Can I fit a cassette with a larger range with my Shimano Tiagra 10-speed ( GS-4600) derailleur?

Question

I'm currently running a 2x10 shimano tiagra 10-speed drivetrain with a 50/34 compact crankset, a 12-30 rear cassette, and a Shimano Tiagra GS-4600 derailleur (that's medium cage aka road long cage) on a light touring / road bike.

I tend to ride a lot of hills and want a touch more range for tough climbs. Can I make this work with an 11-32 or 11-34 mountain cassette or do I need to get a long cage derailleur?

It looks like I might answer my own questions, becuase the specs say, they say I shouldn't really run more than a 30t max in the rear. However, I'm wondering if anyone else has tried this and had success going past spec with this derailleur or if I should resign myself to spending more cash on a new derailleur.

Answer 1

With the b-screw tightened all the way on the medium cage GS-4600 tiagra derailleur I was able to install the 11-32 cassette. It was obvious from the appearance that I wouldn't be able to squeeze any larger of a cassette on the rear wheel without switching to a long cage mountain or touring derailleur.

There were no issues when shifting with the 34t front chainring in or out of the 32t rear cog.

However, using the 50t front chainring, shifting out of the large 32t cog was a little off. It worked, but it was lagging a bit and having a harder time jumping to the next cog, probably due to the chain being too short since I didn't adjust the chain length.

This should be solved by adding a link or two to the chain. However, I'm going to be swapping in a 46t large chainring, so that should address the lack of slack. I shouldn't even be in the big ring in the back and the big ring in the front anyway to avoid cross chaining.

Answer 2

You are correct. You have answered your own question. A 30t cog is maximum for the Tiagra derailleur.

Using anything larger risks damage to derailleur, derailleur hanger, rear wheel and your frame, since shifting into a cross chain position can tear your derailleur off the bike. At that point it usually ends up in your wheel, and jammed against the chain stays on your frame.

Answer 3

I just modified my Merida Race Lite 903 which has a similar off the store set up like yours a week ago, the hills here are tough (Sangklaburi, Kanchanaburi, Thailand). I changed the Cassete that was 11/28T to 11/34T and it worked without replacing the rear derailleur with a long cage (XT Deore). did this by turning all the way to the bottom the screw of the tiagra short cage RD to adjust the pull of the spring on the chain... noticed that the upper pulley chain guide space is just a few millimeters but not hitting the large cog as i change gears... I did not change the chain either, but i cannot use the large chaining on the largest cog... this combination not a good combination anyway...

Answer 4

Just to add one more perspective: I've done this on a racing route full of hills. I swapped out my medium cage 105 for a mountain bike derailleur (Deore 9 speed). I was teased a bit, but after 85 miles I was asked a lot of questions as to how I did this and why it worked. Large cog was 34, and I had no problems shifting. So consider dishing out for a mountain bike derailleur if this is to be an everyday sort of thing. They look fine, have tons of adjustment and are much cheaper than road stuff.