North asked for our take on tubeless tire retention bumps on rims. If you can't picture what those are, the following photo highlights what we're talking about.
Are these necessary? VeloNews' Lennard Zinn seems to think so, as does one of my "favorite" wheel builders on an Internet forum. These discussions always wind up in a sort of "no true Scotsman" fallacy for me - "no true tubeless rim needs rim tape," "no true tubeless rim lets the bead unlock when flat," "no true tubeless rim needs to be inflated with anything but a floor pump."
To explain further, the purpose of the bead bump is to prevent the tire's bead from disengaging if the tire goes flat, and also to prevent burps that could cause the tire to go flat. When you inflate the tire, it creeps up over the bump and gets locked in place. Simple.
We sell rims that have them, and rims that don't. Easton R90SLs (picture just above) have them, HED Belgium+ don't. White Industries G25As (pictured at top) do, All Road 50s and 38s don't. The most "you can't burp this" rim we've ever used - the Stan's Grail - doesn't, but Cafe Racers, GOATs, and RCGs do.
Here's my take. Considering that tubeless rims didn't exist until about 2010-ish, how did we survive all the flats we got before then? A tubeless tire should be no more likely to go flat "instantly" than a tubed tire. The same things cause flats to both, and tubeless tires are generally (and wisely) used with sealant to prevent and/or mitigate flats. Tubed tires actually did have a history of coming off pre-tubeless rims (Zipp 404s were kind of well known for this, but there were plenty of other rims that were "too easy" for tires to come off of). We forget all of this stuff. People now think that tubeless rims created the "difficult to put tires on" scenario, but take an old set of any Campagnolo rims you want, and a Vredestein pre-tubeless tire and get back to me when you get it installed. Coronavirus will be a distant memory before you're done.
Zinn also notes a lot about burps. I recently saw a mountain bike tire burp for the first time since forever (Katie* put it on an instagram story), and it's such a rare thing to have happen that you basically forgot it could. Road tubeless tires don't burp with any regularity, either. We've talked about this equation before, but it's pressure x volume. MTB tires are low pressure/high volume. Road tires are low volume/high pressure. Cross tires are where it gets fun, because they are low pressure/low volume. You can read a rack of stuff we've written about this here. For cross, Stan's Grails have a bit of a "cheater" (i.e. wide) diameter which means that you might break a tire bead inflating and seating tires (I sure have) but there is zero zip zilch chance you're going to burp them. Easton R90SLs are more of an easy fit, but they hold the tire quite well without burping. Is that the magic of the bump? It could be.
So, are bead bumps necessary? I don't believe that they are. They may be helpful in some use cases, and I think they don't hurt. But the idea of their absolute necessity is lost on me. The Zinn thing in the link references a HED Ardennes rim. Coincidentally, North's other ask me anything question was how to get a Continental GP4000 tire to disengage from the bead shelf. Clearly the bump is not the only thing that keeps the tire engaged.
I'm still not the world's foremost evangelist of road tubeless. It gets better for sure, and we are probably still creeping along toward its ubiquity. But it's not settled science yet, there are big manufacturing standards and variances to deal with, and a big tell to me is how many people want us to set up their tubeless kit for them. It has to be something that almost anyone who owns cycling shorts is completely comfortable doing for him- or herself.
*Katie, who gets mentioned in several of these things, is my former wife. Many of you know that. We are not the typical "that a-hole!" "that bitch" formerly married people.
The response for ask me anything questions has been sparse so if you've got one, hit us up.
Tomorrow's post will be about how the November corporate ship navigates the unknown waters of a rather challenging situation.
Sneeze/cough into your elbows, please.