Below, I post a few comments about buying and tweaking a Gerber 1981 road bike for usage with left hand and right sided Mert hand. Previous posts cover the brake lever and putting the Mert hand to use.
1. Frame size
I like my bike frames to allow for a relaxed grip, and so they should be not too long. If the frame is too large, one extends too far. Also, my disabled arm likes it better to not get extended too far for too long. So I went for an older model bike frame that is tall but not too long.
There is ample brand pride present on that bike. Gerber, Bruno Zingg.
2. Wheels, tyres
The bike that I bought is a 1981 Gerber road bike. It contains the regular 23-622 sized tyres. I got the rims changed from their original tubular tyre setup (collés) to regular tubed clincher tyres. That makes swapping tubes and tyres a lot easier for me.
3. Saddle position
To stabilize the bike when riding, I will place tension between the Mert hand fixed arm and the saddle. For that, the saddle must be ever so slightly angled to the back, not to the front. So I got myself a saddle with a saddle post that allows for these settings.
4. Down tube shift levers, friction shifting
Gear shifting with one sided access is an issue, obviously. So I went for down tube shift levers this time around (after getting the other bike set up with handle bar mounted shift levers). These friction shifters [Wikipedia] have the advantage of being easy to tweak and fix, easy to use (as all you do is sail by ear), and easy to access. Also, one has full control over the position of the derailleur. So I would typically switch gear in the back first, then modify the front derailleur settings until the chain seems to run where I want it to run. Since I rode such a bike as a kid, my fingers seem to find the right shift lever settings by themselves.
I got myself a duplex Paul brake lever.
The problem is to get brakes to stop in an absolute way. You want to just do a wee bit more than just looking at that brake lever and the bike has to come to a full halt.
That means the double pull lever that I mounted has to cause the rear brakes to close before the front brakes close. The way to do it is to fine tune tension very carefully.
6. Prosthetic arm / hand, Mert hand
Comfort when riding with the Mert hand also depends on vibration, effective force placed on the handle bar and degree of extension at the elbow.
Brakes and brake pads
6. Handle bar
I used regular tools and, for the most part, I did not wear any prosthetic arm when working on that bike. I am sure that the usual suspects including Otto Bock, Touchbionics and RSL Steeper would have gotten a kick out of having model amputees utter their usual non-sensical sentences such as waving around the heavy chunk prosthetic with "now that I can use a screw driver I have my life back", or, "it is the little things that make the difference" (while trying to pick up a really tiny washer that just fell down), or, "I rather provide a 300 dollar fix-up job on my bike with a 90'000 dollar prosthesis than paying a mechanic 300 dollars". Bwahaha : )