Greeting everyone. Newbie problems, inquiry on purchases.

[CGosnell]

Hi all, hope all are enjoying their Sunday. I'll get right to it. I would be out riding right now but this happened 2 days ago.

derailleur1.jpg

• CGosnell
• Mar 24, 2019

What's left of my derailleur, freewheel, and chain.

It happened while riding slow and no one or thing was hurt, other than the components.
This is a Walmart $149 bicycle (yay cheap!) with a BBS-02 (speed limiter removed in programming) @ 52v and a 52T chainring. Yes, I know the chainring is too large really but for where I was originally riding it (flat) it worked great (I've hit 39.3 mph on it). Anyway, I need a new freewheel, chain, and derailleur. Oh, and I also bent the axle. The original was a Shimano MF-TZ21 I believe, not sure what the derailleur was as it's completely destroyed.
My questions are:
1) Would the Shimano MF-TZ31 14-34T suffice with the 52T chainring? I'd like the widest range possible as I will be hitting trails more often as my confidence builds back up (I was in a collision with a car in 2017 and have been skittish of riding).
2) The original chain in the lowest gear was stretched quite tight (I believe this is why the derailleur decided to throw itself into the spinning rim (thankfully, the rim seems OK), would an SRAM PC 870 P-link chain (114 links) work with the suggested gear set-up (length)?
3) Which derailleur should I get for the mentioned set? I need a claw mount as the frame doesn't have the mount. I see a long cage is mentioned for that freewheel use (especially given the large chainring). Wouldn't a long cage be in danger of getting beat up on trails? (see chain tension concern)
The factory components held up pretty well for 418 miles.
I am working with a shoestring budget, hence the MF-TZ31.
Advice, help, laughter. Anything? I do not drive and the bicycle is my only mode of transportation.
Thanks all!

 

[hemi.rokingi]

Are you able to fit a smaller chainring? That might make the rest of the decisions a bit simpler.

 

[mark1a]

You'd need to know the capacity of your replacement rear mech. For example, if you have a 14-34 for a rear cassette and then front chainrings of 52-36 - subtract the smallest from the largest for both front and rear, and add the results together. In this case, 52-36=16, 34-14=20, 16+20=36. Therefore you'd need a rear derailleur with a capacity of 36 or more.

 

[CGosnell]

Are you able to fit a smaller chainring? That might make the rest of the decisions a bit simpler.

Yes, I do plan on getting a smaller chainring at some point but not right now.

 

[CGosnell]

You'd need to know the capacity of your replacement rear mech. For example, if you have a 14-34 for a rear cassette and then front chainrings of 52-36 - subtract the smallest from the largest for both front and rear, and add the results together. In this case, 52-36=16, 34-14=20, 16+20=36. Therefore you'd need a rear derailleur with a capacity of 36 or more.

Ok, thanks. I will work from that number which on my bike would be 52-52=0 34-14=20 So I would need a derailleur capacity of 20. I think I will buy the freewheel and derailleur, install them then take the bike to a shop to have the chain installed to ensure that it is the correct length and to have it all adjusted properly. Also to go over the rest of the bike, I am actually surprised the kit was easily installed and worked fine for 400+ miles on that bike. I know I am stressing the bike components far past what they were designed for.