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| When does 32 equal 28?
 When sizing tires, that's when. So please pardon me for a moment while I go on a little rant about one of the great frustrations of the bicycle world. Oddly there still aren't any binding standards in tire sizing. If you buy two different brands of tires that are labeled as having the exact same width, chances are they won't. Brand X may really be a 32mm as marked and brand Y may be a 28. Sadly even among very high-end tires the actual item is often narrower than what is printed on the sidewall. Why? Well, that's kind of a mystery, but Sheldon Brown has a theory about that which you can read here. Why do I mention it? Because when I say a frame has clearance for a 38mm tire I actually mean 38mm as measured with extremely accurate calipers. A real 38mm. But when you buy that 38mm tire it may really be 34. And there will be a little more clearance than you expected. Not a big problem, but a little annoyance. I recently built a tourer with plenty of clearance for a 35mm tire with lots of room for mud and the possibility of a wheel going well out of true on a 3,000 mile expedition. The high end 34mm tires my customer installed were really 28s. He was bummed and had to buy 38s to fit exactly the way he wanted. The 38s were more like 33s. Of course to make things worse, if he changes brands he may find that another company's 38s really are 38s. So this is a good lesson, especially for buying replacement tires in another country while on the road. Sometimes you just have to install and inflate the suckers to find out how wide they really are.
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