Dannihilator

For 9 speed you have this.
1-1,2,3,4,5,6,7,8,9|You have a bash ring and a chain guide in play.

For 18 you have these.
1-1,2
2-3,4
3-5,6
or

1-1,2,3,4,(5)|With this one you have a Bash ring coming into play.
2-(5),6,7,8,9|

For 21 speed you have these as ok combinations.

1-1,2,3
2-3,4,5
3-5,6,7

For 24 speed you have these

1-1,2,3
2-4,5,6
3-6,7,8

For 27 speed you have this

1-1,2,3
2-4,5,6
3-7,8,9

Am I missing any possible combos that are ok? Or are any of the patterns flawed?

Maelstrom 

If I am getting the point of this. I tend to run ALL gears when I used the middle chainring. I go from 1 - 9 according to your method. On the smallest chain ring I run 4 - 9 if I need it. With a large chainring I assume I would run 1-4 or 5.

Thats is if I am understanding where you are coming from.

Dannihilator

What I mean is even though a bike has x speeds, only y speeds can be used together. For a 27 speed you figure to have at least 3 good combos. It figures out to be a 3:1 ratio in this case. 3 gears on the back to 1 gear on the front.

The others I will rethink of.

a2psyklnut

I agree with Mael.

When I'm in my granny gear, it's usually for a long sustained climb, so therefore I'm running 1 - 1,2.

For most of my riding, I use the middle ring. Therefore I use 2-1,2,3,4,5,6,7,8,9

I barely EVER use my big ring, and I should replace it with a Bash ring, but I'm a cheap bashterd so I've kept it on my bike. The few times I've used it is when I'm on the road and honkering down, so: 3 - 7,8,9

L8R

Dannihilator

This is what got me thinking about this, my race bike has a chain guide and bash ring, so I use the 9 set up on that, but ever since I put the bash ring on the trail bike, thus reducing it to an 18 instead of a 27. I noticed that the 3:1 ratio worked for me, all I was doing was trying to make 18 sound as confusing as possible. Trying to figure out a simplified method, by this table, I hoped to see if anyone had a solution to this issue. What gears do I cut out of the combination. I figure it would be 1st 2nd and 3rd on the back because I can climb in a 2-4 combo. This is one of the cases where each person has a preference, maybee I'm missing something here.

a2psyklnut

I'm just lazy. I keep it in the middle ring 90% of the time and just shift with the right/rear. The only time I may drop to granny is for long climbs. Oh wait, I live in Florida and those don't exist.

Have you ever seen that shifter that will run through (at the time the full 24 gears, not 27) in sequence? It was a grip shift type shifter, but both derailleur cables were attached, and as you rolled through the gears, it would shift into sequential gear ratios, so you had 24 different "clicks" that started from the easiest all the way through to the most difficult.

I don't think it ever made production, but it was a complicated solution to a non-existent problem. Kinda cool though!

L8R

Bokkie

Me too! Mostly middle ring (90%). I find cogs 3-7 work best but I never run the chain on 1-2 and 8-9 when on middle. I use granny on 1-3 and Mr.Big on 7-9. I can keep track of what I'm on as my SRAM XO shifters have numbers. None of that red bar mularkey for me, no sir, give me numbers everytime.

Chi

I run my large chainring a lot on the road (when I'm using slicks). I guess that's why it's the most worn down. The middle chainring I use during off-road biking, and the inner chainring like everyone said. I'm running a 24-speed.

My combos are like this:

1: 1,2,3,4
2: 2,3,4,5,6,7 (if I use 1 or 8, the FD will rub on the chain)
3: 5,6,7,8

Downhill is the only time I'm running a weird combo, like:

3: 1,2,3 (not producing power)

Maelstrom 

The reason I run every gear on the middle is I see tonnes of riders with only that middle ring and 9 spd at the back. I think the 'red line' is too tight by most peoples standards.