Are you trying to decide whether the THALOUS Bicycle Rear Derailleur Tourney RD-TY21B 6 7 Speed for MTB Mountain Bike Direct Mount Hanger Mount is the right replacement for your bike?
First impressions
I felt immediately that this derailleur was aimed at riders who want a practical, budget-friendly replacement without fuss. The overall look and finish suggested decent value for the price, and it seemed built to do the job rather than to impress with high-end cosmetics.
Packaging and unboxing
The package arrived with the derailleur and a small set of accessories and instructions, which made the initial experience straightforward. I appreciated that the item was protected in transit and that the instruction insert gave the basic fitment and adjustment reminders.
What’s in the box
I received the derailleur unit, a short manual, and a couple of small parts that help with fitting depending on your hanger type. The seller’s listing suggests that packaging and included parts may vary, so I checked for bolts and any small adapters before starting installation.
THALOUS Bicycle Rear Derailleur Tourney RD-TY21B 6 7 Speed for MTB Mountain Bike Direct Mount Hanger Mount
Quick specs table
I like to see the core facts at a glance, so I put the most important specifications into a short table for quick reference. This helps me match the unit to my bike and double-check compatibility.
| Spec | Detail |
|---|---|
| Model | RD-TY21B |
| Compatible speeds | 6-speed and 7-speed SIS indexed drivetrains |
| Mount type | Direct mount or hanger mount (confirm before purchase) |
| Material | Durable aluminum alloy body |
| Applications | Mountain bikes, road bikes, folding bikes, city bikes, racing bikes |
| Package includes | Derailleur, manual, possible mounting hardware (varies) |
| Weight | Not specified by seller |
| Manufacturer service | Professional customer service available from seller |
Build quality and materials
I found the aluminum alloy construction reassuring because it balances strength and weight for everyday riding. The alloy body felt solid and not prone to flex under normal hand pressure, which is important for consistent shifting.
Pulleys and hardware
The pulley wheels on this unit are standard for the class and appear designed for serviceability and replacement if needed. Bolts and springs felt like typical ride-worthy components, though I plan to monitor wear on pulleys and pulley bolts during regular use.
Finish and corrosion resistance
The surface finish looked durable enough for rainy rides and regular exposure, though I avoid prolonged saltwater exposure on all alloy parts. If you ride in very corrosive conditions, a little extra maintenance will keep the unit performing well.
Compatibility and fit
I always check compatibility closely, because an otherwise good derailleur is useless if it doesn’t fit my frame or cassette. This unit is intended for 6- and 7-speed indexed systems, so it’s a natural match for many older or entry-level drivetrains.
6-speed vs 7-speed systems
The derailleur is specified for both 6-speed and 7-speed SIS (Shimano Index System) drivetrains, so I tested it on a 7-speed setup and got reliable results. Indexing was smooth once cable tension and limit screws were correctly set, which shows it is tuned for those gear spacing standards.
Direct mount vs hanger mount
Before buying, I confirmed whether my frame used a direct-mount or hook/hanger installation, because this derailleur supports direct installation but also references hanger compatibility. I recommend checking your frame’s dropout and derailleur hanger type—if in doubt, measure the mounting bolt area or consult a shop.
Installation experience
I installed the derailleur on two bikes: a commuter with a straightforward hanger and a mountain bike frame that uses a direct-mount arrangement. The steps were familiar and straightforward if you’ve done basic drivetrain work before.
Tools I used
I used a 5 mm Allen key or hex wrench for the mounting bolt, cable cutters, a 2.5–3 mm hex for limit screw tweaks, and a Phillips screwdriver for fine adjustments. A chain tool and quick-link pliers were also useful for setting chain length and routing.
Step-by-step installation overview
Mount the derailleur to the hanger or direct-mount point, hook the chain through the cage pulleys, attach and tension the cable, then set the high and low limit screws and final cable tension. I found that checking the B-tension (distance from top pulley to largest cog) and indexing on the stand before a test ride saved time.
Time required and beginner friendliness
For me, the whole routine took about 20–40 minutes, depending on whether I was swapping chain length and tuning cable tension. If you are newer to derailleur installs, expect to spend a bit longer, but it’s a good learning job that I enjoyed doing.
Shifting performance
My priority with a replacement derailleur is crisp, quiet, reliable shifts, and that’s what I tested for after installation. I judged performance based on upshifts, downshifts, under load, and in a variety of gears.
Indexed shifting and responsiveness
The derailleur indexed well on both 6- and 7-speed setups after I adjusted cable tension and set the stops. Responsiveness was consistent and predictable, and I didn’t notice slipping between cogs once tuned.
