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I own Firefox Rapide 21s, which has Acera 7s(14-28t) groupset are rear and Tourney 3s(28-38-48t) groupset at front.

In a recent accident, the rear derailleur took some impact and is bent now, it doesn't latch on to 7th &1st gear. I went to a mechanic he applied some pressure to make it straight, he said it(method) could potentially make the derailleur straight, and I don't want to spend money in getting a new one.

While coming back home, I tried to shift up to 1st gear to see what happens -- it dug into one of the spokes, locking the tyre, making me fall. Now that spoke is bent and has become loose.

However, the real question is: Now, I don't like the method he has proposed to straighten it. Hence, I have decided to remove all the gears and make it a single speed. My focus always has been higher speed, so I'm thinking of getting 53t×11t(chainring×sprocket). But I'm also thinking - the ratio that setup makes might be a little bit too much for me in all circumstances. Therefore, I was thinking of fitting a double crankset up front(possibly 34-50t or 39-53t) and single sprocket(possibly 12t or 14t, respectively). Or is that even possible?

I goolged and looked at most places, but could find any answer.

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    The issue that led to your accident was not righting the bent derailleur. Much rather it was failing to set the limit screw that prevents the derailleur from pushing the chain over the largest sprocket. Moreover, if the derailleur is unreliable a protector disc needs to be between spokes and cassette. It is shoddy work, that ought have been noticed by the mechanic right away when testing the bike. – gschenk Mar 31 '18 at 20:04
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    Yeah, bike snobs turn up their noses at spoke protectors, but they can save your butt when a derailer is misadjusted or gets bent. – Daniel R Hicks Mar 31 '18 at 21:46
  • As a test, try setting your bike in those gears only and see how it feels to ride just those combinations. 53:11 would be horrible even on a still-wind day, would not recommend. – Criggie Apr 1 '18 at 0:08
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    @Criggie no, no problems before that accident. The hanger got bent- has scratches on it and the derailleur too. – Rajesh Kharat Apr 1 '18 at 16:31
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    They derailleur hanger is still badly bent or not properly screwed to the frame. One may see in the first figure that it is not flat at the drop out. The derailleur needs to point down nearly perpendicular to the wheel's axis. – gschenk Apr 1 '18 at 16:54
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The derailleur itself was possibly not bent. It was most likely the derailleur hanger, which is meant to bend to save the derailleur from damage.

I would not use that mechanic again as he failed to set your bike up correctly ultimately causing more damage and putting you in danger of a crash - or - if in fact you tried to save money by demanding only the minimum fix, you just learned a lesson about false economy.

You seem to want to convert the bike to single speed to avoid paying for a new derailleur, but the conversion will certainly cost more! You mentioned getting a double crank to replace your triple, that is not an insignificant cost. You will also need a chain tensioner and single speed freewheel.

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  • Yes, I did learn a lesson. By the way, I just added images to the question, check them out, thanks. – Rajesh Kharat Apr 1 '18 at 17:17
  • Classic bent hanger. They can be straightened once or twice. Get a descent mechanic to straighten it and readjust the derailleur (and fix your spoke). – Argenti Apparatus Apr 1 '18 at 18:27
  • In the photo, looks like someone used the derailleur protector as a lever and has buggered it all up. Time to get a new mechanic! – Criggie Apr 1 '18 at 22:59
  • Is the pic before or after the 'fix'? – Argenti Apparatus Apr 1 '18 at 23:17
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Without a rear derailleur one cannot switch gear on the front chainring. The length of the chain would differ between chain rings. The derailleur compensates this by running the chain a longer path that may be shortened by moving the derailleur arm. It also tensions the chain due to its spring, which hold the chain on the chainring.

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  • Yes, that will have to be put in place to compensate the chain slack. But can we get this done? – Rajesh Kharat Mar 31 '18 at 19:49
  • If you need a rear derailleur anyway, you simply may use a cassette on the rear. Having a derailleur and only one big wouldn't free you from adjusting the derailleur properly. – gschenk Mar 31 '18 at 19:59
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    You could try a chain tensioner rather than a derailleur, not sure if you could take up that much chain slack with one though. – mattnz Mar 31 '18 at 21:16
  • @mattnz chain tensioners that allow such length difference might also have trouble with lateral movement of the chain. – gschenk Mar 31 '18 at 21:27
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Your proposal makes little sense.

  • Instead of just replacing the rear derailleur, you’re proposing to replace the cassette and chainrings, which may also require new cranks, giving a setup that will still need a rear derailleur anyway. So you’ll be spending much more money to get a less capable bike.

  • 34x12 is a reasonable ratio for a single-speed bike but 50x12 is a pretty high ratio that I only end up using when going down decent hills.

  • I suspect that your suggested setup with only one gear at the rear will require very precise adjustment to avoid the chain falling off in exactly the way it’s already done. It’s hard to see this being reliable.

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  • Recently, I was making myself used to the highest setting -> 48×14, and after 2 couple of days, I felt it was short. I would at least want a 48×12 or 50×12. – Rajesh Kharat Apr 1 '18 at 17:14
  • I'll contemplate on the points you have put forth, thank you! – Rajesh Kharat Apr 1 '18 at 17:15
  • I agree that your idea can end up costing more than a new derailleur. On the other hand I have ridden a lot of time a Peugeot with a broken rear derailleur that only did the chain tensioning work, so I was using mainly 52-16 and 42-16 , and I must say the simple hard/easy gearing was very very effective, and I have asked myself same question as you. Too expensive. Also, work on your cadence because a 48x14 can give you plenty of speed, and is by no means an easy gearing, you would have a very hard time climbing with it. – gaurwraith Apr 1 '18 at 20:28

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