipped or damaged jockey wheels means your gears don’t work well. Plus it’s noisy, which is really annoying.
Fortunately, they’re easy to replace. And look at the pretty colours you can get, too!
Clutch derailleur
Sometimes called: stabiliser derailleur, Shadow+ derailleur, Type 2/Type 3 derailleur
Sometimes confused with: chain catcher, chain retention device
What is a clutch?
A clutch is a mechanism found in rear derailleurs, often on gravel bikes but most commonly mountain bikes. It stabilises the derailleur cage to help manage chain tension and stop excessive bouncing, especially over rough terrain, and keeps the chain properly aligned.
It also helps prevent chain drop, which is when your chain comes off the cassette or chain ring and sometimes gets jammed in the spokes or part of the frame. (Fun!)
The clutch's function is particularly important if you’re running a wide-range cassette, where the jumps between the gears are greater.
Shimano uses the term ‘Shadow+’ to designate their clutch derailleur. SRAM calls their clutch derailleurs ‘Type 2’ or ‘Type 3’. These names are specific to each brand, though, and not a generic catch-all. (Clutch-all? Ah, hilarious.)
A clutch derailleur is sometimes mistakenly referred to as a chain catcher or chain retention device. Chain catchers and retention devices are not derailleurs; they’re physical barriers designed to prevent chain drop and protect the frame.
If you’re riding off-road, a clutch derailleur is valuable component to keep your gears shifting quietly and smoothly, so you can concentrate on avoiding other obstacles instead. Does it also need servicing? Of course it does.
Cross-chaining
Sometimes called: what’s that noise?
What is cross-chaining?
Cross-chaining happens when you use a gear combination that results in the chain running at a diagonal angle.
It usually happens in the largest chain ring plus the largest cassette cog, or the smallest chain ring and smallest cog (otherwise called ‘big/big’ and ‘small/small’).
You’ll normally know it’s happening because the chain is rubbing against the front derailleur. (That’s that krgghghghghhhghghghghh noise you’ve been hearing.)
It may come as a surprise, but your gears are not designed to run in the big/big or small/small combinations, and all major component manufacturers also state that these combinations shouldn’t be used.
A chain running at an angle like this is being dragged across the cogs. The increased friction and stress means it won’t move smoothly between the gears, and can also end up breaking the chain, if not the derailleur.
Remember: you’ve got a bunch of different gear combinations you can use. Usually the big/big and small/small ratios will be doubled up somewhere amongst the range, so explore those options, use them instead, and keep your chain in a straight line and happy.
Trimming
Sometimes called: micro-adjustment
What is trimming?
Gear trimming is when you fine-tune your front derailleur to stop your chain rubbing. (And not just in the forbidden big/big, small/small combinations, either.)
Say you shift from the big to the small chain ring. The front derailleur cage moves in order to guide the chain over, but now it might not be perfectly aligned with the chain. Your chain is rubbing on the front derailleur, because you—and everyone else—can hear that all-too-familiar kgrrrghghghghghghg.
How do you fix it? You trim your gears. (Or you ignore it and keep riding until the chain wears a hole through the derailleur cage, which we’ve seen on several occasions.)
How you trim depends on what kind of system you’re running, and whether it’s mechanical or electronic.
For mechanical setups, Shimano shifters have a half-click option which will move the front derailleur either slightly inward or slightly outward to clear it from the chain. Campag shifters have multiple trim positions, too, because they love being fussy. SRAM’s front derailleur cage has Yaw built in, which means that it swings in a particular arc to clear the chain; theoretically no trimming is required. (If it’s set up correctly, of course.)
If you’ve got electronic gears, though, your life is a lot simpler. Whether it’s Shimano Di2, SRAM eTap or Campag EPS, these systems automatically trim the front derailleur for you, so you don’t need to do a thing.
Trimming is essential to keep your gears running smoothly, and to prevent premature wear on your chain and derailleur cage. Whether you’re doing it manually or your system is doing it for you, it’s your drivetrain’s friend, not to mention your ears’.
You're done with part one!
Now you'll be able to confidently correct someone when they talk about reaming a brake hose or how it's OK to run the big/big gear combination.
While you're winning bike-related trivia nights at the local pub, we'll get started on part two, coming soon.
Got a term that you’re confused by, but too shy to ask your cycling friends? Ask us!
Not fussed about terminology but need your bike fixed? We can do that, too.
