It’s all too common to just tolerate inferior shifting performance. But if your drivetrain occasionally skips, mis-shifts, grinds or binds, then it can surely be better.
While this article isn’t a complete solution to perfect shifting, these are the problems shop mechanics are likely to resolve first.
It’s worth pointing out that the solution to each suggested cause requires some level of mechanical knowledge. If it’s not working out, it’s well advised to get the assistance of a good mechanic – after all, what’s the point of owning a quality bike that doesn’t function as intended?
1. Cable tension and limit setting
The most obvious and common causes for poor shifting are down to poor adjustment and the most common thing to go out of adjustment is cable tension. Indexed drivetrains rely on correct cable tension so that the shifters pull the derailleur to the intended spot. Cable systems wear and ‘stretch’, and will inevitably lead to a loss in shifting precision.
In the simplest of terms, sluggish upshifts can be caused by too little cable tension; while slow downshifts could be too much tension.
Limit screws set the extremes for which a derailleur can travel. Too often people wrongly play with these screws when shifting goes bad.
- How to adjust the gears on your bike – video
- How to adjust a rear derailleur
- How to adjust a front derailleur
Another to consider is B-tension, which adjusts the rear derailleur body angle (or more simply, the height gap between the derailleur and cassette). It's something that Dylan Coulson of SRAM Australia Dealer Service Direct sees as a common cause for poor shifting on 1x drivetrains.
Notably, a bent derailleur hanger is common cause for what can seem like a wacky limit adjustment (more later).
2. If the cable ain’t slick, give it the flick
A mechanical drivetrain relies on the cable being as drag free as possible. If your cables are old, dirty, rusted, kinked or just poor quality, then they’re likely hindering that shift – replacement is the answer. It’s why electronic drivetrains are said to be so ‘set and forget’, as they just don’t suffer from these cable woes.
“Replacing with good quality cables on a regular basis is a great help to better shifting,” says Matthew Potter, a technician and neutral service mechanic at Shimano Australia. Coulson at SRAM repeated this solution, stating it's the very most common issue seen.
As Potter pointed out, electrolyte or sugar-based drinks have a habit of gunking up cables, and if you’re on a road bike, it’s always worth cleaning out the cable guide that sits beneath the bottom bracket.
Personally, I like to use quality, but non-coated stainless steel inner cables. The issue with many fancier (and expensive) coated cables is that the slickness doesn’t last, and often leads to more gunk within the housing as the cable coat wears off. It’s good practice to replace the housing (the sheathing that the inner cable runs through) when you replace the inner cable too.
3. Rear derailleur alignment
This one I’ve mentioned before, but rear derailleur hanger alignment is such a common issue because of the fragile hangers on most modern bikes. If you ever travel with your bike, have others leaned against it or just bump it wrongly, there’s a good chance your rear derailleur is sitting skew.
Even if you’ve never done any of these things, it’s possible the hanger was bent from new. One shop I worked at taught me to check hanger straightness on every bike build, with over a quarter proving to need a tweak. Speaking from firsthand experience, plenty of shops don’t do this.
Although there are DIY methods, a derailleur hanger-straightening tool is the best option for ensuring the hanger is square to the cassette. These tools can be had relatively cheaply, with the likes of LifeLine or X-Tools (they’re the same) offering copies of the proven Park Tool design.
Before you use such a tool, make yourself familiar with how it works, ensure your wheel is straight and tight in the dropout and the hanger is snug. Also, I use the valve stem as a reference point, this is so wheel trueness won’t have an effect on the measurement.
4. Chain health, lubrication and cleanliness
When was the last time you closely inspected your chain for damage or wear? Measuring a chain for wear will not just save you from replacing your cassette and chainrings prematurely, but it’s likely to help achieve precise shifting.
Even if your chain isn’t worn, it’s possible a bad shift damaged it previously. Look for kinks, pins pulling out or stiff links. One tip for this is to slowly back pedal the crank with your hand. Look at the rear derailleur pulley wheels – you should see them jump if there is an issue with the chain.
Additionally, a filthy chain/drivetrain will not just wear out quicker and cause drag, but it will be more sluggish to shift, so best keep it clean. Likewise for a dry chain that squeaks along with every pedal stroke. Lastly, if your chain length is wrong, it could be a cause for poor shifting in extreme gear combinations.
5. Housing lengths
This one often goes by unnoticed, but how long the cable housing is can greatly affect your shift quality and consistency.
Too long, and you’ll be adding unnecessary friction to your shifting and risking a snag with someone or something else. However, go too short and you may find the housing changes cable tension on its own or the bend is too tight for the inner cable to move freely. This is most apparent in the segment from the chainstay to the rear derailleur, where the housing can be pulled with the rear derailleur when a front shift is actuated.
The importance of housing length is amplified on full suspension mountain bikes, where the suspension action can commonly cause a change in cable tension if the housing length is insufficient.
6. Front derailleur position
Front shifting is something that so many look at as a dark art. With this, a common issue (beyond cable tension and limit screw setting) is incorrect derailleur height. The outward cage of the front derailleur should sit as close to the big ring as possible without making contact. The use of a thin coin as a gauge may help.
Additionally, the angle at which the derailleur sits will commonly affect shifting. For most derailleurs (SRAM Yaw excluded), the outward cage should run parallel to the big ring. Some experienced mechanics may tweak it differently, but I won't get into that.
7. Just worn out?
No matter how well you adjust everything, if the parts are worn, they aren’t going to be precise. The chain, cassette and/or chainrings are the most likely items to wear out and will typically give visible or measureable cues – such as hooked teeth or a lengthened chain.
That said, derailleur springs will lose tension overtime, and pivots will get sloppier. Shifters can wear out too (if you ride enough), and most cannot be serviced back to health. But before you go sinking money into these more expensive components, best try a new cable/housing or get a second opinion.
8. It could be the frame
Unfortunately, some frame designs can be the cause of crappy shifting. This is most true for internally routed frames from a few years prior, where thin guide sheaths or tight bends would cause excessive cable friction, with no respite available. Ever seen a new frame model claim ‘improved cable routing’? It’s because the old version was terrible.
This most definitely applies to time-trial and other slippery frames, where cables are run internally through multiple strange angles. In some cases, standard cables and housing just won’t work, and you’ll need to resort to more expensive, low-friction stuff that can handle tight bends.
As Potter points out, “Because it’s such a nightmare to change, they're not replaced as often as they should be.”
9. That chain line
Chainline refers to the position of the rear cogs, or front chainrings' crank, in relation to the midline of the bike. Effective chainline is thought of as the position of the front and rear cogs in relation to each other. That all said, chainline is a topic that would quickly blow the word count of this article and so I’ll keep it overly simple.
If you’re struggling to use certain gears without strange rubbing, chain dropping at the front or your chain appears to be a wild angle in ‘usual’ gears, then it’s possible that the relative position of your chainring/s is off. Older three-piece crank systems allowed this to be adjusted by changing the bottom bracket spindle length, some newer crank designs allow this to be adjusted with spacers, while others just say ‘tough luck’.
10. Perhaps you’re just doing it wrong
In the end, even if everything is set up perfectly, there’s still the human aspect. Shifting under power or not clicking the shifters into place correctly are both likely to result in poor shifts, or worst, damage to the components. Learn to ease up on the throttle (your legs) when you actuate a shift – your bike will love you.