Thursday, January 18, 2007

Hang on a Sec

It's been seen here and here; and from another angle here, and gosh, folks love the stoker bar. Lets the little ones ride on the back of the Xtra without fear of falling off. Wished I'd have thought of it, but I must confess, I stole it from this design.

It's very simple to make an Xtracycle stoker bar. Mine is simply a sawed-off, cheapie mountain bike handlebar, a threadless mountain bike stem, a seatpost shim and a pair of grips.

The most difficult part would probably be finding a seatpost shim in the correct size, but most competent bike shops should be able to help. You'll need to know the inside diameter of the threadless stem—in my case, it's a 1-1/8 inch, which converts to 28.6 mm. Then, find the diameter of the seatpost (26.6 in my case) and subtract to find the difference. The part that won't compute at most shops is that there is, for example, no 28.6 to 26.6 shim. So I just looked at the catalog at the shop and found a shim close to those two diameters that had a difference of roughly 2.2 mm. These shims are slotted their entire length, they allow some expansion or contraction of their overall diameter to get the fit you'd need. For $8 and a couple of days of waiting, I ended up with a shim for 27.2 to 25.4—both very common sizes, but only 1.8 mm of difference. A seatpost-frame combination won't brook that much difference, but the threadless stem that I used easily drew .4 mm of extra tightening and has been very secure. I pick up the bike by the stoker bars as a matter of course, and the seatpost will shift in the frame before the stem will budge.

I sawed off the ends of the old mountain bike handlebars with a hacksaw, cleaned up the ends with a file, popped the grips on and put it all together. Sheer joy for the youngsters.

More views of the completed stoker bar

and a close-up of the shim.

Other variants can be seen here, here and here.


Tarik Saleh said...

Nice job. Have you ever ridden a full size person on the back? I am hoping I can drag elena around on the back when she is too lazy to ride from time to time. You are hyping my Big Dummy jones to higher and higher levels. Thanks Pal.

Mauricio Babilonia said...

You're welcome. Always happy to stoke the cargo bike meme. And yes, I've hauled a full-size adult for a short distance. Xtracycle's official propaganda says 200 pound limit for the Free Radical and 350 total for the whole rig including the person pushing the pedals. Looks like ample evidence over on Xtracycle's galleries of people pushing this limit here, here, here, here, and here.