Eggywootah

I have a Shimano 105 8-sp short cage derailleur with a 12-26 cassette. What is the maximum gear range I can use for the cassette? Anyone know?

Al1943

If I understand your question the maximum range would be limited to the chain wrap capacity which is probably the same as a newer 10-speed short cage Shimano rear derailleur, 29 teeth. Shimano's specs are conservative so that limit could be pushed some. If you are thinking about running a triple crank with your short cage derailleur you can do that if you stay out of the small ring and smaller cogs combinations.
On the other hand, long cage derailleurs are pretty cheap.
What are you thinking about doing?

Al

Panthers007

One thing to know is that when people speak of a "8-spd. derailleur," it doesn't mean the derailleur is limited to 8-spd cassettes. The 105's will be equally at home on a 10-spd. cassette or a 5-spd. freewheel.

Dural

You can do at least: 32t with a 42/53, or 30t with a 38/53 small chainring. Might need to add/remove some chain links so you can wrap around the large-large combo without sagging on small-small.

Retro Grouch 

Maybe, maybe not.

In addition to the chain wrap issue there is also a largest cog capability. Shimano rates their road derailleurs, regardless of long or short arms, for a 27 tooth maximum rear cog. Like Al1943 said, you can generally cheat a little on that but 32 teeth is quite a bit of cheating.

The bottom line is that, if I already owned the derailleur, I'd try it to see if I could make it work to my satisfaction. If I were buying a derailleur, I'd be sure to get one that was rated for the gear combination that I was using.

Eggywootah

Thanks, guys. What I have is a single chainring with 48t, an 8-speed cassette, and a short-cage 105 derailleur. I'm guess I'm gonna go up to 28t for sure, then, for a 12-28, but maybe I'll wait and see if I need something bigger.