Sunday, March 20, 2011

Carrying children on your Bike Friday

We often take our kids to local places with our bicycles.  Bike Friday bicycles with their low mono tube design -- as opposed to the traditional diamond frame -- and small wheels create a distinct advantage for pulling children via a trailer rather than a child seat but also present an extra challenge.

After picking up a set of long rack braces I tested out a Topeak child seat on the back of my New World Tourist with a 25-pound bag of rice.  Setting up the rack, by the way, was straightforward but a quite annoying task.  But after an hour of jiggling and fumbling for different adaptors and parts, it was secured to the rear of the bike.  After a quick test ride it was clear that riding with the child seat was sub-optimal.  On a regular diamond-frame bike there is a top tube that one can use his/her legs to push the bike upright when at a stop.

That is, if the bike begins to tip over, one typically uses a leg to push against the top tube to keep the bike upright.

No top tube!

However, the monotube design of a Bike Friday takes away that point of contact such that  one will have to keep the bike upright via leverage on the handlebars or perhaps sliding a leg behind you to lean against the seat mast.  My conclusion was to pass on the child seat and only use the trailer when carrying children.  

While a child trailer is very stable -- all of them appear to be two-wheel designs -- they generally attach to the rear axle of a bike.  Consequently, when mated with the small 20" wheels of the Bike Friday instead of a 700c/27" wheel, the trailer has a noticeable forward tilt.  Particularly with small children who have a harder time reaching the floor and pushing back, this would probably cause them to tilt forward against the restraints and eventually contort themselves into some sort of equilibrium.  My solution is to flip the Burley trailer mount such that it attaches above the axle instead of below it.

Instead of the attaching to a point an inch or two below the axle, it attaches to a point an inch or two above the axle.  Resulting in a much more level trailer and presumably more comfortable kiddies.   


  1. This is cool. I've been considering getting a Tikit but was hoping there'd be a way to put a Burley on it. Do you have any thoughts on how a Burley might work on a 16" wheeled bike like the Tikit?


  2. Well ... based on some quick estimates, the attachment would be about 3/4" lower.

    My NWT as shown (Primo Comet that measures a smidgen more than 30 mm) ...

    (30*2) + 406 = 466 mm diamter

    A tikit with the widest tire (Greenspeed Scorcher that reports to be true to its claimed width of 40 mm)

    (40*2) + 349 = 429 mm diameter

    So the height difference should be approximately, (466 - 429)/2 mm or 37/2 mm or a little less than one inch (18.5/25.2 or 3/4 inches).

    My guess is that it would tilt a little bit more. Since my setup has the bar pretty close to level, I'd think that it would be fine such that flipping the Burley mount would make a much bigger difference than the 406 versus 349 wheel.

    My concern about the tikit would be getting wide enough gearing. The stock tikit has low gears compared to typical road bikes due to the small wheel. When pulling a kid w/stuff in a moderately hilly area like Arlington, however, I think that you would want loaded touring gearing which for most people puts them in the low-20s/high-10s for a bail-out gear. Remember, you probably rather not mash the hell out of the bike where people typically man-handle the handlebar. Whatever you do to get low gearing, you still want to make sure that you have high enough gearing for normal riding without the kids.

    Simply based on calculations in my head, I'd think this means ...

    (1) SRAM Dual Drive: by far the easiest solution here

    (2) Double chainring crank with front derailer

    (3) Really wide planetary gear hub/crank: probably the most expensive and elegant option.

  3. Another way to level the trailer would be to equip it with smaller wheels. but that might be a chore, as trailer wheels are special.

    Yes, you are right about the issue with holding a monotube bicycle upright when there is a load on the rear rack. It can pivot around the line between the handlebar stem and rear wheel contact patch.

    I know someone who used a child seat on a Raleigh Twenty and I'll have to ask how she managed the problem.