Bmx advice

[scottduffy]

Guy's i got my son a nice GT race bmx and built it up for him. Sticking out of the back of the frame at the rear is another smallish bolt (one at each side) which tightens with an allen key. I haven't a clue what purpose they serve. Does anyone know? I am looking and don't see what it could affect apart from maybe centering the rear wheel. I've added a picture of it.

 

[Nod]

Chain tensioner. Read the instructions and it should become clear.

 

[scottduffy]

The instructions unfortunately are part of the problem. They're not bike specific and every page is describing 4 different bearing sets, double and single walled rims etc so i had no idea which ones was relevant to my bike. Thanks though. I'll leave them as they are and look them up now.

 

[Nod]

I feel your pain!

Basically, get the rear wheel aligned as well as you can - look along both sides of the tyre and get the same amount of headstock visible. Make sure the chain doesn't get tight while you're doing that. Have a look for any index marks by the adjusters - they might be accurate!
Now, find the tight spot of the chain by slowly turning the wheel while your finger is gently pressing against the outside of the chain, half way between the sprockets.
Loosen the lock nuts on the adjusters and finger tighten the adjuster bolts.
Going about 1/4 turn each time on each side, adjust the chain so there's a little slack in the chain at the tight point.
Once you're happy with the chain tension and alignment, tighten the axle nuts, check the tension again then (if still happy) tighten the lock nuts on the adjusters while holding the adjusters themselves to stop them turning.

Or, take it to a decent bike shop and pay them a few quid to set the bike up properly!

 

[scottduffy]

I watched a short video so I'll give it a go. To be honest when i got the bike yesterday i thought the back wheel wasn't centered properly so when my son goes to school tomorrow I'll have a go at sorting it.

 

[Nod]

It's harder to describe and read than it is to do in practice.

 

[ancient_mariner]

You find the same kind of adjusters on motorcycles - operation *should* be obvious. Just don't forget to loosen the nuts/bolts holding the axel in the frame ends before adjusting and then tighten them afterwards.

 

[scottduffy]

It's so strange to see a bike that looks smaller than his wee mountain bike. I must say though it looks very nice and the reviews are excellent so fingers crossed he enjoys it. It's light as a feather which is what i was after. According to GT's website the bike is for riders up to 5' 4" so he's got plenty of growing to do.