Hi Andrew,
Thank you very much for taking the time to give me such a thoughtful and considered reply. I really appreciate your help, and the time everyone in this thread has taken to give me their help. I try appreciate it all.
I have a few follow up questions. First of all, what would I do to check of the wheel is out of dish. Is that something I would need to take the bike to a frame builder to check or should a good mechanic be able to help me out with that. I have a similar question about the fork being out of line. I'm not even sure what that means?
I can understand how the wheel being out of dish could affect shifting, but I don't understand how that can't be corrected by aligning the derailleur, or why it would affect the quality of shifting differentially depending on the relative position on the cog, that would strike me as a problem caused by being out of parallel with each other rather than being slightly out of plane. I hope this doesn't seem like I'm being difficult, I'm just trying to understand.
Second, how would the fork alignment affect shifting? How does the front end of the bike affect the shifting on the rear derailleur? Again, I'm not trying to be argumentative- I just want to understand. All of this seems like good news to me because it makes me think I can possibly keep this frame without too much difficulty.
The biomechanical stuff is interesting, but I am really confused about how that would affect shifting. Or were you speaking to the issue of being able to balance?
Do you have any suggestions for me for things I should do and/or say to a mechanic? Incidentally I am going to a bike store tomorrow in Vancouver to test ride a few bikes out (as a way of testing out their frames). It's a bike shop that does mostly custom frame build outs, so I could always ask that guy to take a look too.
Thanks so much,
Brad
Originally Posted by
Andrew R Stewart
Before I would bend a frame I would want to eliminate other issues like wheels out of dish or a fork that's out of line.
To help understand alignment try this- The wheels should be coplanar with each other and with the main frame. The steerer and seat tube should be parallel in the frame's plane. The string test only tells if the axle's mid point is centered WRT the main frame. The wheel can be cocked one way or another but still have the axle centered to the main frame. Think of it as having one chain or seat stay longer then it's mate. The drop outs will be the right width apart and centered to the main frame but the rim/tire will be off plane. So too with the fork. The drop outs should be centered WRT the steerer's axis. Both blades should be the same length. But the axle and crown don't need to be parallel, it just looks better that way
.
This alignment is what some will call the handling one. The way the bike steers/tracks consistently evenly side to side. But there's another aspect of alignment, the biomechanical one.
This second category of alignment is how the body is positioned on the bike, how one's movements are centered WRT the bike. So a BB that's crooked will result in one's legs pedaling in circles that are off plane to the bike. A saddle that's been whacked to one side will set the hips off center. Bars not centered or that are bent will cock shoulders.
A motivated builder can measure/assess all these factors and come back with much more info then most shop wrenches. What this info ends up meaning to any one rider... Andy
When many shop wrenches look at a frame's alignment they often don't have a handle on all the aspects affecting the handling or the