[jmadams13]

Take brake reach and tire clearance issues away (say the brake reach will be fine and tire clears all in any position) what is the best placement for the axle in the dropout in relation to the D hanger to maximize shifting efficiency on a CC. Cassette is 12-27 8sp with a older Shimano 600 (same dimensions as current 105) rear D.

I like to have it as close forward as possible to shorten the wheelbase, but am thinking that there may be a "sweet spot" in regards to shifting. When in drop out as much as possible, shifting was a tad "slow" feeling. Also, it did feel different in middle as well, but not as "slow" as in the far back position. Taking into account the differences in position, the rear D was adjusted before trying these positions.

 

[tihsepa]

1/4 the way back in the drop worked great for me. I never moved it from there until I went SS.

 

[fixedforbroke]

So youre running it SS now?
1/4 should be ok, just be sure you get good purchase on the dropouts so if it slips a little it wont ruin any more than your chain tension.

 

[tihsepa]

I run mine SS. I am far enough in the DO not to have a problem.

 

[jmadams13]

I do nun SS, but placement on SS wold not have shifting implications....lol I'm talking about when geared. I did some experiments in placements today and found about 1/4" from all the way forward to shift the best. Not 1/4 the way, but only 1/4"

This was only short sprints down the street and back (about 1/4 mile) but shifting under full load. I tried about 6 different placements. The dork in me even marked the inside the non drive side dropout and toke notes after each sprint to compare. Did this test 3 times in each placement. I know, I'm a nerd.

 

[toowacky]

Try this...

I like to have it as close forward as possible to shorten the wheelbase, but am thinking that there may be a "sweet spot" in regards to shifting.

I struggled w/ this at first when I built up a CC as a geared bike... I found the following diagram somewhere (perhaps a Sheldon Brown site?), and it helped. I pretty much followed this and the shifting improved.

From memory, I think this originally was a reference for the original SIS shifting, but seemed to work for me...

 

[jmadams13]

^^^ THANKS!!!!

Thats perfect. When the axle is 1/4" in the dropout, brings the angle right at 32. Thanks. I saved that image.