Originally Posted by
easyupbug
I put these new Panaracer 650x28c from Bell's Bike Shop for a granddaughter on
Wheel Master Mach 1 RJ Project 650cc Wheelset HG Road, which advertises a 15mm internal rim, which I verified. As you see here at 70 psi they were only 24mm tall and 25mm wide. I assumed they were fakes or mis-labeled. After several emails Bell's "Service Team" finally replied and I quote "
Listed tire width vs actual measurement with calipers will often not match and will vary from brand to brand. Rim width, tire pressure, and manufacturer molds will all cause variances in the real world measured width on the tire vs the advertised size. just took calipers to several bikes and the shop and the listed width vs actual measurement varied between 3-6mm across several brands." In my 75 years and dozens of road bikes for my wife, kids and grandkids bikes I have never seen anything like this, have I just been lucky.
the nominal width on a tire is kind of meaningless unless the rim internal width is factored in. I run 25mm Vittoria Rubino Pros on two wheel sets - on the 17mm width wheels, these « 25s » are an actual >27mm diam. On the older 15mm width wheelset, the tires are actually 25mm diam. Likely your tires were « calibrated » for something wider than a 15mm rim. 15mm is effectively obsolete these days.