Wobbling Weeny

Hello everyone, I'm a newbie to the Bike Forum (or any forums for that matter). I apologize in advance if I commit a "faux pas" or some other mistake in protocol. Just be patient with me. I'm old and slow, but I get there...eventually. My question is...will I need to change the Tiagra RD on the 2017 Cannondale CAADX to accommodate a 12-32 cassette versus the 12-28 that came stock on the bike?
The chainrings are FSA 36/46. I have a friend who is a decent mechanic tell me he thinks I'll need to go with a longer cage RD. Any hints or suggestions would be welcome.

chas58

You would have to look up the specs to be sure. Sometimes you can go a couple of teeth over by adjusting the derailer stop point, and of course check to make sure your chain is long enough. Try putting the derailer on the 28. Is it a tight fit, or is there a lot of room.

Either way, he is right. You might need a longer cage. Or you might not. I'm pretty sure that to stay within Shimano's specs you will need it (and you may or may not be able go get away with what you have).

Alternatively you could go down a little in your small chain ring.

Banzai

wheelsmcgee

chas58

I've heard of people going +2 on shimano's numbers. +4 teeth might be a bit much...

shoota 

This right here.

In fact, I basically did this very thing to my wife's bike. Put on a 32t cassette, left the original short cage rd on there. It will either work or it won't, if it doesn't then you put the 28t cassette back on until you get a mid cage rd. Then I would suggest putting on a 34t chainring as well. Easier, cheaper, and guaranteed to work. Or do both.

Wobbling Weeny

Shoota, did it work on your wife's bike?

shoota 

Of course, that's why I suggested it. It works more often than it doesn't.

pesty

Another option if it doesn't fit would be to get a Wolftooth roadlink. For $22 it's cheaper than buying a GS rear derailleur or a new chainring. I figure if it can get a GS up to 40t, it should be able to get an SS up to 32t. With the close range of the front rings at 36/46 you should still be fine with the wider range cassette and the total capacity.

tFUnK

Was able to get a 6700 short cage rear derailleur to work with a 32t cassette. Ymmv. Needed a longer chain, though

wipekitty

I'm currently running 46/36 in the front, 11-32 in the rear, with a 5800 SS (105 short cage) derailleur. ~100 miles in and some steep climbs, and it's been fine.

I'll note that specs for 5800 SS claim the maximum rear cog is 28 teeth, and the maximum capacity is 31 teeth. So in this case, I'm within the specified capacity, but out of the specified range on the rear cog. I would suspect that your case would be similar, so long as you continue to run 46/36 in the front.

ph0rk

I have the long cage Tiagra 4700 RD, and I have been running an 11-36 for about a year (+4). Plenty of hills to climb here, so I use the 36t cog often. Works with minimal noise in big/big, too, and this is with a short (for me) chainstay of 420mm.

OP is in a similar geographic area to me, so I'd look at changing the front rings and the rear cassette. Most compact double cranksets are a pain to go lower than 34t in front, though, which is stupid but where we are.

I have a road bike with 34x36 available and a commuter with 32x36 available, and both are very handy for the 15% (or worse) grades around here.

It looks like a new Tiagra GS rear derailleur will run around $45 - that would let you go all the way up to 36t.