Why does my rear derailleur won’t shift to lowest gear?

Since it’s summer, riding uphill is getting too difficult. Cyclists going crazy in sweat and dehydration is a common scenario in this season.

Even the riders used to troll eBikers wish to get an eBike while riding uphill.

However, experts suggest riding the bike on the lowest gear while climbing uphill so that you can save energy. But, what if it stuck and won’t shift to the lowest?

You don’t need to answer. I know it would be the worst nightmare. But, in reality, this nightmare is becoming true for some riders.

And what happens next? I have described it at the end of the post. Keep reading.

Why does my rear derailleur won’t shift to lowest gear?

Simply it occurs because the alignment of the rear derailleur is not proper.

bikerepairoffer

1. Firstly, It can happen because of low cable tension. When the cable tension is not optimum, shifting power loses to cover up the lack of tension.

As a result, the guide can’t travel enough to shift the gear to the lowest cog.

2. Secondly, it can happen because the Limit-screws are too tight or too loose.

Limit screws determine how far the rear derailleur can travel and prevent it from going too inward (spokes) or too outward (frame).

3. Lastly, the shifting cable itself can be the culprit. When the cable gets rusty or severely damaged inside, it can’t move freely and stuck the rear derailleur.

Freaky Tip: If the shifting cable itself is the culprit, it’s better to replace the cable instead of fixing it.

Best Bike Cable: Road / MTB

What is the solution to the gear shifting problems?

derailleur won't shift to lowest gear

Fine-tuning!

Yes!

As I said before, the problem arises from the wrong alignment of the rear derailleur or low cable tension; the best solution is to keep it tight and align it right.

Thus, the shifting will be smooth, and the rear derailleur will be able to travel within the required distance.

However, for fine-tuning, you will need a pro solution. I have described the process of basic fine-tuning. Follow it to get rid of any kind of rear derailleur-related problem.

Freaky Tip: Bike chain health is also crucial for smooth shifting power. Bike chain cleaning & maintenance is necessary to get a healthy chain.

Anyways, you must have few more questions regarding gear adjustment. I have tried to answer them in the FAQ section. Keep reading to know the answers.

Read Also: Front derailleur won’t shift

Fine Tuning 101

Before starting the job, you will need a few tools to be ready.

Tools are ready. Now hang the bike on a repair stand and go step by step to fine-tune the rear derailleur.

Step-1: Dialing H Limit Screw

H Limit screw prevents the chain from going too outward (frame). Tightening the H-Screw can help to bring the chain inward.

If you loosen the H-screw, it will go more outward. However, go step by step to set the H-Screw in an optimum position.

1. Firstly, identify which one is the H screw. It is marked with an “H” latter on the derailleur arm. If it is not marked, rotate both screws with the screwdriver or hex wrench.

While rotating them clockwise, which screw will move the derailleur arm inward is the H-screw.

2. Secondly, shift the gear to the largest crank and the smallest cog. Even if the chain has come to the smallest cog, keep clicking the shifter until there is no click remains.

A possible scenario can be the chain is not shifting to the smallest cog. It’s a symptom of too tight H screw or a wrong shift position.

3. If the H-Screw is too tight, rotate anticlockwise to loosen it. If there is any problem in shifting position, turn the barrel adjuster clockwise.

Then, keep rotating the pedal and click the shifter to check if the chain is shifting to the smallest cog properly. Otherwise, turn the barrel clockwise a couple of times.

4. Even if the chain shifts properly, you can hear an unwanted sound from the derailleur.

It can happen because the chain is rubbing with the nearby cog. Readjust the barrel and align the chain to an acceptable shifting position to eliminate the rubbing problem.

5. Lastly, keep rotating the pedal and shift to the higher cogs (except the largest one).

Check if there is any unwanted sound after shifting. If you hear it, readjust the barrel to rectify the rubbing problem.

Step-2: Indexing Adjustment

Indexing refers to the alignment of the guide pulley with cogset. When the chain guide is aligned precisely parallel to all the cogs means the Indexing is perfect.

However, once again, go step by step to get the proper indexing.

