I bought a bike used which came with a worn pair of WTB All-Terrain tires and I would like to order a replacement pair of tires, but it looks like I can only find them in 32mm+. I wanted to know why the sidewall of these tires say they're sized as 30/32 and if maybe the size of the tire changed over time? Is it possible these tires can be both 30/32? Or maybe I'm reading it wrong?

weird tire sizing


2 Answers 2


The 30/32 is WTB's old slightly gimmicky sizing system where the two numbers are tire casing width and tread width at widest point in millimeters. WTB is not using it any more, but it's still explained at Sheldon Brown's web pages. The rim diameter is the same for different tire widths, so any tire with same diameter and width somewhere close will fit.

  • Very interesting! I think I even saw the "Wilderness Trail Bikes' Global Measuring System" labeled on the tire so I should've known. I think you're right, thanks for the help!
    – jcarey
    Jun 22, 2022 at 18:51
  • so does that mean this tire would be called a "30mm" tire in today's standards? or is the "32mm" tire offered on their site the same?
    – jcarey
    Jun 23, 2022 at 18:01
  • In principle it's 32mm. In practice tire sizes are not precise enough that 2mm would matter, and fashion had moved towards wider tires. I wouldn't try to find an exact replacement, 32mm is really narrow for off road riding and those knobs aren't great for paved roads.
    – ojs
    Jun 24, 2022 at 5:53
  • Check tyre clearance with the present old tyres. How much space your frame and brakes have around the tyres is the only thing holding you back from getting wider tyres. These won't be necessarily slower but will offer more grip and comfort.
    – gschenk
    Nov 29, 2022 at 22:41

I believe 32 is the tire width, and is measured in millimiters (mm) not centimeters. On their website I see this model is described as 30TPI (threads per inch, describing the structure of the fabric under the rubber) and 32 width. Maybe that's why you see 30/32 on your old tires' side wall. Or perhaps the manufacturer specified a width range of 30 to 32 mm depending on the rim width you install the tire on; the tire will be effectively wider if installed on a wider rim.

Here's a guide for choosing the correct tire size: https://www.rei.com/learn/expert-advice/bike-tires.html I'm sure there are also plenty of questions on this website as well regarding the topic.

enter image description here

  • Woops! Got the units wrong, thanks. Yea looks like the labeling or sizing has changed and I wanted to know if the product you listed is a different size than the ones I have. I uploaded a photo of the strange labeling
    – jcarey
    Jun 22, 2022 at 18:50

Not the answer you're looking for? Browse other questions tagged or ask your own question.