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SirJoey
06-26-2008, 08:27 AM
When I weld up my BBs, should I make these der tube angles:
http://img183.imageshack.us/img183/9215/dertubeangle1py1.jpg


match this angle on the bikes that the ders came off of?
http://img183.imageshack.us/img183/3752/dertubeangle2yo5.jpg

Or will the angle be different, since the rear end of the chain is lower than the front on the KC?

http://img384.imageshack.us/img384/7131/sirjoeysigmedij1.gif

trikeman
06-26-2008, 09:05 AM
The angle of the der should be set for good shifting (Brad has some recommendations of 67 degrees in the plans and books for that). The angle of the rear triangle is pretty much set by the height that you weld the thing together for. I think it would only be coincidence that they were exactly the same.

robertwb70
06-26-2008, 11:45 AM
I think the angle you'd want to match is between the tube and the top run of chain.

AtomicZombie
06-26-2008, 12:03 PM
The original seat tube angle (on the rear triangle) is not important. It is the angle at which the chain leaves the top of the front chain ring that counts. So to answer your question, never mind the original angle. The 67 degrees is a good angle that I have found works with the large body front derailleur.

Brad

SirJoey
06-26-2008, 12:04 PM
I think the angle you'd want to match is between the tube and the top run of chain.

Yep, you're right. I'm gonna have to mock up this triangle that I robbed the chain & derailleurs from, & check that angle. Good call, Robert, thanx.

Yea, TM, the plans of course do suggest 67 degrees, but I know that it's not universal, since ders vary. For some reason, I was thinking wrong, to measure the angle from the FRAME of my donor, instead of between the der tube & top of the chain, as Robert suggested.

Thanx, guys!

http://img384.imageshack.us/img384/7131/sirjoeysigmedij1.gif

SirJoey
06-26-2008, 12:06 PM
The original seat tube angle (on the rear triangle) is not important. It is the angle at which the chain leaves the top of the front chain ring that counts. So to answer your question, never mind the original angle. The 67 degrees is a good angle that I have found works with the large body front derailleur.

Brad

Okay, thanx Brad!

http://img384.imageshack.us/img384/7131/sirjoeysigmedij1.gif

TheKid
06-26-2008, 03:53 PM
It also depends on the pulley. A larger pulley brings the chain angle lower than a small pulley, which would require a shallower der tube angle.
So if you're using a different sized pulley than the plans suggest, you should alter the der tube angle accordingly. On mine, because I used no pulley, I set the der tube angle at the usual angle. I've since changed the chain arrangement, and have no need for a front der tube at all.