I'm starting to home in on what I'm looking for in a tadpole trike and what some options are (see my post on suspensions). Can you pick apart my logic on gearing and rear wheel size. I am kind of analyzing in a vacuum, although I do understand the gearing on my road and mountain bikes.

The executive summary: It's easier to get much lower gears on 700c wheeled trike than it is to get much higher gears on a 20" trike. There may be other factors such as stability and smooth ride that should be considered.

Read on...

Given the same crank and cassette, I understand that 20" drive wheel will result in a much lower low gear as well as a lower high gear compared to a 700c. It seems like 50-39-30 and 11-34 cassettes are fairly standard. I know what high and low gears (and gear inches) I need for my road bike to be comfortable in the hills I have around here and I'm assuming I'll want quite a bit lower gearing with the trike.

But I'm also concerned, to a lesser extent, about high gearing, again roughly comparing to my road bikes. I don't need to meet or exceed the high gearing of my road bike but I don't want it to be a huge difference.

I've been using some gear inch calculators and I'm thinking it is pretty easy to get much much lower gears on a 700c bike because of commonly available mountain bike triples. (one of which I can scavenge from my stable). For example, a 26X34 low gear is a lot (lot!) lower than my road bikes and within a gear inch or so to the 20" trike at 30X34.

For what it's worth, I understand rear derailleur specs - largest sprocket and chain wrap - so know I have to pretty much stay within those specs. Also for what it's worth, the effort of doing this modification is not a factor, I like doing it and have the tools and know-how to change cranks and chain wheels, etc.

On the other hand, there is not a heck of a lot that I can do with the high gearing on any bike or trike. You can't commonly get a smaller cassette sprocket than 11t. You can go up as high as 54t for most road triple cranks, depending on the chain wrap capacity of the rear derailleur. But from the calculators, even with the 54t ring, it seems to me, I would probably not be happy with this. It's not even close to what I'm used to. I'm certain I'd be unhappy with the stock 50X11 with 20" wheel.

So, am I thinking straight? That I can probably get a 700c trike nearly as low as a 20", but I can't get the 20" even close to the high gearing on the 700c? Has anyone gone through this sort of thing?

And, are there other factors II should also think of? For instance, the longer wheelbase 700c vs the shorter wheel base 20". Which would generally be more stable at speed going down hill? Which size wheel, in general, would tend to roll smoother over stuff you generally encounter on paved roads ( know that tire volume and PSI matters a lot here,).

I appreciate any comments you have!