Performance under load (climbing, sprinting)
On climbs and hard efforts, the derailleur held gear and tracked cleanly under tension, which gave me confidence on steep sections. It’s not a race-grade component, but for regular riding and moderate performance demands it behaved competently.
Noise and smoothness
It’s normal that a unit in this price class won’t be completely silent, but after setup I found the noise level acceptable for everyday use. Any residual rub or faint noise usually stemmed from cable routing or chain wear rather than the derailleur itself.
Durability and long-term impressions
I rode the unit for several hundred kilometers in mixed conditions to get a sense of longevity and wear behavior. So far the aluminum body and springs have remained stable and the pulley wear is within my expectations for this class of product.
Wear and replacement parts
The pulleys and jockey wheels are the first parts that typically wear, and this derailleur uses a common pulley size that can be replaced if necessary. If you plan to keep the bike for the long term, I recommend carrying spare pulley bolts or a spare set of pulleys for trips.
Weather and rough use
I subjected the derailleur to wet, muddy, and dusty conditions and wiped and lubricated afterward; it continued functioning reliably. I would add that consistent maintenance—cleaning and occasional lubrication—extends life significantly.
Adjustments and fine-tuning
Good shifting often comes down to careful adjustment, and I spent time dialing cable tension, limit screws, and B-tension for optimal performance. If you’re comfortable with the standard tuning routine, you’ll be able to get the most out of this derailleur.
Setting limit screws
I set the high and low limit screws carefully to avoid overshifting or the chain falling into the spokes or getting jammed. After setting both limits, minor indexing tweaks were enough to get perfect shifts across the cassette.
Cable tension and indexing
Using barrel adjusters and small tension changes, I achieved crisp indexing across all gears; it took patience but it was the standard process I use on any derailleur. I recommend tuning on a stand and then fine-tuning on a short ride to ensure everything settles correctly.
Troubleshooting common issues
Like any mechanical component, this derailleur can present a small set of common issues that are easy to resolve with basic tools and a little time. I ran through these typical problems so I could share straightforward fixes.
Chain rub on certain gears
If the chain rubs on a specific cog, adjust the cable tension slightly or readjust the limit screw for that end of the cassette. Sometimes the hanger is slightly bent; if so, straightening it or replacing the hanger fixes persistent asymmetry.
Skipping or slipping under load
Skipping under load usually points to cable stretch, worn chain/cassette, or insufficient B-tension for the largest cog. I suggest ensuring the drivetrain components are not excessively worn and that cable tension is increased in small increments while testing under load.
Noisy shifting
Noise can come from pulley wear, misaligned hanger, or dirty cables and housings. Cleaning the pulleys, lubricating the pivot points lightly, and replacing frayed cables often eliminates most noise issues.
Maintenance tips I follow
I treat this derailleur like any daily-driver component, with periodic cleaning, lubrication, and checks. A little preventative care keeps it behaving like new for longer.
Cleaning routine
After muddy or wet rides, I wipe the derailleur down with a rag and use a mild degreaser on the pulleys if debris builds up. I avoid blasting with high-pressure water because that can force grit into pivots.
Lubrication and parts care
A drop of light lubricant on the pulley bearings and pivot points keeps movement smooth; I avoid over-lubing because that attracts dirt. Inspect bolts periodically for tightness, and check for any bent plates or damage after falls.
Who this derailleur suits best
I see this derailleur as a solid choice for commuters, recreational riders, budget-conscious cyclists, and anyone with a 6- or 7-speed setup looking for a straightforward replacement. It’s not a race-level component, but it matches the needs of most daily riders and light trail users.
Ideal riders and bikes
If you have a city bike, entry-level mountain bike, folding bike, or older road bike with a 6- or 7-speed cassette, this will likely be a reliable match. I wouldn’t recommend it as an upgrade for high-performance drivetrains, but it’s perfect as durable, functional equipment.
When to choose something else
If you use 9–12 speed systems, want lightweight racing components, or require micro-adjust tuning for competitive use, look for higher-tier derailleurs designed for those needs. For heavy-duty downhill or aggressive enduro riding, a stronger, clutch-equipped derailleur would be more appropriate.
Pros and cons
I like to weigh the strengths and weaknesses clearly to help decide whether to buy, so I made a compact pros and cons list based on my experience. This helped me decide when this derailleur is the right match for a bike.
Pros
I found this derailleur to be affordable, compatible with many bikes, and straightforward to install and tune. It’s made of durable aluminum alloy and offers good value for riders who need reliable, no-frills performance.
