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I changed the rear wheel on my child's bicycle today. Once I was done and put it back together, the chain is inexplicably longer; there is a lot of slack.

How did this happen and how do I resolve it?

enter image description here

Edit: looking at the photo, I think I may have to move the rear axle backwards.

Edit x2: Photo of successful results, following my suspicions and Blam's answer.

enter image description here

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1  
Thats not a nice looking brake cable. –  Batman Jun 16 at 6:42
    
The frayed end? Came unraveled a bit when I was loosening it so I could take the wheel out. I twisted it a bit more into itself after the photo was taken. –  JoshDM Jun 16 at 14:27

2 Answers 2

up vote 7 down vote accepted

Move the wheel back in the dropout. Equal on both sides. Go for 1/2 to 1 inch of play in the chain.

And that valve stem might be leaning a bit. Probably not enough to matter but ideally it is straight.

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Amateur here. The dropout holds the rear axle? –  JoshDM Jun 15 at 17:10
    
Yes the dropout holds the rear axle. –  Blam Jun 15 at 17:11
2  
Like those "spot the difference" photographs! –  PeteH Jun 15 at 17:55
3  
Check the position of the brake pads as they seem to 'bite' into the tyre. –  Carel Jun 15 at 18:45
1  
The brake cable looks frayed. Replace & put on a proper end-cap. May cause nasty wounds! –  Carel Jun 16 at 7:14

It seems you're missing the 'tensioners'. They go on each side of the axle with the cap hooked on the end of the dropout. You can then adjust the tension of the chain by fastening or loosening the nut on the end (first loosen the axle nut, of course).

Chain tensioners by 1-1111
Chain tensioners by 1-1111.

Not all bikes have these, though.

‡: I couldn't find the correct translation, but their Dutch name would translate to "chain tensioners".


Additionally, you usually can see where the axle used to be by the markings on the dropout.

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