The rear derailleur turns bicycles into conquering machines by allowing cyclists to conveniently switch between gears according to the terrain ahead.
Within a couple of clicks, the rider can find a cog and chainring combination maximizing the covered distance and sparing muscular energy.
But shifting isn’t the only job of the rear derailleur. It has to maintain proper chain tension at all times too. In consequence, the rear mech is under constant stress.
And since the rear derailleur is made of multiple parts including springs and small bearings, a question in regards to its durability and lifecycle wouldn’t be out of place.
How long should a rear derailleur last?
The rear derailleur is a sophisticated but also a surprisingly resilient piece of equipment when made by a reputable brand.
Outside of a hit, it will last many years even if the bicycle is ridden frequently. The jockey wheels are usually the first to wear out.
The Life Cycle of a Quality Derailleur Could Be Scary Long
A rear derailleur produced by a reputable brand (e.g., Shimano, SRAM, Campagnolo…etc.) has a very strong chance of outliving all components on a bicycle beside the frame.
There are numerous stories of people accumulating a very high mileage on their rear derailleurs (e.g., 20 000 miles/32 186 km) without a noticeable play in the joints or degradation in shifting.
A while back, I talked to a random bike courier about his bicycle. He told me that he’d built it entirely out of second-hand parts except for one of the rims. The bike had a rusty frame and components of mismatched colors.
The derailleur on the bike was a dirty 10-speed Shimano Deore RD-T610 bought second hand from a local website. It had scratches all over the body,
The courier told me that he alone had amassed 10 000 miles/16000 km with that derailleur over the last year. The total mileage of the derailleur was impossible to know. Those numbers sound impressive but didn’t shock me.
I have a Shimano Altus RD-M310 (image below) on my hardtail – a low-end model in Shimano’s groupset hierarchy. The derailleur is not fancy, but I have only positive things to say about it; it’s cheap and has been performing flawlessly for over two years.
For a little over 12 months, I was commuting on it in all kinds of weather, and it never gave me serious problems even though I’d only clean it once in a couple of months.
I also have a second-hand Shimano Tourney TZ 6/7-speed derailleur that came with an old-school German MTB under the brand of Kenhill. The bike itself is over 20 years old, and my guess is that so is the rear mech. Yet the derailleur still works.
Ultimately, a rear derailleur is expected to have a long lifecycle under normal use.
What Is The Most Common Reason For Derailleur Failure
The most common reason for derailleur failure is an external hit inflicting instant and direct mechanical damage.
Most derailleurs “retire” not because they’re “tired”, but because they’ve been destroyed during a fall or by an object wedged into the drivetrain (e.g., a rock, a tree branch…etc.).
It’s also possible for the rear derailleur to get pulled or pushed into the spokes of the rear wheel. This can happen as a result of a fall, a hit, or a fallen chain. (Hence why you find a spoke protector on entry-level bikes.)
Mountain bikers are the group of riders the most likely to mechanically break a derailleur due to the stunt elements of the sport (jumps, drops, manuals…etc.) and the high density of obstacles found on the terrain.
Note: Most geared bicycles come with independent derailleur hangers connecting the derailleur to the frame.
The derailleur hanger is a strategic point of failure. It’s made of soft aluminum meant to bend or break during a fall. The goal of this functionality is to minimize the stress on the rear derailleur and the frame during an accident.
If the derailleur hanger gets bent, it will have to be replaced or realigned to ensure smooth shifting.
Which Parts Of The Rear Derailleur Wear Out The Fastest
The two most common rear derailleur problems caused by extended use are joint play and deterioration of the jockey wheels and their bearings.
For that reason, jockey wheels are also the most frequently replaced part of the rear derailleur.
What Are The Signs of Jockey Wheels Wear
The most obvious sign of jockey wheel wear is the shape of the teeth. If they’re pointy and sharp like a ninja throwing star, then the jockey wheels have to be replaced.
Having said that, the process of getting a jockey wheel to that state is rather long. Also, the rear derailleur can perform well even with somewhat worn jockey wheels.
A worn jockey wheel can potentially cause slow shifting and some slipping.
However, if the chain is slipping, more often than not, the cause is a worn-out cassette rather than a jockey wheel.
But if the cassette, the chainring(s) and the chain are new, and yet the gears are still slipping after proper indexing, the culprit could very well be a worn jockey wheel.
The bearing of a jockey wheel can be a source of problems too. Worn or broken ball bearings do not roll smoothly, and in some cases, they may jam and cause the jockey wheel to seize completely.
When that happens the chain may cause further damage to the derailleur by pulling the seized pulley.
FAQ: What type of material are the jockey wheels made of and why?
The average jockey wheels found on most bicycles are made of nylon – a plastic with long and heavy molecules.
The main reasons for choosing it over other materials are:
Low weight, low price, decent durability. Plastic jockey wheels are cheaper than the more sophisticated metal ones.
Less wear on the chain. Nylon is softer than metal and easier on the chain than steel.
Stress resilience. Some people believe that a nylon jockey wheel has a built-in safety mechanism. If the bearing seizes, then the wheel could continue to turn by sliding around the outer shell of the bearing. It’s debatable to what extent this could happen in practice.
FAQ: My upper jockey wheel has some play in it. Is that a problem?
Not necessarily. The upper pulley of Shimano derailleurs is designed to move a bit to reduce excessive chain noise and to compensate for slight imperfections in gear indexing.
The floating jockey wheel of Shimano is patented and considered one of the reasons why it was so hard for SunTour to match Shimano’s shifting performance in the past.
FAQ: Are jockey wheel upgrades worth it?
Truth be told, most riders can’t tell the difference between ordinary jockey wheels and the high-tech ones. You can experiment if you want to, but jockey wheel upgrades are not considered vital.
