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Old 01-17-13, 05:54 AM   #1
redred99
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Chain stay clearance

Hi Bike Forums,

I have a problem:

I have a steel Harry Perry frame that i'm looking to put a modern groupset on, specifically Campagnolo Veloce. I had some crappy parts that i picked up cheaply from the second hand box at my local bike cooperative, but am now looking to upgrade. My issue here is that what i was using a 52 tooth chainring paired with a 120mm square tapered bottom bracket, which gave me enough clearance between the drive side chain stay and the chainring (i'm unable to check what the exact measurements were as the parts have now been stripped and sold back). I know that the Veloce uses the power torque integrated bottom bracket system, and research tells me that combined with the outboard bearing cups that it gives me a total axle length of 110mm.

My man at the local shop doesn't seem to think that will be long enough, and that the chainring (53th) will come in contact with the chain stay. I'm not sure if he's right or not.

I would go for a brand other than campagnolo except that i'm limited to it, as i've got a rear hub that'll only take a campag casette.

what i really want to know are my options as i've become a bit stuck in knowing what to do. Do spacer kits exist for that kind of problem? Does anyone have any experience dealing with this kind of problem?

Thanks a lot in advanced for any replies
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Old 01-17-13, 04:00 PM   #2
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your current crankset, measure the "chainline". thats from the midline of the seat tube (like where the front derraileur is attached) to the center of the front chain rings (the middle ring if its a triple). typical for road bikes is 45mm.
see... http://sheldonbrown.com/chainline.html#front (but read the whole page for more info)

Now, look up the target chainline number for the crankset + BB combination you're considering, are they the same? if so, you should be gold, the chain rings will end up exactly where they are.

the mystery here is that different cranksets use different width axles to end up at the same place, and that magic number isn't published
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Old 01-17-13, 04:23 PM   #3
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Axle length is only half the story. The other half is the offset built into the cranks that determine where the chainrings and pedal are with respect to the end of the spindle.

Iver the years, spindles have gotten shorter and crank offset bigger by the same amount, so a modern 103mm spindle and crank, can give you the identical chainline as an older 120 spindle and crank.

20:1 odds are that the new crank and BB will work on your bike without problems, since the offset between the right face of the BB shell and chainstay where the chainrings clear has remained virtually unchanged for 40+ years.

BTW- I'm disappointed to hear that the shop staff told you otherwise. If your frame is unusual they might be right, but I suspect that they're simply unknowledgeable. (ignorant is too strong, though it may be true).
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Old 01-17-13, 04:48 PM   #4
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one thing, a wider rear axle allows the cog cluster to move to the right.
up to a point the space was needed to add a 'speed' back there..

120 BB axle is extraordinarily long check your measurements,,
Don't include the threaded bolt end if it's a solid axle..

new crank and new BB are a Set, use them both..
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Old 01-17-13, 06:10 PM   #5
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Quote:
Originally Posted by fietsbob View Post
one thing, a wider rear axle allows the cog cluster to move to the right.
up to a point the space was needed to add a 'speed' back there..

120 BB axle is extraordinarily long check your measurements,,
Don't include the threaded bolt end if it's a solid axle..


new crank and new BB are a Set, use them both..
You mean that I should just be measuring the cartridge? With the square taper axle it is definitely 120mm. Unfortunately i no longer have the crank set i was using so i can't measure the chain line from that. However, i have found a manual for the crankset or 'power torque' system from campagnolo, which has technical specs and measurements. It says the chain line is 43.5 mm on a standard 53/39 double. I can probably devise some way of measuring that against the bike using the dimensions i can get from the manual.

My bike isn't particularly unusual in it's geometry i don't believe. The chain stays are 405mm long, that is the only thing that's maybe unusual, or maybe it isn't.

Thank's for help
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Old 01-17-13, 08:30 PM   #6
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Quote:
Originally Posted by redred99 View Post
You mean that I should just be measuring the cartridge? With the square taper axle it is definitely 120mm. Unfortunately i no longer have the crank set i was using so i can't measure the chain line from that. However, i have found a manual for the crankset or 'power torque' system from campagnolo, which has technical specs and measurements. It says the chain line is 43.5 mm on a standard 53/39 double. I can probably devise some way of measuring that against the bike using the dimensions i can get from the manual.

My bike isn't particularly unusual in it's geometry i don't believe. The chain stays are 405mm long, that is the only thing that's maybe unusual, or maybe it isn't.

Thank's for help
Your current chainline is easy enough to measure. Measure from the downtube to the center between both chainrings, then add 1/2 the diameter of the downtube.

If you're good with eyeball measurements you measure directly from the center of the chainrings to the center of the down tube (or seat tube). With a decent eye this will be accurate to within 2mm or so, which is good enough for your purposes.
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