Bike drive train question?

Ok, that just flew right past me. I am a true "beginner" I guess. Could someone explain that too me when they answer the question to me. I am curious now as I have no idea how/what my bike has. Thanks.

I have three chain rings on the front. The largest ring has 46 teeth, the middle ring has 33 teeth, and the smallest has 21 teeth. The rear cassette has 7 cogs the easiest is the largest with 23 teeth. So when I climb, I use the 21 tooth small ring on the front and the 23 tooth big ring on the back. I am worried that 39 tooth front and the 25 tooth rear will be too hard for me to climb in. I have learned that there is a shimano ultegra 9 cog cassette that has 27 teeth that I can buy, but I was hoping someone knew something about how what I have will compare to what I am thinking about getting.

Got it! Thanks. I knew it had to be something easy to understand, but just didn't understand the speak.

Unfortunately, I just spoke to a guy at a local bike shop and he told me to stop using the 21 ring... In fact he said I should have it taken off my bike. I think my worst fears are being realized. I am going to have to hire a personal trainer for leg day at the gym just so I can use the new bike that I want.

That chainring on your current bike is tiny, standard triple on today's bikes is like a 52/42/30. I have a triple on my two road bikes and seriously debated sticking with the double (53/39) when I bought the last one. I live in a flat area and never use the small chainring (and seldom use the large chain ring) here. In the end I went with the triple because i do an annual ride at Lake Tahoe, really use that granny gear there.

Can't you get a triple on your new bike? Alternatively,Shimano does make a cassette with a 27T gear, other maufacturer make bigger compatiblle cogs. I'm looking on the Trek website at a SRAM 11-32 on their touring bike.

I'm in Pennsylvania and we have enough hills that this really is an issue for me. The largest I had seen was a 27, so I will look into that 32. Thanks. BTW, I have been looking at Tri specific bikes F22 Felt, and the P2K Cervelo and they seem to go for the doulble to save weight. Either that, or it never occurred to them that someone would be so weak that they couldn't push a 39 up a big climb.

Don't know about compatibility issues, but Peter White Cycles (http://www.peterwhitecycles.com) sells chainrings in sizes ranging from 58-tooth down to 20-tooth, also sells a Shimano XT 9-speed 12-34 casette.

I guess the bigger question isn't how much time you spend on the 21-tooth chainring but how much time you spend on the 23-tooth cog while you're on the small chainring. The 21/23 combination has a gear ratio of 0.91. You would need a 43-tooth cog to go with the 39-tooth chainring to give you a similar gear ratio.

Or you could just get a stronger motor!

Did the guy at the bike shop give you a reason why you should stop using it? Soounds pretty drastic unless it is just inefficient for climbing.......more leg RPM's than wheel RPM's....