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    Help understanding rim width


    Hi all,

    I’ve got these Velocity Blunt SS 27.5 rims on my gravel bike: https://www.velocityusa.com/product/rims/blunt-ss-584

    I’ve been running 48mm Pathfinder Pros this year, and they’ve been great for both gravel and road. Due to an upcoming move where I’ll no longer have any access to gravel, I’d like to switch to a slightly slimmer slick tire. The website says that the optimal tire width on these rims is 45-65mm… but what does that mean in practice? Would I run into issues if I use 42mm slicks… or even 38mm?

    Thanks in advance!

    by box_guardian

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    4 Comments

    1. AutoModerator on

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    2. EnvironmentalChip696 on

      Its a 650b hooked rim, tire selection may be limited for 650b, but you can essentially run any tire you would like down to the same internal width as the rim with little to no issues. Optimal tire width for gravel or mtb use is far different than optimal for road use. Find a tire you like and run it, you wont have any issues.

    3. sitdownrando-r on

      The internal rim width is 26-27mm. We’ll round up to 27mm.

      Refer to ETRTO tire standard chart [(here’s Schwalbe’s](https://www.schwalbetires.com/media/16/8f/9b/1654668257/reifen-felgenkombination-etrto-22-en-2.pdf)), a 27mm internal is safe for 35-83mm tires. Narrower than 35 and the beads of the tire could become too splayed out, impacting handling. Much wider and you can get a lightbulb effect that may cause the same.

      It should be noted that these are conservative measurements and many manufacturers are good with pushing the limits. Personally, I’d figure as narrow as a 32mm tire will probably be alright but I’d never run that narrow on a gravel bike anyway (I have 44mm slicks that are plenty fast and use 48mm on my 650B setup). My opinion likely aligns with Velocity’s recommendations.

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