How-To: align a drivetrain (and how to gauge/measure alignment or 'trueness')

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7/28/2014 7:35 PM

My past bmx's were always cobbled-together, hand-me-down parts thrown together on a couple decent frames.. I've learned how to build/tune most parts on a proper bmx setup, but euro bb's and cassette hubs are still difficult for me to do anything besides remove/re-install.
Anyways, i need to learn how to align and gauge a drivetrain's straightness- for my bike, because i'm about to buy a new, thicker (guarded) sprocket & i've already thrown the drivetrain out of alignment by installing a drive-side hubguard, *and* my brother got a bike off craigslist recently and his cranks are a mess, the rear wheel and part of the cranks are aftermarket, and they're not properly aligned.

How does one gauge the alignment of their cog:sprocket, aside from the obvious & useless way of just eyeing it? And:
How does one approach adjustments? Is it sprocket spacers, or spacers at the cog/cassette? What are these spacers called and do they need to be specific, or can I go to home depot and find what I need (even if it's ugly/raw steel)?

Thanks for any thoughts / tips here, i'm really at a loss... my best idea so far is to buy a steel yard-stick, and use that to try and gauge cog:sprocket alignment, but that really doesn't seem too-great a measure and is probably an inefficient approach!


7/30/2014 4:27 PM

[i'd also appreciate any links to comprehensive or 'library style' collections of bmx tech stuff, like everything from product manufacture to repairs (I don't mean "what's new" i mean the science behind the geometry, the ride, the materials, the testing etc etc)


10/10/2014 9:36 PM

Its actually quite simple
The main goal is when looking and the sprocket and driver is for them to be inline with eachother.
In order to adjust it you can use crank spacers(take off and add)
**Sometime it won't always be able to get 100 percent straight, but that's ok because chains have some movment in them so the chian line can be slightly off**
Hope this makes sense


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