sammy5001

I currently use a full Shimano 105 group set with 39/53 chain rings and 12/25 cassettes. After weeks of brutal low-gear grinding and muscle training I've finally managed to spin at 90 RPM on a 5% grade (I started out cranking at 30 RPM haha). With this setup the most I can handle is a 15% grade (cranking at 30 RPM). Any grade higher I'll just have to get off and walk because I don't want to risk injuring my legs.

So I was thinking of replacing my 12/25 cassette with a 11/32. Will that be compatible with my rear dérailleur? Any drawbacks with a 11/32 cassette? I'm also considering an 11/28 too but I'm not sure which is better.

dauphin

pretty sure sram is compatible...they make an 11-28...and I think there is now an Ultegra 11-28 if you want to keep it all Shimano...anything bigger and I think you would need to change your rear derailler.

Rogue Leader

32 is quite a steep gear, you would need some sorta nasty hill to climb to ever need that. That said you likely would have to change your derailleur with that. 11/28 should work fine however and that gear range seems a bit more useful. Don't forget the more you ride the better your conditioning will be and you won't need that huge gear.

sammy5001

If I switch my rear cassette from 12-25 to 11-28 will I need new chains?

Panthers007

If the current chain isn't new, then getting a new chain with a new cassette is a very good idea. It will skip otherwise.

Jeff Wills

As others have said, a 28 tooth large cog is all your current derailleur can handle. Some people have pushed the 105 derailleurs to 30 or 32 teeth, but that takes the right setup and some luck. To do this with complete assurance, you can replace your rear derailleur with a mountain bike derailleur. It will work fine with your current shifters.

My touring bike has a Deore XT rear derailleur and a triple crank up front- the low gear is 24/34... which allows me to pedal 60 rpm at 3 mph- just barely above walking speed. I've climbed 15%-plus slopes with a full touring load without a problem.

Definitely put on a new chain if you install a new cassette.