How To Change Gears On A 21 Speed Mountain Bike Like a Pro

Riding a 21 speed mountain bike can be a thrilling adventure, but for many riders, using all those gears can feel confusing. You may have wondered: When should I change gears? Which levers control what? How do I shift smoothly and avoid chain problems? If you’ve asked yourself these questions, you’re not alone. Understanding your bike’s gearing system isn’t just about speed—it’s about control, efficiency, and enjoying every ride, no matter the terrain.

Many beginners try to “figure it out” as they ride, but this often leads to rough gear changes, chain drops, or even damage to the bike. The good news? Shifting gears on a 21 speed mountain bike is straightforward once you know how the system works.

This article explains, step by step, how to confidently change gears, what each of the 21 speeds really means, and how to master gear selection for different trails and conditions. Along the way, you’ll get practical tips, real-world examples, and answers to common questions most riders have.

Whether you’re new to mountain biking or just want to ride smarter, this guide will help you unlock the full potential of your bike—so you can climb hills with less effort, cruise flats with speed, and descend with control.

Understanding The 21 Speed Gear System

A 21 speed mountain bike uses a combination of front and rear gears. The system includes 3 chainrings at the front (near your pedals) and 7 cogs at the rear (on the rear wheel). The math is simple: 3 x 7 = 21 possible gear combinations.

What Are Chainrings And Cogs?

• Chainrings: The larger gears by your pedals, usually controlled by your left shifter.
• Cogs (Cassette): The smaller gears on your back wheel, controlled by your right shifter.

Each combination gives you a different mechanical advantage. Lower gears make pedaling easier (good for climbs), while higher gears make you go faster (good for flats and descents).

Why 21 Gears?

You might wonder why so many gears are needed. The reason is flexibility. Having 21 speeds means you can fine-tune your pedaling effort for every type of terrain, whether steep hills or smooth roads.

How The Shifters Work

• Left shifter: Changes the front chainrings (1-3)
• Right shifter: Changes the rear cogs (1-7)

The combination you choose affects how hard or easy it is to pedal.

Key Parts Of The Gear System

Before you start shifting, it helps to know the main parts involved:

• Shifters: Levers on your handlebars that change gears.
• Front derailleur: Moves the chain between front chainrings.
• Rear derailleur: Moves the chain between rear cogs.
• Chain: Connects everything and moves as you shift.
• Cassette: The set of rear cogs.
• Crankset: The set of front chainrings attached to your pedals.
• Gear cables: Link the shifters to the derailleurs.

Each part must be in good working order for smooth, reliable shifting.

The 21 Gear Combinations (explained One By One)

Each combination of front and rear gears is a “speed.” Here’s how each of the 21 speeds works, and when to use them. For clarity, let’s list all 21 gear combos as pairs: (Front chainring, Rear cog).

1. (1,1) – Lowest Gear

Front chainring 1, Rear cog 1

This is your lowest gear. Use it for the steepest climbs. Pedaling will be easy but slow.

2. (1,2)

A bit harder than (1,1), but still for climbing. Good when the steepness decreases slightly.

3. (1,3)

Still a climbing gear, but with more resistance. Use when you want a little more speed uphill.

4. (1,4)

Best for gentle slopes or when you’re tired after a climb but want to keep moving.

5. (1,5)

Transition gear from climbing to flat. Use when the terrain levels out.

6. (1,6)

For flat terrain when you want to keep pedaling easily without much resistance.

7. (1,7)

The hardest gear on the smallest front chainring. Use for flat sections if you want to spin faster, but not for speed.

8. (2,1)

Now you’re on the middle front chainring. This gear is for steady climbing, not as easy as (1,1).

9. (2,2)

A versatile gear. Good for rolling terrain—small hills, small descents.

10. (2,3)

This is one of the most commonly used gears. Perfect for everyday riding on mixed surfaces.

11. (2,4)

Great for flat sections and gentle descents. You’ll use this gear often.

12. (2,5)

For fast riding on flat roads. Slightly harder to pedal but gives more speed.

13. (2,6)

Now pedaling gets harder—good for sprints or chasing friends on flat ground.

14. (2,7)

The hardest gear on the middle chainring. Use only when you want speed and the terrain allows.

15. (3,1)

Switching to the largest front chainring, paired with the biggest rear cog. Not used often—can cause chain stress.

16. (3,2)

Similar to 15, but slightly less stress on the chain. Rarely used.

17. (3,3)

These gears (15, 16, 17) are usually “crossover” gears. Better to use (2,5) or (2,6) instead.

18. (3,4)

Now it’s getting practical—use this gear for long, flat stretches at high speed.

19. (3,5)

For fast rides on smooth surfaces. You need strong legs to use this gear well.

20. (3,6)

High-speed gear for descents or strong tailwinds.

