Getting chainline straight on a fixed wheel bike

[JonMcD]

Do chain tugs work on conventional sloping dropouts? I thought they only worked on rear facing ones.

I have taken a chance by ordering "Alloy BMX Chain Adjusters Tensioners" on eBay that look identical to the ones in this thread on LFGSS (first picture). If they don't work there is always the DIY option further down the LFGSS thread.

[robgul]

I experimented with the "star shaped" gizmos that are in the pic down the LFGSS thread .... they have a raised bit on the inside face to locate them in rear-facing dropouts - I ground them off and while I was at ground the star-shaped points off too .. just to make them look tidier (with a quick coat of spray paint)

Yes. they do work on forward facing dropouts but I'm note sure they make a difference - I took them off and resorted to another trick to get the chain tensions : bike upside down, wedge a bit of timber (tile batten is good) between the tyre and the back of the seat tube to push the wheel back and tension the chain (make sure wheel is centred in the stays, tighten wheel nuts - remove wood - turn bike back onto the wheels - tighten nuts again with long 15mm spanner (stand on it to get it REALLY tight!)

Rob

[morzov]

"track" hubs are 120mm OLN. That frame is 126 or 130mm OLN?

Surly do singlespeed hubs for various dropout widths...look here diligently and you will find the distance from centre to flange varies with the OLN..http://surlybikes.com/info_hole/spew/spew_spoke_calculation_info

Somebody, somewhere, will know the centreline to chainline dimension of track/road/mountain/1960's/1970's/1980's/etc. bikes, but it isn't me, and I can't possibly know if your bike has a "standard" chainline anyway..

The wheelbuilder can't see your bike when he builds your wheels...the observation "I can't quite see it from here, can you hold it a bit nearer the phone"....is not always received in the spirit in which it is offered!

Bottom line....I suggest if you are wanting your chainline "spot on" you buy the hub and sort out the chainline before you get the wheel built.

No I have got a track hub but it's got spacers so that it does fit my frame which I think is circa 1992 - so 126mm OLN.

The method I used to calculate was taken from a Sheldon Brown article:

-With wheels in dropouts measure distance from inside of dropouts to centre of sprocket
-take half of the dropout measurement and subtract the dropout-to-sprocket number and you have the centreline-to sprocket measurement
-upfront its the centreline of the bike to chainring measurement

So I calculated 126mm between dropouts and 17mm from inside of dropouts to sprocket

63-17 = 46mm = Centreline to sprocket dimension

Centreline to inner chainring dimension (the one I'm using) = 50mm

So as I say chainring is about 4mm outboard of sprocket or 1/6in in old money which when you think about it isn't that much!

I

[531colin]

You have a 120mm hub.
It has spacers to take it up to 126mm.....ie. 3mm each side...these space the axle, not the sprocket.
So the spacers take the sprocket 3mm. further from the dropout than the "un-spaced" hub ....which is just about the chainline "error"...this may be pure co-incidence, I don't know.
If the hub has conventional cup and cone bearings, and you only needed it single-sided (ie not flip-flop) you could improve the chainline by re-arranging the spacers, removing them from the driveside and putting them the other side....the rim would need re-centering, now its built.
Its quite possible that a Surly 130mm hub would "spring" into your 126mm dropouts, and place both sprockets (on a flip-flop) 2mm further out than the chainwheel.

[PW]

Oh bliss. There's an old sports frame I'm setting up as a winter fix just to say I've ridden one. Selection of c/sets and B/B units in the scrap bucket, 135mm frame, 126mm nutted Campag screw on hub (it'll have 2 brakes and a B/B lockring!). As soon as I've got the tourer running and some spokes from the brain dead down the road I'll start playing with the wheel. Oh delight!

[531colin]

Oh bliss. There's an old sports frame I'm setting up as a winter fix just to say I've ridden one. Selection of c/sets and B/B units in the scrap bucket, 135mm frame, 126mm nutted Campag screw on hub (it'll have 2 brakes and a B/B lockring!). As soon as I've got the tourer running and some spokes from the brain dead down the road I'll start playing with the wheel. Oh delight!

Well, look on the bright side (is it time for LOTBS?) at least you will only have a single-sided hub to worry about, thats just one chainline!
I'm guessing it will need spacers removed from the block side and put the other side....I would sort out the chain line before you buy spokes, you could end up in the novel position of having a wheel dished the "wrong" way!
Is the axle long enough to get a few threads in the nuts? I guess you could spring the frame in a bit, that's different too!

[Ribblehead]

I have heard of an adjustable BB that allows you to alter the position of the chainset. Not sure if they were any good or are still available but I can recall they were a bit fiddly to set up.

This product is mentioned on the Sheldon Brown website, scroll down until you get to 'Phil Wood Bottom Brackets'

http://sheldonbrown.com/chainline.html

In my humble opinion, the maximum allowable mis-alignment for fixed should be less than 2mm, the consequences of unshipping a chain at over 120rpm don't bear thinking about. At low mis-alignment, efficiency will be maximised and chain and sprocket life will be increased due to less rubbing. Also, some singlespeed/fixed chains are intolerant of imperfect chainlines and may be weakened.

Currently I have a flip-flop and my fixed mis-alignment is ~1mm and my free mis-alignment is ~2mm. This is best as I have the least misalignment on the side which will cause me most grief if something were to go wrong.

Please let us know how you get on!


Edit: Forgot so say, correct chain tension is as important as a good chainline. Get someone experienced to check it out before you throw yourself down a hill with the pedals whirring.

[Ribblehead]

I have heard of an adjustable BB that allows you to alter the position of the chainset. Not sure if they were any good or are still available but I can recall they were a bit fiddly to set up.

See this page:

http://www.philwood.com/products/bbhome.php

and section 2.E. here:

http://www.philwood.com/philpdfs/crankbearinginstallationguide.pdf

[PW]

Thanks Colin I think the solid axle has enough spare length to space it out. I'll play with it in the frame before I start wheelbuilding. Reverse dishing wasn't on the agenda but if I have to it's only 2 turns on the short side before I start tensioning.
A mate of mine had a saying, - "A man under stress needs a good daft hobby".