Monday, August 22, 2011

Do you really use all 72 gears?

My trike has 72 gears. Do I use all of them? No.

While explaining some info and sharing some opinions on trike gearing to one of the fellow members of the bentrideronline forum here, I analyzed my gearing and calculated how many of the 72 gears I actually use. Let's start with what I do NOT use.

- I never engage the IGH while in the middle chain ring.
That means the available gears in both low and high gears of the IGH are unused in the middle chain ring. It would be redundant to do so b/c it would pretty much just give me many of the gears I could otherwise just get by not engaging the IGH at all and just shifting to one of the other (smaller/larger) chain rings.

Since the IGH has 3 gears (neutral, low and high) and is matched with an 8-speed cassette, there are at least 8 x 2 = 16 gears I do not use.

- I also never engage the IGH to the low gear while in the large chain ring.
That's 8 unused gears. That's too similar to the gears in the middle chain ring w/o the IGH engaged. Remember that the IGH has some inefficiencies when engaged. In the neutral position, it's 100% efficient. So therefore, it's much preferred to not engage the IGH unless you have to.

- I also never engage the IGH to the high gear while in the small chain ring.
That's another 8 unused gears. This setup introduces more usable gears than the situation above, however switching back and forth btw chain rings and engaging/disengaging the IGH is something I want to avoid. For simplicity, I'd like to engage the IGH only t0 reach the extreme high and low gears for equally extreme situations. It is not to be used during normal riding.

- I don't use about 5 of the lowest cassette gears while on the largest chain ring with the IGH on high.
That's 5 unused gears. Since I've reserved the IGH for only the high and low end gears, there's really no use for all 8 gears in the large/small chain rings with the IGH engaged.

- I don't use about 4 of the highest cassette gears while on the smallest chain ring with the IGH on low.
That's 4 unused gears. Same as above.

So of the 72 gears on my trike, 16 + 8 + 8 + 5 + 4 = 41 are unused. I guess you could saying having these 41 "extra" gears is a side effect to the drivetrain modification that enables me to have ultra low 8GI and high gear inches of 97.

Q: So again, how many of the 72 gears do I use?
A: 72 (available) - 41 (unused) = 31 gears.

Wow, that's pretty astonishing! I only use 31 gears? That's less than half the gears. I just realized that! Time for a graphic.

Taking a closer look at the bottom left corner and top right corner of the gear chart, you'll notice there are overlapping gears when compared to the center three columns. Technically, the IGH only needs to be used to achieve the lowest granny gear producing an 8.9GI.

The second to last lowest gear of 11.7GI is too close to the IGH in neutral while in the smallest chain ring. That produces 11.9GI's. I can't say I can notice a 0.2GI difference.

This all means I don't really need three of the lowest gears with the IGH engaged on low while in the smallest chain ring.

Using the same logic with the high end gears with the IGH engaged on high, I don't really need the 68.8GI gear. The use of it would be purely for convenience. There are other ways to achieve this GI (w/o engaging the IGH).

So in real life use of trike, I actually only use 31 - 4 = 27 gears! Does that number look familiar? It's what's attainable with a 9-speed 3 chain ring crankset road bike. Though the number of gears are the same, the range definitely isn't equal to my setup.


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