# Singlespeed & Fixed Gear - Help with chainline math.

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View Full Version : Help with chainline math.

zerobug
09-14-05, 02:03 PM
Building up a BareKnuckle for the 'drome. Can someone double check my math and make sure I went about this correctly.

I have a Sugino 75 crank which with the Sugino 109mm BB should give me a 42mm chainline. I measure the distance between my rear hub flanges (Paul) and get 65mm. Then the distance from the nondrive side hub flange to middle of cog is 78mm. Therefore my hub w/cog has a chainline of 45.5 = [ 78 - ( 65 / 2) ]

So... if I want to correct the chainline using the Sugino crank and my previously measured hub I need to gain roughly 3 mm per spindle side. So 109mm (Sugino BB) + ( 3 mm x 2) [gain per side x 2 sides] = about 115mm

If this is correct I'll need a 115mm or 116mm BB spindle to correct the chainline, right?

I've gone through this so many times but I wanted to run it by you guys before I plunk down money on a Phil Wood BB or try to find a Shimano that will work.

Jose R
09-14-05, 02:19 PM
I find it hard to believe you would get a chainline of 45.5mm.

Chainline should be 42.5mm. Most hub and sprocket combinations will give ~42.75-43.5mm chainlines. What cog are you using?

Also see Sheldon Brown's chainline (http://sheldonbrown.com/gloss_ch.html#chainline) description, if you haven't already done so.

shants
09-14-05, 02:23 PM
generally speaking, the actual chainline of most track setups is more like 42.5-43 than the mystical 42.

assuming accuracy and precision in your hub measurements, your math is kosher. however, i, like jose r, find it hard to believe that the paul track hubs would actually have that chainline.

anyhow, if you are correct, you figure that you'll need to push your chainring out somewhere between 2-3mm.... or, alternatively, that you need to bring your cog the same. that would be my recommendation -- if you currently have the flange of the cog facing outward, you can probably cut around 2-3mm by flipping your cog so that the flange is inward.

i would go ahead and buy the 109mm sugino 75 bottom bracket (or a 107mm shimano or some such) and not try to engage in any ghetto-riggery. this way, you'll always have a proper track chainline up front should you wish to switch to different wheels, put the cranks on a different bike, etc.

if the cog in the rear is already flipped around and you still have around a 45.5 chainline, then you'll probably want to go with a longer bottom bracket. just be absolutely sure that your hub measurements are accurate (i'd probably try to contact paul for the actual specs) before you go dropping cash on a bottom bracket that you'll only really be able to use on that particular setup (that is, the 75s with pauls).

hope that this makes sense.

zerobug
09-14-05, 02:26 PM
I've checked Brown's pages. According to Paul the hub is 39mm center to the shoulder of the threads. Add 6.73mm for a 1/8th EAI cog you get 45.73.

Is it safe to flip around a cog and thread it on with the teeth on the inside?

baxtefer
09-14-05, 02:51 PM
There are a bunch of hubs that are designed around a ~45mm chainline so you can use the outser position on a road double, or the middle position of a mountain triple.
off the top of my head... Goldtec, ON-one/Kogswell, ENO, Level.
Since the Paul hub was designed around messengers instead of track riders, the 45mm chainline doesn't really surprise me.

If your chain still clears the spokes, you can try doing that. I believe Ken Cox is doing this.
A 115mm BB should in theory line up your chainline. Provided that it's a symmetrical spindle. I'm sure if the Shimano UN 73/53 115mm is symmetrical. anyone?

shants
09-14-05, 02:52 PM
yeah, it's totally straight to flip a cog around.

zerobug
09-14-05, 02:57 PM
There are a bunch of hubs that are designed around a ~45mm chainline so you can use the outser position on a road double, or the middle position of a mountain triple.

That makes a lot of sense now... too bad I find this out after building up these hubs for track use. I'll try flipping the cog around tonight.

Thanks guys!

jonb
09-14-05, 03:20 PM
Sorry newbie building question, if I have not bought a bottom bracket yet and and have a sugino 75 crank and pro max hubs, what do i do to figure out the correct chainline etc? I was just planning on buying the sugino 75 BB and assuming it would all line up perfect... no?

baxtefer
09-14-05, 03:24 PM
Sorry newbie building question, if I have not bought a bottom bracket yet and and have a sugino 75 crank and pro max hubs, what do i do to figure out the correct chainline etc? I was just planning on buying the sugino 75 BB and assuming it would all line up perfect... no?

it'll end up being perfect to within ~1mm, which is perfect enough for me.

if you don't want to spend the \$\$ on the Sugino BB, a 107 or 110 shimano UN53/73 will work as well.