I have ridden a Marin + Xtracycle 365 for a couple of year nows and, having done my initiation with insane loads, have now settled down to realise what I use it for and a lighter frame design would be fine. I really liked the look of your Xtravois and Vanilla has just now caught my eye.

A request for ‘open source’ drawings on the web please … or at least some drawing with problem/advantage items pointed out.

A couple of questions/observations;

a) why would one NOT want to make a ride as short as possible? Surely this is going to strengthen the rear end stop lateral (?) flex.

b), I note what you say re bottom bracketing being too high. Used to road bikes, I find this with the Marin already and would like to go up to 700c on it, at least on the front. I only ride on tarmac and would like a less aggressive ride.

Would it be possible to have the seat tube extend downwards below the chain stay to hold the bottom bracket shell, as on some consumer model bicycles (mostly cruisers/shoppers)? I don’t know the name of this. The X would also allow for the third down tube of a classic mixte frame.

My background is actually as a reformed biker (motorcyclist) and I am loving the lines of these frames. They are exactly like the ‘classic’ hard tail chopper frame and I reckon you frame builders could learn a little about finishes and details from looking at chopper design, e.g. on the Xtravois, the rear upright could be curved to follow the line of the wheel not straight.

Just a word on the Muirwood, if ever it comes up. I cannot recommend it for use with an Xtracycle and would actually actively warn off it. The dropouts (?) are deeply recessed and interfere with the chassis of the Xtracycle. I bought a bike for specific use with an Xtracycle and wanted a steel frame and the shop put it all together but did not tell me or point this defect out.

I am not entirely sure how much contact I have with the tophats going on down there. Was worried to begin with and always promised to go down with an angle grinder once the bike got older and “fix” things. Then, as I did not die, forgot about it. but is it still a concern, hence my interest in custom built frames.

As an aside, I also do not appreciate the X’s flat metal bracing brackets and cutting ‘U-extension’ onto tube where it joins the frame. Perhaps you or they could offer some machined spacers to fit narrow cross tubing? It could be more elegant. Again, I am waiting until I do a strip down to see how much damage is done by that painted metal to painted metal join … which is bound to rust and lead to fracture at some point.

Other wish lists are a fender busting, single hard/dry case storage container that could fit onto the mounting posts of the X … or a frame to build the likes around … or a box to fit in the space between the frame and the X which fitted onto the old brake bosses. I mount my U-lock there right now but it a great waste of very central space and it would be nice to have a little secure tool container etc.

Yet Cannondale used huge, round boom tubes. What was the net effect? Probably not much difference in ride, but a lot of wasted material. All this is a long way of saying, one has to be careful making judgements. Things that look stong aren’t necessarily so. The last 30 years of tandem development have left a lot of good-looking ideas by the way-side. Long-tails are some 6 years old. I reckon there’ll be a false start or two. :-) I’m glad there’s so many players taking to the field.

A long time ago I asked Xtracycle’s product manager why the stays of the FreeRadical rear of the front bridge were curved instead of straight — wouldn’t it be stronger and lighter if straight? And the answer was basically that it looked unsexy straight. Since then I’ve looked upon the freerad as a sculptural object to admire. The curves also serve as emergency footrests and supports for the footsies, which function is served in the Surly design by separate arced tubes welded on to the straight stays. Which is really more functional?

About those chainstays. Xtravois has a round boom between the bottom bracket and the front bridge. The Surly design has an ovalized tube. Sacha’s got twin stays much like a regular bike. My intuition suggests that round is best at resisting torsional, and twin stays best at resisting lateral flex, with ovalized somewhere in the middle for a given material weight. I think twin stays are prettiest paired with the double tubes above.

My current running configuration is a Kona Dew Deluxe, which is not particularly a lightweight frame, with Xtracycle and 50-100lbs of cargo (SM + stuff). If a_sport_utility bike is the goal, this configuration is too whippy. Sporty here meaning the ability to deliver/withstand high-performance, as well as load-carrying capacity.

Travelling at 20+mph with those loads, the bike’s torsional flexion while cornering begins to feel like 2 separate bikes; the rear wheel tracks at a sigificantly different rate than the front. This is particularly pronounced while negotiating a bumpy corner, where the backend begins to dictate the path through the corner by hopping over bumps and swinging through the air, however briefly, inducing a whip-like motion to the front-end. This means that the bike can alternately oversteer or understeer, depending on how the rear wheel attempts to negotiate the turn. I suspect this is due to the front-heavy nature of this X-conversion, combined with a fairly significant amount of rear-weighting. The unpredictability reminds me of the older rear-engine Porsche’s.

I guess it all comes down to the goals of the designer and buyer. A leisurely cruiser with cargo-carrying capacity will probably not be the same design as a true sport-utility bike. Sign me up for the latter, while I look at and admire the former.

having run into such difficulties with his own expert hands, sacha told me how much more impressed he was with the FreeRadical, and I’ve felt the same about Xtravois — best way to appreciate something is to try to improve it!

I’m starting to modify my own way of thinking as well. I’m backing away from wanting a bike that can easily and regularly haul 200+ pounds of cargo to wanting one for 50-75lbs.

I’m beginning to think it is about the space, not the capacity: Volvo Station Wagon vs Chevy Crew Cab pickup. So to speak. But, boy do I have a soft spot for those old 3+3′s with a full size pick-up bed. :-)