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I'm a novice to the cycling world and am wanting to learn to do my own maintenance, so I'm quite unsure of a few things.

More specifically, I have a Dahon Eco C7 foldable bike that I got used and was neglected some. The freewheel is fairly rusted and I want to replace it. The current rusted freewheel is a Shimano Tourney MF-TZ21, but I can't find many places that still carry this, so I suspect it's no longer in-production. I did however find the Shimano Tourney MF-TZ510-7, which has the same number of sprockets and same number of teeth. I suspect it's the successor to the MF-TZ21, but don't know how to be certain.

I will likely also need to replace the derailleur and chain as they are both also showing signs of rust. The chain ring seems to be okay though.

My main question, in short is, is the MF-TZ510-7 a compatible replacement to the MF-TZ21?

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    Those products are freewheels, not cassettes. Your bike can not use a cassette. A cassette is just a collection of cogs that you put on a freehub that is integrated into a wheel hub. A freewheel is screwed onto the hub and contains the freewheeling mechanism itself.
    – Vladimir F Героям слава
    Commented Sep 30, 2023 at 9:33
  • Are you considering the Megarange type or do you just want to consider compatibility when keeping the gear range? When changing the range you must check also the derailleur specs and adjust the chain length.
    – Vladimir F Героям слава
    Commented Sep 30, 2023 at 9:40
  • Right now I am only considering compatibility, but am open to advice on upgrades. I will likely have to replace the derailleur as well, so it's not a bad time for an upgrade. Regarding your first comment, I apologize for using the wrong terminology. The Dahon website called it a cassette/freewheel, so I thought they were the same.
    – Iceape
    Commented Sep 30, 2023 at 9:52
  • But that is about compatibility. If you change the sizes of the individual cogs it may or may not be compatible. The products you linked come in several variants and not all of them have to be compatible, that's why I asked for clarifications. We have to say which of them you are considering and with which derailleur.
    – Vladimir F Героям слава
    Commented Sep 30, 2023 at 9:54
  • Sorry, I didn't realize the products I posted had different variants. For the MF-TZ510-7, you are referring to the 14-28T and 14-34T variants? The freewheel currently on the bike is a 14-28T. I honestly don't understand what the difference would feel like between the two.
    – Iceape
    Commented Sep 30, 2023 at 10:08

2 Answers 2

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Yes, all freewheels from major brands that are 7 speed and with the same gear range should be compatible. All recent ones should use the ISO threading and hence it wil be possible to put them on. They all have the same gap between the cogs. They should also mostly use the same frewheel tool for loosening. Some non-Shimano ones may not have the HG tooth ramps for easier shifting, but they are not essential.

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  • Great to know. Thank you for the useful information!
    – Iceape
    Commented Sep 30, 2023 at 10:49
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Nice bike! Yes, as long as the fitment between the freewheel and the hub on your bike's rear wheel is the same, the unit is interchangeable.

You need the same number of cogs as the old one, because that matches the shifter on the handlebars.

The most common range found will be 14 teeth on the small, and 28 on the largest gear, with some gradual increase in tooth count across the cogs. Depending on how you ride and what gears you find comfortable, it may suit you to search out one with more teeth on the largest cog.

Sadly 14 tooth is the smallest toothcount size for a freewheel, so if you find yourself running out of gears when going fast, not a lot can be done cheaply.

On the other end, a 30 or 32 tooth big cog can help with hill climbing. You'll likely need to size your new chain one or two links longer, and there's a chance the rear derailleur may need some twiddling to get it right.

I have a similar bike, which started life as a 1x7 gear setup with a freewheel same as yours.

Now its a 3x9 based on a cassette, however this required rebuilding the rear wheel onto a different hub, a cassette, new rear derailler and handlebar shifter. I also had to mount a front derailleur and shifter, and fit a triple crankset. Not something I'd do again, though low-low gear is only 15 gear-inches which can be good for towing a heavy bike trailer, very slowly.

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