Chainline - measure vs visual?

Hi, I recently watched that video of Bob's Garage where the guy works out chainline by doing lots of measurements.

Surely it's just as effective to look at the chain on the rear cog and observe the cog's teeth as the chain goes round. On the conversion I'm doing it's possible to see that chainline is out by 1-2mm - not much - but probably enough to warrant a spacer on the rear hub.

why not just measure it? it takes 30 secs and is much more accurate.

Just post a pic on here. I'm sure you'll soon be told...

;-/

its like asking why use a torque wrench, when a spanner or allen key will do?

I have a bionic eye like Steve. I could measure your chainline just by looking at it.

I won't, as I have slow motion criminals to catch.

diggerdiggerdiggerdiggerdigger

Vernier calipers for the (anal retentive) win.

Vernier calipers for the (anal retentive) win.

Vernier calliper is for a quick and dirty estimate; it assumes that the frame alignment is precise, i.e. that a plane orthogonal to the BB spindle and coplanar with the centreline of the seat tube will precisely bisect the rear wheel spindle axis. Since this is unlikely to be the case, it is necessary to set up the bicycle on a surface plate and make careful measurements with a dial gauge to check that the pitch circles of the chain ring and sprocket are precisely coplanar.

Geek.

Mmmm - I could spend more than half a day applying that calipers method and be none the wiser!!! Just gonna go on the visual...like I described!

Ask for help.

ignore help.

Job done.

It's like Paul michel all over again.

There is a quick and accurate method; just clamp a straight edge to the chain ring and see if it hits the sprocket. If it doesn't, move the sprocket out a bit. If it presses on the sprocket, move the chain ring out a bit, etc.

Ideally, the straight edge should make a chord to the chain ring as large as possible without interfering with the chain ring bolts and spider, and of course you need to avoid the stays. As it turns out, a 1U 19" face plate is a pretty good tool for this job, the thicker the better as it makes it easier to clamp. A couple of small G-clamps are all you need to hold it in place. You may need to make compensating adjustments if the ring and sprocket thicknesses are not the same, e.g. Goldtec rings are cut from 4mm plate, so the tooth centreline is 2mm inboard of the outer face, not the 1/16" you would expect.

It's like Paul michel all over again.

you may have a point...

there's a lotta weapons out there. Watch out folks.

That picture is giving me the fucking creeps. I feel like he/she/the child/the dwarf is peering right into my soul and feeling pretty disappointed with what's there.

Dunno why but that baby makes me instantly think of Ray Winstone!

I've got problems with chainline on my Kona MTB and I believe I now have the solution - visual! Maybe a straight edge at a push. I'll see if IT Manager has the recommended 1U 19" face plate :-)