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I'm building up a 36-spoke dynamo front wheel for a Mongoose Envoy cargo bike. It will be used casually for short trips, but I weigh 230 lbs and I may have a child or a load of groceries on. The stock tires are 60mm wide.

I have a 25mm wide, aluminum rim from an old Mongoose mountain bike, however it is a single-wall rim. I have never ridden or even seen an aluminum single wall rim and I want to know if it will be strong enough or if I should buy a more modern rim such as a Sun Rhyno Lite. As far as I know, disk brakes put more load on wheels than rim brakes and, since disc brakes didn't exist when this single wall rim was made, will there be a problem using it on a disc brake wheel?

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  • Good choice going for 36 spokes minimum. – Criggie Aug 29 '20 at 4:20
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Single wall rims on disc brake wheels aren't especially any more problematic than with a rim brake. It's a pretty cynical way for bike manufacturers to allocate parts dollars, so thankfully it's not super common.

Putting a single wall rim on a cargo bike is a bad idea though. Single wall rims are far less structurally efficient than double wall, typically manifesting as being less rigid and able to support less spoke tension. (Specimens do exist that go the other direction and are strong but very heavy.) Typical singlewall aluminum ATB/hybrid rims can't really be built to more than about 70 kgf before buckling in the stand or having major fatigue problems, compared to 100 minimum for even a basic double wall. That's a massive difference in strength. Also, 25mm external is very marginal for a 60mm tire.

A Rhynolite or Rhynolite XL is an okay choice, but the world has moved on from the days when they were a great choice for something like this. They're not disc-specific, and you do get extra strength for the weight out of a proper disc-specific rim.

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    I prefer to buy a rim-brake rim, because I may want to add cantilever brakes in the future. The crazy thing about the Envoy is the tires measure 61mm wide (with calipers) but the rims are only 19mm wide on the outside. This doesn't look right, so I thought a 25mm wide rim would be better at least than the stock one. What is the appropriate width of rim for a 60mm-80mm wide tire? – BetterSense Aug 29 '20 at 3:42
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    @BetterSense check bicycles.stackexchange.com/questions/52587/… there's a bunch of width tables. – Criggie Aug 29 '20 at 4:21
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    If you want to be able to reasonably go up to 80mm, something with internal width 35mm-ish is what I would look at, i.e. a true plus rim. WTB does some in 26. – Nathan Knutson Aug 29 '20 at 4:36

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