Adaptive Seat Tube - Your experiences and opinions?

[TroySmith80]

Hi All, first post. I searched and didn't see anything.

I'm roughing out a design for a utility cycle and would really like it to fit both my wife (5'5") and I (6'0") as well as possible, and also just a spectrum of riders in general. In my research i've been extremely impressed with the design of the Xtravois 2.0 by Quixote Cycles. This bike incorporates (for the very reason i mentioned, i suppose there is no other reason to do such a thing) "Adaptive Seat Tube Technology" which they attribute to Henry Cutler's Workcycle Fr8 bike.

Basically, instead of terminating at the BB shell like normal, the seat tube terminates on the DT a few inches ahead of the BB. This gives a smaller ST angle. The idea is that as you extend the seatpost you get both a longer reach to the cranks and a longer reach to the handlebars. The as you extend it, the seat is supposed to arrive in a position very similar to what you would normally get with the next size larger frame. Combined with a telescoping steerer or adustable stem, this would in theory provide a bike that could very well suit riders of varying sizes.

You probably knew all of that.

My question is, does it work? I don't think there are any bikes in my area that i can try. Maybe when i'm in Portland I could try one, but i don't get up there often. I'd love to here the experiences and opinions (hopefully informed opinions) on how this all plays out in the real world. Any big compromises or downsides to the design? I'm sure it isn't perfect, but is it reasonably good? Good enough to incorporate into a design?

After that, the next question would be, what legal considerations are there when considering use of this design feature.

Thanks,
Troy

[Andrew R Stewart]

The highly angled back seat tube will shift the butt/knees behind the crank as the seat is raised. Seems to me that if this was the best body position for tall guys most all tall frames would be set up with the seat 15-20cm behind the BB (to pick a number). Perhaps this is not an issue for a utility bike...

Have you thought about using extending ST and stem? Maybe like a CoMotion periscope tandem with a similar stem.

As far as legal aspects that would depend on whether you sell your creation or not. Have you done a patent search yet? After a hundred + years don't be surrised
with what you find. Andy.

[TroySmith80]

Yeah, getting the knees too far back in relation to the crank could be a problem. I'm sure this Adaptive Seat Tube (AST) is a compromise, but i wonder if it's better than "normal" in it's ability to suit different sized people. Keep in mind, this is a utility town bike, so it's not something that anyone will be pedaling for hours at a time. It'll be 10 minutes here, 20 minutes there. It would probably be very rare for it to be in motion for more than 30 minutes at a time.

When you say "extending ST" do you mean something different than what is standard? I've definitely thought about extending stems, i mentioned it in the first post in combination with the AST. I've seen a fairly nice extending steering tube on a Bullit long-john. Something like that might work nicely.

I doubt my bike would ever make it to market, but who knows, it would be nice for that to be possible.

Thanks for the feedback. I've been googling for reviews or impressions on the AST but haven't been able to turn much up.

[edelbikes]

I've discussed this a little bit with Henry in the past, if you decide to use his design you should get in contact with him before. If it's just a personal project I think it won't be a problem for him. He seem to be a really nice guy, so it's good to acknowledge the work he has done on the subject.

[TroySmith80]

Hmm, I must say it had never occurred to me to speak to him directly. It seems to me like contacting a Ford design engineer regarding my garage project car. But perhaps it isn't. I noticed another bike today with the same thing, a Pathfinder Mini has essentially the same feature.

[edelbikes]

If I remember well, Henry has a kind of gentleman agreement with Mike at ANT for his basket bike:

Basket Bike 2010 par antbike, sur Flickr