@Maoira (I'm not an REI employee, but...) Probably not since the extra cog(s) add space, and the dropouts on the frame that the wheel goes into are a fixed distance, but even if you could you'd have to replace the shifters for sure and possibly the derailleur and a longer chain as well, it starts getting more reasonable to just wait until sizing up to a 24" bike for more gear range. You could try to find a different 6 speed cog set with more range, but there's only so far you can go with that before making the jumps between gears more awkward and clunky. If you do ever try that, it looks like it's actually a freewheel and not a cassette: the difference is minor on the outside, but major on the inside and how it attaches to the wheel hub, making the two system incompatible. And it still might need a different derailleur and chain to accommodate any larger cogs without over-stressing the chain.
I guess I should’ve rephrased the question to ask what the free hub was compatible with more than a 6 speed cassette.
This bike will go through at least 2 more kiddos, so it’s reasonable to think that St some point I’ll need to update. Just wondering if I need to upgrade the free hub if I want to go above 6 speeds.
@Maoira That's part of what I was trying to say, but maybe I was unclear. I also did some additional digging.
Yeah it might actually be possible to change to a 7-speed, but because of having to change other parts besides the hub too, it's probably more money and headache than is worth it. If it were me I'd just replace with another 6-speed if it gets worn out as it moves through the kids (changing the chain regularly will of course help it last longer).
The product page for the Rev20 lists the rear cogs as "Shimano Tourney, 14-28, 6-speed", and based on this and images, it seems like it is this https://bike.shimano.com/en-EU/product/component/tourney/MF-TZ500-6.html on Shimano's site. This is a freewheel, which means there is no freehub at all, and no cassette of any speed is compatible, they're two totally separate ways of implementing rear cogs. I'm just going off these webpages though, @REI-JimL and @REI-AlyS suggestion of email@example.com could definitely tell you for sure if this is correct.
There are freewheels that come in 7 speed (it's rarer to find 8 speed freewheels), and they would probably thread onto the wheel just fine as it's a standard threading. After doing a little more research, there actually probably is a good chance too that it would fit back into the frame, since the spacing between cogs on a 7-speed is often 0.5mm smaller than a 6-speed. Again, firstname.lastname@example.org could give better assurance for whether any specific freewheel would fit in the frame and any other compatibility issues. Would still need a new rear shifter and rear derailleur though to be able to access the 7th gear, that's unavoidable.
Lastly, would you want 7 speeds for your kids to go faster in a harder gear, or to climb hills easier in a lower gear? Because you're unlikely to find much for going faster: the highest gears are those with the fewest teeth (in back anyways), and those rarely go below 13 or 14 teeth on freewheels. Going up to 7 speeds is much more likely to give you an extra lower gear for climbing, with your high gear unchanged. So depending on what you want, "upgrading" may not even get the result you're after.
A lot of information, I know, but I hope it helps!
The end goal would be to get a higher climbing gear. Which would probably need a rear derailleur upgrade anyway. Possibly getting <36 big ring. But I’m not sure that’s possible.
@Maoira Doesn't look like 36 is possible, but I am actually a little shocked it looks like there's some that go up to 34, even in 6-speed. There's an absolute monster of a shift gap from the 34T to the next lowest gear, but evidently they make them... Shimano's MF-TZ30 (6-speed) and MF-TZ500-7 (7-speed) are a couple, with what they're calling their "MegaRange technology" and I've found some from Dimension as well (also 14-34T both 6 and 7). So if you really want to go for it with new derailleur etc, it's looking more and more like you could in principle. I don't see any freewheels on REI's site, you'd have to research where else you could get them if you go that route. Going up to 34T, I do have to wonder though with a bigger derailleur how much ground clearance would be reduced, if it would get smacked around by rocks or curbs easier.
Another possible way could be switching out the front chainring for less teeth? Kind of a nuclear option since it would kill the higher gears too, but it's there...
Yeah I was thinking the front chain ring cause that I believe is a 36? I was wondering if I can get down to a 32 or even a 28. It would be less moving parts but still will get the climbing gears I want for the little one.
Hey there @Maoira!
Thanks for reaching out to the Community! I see you already received some advice from one of our community members. I wanted to just let you know that we do have certified bike technicians available to help you as well! They can be reached via email at email@example.com.
I’ll also tag a few of our cycling experts to see if they have additional advice for you that may prove helpful!
Thanks again for being a part of the Community!
Hello @Maoira thanks for the question, and sorry about the late reply! I did some research and, while you can most likely get a 6/7/8 speed cassette on your rear freehub (these speeds all share the same chain width and spacing), you would need to change the right rear shifter and rear derailleur, as both of these are only 6 speed compatible. Shimano does make 7 and 8 speed options. As @TomV said though, you may also need to get a new, longer chain and check for other compatibility issues.
If you are interested in upgrading to a wider gear range, I would second @REI-AlyS' idea of contacting firstname.lastname@example.org to speak directly with one of our technicians who can guide you to the right parts and even a local REI shop that could get you an idea of price and timeline.
Hope this helps!
"...you would need to change the right rear shifter and rear derailleur, as both of these are only 6 speed compatible."
Aww, was expecting it to be fully customizable.