b-screw adjustment
 

Lay some knowledge on me, fine people of BF. My wife's bike is a tiagra triple 9-speed and I obtained a 11-32 cassette to put on her wheel instead of the 11-26 that came on it due to excessive complaining about how hard hills are. (she's had hip replacement surgery and getting in and out of hour street requires a few pitches of about 18%, so it's really not just whining)

Anyway, I cannot get the RD off the cassette. The b-screw doesn't appear to have any positive effect. One theory I developed on Sunday is that perhaps the chain is too long - I can put the bike in the large chainring, large cog and the RD still has plenty of take up. If I push down a bit on the chain between the crank and the cassette, the RD moves off the cassette quite nicely, leading me to think maybe losing a pair of links would work. It's highly probable this drive train isn't meant to accommodate a 32 tooth cog, so if there's a possible way to engineer a solution, I'm interested. She spends more time in the low gears than the high as it is.

https://cimg7.ibsrv.net/gimg/bikefor...98520a99ab.jpg

When I moved up from a 12-25 cassette to 11-28 I had to put the B-screw all the way in to keep the jockey wheel off the cassette, and that reduced shifting speed and accuracy. Removing one or two links from the chain improved the situation significantly, and I was able to back-out the B-screw a bit. So you may be on the right track.

You want to first assure that you CAN remove a link or two. You should follow online instructions from Shimano, Sheldon Brown, etc. on how to calculate chain length. The last thing would would want to do is end up in a situation where shifting into the large chainring while still in the largest rear cog (something you probably wouldn't do intentionally, but could easily do accidentally) causes an explosion of drive train parts.

You may also be experiencing a limitation of your rear derailleur. My RD is designed for up to 27t, which I wasn't aware of when I moved to a 28t cassette. It works well enough. But you've made a larger jump, and may have a harder time getting it to work. There are derailleur hanger extenders that may help. But it's possible your RD just cannot accommodate that many teeth. The manufacturer's spec sheet for your RD should say for sure. In my experience it seems possible to go one tooth larger. Some people have success going a couple teeth larger than the spec. YMMV.

Yes the upper pulley is so tight against the underside of the 32T cog that it is trapped by the chain from moving sideways. As mentioned the large cog capacity for this der is 27T IIRC.

A few solutions- You could mount the rear der on a Wolf Tooth or similar device that effectively lowers the der's mounting point. You could install a 9 speed MtB rear der that has a greater capacity. You could go back to the 27T max for the Tiagra der and instead mount a inner ring smaller then the 30T that is the OEM size. I run 26T grannies on a few of my otherwise lightweight bikes (for the Finger Lakes and my old body).

My vote is both the MtB rear der and the smaller granny ring. This way you get both the larger rear cog capacity as well as the greater chain wrapping capacity that a MtB der has. BTW I also run a smaller middle and large ring, then is the typical stock spec. on all my bikes. 26-36-46 is on a number of my bikes. Andy

Chain too long.
Is that a 9sp chain?

+1 I have exactly the same thing on my most ridden bikes and I believe I'm at least your age or older. The Finger Lakes have some really big climbs. I've ridden Bon Ton Roulet for the past several years and i think i've seen most of the hard ones. Then too, where i live is no slouch for climbs either as the annual "Dirty Dozen" ride wiill demonstrate to anyone wanting to try it. Low gears are your friends.

I'll check the math but just based on how much loose chain there is when it's on the big/big, my guess is I can. I'm pretty sure I did not install this chain, so it came too long from the shop (and the original cassette was even smaller).

Oddly, it shifts just fine even with the upper pulley where it is - it's noisy though because of the contact. It *is* a triple RD though, I don't think it's any shorter than my own wifli rear derailleur...

What physically changes about the RD to allow a 28 tooth or 32 tooth cassette in the back? (aside from chain take-up considerations)

9 spd yes, and probably. Came installed that long, I haven't touched it (yet). Strangely, it looks like I captured a quick disconnect link in that pic.

I spent four years in Ithaca and even rode my bike, but there are some streets I don't even want to walk up, much less ride up (Buffalo? Yuck!)

Time for a Wolftooth.

"What physically changes about the RD to allow a 28 tooth or 32 tooth cassette in the back? (aside from chain take-up considerations)" TrojanHorse

The distance from the axle (and thus the cogs' undersides') to the cage pivot is greater. The offset from the cage pivot to the guide pulley's axis. A smaller guide pulley (although this isn't what is done it will provide more cog/pulley gap). A greater angle to the slant of the parallelogram's movement, to better track the increasing diameters of the cogs. Placing the guide pulley further behind or more in front of the cogs. There may be more design details but these are what I think of. Some are done by most wider range ders, some not so.

One way to see this is to hold a wide range and a narrow range der of about the same era from the same brand in each hand and look at them. Andy.

They seem to be reluctant to specify anything for anything other than shimano 10 or 11 speed... and say it's generally not for triples. can't imagine why it would be a problem and it would certainly be one of the less expensive fixes.

Slight more would be a deore SGS cage rear derailleur, those take 34 tooth cassettes and hey - 2 day Prime shipping! $38!

Thanks for the comments Andy - I don't have an old wide-range RD to compare but I might soon. :thumb:

I would probably go back to the 27T (or maybe a 28T if one is made in the appropriate configuration). 28T is pushing things a little, but as I've discovered on my 105 RD it's workable. And then in front do as suggested, moving from a 30t small ring to a 26T or 28T. The problem here will be a matter of whether the FD can handle the tooth-difference between the smallest ring and largest. On my bike I have 30/39/50 up front, and I don't think I could go smaller than 30 without moving down to a 48T big ring. But the OP may find his FD can handle this just fine. Usually the manufacturer's specs would list the FD capacity.

Seems to me like the first thing to try is to shorten the chain until it's only just long enough to make it over big/big with the 34t on. Another 2mm of B-screw can be had by reversing the screw so it sits on the head.

Then if that doesn't work, it's time to start thinking about buying more bits.

It's been my experience having done more then a few 30T to 26T (+ or -) granny exchanges that the shifting can be quite fine. But this is where the rider can contribute a lot to the results. In that their technique far outweighs any ft der aspects. If the rider knows how to and actually does shift with "soft pedaling" technique the resulting expansion of range (the smaller ring) is no big deal. If the rider jam shifts then even within the stated range the results are poor shifting response. This is a case where the rider has a lot of control as to how their experiences will go. Andy