In most cases, cleaning the drivetrain regularly would give you better results than spending money on fancy pulleys.
How Long Do Jockey Wheels Last
The jockey wheels are the first part of the derailleur that wears out as a result of extended use, but they still last a long time. In many cases, you can use them for years without performance issues.
What Does It Take To Maintain The Jockey Wheels?
The jockey wheels should be cleaned and inspected for wear regularly. Having said that, you don’t have to be a fanatic. A good rear derailleur can operate even when it’s not perfectly clean.
Most derailleurs come with bushings instead of bearings. Those types of pulleys would benefit from regular cleaning, but putting grease on them results in dirt accumulation rather than improved performance.
I also have bushings on my derailleurs, and the only maintenance that I do is cleaning the parts once in a while.
Bushings may be considered primitive, but they’re actually less prone to problems such as sudden seizing thanks to the simplicity of the system.
The downside of bushings is extra friction. It’s debatable to what extent that even matters in practice.
More sophisticated jockey wheels come with ball bearings which require more intensive servicing consisting of the following steps:
- Remove the jockey wheels from the derailleur. (You will need an Allen key.)
Tip: Before removing the jockey wheels, you can take a picture with your phone. That way you won’t have to rely on your memory to remember the orientation of the jockey wheels when reassembling the derailleur. Of course, you could also Google the model of the derailleur and search for an image online.
2. Clean the jockey wheels with a towel.
3. Remove the spacers and the seals of the jockey wheels.
4. De-grease the bearings and the seals.
5. Put fresh grease into the bearings and put the seals back in place.
This procedure could also revive a seized jockey wheel.
In Which Gear Should I Park My Bike To Prevent Derailleur Strain?
In general, shifting to a smaller chainring and cog reduces the stress on the derailleur’s spring as well as the cable and the shifter. Having said that, the effect of that practice isn’t all that strong. A good derailleur shouldn’t be harmed if left in an “improper” gear.
How The Climate Impacts The Life of a Derailleur
The rear derailleur’s function and position make it vulnerable to dirt coming from the chain, the ground, the shoes of the cyclist, and the rear wheel.
Unlike the front derailleur, the rear one cannot be protected from the elements with a full fender because the dirt and water reflected by the fender fall down into the spokes.
As a result, the rear derailleur gets contaminated very quickly. The effect is accelerated during winter when the roads are covered with sand, salt, and various anti-freezing compounds which have a corrosive effect on some materials.
A derailleur consistently exposed to water, grit, salt, and sand will have a shorter lifespan than one ridden in sunny conditions.
Minimizing The Effect of Bad Weather on a Derailleur
Here are some tips that can reduce the effect of bad weather on a derailleur:
1. Make a winter “beater” bike. (cheat winter)
A cheap but otherwise functional bike (e.g., a retro MTB) can be easily turned into a very good winter/rain commuter. Even with lower-end components (e.g., Shimano Tourney), the bicycle should ride nice enough.
By using it only on rainy/snowy days, you will spare your nicer derailleur while introducing some variety to your commuting experience.
If you really want to keep things simple during the winter for the sake of lower maintenance, you could build/buy a single-speed bicycle and eliminate the need for a derailleur altogether.
Of course, this option isn’t for everyone. Some cities have too many hills to cover the distance without gearing.
2. Develop a clean & protect policy
Cleaning the derailleur after every winter ride will prevent a lot of damage and prolong the life of the component.
For example, you can wash the derailleur with water, dry it with a cotton towel/rug, and then spray it with WD-40 or a product with similar functions.
The WD-40 will create a layer of protection reducing the chances of corrosion. It will also lubricate the mechanical components of the derailleur.
If you want even more lubrication, you can put a few drops of the oil that you lube your chain with on the pivots of the derailleur.
3. Cover the derailleur with a boot
The company Lizard Skins offers a derailleur boot named Grunge Guard. It covers the entire derailleur apart from the lower pulley and protects the mech from impurities.
Is It Worth Repairing a Rear Derailleur?
It depends on the damage.
A while back, I bent the cage of my Shimano Altus rear derailleur. I re-bent it back by hand, and it began shifting accurately again. I am still running this derailleur on my bike.
However, in case of more severe damage, repair of cheaper derailleurs becomes of questionable value because it’s often difficult to find the needed parts.
If you are running a similar derailleur or of lower quality, and you can’t fix the problem with what you already have, buying a new one would be a logical solution.
But if you have a high-end derailleur that costs a lot of money, it will be worth it to put more effort into repairing the damaged component.
I recommend joining a Facebook group for your style of riding and asking for parts there.
The Rear Derailleur Is Not Always The Source of Shifting Problems
The rear derailleur is naturally associated with shifting problems at the back, but in a surprising number of cases, the culprit is found elsewhere.
If you are experiencing inaccurate shifting, and the derailleur looks fine (straight), the sources of the issue could be:
1. The derailleur hanger
If the derailleur hanger is bent, it will cause funny shifting even if the derailleur itself is in perfect condition.
2. Shifting cable + Housing
A worn out and/or improperly rooted shifting cable can create a great deal of shifting problems.
Cyclists often buy new derailleurs and talk about how great they are in comparison to the old ones. Ironically, a lot of the improvement often comes from the new cable accompanying the upgraded derailleur rather than the mech itself.
3. Worn cassette/Freewheel
A worn cassette or freewheel can cause serious gear slipping, especially when combined with a new chain.
If the derailleur hanger is fine, the next step to fixing slipping gears would be to change the cassette or freewheel as well as the chain.
4. A contaminated shifter
If the shifter is contaminated, it can cause shifting problems. In similar situations, one of the options is to take off the cap if it’s removable and spray WD-40 or a similar product while clicking the shifter up and down.