little person road bike

[jgerhardt]

I am working on a new frame for a little person and I would love some help with the design.
The guy this frame is for has dwarfism and is 4'-2" tall. His torso is proportionally longer than the rest of his body and also due to a lack of flexibility will have a rise to the handlebars instead of a drop.
Also, one of the bigger design issues is the fact that he wants to have a wheel size no smaller than a 24" wheel, originally he wanted 650b, but I nixed that as the saddle would be a couple of inches shorter than the wheel unless he had a crazy high BB height.
FEC1406-Jake-V1.jpg
We will be using compact cranks that have been shortened down to 100mm.
Even with the lowered BB height of 196mm he still will have to jump up to the saddle, due to this we are going to go with a dropper seat post to make it easier to get into the saddle.
One of the bigger design issues I am having is chain interference with the seat stay. To avoid the front der. hitting the seat stay I was planning on going with a segmented/wishbone style.

So, what am I missing? thoughts? ideas?

[Michael Gordon]

Hi Jeff,

It looks like you still have some room for a little bit taller seat tube. Keeping the top tube at the same height, can you go with a taller seat tube, and take the seat stays up a little higher to clear the chain. It would be like a traditional women's frame.

women's frame.jpg

[jgerhardt]

Since I am going with the dropper seat post, the maximum insertion is 150mm. I have it set right now so that he can lower the saddle height 15mm. At 300mm this is the shortest dropper post out there. With that post there is no option of using a longer seat tube. My original design is very similar to what you mentioned.

[Eric Estlund]

I've built a number of these before my Winter days. 20" wheels and flat bars will help with a lot of issues. You may or may not find that a diamond frame is the best option. I think some of the issues leading you to a dropper post can be overcome without the challenges it will create for you and him.

Keep an eye on BB drop, and if using a derailleur system, cage length and gearing. Factor in rider strength with crank length, chain ring and tire size when looking at gear ratios.

Odds are good that your client is used to poorly fitting and poorly designed equipment. I would recommend helping him towards better solutions, even if they initially run counter to some of his preferences.

[christian]

Could you potentially go to a 20" front wheel, do mixte-style laterals from the head tube or a 2004-Cannondale-Jekyll style trunion mount, and pass the seat post through that space. You could then triangulate the laterals to the down tube, making a design not dissimilar to a Moulton. I think the geometry of this would be much easier with a 20" front wheel though.

Not sure that's superhelpful but might get you thinking.

You could also look at the Elephant kid's bike:

[christian]

M-gineering may also be informational:

http://www.m-gineering.nl/heresy.htm

[Rayburn Shaun]

What is he riding currently?

[BShow]

I have zero relevant experience and not a builder so I have no idea the feasibility of my thoughts here.

That said, there are two possibilities that jump out at me... 1) a segment of tubing angled upwards to connect to connect the seatstays higher, almost creating a second seat tube (albeit at an extremely slack angle and capped off). Aesthetically, I think this idea “sounds” like a pile of poo. 2) Use radically curved seat stays that angle up from hte seat tube and then curve down to the dropout. If that makes the rear end too noodly, you might be able to use beefier chainstays to mitigate the adverse effects. Aesthetically, this might not look horrible if you can curve the top tube a bit to compliment it and even give a bit more standover... though it looks pretty tight as is in your design. Also, this could open up the rear end for a cleaner disc setup if you're so inclined.

What about a hammerschmidt chainset rather than a traditional front derailleur setup. Or maybe even a 1x with a wide range cassette?

Idea #2:
bike.PNG

[jgerhardt]

I've built a number of these before my Winter days. 20" wheels and flat bars will help with a lot of issues. You may or may not find that a diamond frame is the best option. I think some of the issues leading you to a dropper post can be overcome without the challenges it will create for you and him.

Keep an eye on BB drop, and if using a derailleur system, cage length and gearing. Factor in rider strength with crank length, chain ring and tire size when looking at gear ratios.

Odds are good that your client is used to poorly fitting and poorly designed equipment. I would recommend helping him towards better solutions, even if they initially run counter to some of his preferences.

Eric, I agree with you that 20" wheels with a flat bar would be ideal, however he wants as "normal" of a bike as possible. As for the gear ratio's, I am going as low as possible with that super short crankarm.

[Eric Estlund]

I hear you. Sometimes it's hard to steer people away from what they have decided they want.

My point is that cramming stuff on there that doesn't fit makes the bike less normal then one sized and scaled appropriately.

[whydomylegshurt?]

How about running the seat stays to the top tube? You could have the stays at a slightly more normal angle that way and still maintain the standover clearance. It would be sort of a reverse GT triple triangle.

Mike Busch