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PostPosted: Thu Aug 23, 2012 9:31 pm 
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I do it by eye. As for getting magic gear you have a chain ring and a casette. Wrap you chain around and bring together. Note how many 1/4" you are from joining. ever tooth you add or take away from the front or rear adds/takes away 1/4" from the length of chain needed.

So if a 32:16T is 1/2" from joing then a 34:16T would join or a 36:18" would join with a extra 1" of chain.


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PostPosted: Thu Aug 23, 2012 9:48 pm 
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Location: Fircombe.
Woz wrote:
I measure the front chain line by putting an engineers metal ruler pushed next to the seat-tube over the chain ring, read it off then add half of the seat-tube diameter. It's more precise and less fiddly as you don't need to guess where is the center of the seat-tube.

Then take the above number, subtract it from half of the rear axle OLN distance and you have the required rear matching chain-line measured from the center of rear sprocket to the RH axle / inside drop-out.

Taller sprocket teeth are far more important than a chain line within +/- 1mm.
No they're not!


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PostPosted: Thu Aug 23, 2012 9:49 pm 
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oldave wrote:
Don't some folk like to make life difficult! A straight edge really does do the job!


It certainly does! :wink:


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PostPosted: Thu Aug 23, 2012 10:14 pm 
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Location: UK Southwest
If you have one!!! :lol:


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PostPosted: Fri Aug 24, 2012 9:33 am 
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Location: Nottingham
A broom handle will do if nowt else to hand!


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PostPosted: Fri Aug 24, 2012 10:01 am 
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It could easily be a few mm out over the required length. Really you need a proper 1/2m straight edge which I would guess alot of people (including myself) don't have.

So if you have a straight edge but no caliper then use the straight edge method. If you have a caliper but no straight edge, measure it. If you have neither get yourself a cocktail stick and use the method in that link posted earlier on. :wink:


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PostPosted: Mon Aug 27, 2012 10:27 am 
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Location: Manchester, UK
I wince whenever I read the terms 'magic gear' / 'not using a tensioner' in a thread.

Respect to anyone who is doing so, but I think it's daft. The only way to get correct tension ALL THE TIME with vertical d/outs is with a strong sprung tensioner.

Rings are often not 100% perfectly round for starters, and magic gears only 'work' in a small range of ratios. Plus aren't you straining the drivetrain?

And don't get me started on that mech hanger just dangling there with nothing in it! :lol:

I do however like that chainline checking method, from the Mtbr forum :D


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