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Setting the correct chainline - SS
http://www.retrobike.co.uk/forum/viewtopic.php?f=41&t=216743

Author:  GT-Steve [ Mon Aug 20, 2012 1:04 pm ]
Post subject:  Setting the correct chainline - SS

I'm in the midst of building my first SS project, and I need to know how to set up, or achieve, the best chainline, to avoid the associated problems.

Anyone got any advice? OR a link to tech info on this little job?

Cheers

Author:  unkleGsif [ Mon Aug 20, 2012 1:10 pm ]
Post subject: 

Its not that difficult really, and nowhere near as many things to consider as when setting up geared systems.

If you are using a SS kit on a freehub, with the spacers that fit on the freehub, just shuffle them and the sprocket around to acheive the straightest chain with the chainwheel.

This is assuming a "magic gear" or verticle droupouts. If you have a tensioner, you might have to either adjust that to suite the position of the chain, or fiddle with the spacers a little more to get it lined up.

Chainwheel can be fitted either inside the cranks (middle ring) or outside (large ring) to get the best results


G

Author:  hollister [ Mon Aug 20, 2012 1:10 pm ]
Post subject: 

Is this for real?

Author:  unkleGsif [ Mon Aug 20, 2012 1:12 pm ]
Post subject: 

hollister wrote:
Is this for real?


:?: :!:


G

Author:  Jussa [ Mon Aug 20, 2012 1:13 pm ]
Post subject: 

With my TREK SS i just used the Mk1 Eyeball!!!! you can see it the chain is not straight. Having a selection of spacers for my rear sproket means you can at least try differenct combo's out till you get it spot on. :D

Author:  JamesM [ Mon Aug 20, 2012 1:30 pm ]
Post subject: 

You can do it by eye or measure from the centre of the seat tube to the teeth on the chainring and then make sure the rear sprocket is the same distance from the centre of the hub.

Author:  xerxes [ Mon Aug 20, 2012 1:56 pm ]
Post subject: 

Quote:
With my TREK SS i just used the Mk1 Eyeball!!!!


I have the newer MkII and that's even better, it comes with the "not walking into things" app. :P

Author:  Jussa [ Mon Aug 20, 2012 1:58 pm ]
Post subject: 

xerxes wrote:
Quote:
With my TREK SS i just used the Mk1 Eyeball!!!!


I have the newer MkII and that's even better, it comes with the "not walking into things" app. :P


I must up-grade, although my broken little toe has fully healed from walking into the Bed a few months ago. havig the Mk2 will prevent further mishaps........ ;)

Author:  danson67 [ Mon Aug 20, 2012 2:36 pm ]
Post subject: 

I run a long steel straightedge across the chainring and see how it lines up with the sprocket. Straighter the better, but don't worry about the odd few millimetres.

Actual chainline (relative to the centreline of the bike) makes very little difference.

There are too many combinations of chainring positions, chainlines, hub widths etc to be more definitive.

All the best,

Author:  oldave [ Mon Aug 20, 2012 4:40 pm ]
Post subject: 

"I run a long steel straightedge across the chainring and see how it lines up with the sprocket. Straighter the better, but don't worry about the odd few millimetres."

Precisely so. I built/converted many fixeds, where chainline is more important than single free. Mount the ring as far inboard as bottom bracket/frame allow, then the straight edge to indicate ideal placing of sprocket (it's nearly always easier to fine tune the rear than the front). Even with fixed, +/- 5mm is OK.

Author:  GT-Steve [ Mon Aug 20, 2012 5:33 pm ]
Post subject: 

Cheers fellas, 8)

The frame doesn't have horiz dropouts, and I'm gonna attempt without a tensioner as well. :shock: I owned a cannondale SS before (but didn't personally build it) and this was the same set-up without any problems of the chain jumping off, even when I was bouncing around at max cadence.. 8)

Author:  danson67 [ Mon Aug 20, 2012 5:39 pm ]
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You might be able to get away without a tensioner :D
Have a look at the Fix Me Up calculator first.

All the best,

Author:  suburbanreuben [ Mon Aug 20, 2012 8:54 pm ]
Post subject: 

A velosolo spacer kit is your chainline friend!

Author:  sic_nick [ Tue Aug 21, 2012 5:20 pm ]
Post subject: 

Check out post #7 for a very neat way to get your chainline spot on:

http://forums.mtbr.com/singlespeed/why-does-happen-736137.html#post8417452

Author:  danson67 [ Tue Aug 21, 2012 6:06 pm ]
Post subject: 

That's a smart method...like it :D

Just make sure of the rear hub/dropout width and halve it for the length of the 'skewer' indicator.
Should be OK if it's a MTB cassette conversion, but dedicated singlespeed hubs can be different.
It's not always 135mm, could be 120, 126, 130 or 135mm, or even bigger these days. :twisted:

All the best,

Author:  JamesM [ Tue Aug 21, 2012 9:47 pm ]
Post subject: 

sic_nick wrote:
Check out post #7 for a very neat way to get your chainline spot on:

http://forums.mtbr.com/singlespeed/why-does-happen-736137.html#post8417452


JamesM wrote:
measure from the centre of the seat tube to the teeth on the chainring and then make sure the rear sprocket is the same distance from the centre of the hub.


:wink:

Author:  danson67 [ Wed Aug 22, 2012 8:37 am ]
Post subject: 

Quote:
measure from the centre of the seat tube to the teeth on the chainring and then make sure the rear sprocket is the same distance from the centre of the hub. :wink:

True, James, it is the same thing really, but it's not easy to find the centre of the hubshell, or to measure from it avoiding the flanges and spokes. The method above is extra smart as it uses only one measurement and the dropout face as a fixed and firm reference.

I still prefer a bit of maths, or a straightedge myself :wink:

All the best,

Author:  Woz [ Wed Aug 22, 2012 11:56 am ]
Post subject: 

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.

Author:  oldave [ Wed Aug 22, 2012 12:03 pm ]
Post subject: 

Don't some folk like to make life difficult! A straight edge really does do the job!

Author:  JamesM [ Thu Aug 23, 2012 7:58 pm ]
Post subject: 

If you have a straight edge long enough!!!

Author:  bm0p700f [ Thu Aug 23, 2012 9:31 pm ]
Post subject: 

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.

Author:  suburbanreuben [ Thu Aug 23, 2012 9:48 pm ]
Post subject: 

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!

Author:  suburbanreuben [ Thu Aug 23, 2012 9:49 pm ]
Post subject: 

oldave wrote:
Don't some folk like to make life difficult! A straight edge really does do the job!


It certainly does! :wink:

Author:  JamesM [ Thu Aug 23, 2012 10:14 pm ]
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If you have one!!! :lol:

Author:  oldave [ Fri Aug 24, 2012 9:33 am ]
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A broom handle will do if nowt else to hand!

Author:  JamesM [ Fri Aug 24, 2012 10:01 am ]
Post subject: 

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:

Author:  Dead Rats [ Mon Aug 27, 2012 10:27 am ]
Post subject: 

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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