21. (3,7) – Highest Gear

Front chainring 3, Rear cog 7

This is your highest gear. Pedaling is hardest, but you’ll go fastest. Use for sprints, descents, or when you want maximum speed.

Gear Overlap And “crossover” Gears

Not every combination is useful. Some combos, like (1,7) or (3,1), are called crossover gears. They put the chain at a sharp angle, which can cause wear and poor shifting. It’s better to avoid these.

Common Crossover Gears To Avoid

• (1,7)
• (2,1)
• (2,7)
• (3,1)

Instead, choose gears that keep the chain as straight as possible.

How To Shift Gears Smoothly

Changing gears is simple in theory, but doing it well takes practice. Here’s how to shift like a pro:

• Ease Pedal Pressure: When shifting, reduce force on the pedals. This lets the chain move smoothly.
• Shift One Gear at a Time: Don’t jump multiple gears at once, especially under load.
• Anticipate Hills: Shift before you reach a hill, not while you’re climbing it.
• Listen to Your Bike: If you hear grinding, you may need to adjust your shifting.
• Don’t Cross-Chain: As explained, avoid the most extreme gear combos.

Example Scenario

Imagine you see a hill ahead. As you approach, shift to a lower gear while still on flat ground. When you hit the hill, your pedaling will already be easier, and you won’t stress the chain.

Practical Examples For Each Gear

Let’s look at when you might use each of the 21 gears:

• (1,1): Climbing steep, rocky hills.
• (1,2): Long, steady uphill sections.
• (1,3): Short, sharp inclines.
• (1,4): Transitioning from climb to flat.
• (1,5): Recovering after a tough climb.
• (1,6): Soft surfaces like sand or mud.
• (1,7): Spinning fast on a flat field.
• (2,1): Rolling hills, mixed terrain.
• (2,2): Urban streets with some bumps.
• (2,3): Commuting, light trails.
• (2,4): Leisurely rides on smooth paths.
• (2,5): Fast road cycling.
• (2,6): Sprinting on flat ground.
• (2,7): Fast group rides.
• (3,1): Downhill with slow traffic.
• (3,2): Fast, gentle descents.
• (3,3): Gaining speed before a climb.
• (3,4): Racing on open roads.
• (3,5): Endurance rides.
• (3,6): Chasing a friend downhill.
• (3,7): Maximum speed on a steep descent.

Gear Selection For Different Terrains

Choosing the right gear makes every ride easier and more enjoyable. Here’s how to match gears to terrain:

Climbing Hills

Use the smallest front chainring (1) and largest rear cogs (1-3). This combination makes pedaling the easiest.

Flat Roads

Switch to the middle chainring (2) and choose mid-range cogs (3-5). You get a balance of speed and comfort.

Descents

Use the largest chainring (3) and smallest cogs (6-7). This is your high-speed setup.

Technical Trails

Stay in the middle chainring (2), with lower cogs for quick response.

Windy Conditions

If riding into the wind, shift to a lower gear to maintain cadence. With a tailwind, try higher gears to go faster with less effort.

Gear Ratio Comparison

Different gear combinations give you different gear ratios. Here’s a comparison of typical ratios you’ll find on a 21 speed mountain bike:

Front Chainring	Rear Cog	Gear Ratio	Use Case
22T (smallest)	32T (largest)	0.69	Steep climbs
32T (middle)	18T (middle)	1.78	Flat roads
42T (largest)	12T (smallest)	3.50	High speed/descent

Note: T stands for teeth, the count on each gear.

What Beginners Often Miss

Most new riders focus only on “hard” or “easy” gears but overlook a few key points:

• Cadence Matters: Pedal speed (cadence) is as important as gear choice. Aim for a comfortable rhythm, usually 70–90 revolutions per minute.
• Chainline Angle: Keeping your chain as straight as possible reduces wear and improves shifting. Don’t just chase “hardest” or “easiest” gears.

Another common mistake is shifting under heavy load—like standing up on the pedals during a climb. This can cause the chain to skip or even break.

How To Use Both Shifters Together

Some riders only use one shifter, but using both effectively gives you the most options. Here’s how:

• Left Shifter (Front): Makes big changes. Use when the terrain changes a lot.
• Right Shifter (Rear): Makes small adjustments. Fine-tune your pedaling effort.

Example: You start climbing a hill. Shift the left shifter down to the small chainring, then use the right shifter to find the best rear cog for your legs.

Common Gear Shifting Problems (and Solutions)

Even good riders face gear issues. Here’s how to fix the most frequent problems:

Chain Skips When Shifting

• Cause: Dirty chain, worn gears, or poor adjustment.
• Solution: Clean and lubricate your chain. Adjust the derailleur if needed.

