Hello everyone, I've been lurking a bit here and learning from the many very talented builders on this site. I am not a framebuilder but am hoping to attempt my first this winter. Lots to talk about there and I'm not going to bother you with it, at least not right now.
For now, i'm interested in feedback on my design.
Anyway, here's my design. Please let me know what is stupid and should be changed or what could be done better. There are a few design compromises i'm aware of but have chosen for important reasons:(SKIP THIS IF YOU'RE ADD)First, the reasoning and experiences leading up to it. My wife and I each have longtail cargo bikes right now. We like them a lot in many ways, and we love what we can do with/on them, but they are also a pain in the butt in other ways. They take up a lot of space in the garage and can't be hung on the rack with the rest of our bikes. We can't put them on our roof-rack and take them places. They can't be put on a bus rack. For my wife, they are heavy, difficult and awkward to move around and deal with (she's not very strong). They also don't handle as nicely as a normal bike. Lastly, we find that we very rarely use their full cargo capacity, and could get by with less.
So i've been thinking about what would work better. A regular bike with a couple large panniers and a large front basket would do pretty well, but that's too easy! Also, while you can fit a lot of small items in the panniers, it's hard to fit one large item. Front baskets make the bike tip over and make the steering difficult. That led me to thinking about cycle trucks with their frame-mounted front racks mounted low over 20" front wheels. Then i thought why not do the same in the back as well--another 20" wheel and another large and low rack. Some googling revealed that i'm far from the first to think this might be a good combination and i found several bikes that resemble very closely what i was envisioning.
- James Black Cycle Truck
- Kemper Lorri
- EBS Turn (scroll down a little)
- Humble Mini Cargo
- Also influences are two of the most well thought out bikes i've come across: Quixote/Clever Cycles Xtravois 2.0 and the Juiced Riders ODK
I contacted a few of these builders and they were able to give me some direction in sorting out geometry. I did a lot of research and found tons of info regarding bicycle geometry but it was almost without exception written assuming a 26-29" wheel size and i was unsure if it could be applied directly to a bike with 20" wheels or if i would need to change things. Researching mini velos and folding bikes provided some help as well, but there is far less information about those than about "normal" bikes.
- The seat tube is cantilevered WAY out past the mixte style chainstays. This is because very low step through height is critical and because i wish to use a standard 27.2 x 350mm seatpost. I'm thinking of using a straight guage 4130 tube 1-3/8" x .095" (34.9 x 2.4 mm) tube for the seat tube, with a sleeve in the top 4-6" to fit a 27.2 post. This is one of the things i'm unsure of.
- The chainstays are abnormally long. This allows for an e-assist battery to be mounted between the seat tube and the rear wheel, and also allows for lots of heel clearance for panniers and other rear loads.
- Racks: Bikecad only displays relatively standard racks. These are just placeholders for whatever rack design I eventually decide on. The front rack will be frame mounted (not fork) and both racks will be removable so that they can be replaced with a better design or a different modular accessory.
I'm hoping the bike can be fairly suitable for both my wife (5'5") and I (6'0"). I'm thinking of using a Montague Octagon extendable steer tube to allow for quick adjustment of handlebar height by several inches. I had thought about using Workcycles' Adaptive Seat Tube design as well, but have decided against it for now, mostly for the sake of simplicity since i've already got a fairly unconventional build ahead of me.
Wheels 20" ETT 560 ST C-T 530 Est BB height 265 CS 465 HT Angle 73.5 ST Angle 71 Fork offset 30 Trail 41 HT Length 240
These first two pictures show the bike setup for my wife's height, the third is for my height.