My sons bike has a crappy old 5 speed falcon rear derailleur and grip shift. The bike has 20” wheels.

The derailleur is a pos from day one and has never worked good, and I’ve adjust it for hours and it’s just a poor quality part. (And old)

My other son has a 6 speed shimano unit on his bike and it works great. I want to get something like that to replace the 5 speed on my other sons bike so his shifts and works nice as well.

my question is how and what do I order for a derailleur, cog set, shifter and chain? I’ve heard a 5-6 speed cog set are identical width and should interchange just fine, but can I use a shimano derailleur with say a sram grip shift?

at what point do the cog sets get to wide to work on a smaller kids bike? (Example can I use 7 speed cog set?). Looks like there is approx 130mm between the dropouts. Is this standard? It’s a steel frame so I could bend it out a bit if needed.

thank you!!

5 speed chain ok with 6 speed?

A 6-speed setup is not necessarily better quality than a 5-speed. It just goes to 6. Quality is a matter entirely unrelated to how many cogs it has.

The shift quality may have as much to do with the shifter as the derailleur. It has nothing directly to do with how many clicks it has.

See where I'm going with this?

Certain SRAM shifters work with standard spacing and Shimano derailleurs. The gaps between the cogs are the same for 5s and 6s standard freewheels. But some shifters have more clicks.
A 6s freewheel is wider than a 5s of course, so you will probably have to respace the rear axle to accommodate the wider freewheel. Then you will have to re-center the rim.
Not needed. 130mm will certainly accept a 7s freewheel. But you would have to respace the rear axle even more because the 7s freewheel is wider still than the 6s.

So, yes, 130mm will accept anything from 7s to 11s rear hubs, but they would be kind of a silly indulgence on such a bike.

Thanks for the replies

sorry did not mean that 5 speed was worse or better than 6 speed only that I though 5 speed was old school and I’ve not seen it used much now-a-days.

ive tried replacing the shifter as well with a quality sram unit and no luck.

knowing what sram shifters will work and what don’t is what I’m not sure. How do I know? Something to do with ratio???

respacing the rear wheel is something I never thought of, not have I had to do that before so better to leave it alone. Just curious is it difficult to do?

I’m going to try and find a new 5 speed derailleur, cog set (as I’d imagine the hyperglide style is newer and easier to move between gears) as well as a new chain. This cogset is old anyhow and looks abit warm.

thanks for the info!!

Sorry I meant that bringing a Walmart bike to a pro bike shop will cost more to fix than the bike is worth.

ive relaxed the shifter cable and all the housing with new. I’ve also tried to replace the shifter with a sram unit and spent an hour trying to get it to index correctly. As the previous poster suggested the falcon units are not unheard of to index correctly. So I’ve tried the simple (cheap) stuff.

I’ve actually got an old shimano xt unit (9 speed) floating around that I might have a go with but could I use a derailleur that was 9 speed with index shifters (index shifter is long gone) with a 5 speed and grip shift??

so those worried about cost fear not! The xt derailleur I have is free and has been sitting in a box for years