Chain Drops Off

• Cause: Shifting too many gears at once or misaligned derailleur.
• Solution: Shift one gear at a time. Check derailleur alignment.

Grinding Or Noisy Shifting

• Cause: Cross-chaining or dry chain.
• Solution: Avoid extreme gear combinations. Lubricate chain.

Stuck Gears

• Cause: Cable tension problems or bent hanger.
• Solution: Check and adjust cable tension. Visit a bike shop if unsure.

Table: Gear Combinations And Recommended Use

This summary helps you pick the right gear instantly.

Gear (Front, Rear)	Type	Recommended Use
(1,1)-(1,4)	Low	Climbs, rough terrain
(2,2)-(2,5)	Medium	Flats, rolling hills
(3,5)-(3,7)	High	Descents, speed

Credit: kent.bike

How To Practice Shifting

Skill comes with practice. Here’s how to get comfortable:

• Find a quiet, flat place: Like an empty parking lot.
• Start in an easy gear: (2,2) or (2,3).
• Shift one gear at a time: Feel how the bike responds.
• Try shifting under different speeds: Notice how shifting feels when you pedal harder or softer.
• Practice on hills: Start with gentle slopes, then try steeper climbs.

Tip: If you hear a lot of noise or the chain feels rough, you may need to adjust your derailleurs. Regular maintenance keeps shifting smooth.

Maintaining Your Gear System

A clean, well-tuned gear system is safer and more fun. Here’s what you need to do:

• Clean your chain: Use a brush and degreaser every 2-4 weeks.
• Lubricate the chain: After every wash or ride in rain/mud.
• Check cable tension: If shifting feels stiff or slow.
• Inspect gears: Look for worn teeth or bent cogs.

A well-maintained bike shifts better and lasts longer.

Credit: www.ebay.com

Table: Maintenance Schedule For Gear System

Here’s a quick reference for keeping your gear system in top shape.

Task	Frequency	Notes
Clean chain	Every 2-4 weeks	More often in wet/muddy conditions
Lubricate chain	After every wash or rain ride	Wipe off excess oil
Check cable tension	Monthly	Adjust if shifting is rough
Inspect cassette/chainrings	Every 3 months	Replace if teeth are sharp or bent

Tips For Smooth Gear Changes

• Shift while pedaling gently: Don’t force the pedals hard.
• Don’t wait until it’s too late: Shift before you need to.
• Listen and feel: Good shifting should be quiet and smooth.
• Practice makes perfect: The more you ride, the better you’ll get.

Advanced Gear Strategies

Once you’re comfortable, try these strategies:

• Cadence control: Find your ideal pedaling rhythm and shift to keep it.
• Anticipate terrain: Shift before the trail changes.
• Use mid-range gears: They wear slower and offer good chain alignment.

When To Shift Gears

You should shift whenever your pedaling feels too hard or too easy. Don’t be afraid to shift often—mountain bikers change gears hundreds of times on a single ride.

Gear Myths And Facts

Myth: “More gears always mean more speed.”

Fact: The right gear at the right time is what matters.

Myth: “You should only use the big chainring.”

Fact: All gears are useful—choose based on the terrain.

Learning From Mistakes

Every rider makes mistakes. The most common are:

• Shifting under full power
• Using crossover gears
• Forgetting to maintain the gear system

Learning from these will make you a better, more confident rider.

Credit: www.amazon.com

Useful Resources

If you want to dive deeper into bike gear systems and shifting, visit Wikipedia’s Bicycle Gearing page for detailed explanations and diagrams.

Frequently Asked Questions

What Is The Best Gear For Climbing Hills?

The best gear is usually the smallest front chainring (1) and the largest rear cog (1 or 2). This setup makes pedaling easiest and helps you climb steep hills without tiring quickly.

How Do I Avoid My Chain Falling Off While Shifting?

To prevent the chain from falling off, shift one gear at a time and reduce pressure on the pedals during the shift. Avoid extreme gear combinations like (1,7) or (3,1), as these put stress on the chain.

Why Does My Bike Make Noise When I Shift Gears?

Noise usually comes from poor chain alignment or a dry, dirty chain. Regular cleaning, lubrication, and avoiding crossover gears will keep your shifts quiet and smooth.

Is It Okay To Shift Gears While Not Pedaling?

No, you should always be pedaling gently while shifting. Shifting without moving the pedals can jam the chain or damage the gear system.

How Often Should I Maintain My Gear System?

Clean and lubricate your chain every 2-4 weeks or after riding in wet/muddy conditions. Check your cables and adjust the derailleurs monthly for the best performance.

Learning to shift gears on a 21 speed mountain bike takes practice, but with these tips and a little patience, you’ll soon ride more efficiently, tackle tougher trails, and enjoy every mile. Remember, the right gear at the right moment turns a tough ride into a smooth adventure.

Happy cycling!