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

[TroySmith80]

That's the bike i want to build, but with 20" wheel on the back too, and another basket over it.

I guess nobody here has first hand experience riding bikes with this seat tube design eh? I've had a hard time finding many impressions of how well it works.

[jitahs]

Rode an fr8 a bit...the AST precludes you sitting up like a Dutchman, slack and somewhat low seat. Once I started to lean forward to get some power down or climb the seating position is way too slack for that for me. I'm 5'11" with medium-short femurs.

The delta between you and your wife is the same as btwn me and mine, 7 inches. She and I were both able to comfortably ride the unladen one-size-fits-all Yuba Mundo and Xtracycle Radish with standard seat tubes and moderately swept bars. They seem to have nailed it.

Might want to go with a super set-back post for you, switch to standard for your wife. There are ways to get more sb if you can't get enough with stock, aside from custom.

Edit: Seems like all the cycle trucks I see spec sheets for have a native 69 deg. sta, fwiw.

[edelbikes]

Some more information here:
Bakfiets en Meer » Blog Archive » Inspirations and Hypocrites

[suspectdevice]

Giant, Trek, Electra and tons of other megacorps offset the seatube like that. It's super, duper, duper common.
I can't remember which one calls it "flat foot geometry".
I think Giant and Electra have been suing each other lately. Not being able to shift your weight forward makes for a bike that isn't much fun to ride, but that's not really the point with cargo or comfort bikes, is it?

Remember that absolutely every possible frame design and configuration had already been developed and patented before the beginning of the previous century.

[jitahs]

Giant, Trek, Electra and tons of other megacorps offset the seatube like that. It's super, duper, duper common.
I can't remember which one calls it "flat foot geometry".
I think Giant and Electra have been suing each other lately. Not being able to shift your weight forward makes for a bike that isn't much fun to ride, but that's not really the point with cargo or comfort bikes, is it?

Remember that absolutely every possible frame design and configuration had already been developed and patented before the beginning of the previous century.

Dude, you're wrong. Look at the st angle - traces a dif path. Electra calls it Flat Foot Tech and it's bogus. BB is set forward of where the ST hits the frame, whatever you call that.

One of my fave things to do on my cargo bike is to make God's gift to cycling haul the mail to drop me. Single tracks, jumps, track stands.

So. Fun.

[progetto]

Giant, Trek, Electra and tons of other megacorps offset the seatube like that. It's super, duper, duper common.
I can't remember which one calls it "flat foot geometry".
I think Giant and Electra have been suing each other lately. Not being able to shift your weight forward makes for a bike that isn't much fun to ride, but that's not really the point with cargo or comfort bikes, is it?

Remember that absolutely every possible frame design and configuration had already been developed and patented before the beginning of the previous century.

I thought Steve Bauer had the patent on that geometry. If you are old enough you will know what I mean.