1. Firstly, shift your chain to the 2nd largest crank and the smallest cog. Rotate the pedal and try to shift the chain to the 2nd smallest cog.

A possible scenario can be the gear is not shifting to the higher cog.

2. If it’s not shifting, keep clicking the shifter until no click remains. Now, rotate the barrel anticlockwise and check if it is shifting or not.

Repeat the procedure until it shifts.

3. If the barrel adjuster comes out in this procedure, the cable tension may be too low. In this case, rethread the barrel fully.

Ensure the gear stays on the smallest cog, and no click remains. Then, loosen the cable holder screw and pull the cable end to increase the tension.

Make sure the derailleur arm doesn’t move a millimeter in this process.

4. In another scenario, you can notice that the guide is traveling two sprockets with a single click.

In that case, turn the barrel clockwise until it fixes. Then, rotate the pedal and hear if there is any excessive noise.

If there is no excessive noise, then it is fine-tuned. Otherwise, readjust the barrel to ensure an acceptable alignment.

5. Lastly, keep rotating the pedal and shift the chain to the higher cogs. If there is any rubbing or slow shifting problem, turn the barrel clockwise until the problem solve.

Read Also: bike maintenance

Step-3: Dialing L Limit Screw

Why does my rear derailleur won't shift to lowest gear

L Limit screw prevents the chain from going too inward (spoke). Loosening the L-Screw can help to bring the chain outward.

If you tighten the L-screw, it will go more inward. However, go step by step to set the L-screw in an optimum position.

1. Firstly, shift the chain to the smallest crank and 2nd largest cog. Rotate the pedal and try to shift the gear to the largest cog.

No shift, slow shift, or excessive noise? All are symptoms of a too-tight L-screw.

2. Turn the L-screw anticlockwise to loosen it. Make sure the alignment is acceptable after that.

For that, rotate the pedal and hear if there is any excessive sound. If there is no excessive sound, then the alignment is okay.

Tighten the L-screw if there is excessive sound.

3. Lastly, shift the chain to the lower cogs and again shift to the largest. If there is no click remain on the shifter, the L-Screw is all set.

Step-4: Dialing B Screw

B Screw determines the distance between the guide wheel and cogs. A gap of 5-6 mm is considered optimum.

However, it can vary for different manufacturers. Just make sure it’s not too close or too far.

1. Firstly, shift the chain to the smallest crank and the largest cog.

2. Secondly, use a hex wrench to guess the distance. If you wanna increase the gap, tighten the B screw. Loosen it if you wanna decrease the gap.

3. If you have made any significant change in B-Screw, double-check the derailleur for the rubbing problem.

Freaky Tip: After you are done with fine-tuning, go for a test ride and check if the gear is shifting correctly or not. If it is not shifting properly, give a quarter turn to the limit screws and barrel adjuster.

Frequently Asked Questions About Derailleur

What do the H and L mean on derailleur?

There are two limit screws on a derailleur. They are H and L screws. The H stands for high gear, and it brings the derailleur to higher cogs.

The L stands for low gear, and it brings the derailleur to the lower cogs.

Which gear is hardest to pedal?

The highest gear is the hardest to pedal. When the chain is on the largest crank, the smallest cog is considered the highest gear.

The highest gear can help to accelerate the bike while riding downhill.

How does the B screw affect shifting?

B- screw or Body angle screw determine the distance between the chain guide and cogs.

If the B-screw is in the optimum position, shifting will get smooth and efficient.

Wrong alignment of B-screw can lead you to inefficient shifting or derailleur damage.,

Conclusion

When your gear doesn’t shift to the lowest cog, you may have to ride the bike in a higher gear. But, riding uphill with higher gear will drain your energy quickly.

Thus, you will get sweaty and dehydrated soon. The tendency of vomiting and respiratory issues will appear next.

Risking your health for compromising the bike issue is not worth it. After all, you ride for good health, not for getting sick. It’s easier to fix the bike issue, too.

However, I have described how to deal with the issues and adjust the gear. I hope it will help you to get a smooth-shifting power and solve all the gear problems.

Wish you a healthy ride.

Cheers!

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