Bicycle Mechanics - cassette/derailleur capacity question

Hello. I have a Kona Jake that I'm thinking of upgrading to 9-speed. I realize I'll need new shifters, cassette, and chain. My question mainly focuses on the size of the cassette I can put on. My gearing is currently 30/39/53 on a 12-25 8-speed cassette with a Tiagra 4400-GS RD. I was looking at putting a SRAM PG970 11-32 cassette on. If I did this, the RD capacity would need to be 44 teeth, but the 4400 is rated at 37 teeth. I know Shimano is fairly conservative with these numbers, but would this be a major issue? I'm well aware of the pitfalls of cross-chaining, so the chances of me doing that are pretty slim. If this is an issue, would a PG950 11-28 be a problem, too, or should I just stick with the 11/12 to 25/26 cassettes?

The chain wrap capacity won't be a problem if you stay away from the small-small combinations as you are aware.

What will be a likely problem is Shimano's road rear derailleur published limitation of a 27T big cog maximum. In practice these derailleurs will always accept a 28T cog, will usually work with a 30T and will almost never take a 32T cog.

Ahhh, thanks for pointing out the 27T max--I missed that one. I think I'll probably go with the 11-28 cassette then. I'm planning on doing a bit of touring/camping in the spring and I want to make sure I'll be able to deal with any hills I might encounter. Thanks for the input.

Ahhh, thanks for pointing out the 27T max--I missed that one. I think I'll probably go with the 11-28 cassette then. I'm planning on doing a bit of touring/camping in the spring and I want to make sure I'll be able to deal with any hills I might encounter. Thanks for the input.

Or you could install an LX rear derailleur to go with the 11-32 cassette. That's commonly done. Most new road tandems come geared that way.