cth6

All,

I have an '09 Trek 4.5; Shimano 105 50/34 and Shimano 105 11-25, 10 speed. This is my first bike with a compact crank and 10 in the back.

When in the 34 on the chainring, I can not use the 3 bottom cassette gears (14, 12, 11 [I think]). I get the 11 will tweak the chain. The other two are hitting metal rivets on the large chainring. Is it normal to lose out three gears when in the small chainring on a compact?

Thanks in advance.

CT

AEO

yes, normal.

Beaker

It's called cross chaining - you might be able to get away with trimming the FD a little (can you nudge it over a little without switching to the 50T ring?), but 34x11 isn't meant to be ridden for any length of time.

cth6

It is actually not the FD. There are some rivets on the 50T ring. Almost like they were put there for balancing the ring. (I doubt it, but no other idea what they would be there for). These rivets stick out about 4mm to the inside of the 50T ring. Just enough to catch the chain. The FD still has plenty of room.

I understand about the 34x11, but I was surprised about the 34x12 and 34x14.

I will see if I can get a good pict of them.

AEO

the rivets are pick up pins meant to aid in shifting from the small ring to the large ring.

good read for you:
https://www.sheldonbrown.com/gears.html

cth6

It is actually not the FD. There are some rivets on the 50T ring. Almost like they were put there for balancing the ring. (I doubt it, but no other idea what they would be there for). These rivets stick out about 4mm to the inside of the 50T ring. Just enough to catch the chain. The FD still has plenty of room.

I understand about the 34x11, but I was surprised about the 34x12 and 34x14.

I will see if I can get a good pict of them.


Added link to a picture... https://www2.snapfish.com/slideshow/A...NAME=snapfish/

cth6

Thanks for the feedback. Glad I did not take the angle grinder to them then.

Sheldon's site has some great info, but I found nothing about the pins. Actually tried a few places on the web and books I have collected over the years before I posted. It was driving me crazy.

I thought that cross-chaining was really only an issue on the opposites (big and small / small and big) everything else was pretty not much of an issue on the chain.

jimblairo

Normal for 105 and Ultegra but you can cross chain with Dura Ace.

dstrong 

I recently switched to the same setup you have after riding both a triple and a standard double. I was a bit bothered by the chain hitting those pick-up pins (after i figured out what it was) but now I use it as a sign that I should probably shift up to the 50 ring.

AEO

depends on the cassette you use, but generally for me it's
30km/h and under = use 34T
30km/h and higher = use 50T

cth6

I live in FL, so we are pretty flat. Overpasses provide hill training.

I ride around 108-110 cadence and am right in between the 34T and 50T for most rides. Climbing the hills we have in central FL drops to the 34T and down the backside I need the 50T. Riding the rollers, it sucks because I really wish I could use the 12 and 11 on that 34T. The 16 and 17 with the 34T are great for climbing up them.

dstrong 

Thought about a standard double? Sounds better suited for your cadence and the terrain.

cth6

Never put any thought to a standard. Something to look at next trip to the LBS.

AEO

you might be interested in a 42T.

it's good from 15mph to 33mph @110rpm with a 11-25 cassette.
https://www.panix.com/~jbarrm/pcgi-bin/c41strt.cgi