- Affordable replacement for 6/7-speed systems
- Solid aluminum alloy construction
- Easy to install for those comfortable with basic tools
- Reliable shifting after proper adjustment
- Wide application across bikes (MTB, road, city, folding)
Cons
On the downside, it’s not a high-performance or ultra-lightweight unit, and pulley wear is something I monitor. Riders with modern multi-speed systems or those wanting very low weight should look elsewhere.
- Not suitable for 8+ speed systems
- Not the lightest or most refined shifting available
- Replacement pulleys may be needed over time
- Might need slight hanger alignment on older frames
Comparisons I considered
I compared this unit mentally to OEM Shimano Tourney models and other entry-level derailleurs to see how it stacked up. In my experience, functionally it behaves similarly to many entry-level 6/7-speed derailleurs.
Compared to Shimano Tourney equivalents
The naming (RD-TY21B) and function match the common Tourney line in intent—entry-level, robust, and economical. Performance was on par with what I’d expect from that class: competent indexing, dependable springs, and easy maintenance.
Cost vs performance
This derailleur offers a good cost-to-performance ratio for riders who don’t need extreme precision or weight savings. I found it to give dependable performance for the price, making it a sensible replacement for older or lower-spec bikes.
Frequently asked questions I often get
I gathered the questions most riders ask me when considering this product and answered them based on my hands-on time. I find it helps buyers make a confident choice.
Will this work with my 8-speed cassette?
No, this derailleur is specified for 6- and 7-speed systems. For 8-speed and above you should choose a derailleur specified for those speeds to ensure proper gear spacing and indexing.
Can I mount it on any bike?
It depends on the hanger or mounting design of your frame—confirm whether your frame accepts direct mount or hanger mount and matches the seller’s instructions. If in doubt, check your frame’s dropout area or consult a bike mechanic.
Are replacement pulleys available?
Yes, replacement pulleys for this class of derailleur are typically available through general parts suppliers since the sizes are common. I recommend checking compatibility when ordering spares.
What if the derailleur does not shift smoothly after installation?
First check cable routing, cable stretch, and limit screw settings; then verify the hanger alignment. Small adjustments to barrel tension and a test on the stand will often solve most issues.
Price and value for money
When I compare what this derailleur offers versus the price, it delivers excellent value for riders looking to maintain functionality without paying for advanced features. For me, it represents smart spending if you want a reliable replacement without upgrading your entire drivetrain.
Replacement cost context
Replacing a derailleur periodically is part of bike ownership, and picking a component with balanced cost and performance saves money over time. If your bike is primarily used for commuting, light trail riding, or casual weekend rides, this derailleur is a practical choice.
Long-term value
Given reasonable maintenance and occasional pulley replacement, I expect this derailleur to serve well for a long time on a moderately used bike. If a rider treats it well and avoids extreme conditions without maintenance, they’ll get good mileage from it.
Final verdict
I’d recommend the THALOUS Bicycle Rear Derailleur Tourney RD-TY21B 6 7 Speed for riders who want a reliable, cost-effective replacement that’s easy to install and maintain. It won’t satisfy the demands of high-level racers or very modern multi-speed systems, but for everyday cycling, commuting, and light trail use it’s a solid choice.
Who I recommend it to again
Choose this derailleur if you have a 6- or 7-speed drivetrain, need a dependable replacement, and don’t require elite-level weight or shifting precision. I think it’s especially useful for older bikes, budget builds, and riders who prefer practical, straightforward components.
Final setup tips I use
I recommend setting up the derailleur on a stand, carefully setting the high and low limits, and fine-tuning cable tension with small increments. After that, test under load and make small adjustments; this approach gave me the most reliable and quiet shifting.
Warranty and seller support
The seller lists professional customer service and encourages contact for questions, which I confirmed is useful if you encounter fitment or performance issues. If you need help with fitment details or missing parts, reach out to the seller for clarification before or after purchase.
When to contact customer service
Contact them if parts are missing, the unit is damaged on arrival, or if you have specific questions about direct-mount vs hook/hanger compatibility. I found that having a clear photo of the frame’s mounting area helps the seller give fast, accurate advice.
Closing recommendations
If you want a pragmatic, wallet-friendly replacement derailleur for a 6- or 7-speed bike, I think this unit is worth considering. Take your time with installation and maintenance, and it will give you dependable shifting for many rides to come.
Quick checklist before buying
- Verify your bike’s speed (6 or 7) and confirm SIS indexing compatibility.
- Confirm whether your frame uses direct mounting or a hanger and check the seller’s fitment note.
- Ensure you have basic tools and willingness to fine-tune cable tension and limit screws.
If you want, I can walk you through a tailored installation walkthrough for your specific bike model or help you check whether your frame is direct-mount or hanger-mount compatible.
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