going from triple to double

dbackmtg said:

I just bought a new bike that has a compact crank on it. (50,36) My current bike is a triple 52-42-30. Most hills I make in the 42 but there are a few very steep hills that I use my 30. My cogset is 12-25. when I'm in the 30 I'm usually 2 or 3 sprockets down from my 25. How close would this be to 36 front and the 25 in the rear. I hope this is understandable. Thanks for your input. I'm a little worried about making the steep grades.

you'll be absolutely fine with the 36. there really isn't very much noticeble difference between 30 and 36 when you start using your rear cog to compensate. if you find you need a lower gear just get a cassette with a 27 tooth. enjoy the new ride.

snaps10 said:

you'll be absolutely fine with the 36. there really isn't very much noticeble difference between 30 and 36 when you start using your rear cog to compensate. if you find you need a lower gear just get a cassette with a 27 tooth. enjoy the new ride.

Thanks for your vote of confidence. Most of it is probably in my head.

Plug both sets of gearing in here and print them out for a direct comparison: http://sheldonbrown.com/gears/

I have a triple on the Tri bike and took the 30t off and fitted a 36, so I now have 36/42/53 with a 12-25 cassette and 650c wheels 😄

dbackmtg said:

I just bought a new bike that has a compact crank on it. (50,36) My current bike is a triple 52-42-30. Most hills I make in the 42 but there are a few very steep hills that I use my 30. My cogset is 12-25. when I'm in the 30 I'm usually 2 or 3 sprockets down from my 25. How close would this be to 36 front and the 25 in the rear. I hope this is understandable. Thanks for your input. I'm a little worried about making the steep grades.

Okay, here's the real-world answer you are looking for:

When the chain is on the 25t cog in the rear + 36t chainring, it will be slightly harder (0.80 per cent ... yes, less than 1 per cent) to pedal than when you are using the 21t cog and 30t granny chainring ... but, easier than the effort of using the 19t and 30t granny (that is, only 91.2 percent the effort) .

When the chain is on the 23t cog in the rear + 36t chainring, it will be slightly easier (0.87 per cent .. again, less than 1 per cent) to pedal than when you are using the 19t cog and 30t granny chainring.

The above presumes a 9-speed cassette ... although, the larger cogs on the 10-speed cassettes are the same, AFAIK.

Of course, BOTH the 23t & 25t with your 30t granny are easier combinations than anything you would have with your 36t chainring.

You would need a 30t REAR COG with the 36t chainring to be equivalent to the 25t REAR COG + 30t granny you currently have.

A 28t REAR COG + 34t chainring is almost equivalent (1.2 per cent harder, by my reckoning) than a 25t REAR COG + 30t.

You should be "okay" based on which cogs you say you are using when you are using the granny on your triple.