apg

Anyone have any simple idea on how to measure for chainline? I'm on a track bike and I'm wondering what size spindle I need in a new BB. I think I've destroyed my old one this winter riding a lot everyday in NYC in the snow and salt and ice.

I know my drop outs have 118mm between them, and the hub and the fixed rear cog is 97mm.

I guess I should take off the cranks and just measure the existing spindle right?

apg

Using the formula below my front is 42.5mm and the rear is 40mm. That means I need to find a spindle that's approx 4mm (2mm each side) shorter, right?

I'm using Campy 165mm Strada Cranks.

If you don't know how to measure the chainline you can do the following (you
will need some calipers):
1. For the front:
a. measure the seat tube diameter.
b. divide this measurement by 2. Call this "X"
c. measure from the edge of the seat tube to the center of the Chainring,
Call this "Y"
d. the chainline at the front is "X" + "Y"
2. For the rear:
a. Measure the rear dropout spacing.
b. Divide this measurement by 2. Call this "X"
c. Measure the distance (with hub installed) from the inside edge of the
right dropout to the track cog, call this "Y".
d. the chainline at the rear is "X" - "Y".

hueyhoolihan

if it were me, yes, i would remove the crank arms and the BB spindle and measure it. beware it may not be symmetrical (right side shorter or longer than left), which could make things a little more complex. good luck.

dabac

If it's a cartridge BB:
Unless I was planning a longer ride, I'd keep riding until I knew I'd need a new BB.

If it's cup & cone, and I have no intention of keeping it I'd do the same.

If it's cup & cone and I'd like to keep it I'd strip and inspect immediately.

apg

It's a cartridge. I think I'll replace it when the snow ends.

Andrew R Stewart 

One measurement is worth a thousand assumptions. Andy

Phil_gretz

Too much analysis will just introduce error here.

Is the spindle-to-crank interface the same (square taper)?

Do you have the candidate new crankset?

(1) measure current chainline
(2) replace old crank/chainring with new crank/chainring
(3) measure new chainline
(4) difference is how much the right hand half of the spindle must change from old to new to properly place the new chainline where the old one was. calculate new spindle length accordingly. So, if symmetrical, add/subtract twice the difference to the overall spindle length. If non-symmetrical, then go back and mount both side of the new crank and adjust the right and left accordingly to what you observe/measure.

(5) find the replacement cartridge bb with proper spindle length, shell width, threading and crank interface to match your bike and new crankset.

(6) install

alcjphil

Spindle length isn't the only thing you have to think about

apg

Really. Why is that? Or are you another ****ing troll?

rhenning

Campy cranks have a different taper than most Japanese cranks. Roger

fietsbob

Tape Measure ..

Center line of the bike is the Base end of the chain line, where the chain is or will be is the other..

they should be parallel.

demoncyclist

Way to get answers- alienate the collective. Yes, you need to know spindle length. But you also need to know the threading of the bb shell- English, Italian, etc. Then you need to know the interface- square taper (ISO or JIS), ISIS, Octalink, etc.

Keep being an a**hat, and we will stop helping.

apg

Haha. I guess I'm too used to people being dickheads on this forums, esp. when posting anything to do with a non road bike. Thanks.

alcjphil

Actually, I should have added the additional information about bottom bracket threading and interface, so I can see how you might have thought I was being a smart alec
Found some interesting information here:
https://www.ebay.co.uk/gds/Identifyin...0241613/g.html

Since you have a Campagnolo crank, you will need a bottom bracket with an ISO taper. As for bottom bracket threading, I am not sure what frame you have, so you will have to figure that out for yourself

apg

So spindle size is 113mm, which means I should buy a 111mm or 110 mm to straighten the chain line right?

CharlyAlfaRomeo

Going by your earlier measurements a BB with a 108 mm spindle would be perfect (113-108=5, 5/2=2.5) but TBH a 2.5 mm is nothing to worry about if you can't find the right length.

Unless of course that crank used an asymmetrical BB spindle which if it's old enough is a definite possibility, in which case you are correct.

However finding an asymmetrical BB in the right length may be an exercise in futility in which case I stand by my statement about 2.5 mm being inconsequential.