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I am using an old Xtracycle Free Radical to convert my hybrid 90s Specialized CrossRoads to a cargo bicycle.

The Free Radical was originally designed for 26” wheels, but many people used them on 700c bikes using disc brakes.

My plan is to stay with the 700c tires, but move to disc brakes because the 26” to 700c V-brake conversion kit was discontinued a long while ago, and the FreeRadical tail does have an area to mount disc brakes from.

My rims are old Araya 700c-PX 45 rims, but years of using the bike with pad brakes has deeply carved out the rims, so I fear that I have no choice but to replace them both in this project to stay safe. In order to cut down on costs, I’m going to build the wheel set and put together the disc brake in the rear. I’m reading Sheldon Brown’s Wheelbuilding site, but I am having a hard time figuring out what components to use to build these rims and the rear disc.

Here are some details about this build: I weigh about 125 lbs. The Xtracycle can haul up to 200lbs (additional). I doubt I’ll ever haul 200 lbs, I’m mainly going to be getting groceries and running errands with it. The Xtracycle can only take a disc brake with a 203mm rotor. I’m attempting to build this economically, so I’m hoping for decent quality, at an affordable price that is lower than buying pre-made new wheels. I do have access to a bicycle co op where I may be able to harvest used parts.

Do you have any suggestions on what type of rim, spokes, hub, rotor and brakes I should use?

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    Welcome to the site! Please note that specific product recommendations are off-topic here because they are not very useful in different parts of the world and quickly become outdated as new products come and go. A general advice on components' properties, however, is very much welcome here as it will help you and future readers to make argumented decisions for years to come. – Grigory Rechistov Sep 16 '18 at 6:03
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    Regarding the wheel building: You can get a set of pretty solid 32 spoke disk brake wheels for a bit over 100€ (e.g. these with quality Mavic and Shimano components). I doubt you can even get the individual components for less; the rims alone easily cost 25€ each. Personally I also hate wheel building, it’s hours of tweaking partially conflicting parameters (e.g. true-ness vs. individual spoke tension). So if you can save yourself the trouble without additional cost, why not? – Michael Sep 16 '18 at 8:32
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    I had to google for what a freeradical was. Turns out its a rear subframe for an upright bike that moves the rear wheel backward, and cantilevers under the original dropouts and the BB housing. One needs to extend the chain and rear mech cable, and any lighting cables and brake cables/hoses. xtracycle.com/wp-content/uploads/2018/03/… is a stock photo. Purpose is to provide more space for load, in Panniers or on the rear rack. – Criggie Sep 17 '18 at 3:50
  • my 2 cents - if you plan to carry kids or any cargo that makes your center of gravity higher, I would reconsider the 700c tires. I have a 26" free radical xtracycle, and would love to change the back wheel to 24". I had about 2 occasions where the bike tipped to the side while standing, with my child in it - and I couldn't stabilize it - and a few scary but successful struggles. it was very frightening but luckily I've learned to avoid this since. regardless - I love the xtraccyle. – Yonatan Karni Oct 10 '18 at 8:25
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Do you have any suggestions on what type of rim, spokes, hub, rotor and brakes I should use?

For cargo bike purposes you obviously should prefer sturdiness over light weight for wheel components.

A wider rim would allow you put wider tires which can help with high cargo weight. For 700c wheels, rims that can accomodate tyres of at least 40 mm width are reasonable.

Previously, one would recommend going with bigger number of spokes per wheel in such wheels — 48 if you are really dedicated to find them as not many vendors offer them, 36 if possible, 32 if no other option, and avoid modern rims and hubs with less than 32 holes. However, I am unsure if this advice keeps up with the times, and it may well be that 28-hole rims are as good as 32-hole these days.

For spokes, use the thickest straight-pull available. For nipples, use brass ones.

For hubs, use compatible ones. Given that you don not plan to spend too much money on the project, just use the best you can find to match the rims and the frame/fork.

I do not think that it makes any difference as of which rotors to use, as even the cheapest ones stop things as efficiently as the fanciest ones, while being only heavier.

For brakes, it depends on the terrain where you would ride this. If the area is mostly flat, I would say any decent modern disk calipers would do the job. If there are prolonged descents, then you'll have to look for four piston downhill-rated options for front wheel. With 203 mm rotors, look after the compatibility — most likely you will have to use adaptors from 160/180mm to 203mm.

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