How many usable gears in a 27 speed set.

[rdk]

With three chainrings and a 9 speed rear hub, my understanding would be:

1 Biggest chainring you could only use the smaller 4 or 5 rear gears to avoid crossing over
2. Middle chainring you could use all 9
3 Smallest chainring you could use biggest 4 or 5 rear gears

This adds up to 19 usable gears out of 27.

Am I on the right track?

 

[boudreaux]

With three chainrings and a 9 speed rear hub, my understanding would be:

1 Biggest chainring you could only use the smaller 4 or 5 rear gears to avoid crossing over
2. Middle chainring you could use all 9
3 Smallest chainring you could use biggest 4 or 5 rear gears

This adds up to 19 usable gears out of 27.

Am I on the right track?

Depends on chainstay length,and you really shouldn't use all 9 in the middle ring. It sits in the same position as the big ring of a double,so figure it out.

 

[Don Shipp]

Depends on chainstay length,and you really shouldn't use all 9 in the middle ring. It sits in the same position as the big ring of a double,so figure it out.

I use all nine on middle with no problems, the chain stays are fairly long as it's a touring bike not a racer. I have a close ratio cassette and a 12 tooth jump between chain rings to avoid duplication. However:-
I really can't be bothered to work out how many different, usable gears I have. It seems to be enough.

 

[Don Shipp]

Just worked it out. 20 different, usable gears. Enough.

 

[dhk]

Depends on chainstay length,and you really shouldn't use all 9 in the middle ring. It sits in the same position as the big ring of a double,so figure it out.

On the middle chainring of my 9 sp triple, I can get the biggest and smallest cogs no problem. But the on the two smallest (13 and 12), the chain touches the inside of the big chainring. It works, but I normally avoid these crossover gears for three reasons: 1) The chain rubs lightly on the big ring; 2) the chain isn't perpendicular to the axle; and 3) it has to bend sideways to line up and get over the cogs. Maybe only a fraction of a % power loss, but I can't afford to waste any.