Tuesday, March 8, 2011

Gear inches revisited

Now that the drivetrain has been redone, here's the new GI chart. It'll be interesting to see how different modifications will change the current gear inches. Let's have a look.

My new 21 gear setup produces these gear inches, a 13.7-60.4 range. I dropped a ton in the low end gears, but at the expense of high end gears. Even with a larger 42T chain ring compared to my old 40T, the high end has dropped due to the larger small cog in the rear. My smallest usable cog is 13T instead of 11T from the old freewheel.

Once I get the correct cables to get the 3x7 IGH working, the GI's will look like this. The range is 10.1-82.2. Much better than the stock 23.7-67.9GI range, eh? I'm getting a ton more low gears and the high end gets boosted up as well.

How does an 11-30 gear inch chart look like?

The top pops to 97.1GI's. The closer I can get to 100, the better.

Let's see if I can get the low end to drop even more. What would happen if I swapped the cassette for a 11-34 one?

The low end drops by 1 GI. The only real difference is the largest three cogs (bottom three rows of the chart). The ratios between gears is much more spread out when it has to go all the way up to 34T. The 30T chart in the previous chart above has a much smoother transition between gears. I'd prefer that one.

Maybe checking out the prices btw the two cassettes will help me make a decision.

SRAM 12-32: $16
SHIMANO 13-30: $19
SUNRACE CSM63 11-34: $19.50
SHIMANO CS-HG30 11-28: $20 (kmart)

I'm having a hard time finding what I was looking for, the 11-30T Shimano 7-speed am. Alternatives?

Shimano HG-50 13-34: $25 (amazon)
Shimano C-201 Megarange 8-speed, 11(13)-32T: $25
SRAM PG-73,0 12-32: $16.99 + shipping (bikeman)
Shimano HG-40 Megarange 8-speed, 11-34: $27

Since I am having trouble locating a 7-speed cassette with the cog sizes I'm looking for, I'm wondering how I can convert the trike to a 8-speed. There are plenty of 8-speed cassettes which have the specs I want.

The problem is that the chain on a 7-speed cassette already rubs the frame when it's on the highest gear (smallest cog). Adding an 8th outer cog doesn't seem possible. I called KMX to ask how they've managed to make it work on their higher end models which come with 8-speeds stock.

The rep confirmed that all KMX frames are the same and suspects the reason I can't get a 8-speed cassette on my Tornado is b/c the wheel may be too wide. It needs a 130mm wide hub. I'm thinking mine is wider which limits the allowable space to have an 8-speed cassette. So much for that idea. Unless I want to spend more cash on a custom narrower 130mm wheel, I'm stuck with the 7-speed. It's good enough for the time being, so I'm sticking with it for now. No need to spend the extra money now.

UPDATE: 3/16/11
I finally counted the cogs on the rear cassette. They are as follows:

13, 15, 17, 20, 23, 26, 30

I must remember that I'm not using the smallest cog. My highest gear is on the 15T cog. I'll be in good shape if I can find something smaller than 15T coupled with something larger than 30T. My actual GI chart looks like this:

Stock Shimano 7-sp G

Shimano 7-sp K


SunRace CSM6
Shimano Megarange 11-34T


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