Those are not tubeless ready.

Around that time period there were some, like me, who experimented with making rims that were not explicitly tubeless ready, tubeless. And we mostly lived to tell about it.

But now that there are fantastic new tubeless-ready rims (like the new 2020 303 Firecrest or 303S) out there, it's just not worth the risk. Just get the new rims, if you can. Or when you can.

That’s funny. Reminds me of my high school days.

I have heard people state that with enough Gorilla Tape and Orange Seal any rim is a tubeless rim, but I would be much more inclined to do something dumb like that with a lower pressure application like a gravel or commuter bike.

Stan’s sold a kit for it: two wraps of rim tape, sealant, valve stems, and Hutchenson tubeless tires.

I used it on some 2003 Ksyrium rims (sans the tape since that rim bead has no spoke holes) and it worked fine, even riding at 120psi. No burps, no blowouts. The overall experience sucked though, mostly because the 1st gen tires were expensive and cornered and rolled poorly. Went back to tubed Contis when they wore out and was much happier.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

What's the risk with a high pressure tire? The tire will blow off? Or burp out air unexpectedly? Or just leak?

All of the above. The first two can lead to some pretty severe crashes

are you sure? i rode the 303 firecrest as tubeless before the new 303 that came out this past year. i honestly don't know (don't remember) if they were listed as tubeless ready. i rode them both as gravel wheels (tubeless), with 36mm and 38mm tires, and i rode them as light gravel with 30mm schwalbe pro ones on them.

i'm not recommending anyone else do so, if they're not supposed to be ridden tubeless, but are you sure they were not tubeless ready?

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Dan Empfield
aka Slowman

I would worry about blowing the tire off the rim. The tubeless tire (or tyre for UK/Euro crowd) has a shelf that the tire bead sits on that locks the bead into the bead hook. Two things would concern me;
1. Many people have had the experience of a poorly installed latex tube sneaking under the bead and blowing out the side of tire/wheel. I imagine a similar process happening with a non-tubeless rim used as tubeless.
2. I also would worry about your Zipp's. I had a set of 404 Firecrests of the mid-2010s vintage and those rims were super easy to install tires on. I tried a set of the Vittoria open tubulars on those wheels and I swear they were so loose the tire would almost fall off the rim when they weren't inflated. I headed out for a ride on a really hot day and I am guessing the the combo of a loose tire and an increase in pressure from the heat did blow the tire completely off the rim. This was on level ground so there were no added issues of heat from braking. Brake heat only adds to the problems because one of the tricks for installing tight tires is to toss the tire in the dryer to add some heat. It has been a few years, but I want to say that was the last straw for those Zipps. I replaced them with a set of Jet 6s and the same tires never were as floppy-loose as they were on the Zipps. I don't know about your 303s, but chances are those might be a bit undersized as well.

Yeah, Zipp was waaay late to tubeless for the 303 Firecrest. Believe it or not, the latest 2020 version of the 303 Firecrest is the *first* tubeless 303 FC. (Here's a 2018 review of the 303 FC, specifically pointing it's not for tubeless use).

Now, 303 NSW is different. Those went tubeless I think around 2017-2018. But still way after 2012.