I need to replace my rim, and I'm hoping to rebuild the wheel myself. It would be really useful to know the ERD (effective rim diameter) of my current rim, so I can see whether a straight swap will be possible.

The rim I've got came standard with my 2022 Ragley Big Al, it's a 29" WTB ST i30. I've tried the WTB website to no avail, and my Google-fu has so far let me down. Does anyone know where to find the specs for my rim?

3 Answers 3


Initially, I, too, could not find a listed ERD for WTB ST i30 rims on any of a few websites and was going to suggest that perhaps one of the many spoke calculators online may be able to help you. Then, however, I came across a discussion of wheel building with WTB rims on another online forum. The biggest take from it, is that one should perform all the required measurements oneself. Reference Sheldon Brown's article on obtaining measurements needed for spoke calculators for the how to's. Obtaining these measurements is a little difficult during the shopping process when you may have neither the rim nor the hubs in hand and thus must rely on the manufacturers listed specs if they can be found.

After continuing a Google search querey of "WTB ST i30 rim ERD" one of the first hits was this website which has the nugget of information you seek, namely, the ERD of the WTB rim ST i30 (30-622, 32 hole) is 603.

  • Thank you @Jeff that's exactly what I needed. I could swear I googled that exact thing and came up with a bunch of retailer sites, plus the WTB site... Which doesn't list the spec!
    – rosscova
    Apr 25 at 1:23

If you're trying to re-use the spokes (which is not necessarily wise, but say you are), you don't care about the rim ERD. You care about the spoke lengths you're working with.

The spoke lengths in your existing wheel are not necessarily perfect.

The spoke lengths in the wheel you're building don't necessarily need to be perfect, just pretty close. (If you're using aluminum nipples they should be perfect though).

Remove one spoke per side and measure it. From there you can work with a spoke calculator to see what rims you can use if you didn't want to replace the spokes.

Once you have a spoke out, you also know the ERD of the rim you have because you can measure it, then measure the hub and the thread engagement of another spoke of the same set, then use those numbers in a spoke length calculator to infer the ERD.

You can use different length nipples to augment the effective ERD a little as needed.

  • Thank you, that's great advice. I am considering reusing the spokes, since the wheel is quite new (just a dented rim). I'll try to do the measurements before trusting the calculators.
    – rosscova
    Apr 25 at 1:25

I emailed WTB the ERD of the 29 st light i30. Is 605 mm. I confirmed that by measuring mine

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