From what I have seen and is pretty well documented is that Stans Rims specifically don't play nice with that style of tire, but clinchers under 30 psi is the danger zone even for 150 lb riders regardless of rim/tire from a pitch flat perspective. The problem seems to really show up with wider rims so you might be fine if you inner rim width is 17mm instead of 23 mm.
The issue is the supple cotton casing you want for good handling is the liability with setups that actual handle well because the sidewalls give too much at race pressure.
Cotton casings also degrade really quickly if not sealed and meticulously maintained and Challenge was the worst even over Dugast of FMB which now factory seal most of their tires.
I were running a clincher I would stick to Clement PDX or MXP, Michelin Mud2 or the Specialized family of tires.
I still think you can't beat the clement family of tubulars on a velocity major tom rim for economy of performance with whatever hub you have laying around.
Running tubeless cross setups is for people that really need to learn a lesson the hard way.
My take: I've run tubulars and clinchers with latex tubes and am in the process of building a set of tubeless wheels. Each has their merits.
Clinchers with butyl are not ideal. Swapping to latex tubes gives much better results. I'm 170 lbs and typically run my clincher/latex set-ups sub 30 psi and have NEVER rolled a tire off the rim. I've pushed the bead sideways enough to get debris stuck between bead and rim (once), but have never gotten the tire off the rim in a riding situation.
I ran a set of borrowed tubs last week and actually ran them too low. They were squirming on me which made me less confident riding. Granted, I did feel faster, but not sure I really was.
Tubeless haven't had the pleasure of trying yet. But there are certainly folks here (Andy and Cliff) whose impressions I respect who have had success.
For me, I am debating the tubeless vs. open tub and latex tube merits. My clinchers currently are all much stiffer than the Challenge offerings and I've had good success with them sub-30 psi. I still need to give pure tubulars a proper shake down, but am not entirely sold yet. Maybe I just need to get used to the squirm.
Thanks Kurt Schauwecker !
That makes me feel better about my decision to get 2 pairs of Mavic Open Pro/ Ultegra wheels (over the velocity A23, HED Ardennes Plus, or a super wide 29er type width rims).
The Inner Rim Width of the Open Pro is: 14.562 mm
Kurt - interesting take. Everything I've seen and experienced flips your input on it's head. Would love to hear more around narrow vs. wide rims and psi vs. rider weight. I've got 20+ lbs on your 150lb "danger zone" rider and have been able to run 30 psi or below since I started racing 5-6 years ago. Maybe I am N = 1, but would like to hear more. As for wide vs. narrow, certainly from a road perspective I've been able to run lower pressures on wider rims (A23s vs. Open Pros/RR1.1/Velomax). I've definitely noticed running my A23s lower in CX situations as well. But again, I am using latex tubes for CX now, which I think make a big difference in the pinch flat resistance area.
Also - for the anti-tubeless folks, I believe Justine Lindine (pretty consistent top 10 American) is running tubeless exclusively this year. I guess we'll see how he does. Also, Jake Wells did pretty well on tubeless during last year's nationals. That sample size is still pretty small, but it is growing.
Well I should clarify a few points, pinch flatting is the #1 mechanism to flat a clincher and a wider rim will help that for sure. I would consider rolling a clincher off of a rim to be the second most likely cause of failure unless you live in an area with a lot of punctures, we don't in Chicago.
30 PSI is a generalization and doesn't apply nearly as much to a rubber tire as much as a cotton open tubular. To put it in perspective, Challenge tubulars (Which I had 2 sets of) get really sketchy under 25 psi where as I have run Clement tubulars at 17/19 PSI with no problem. Cotton/silk sidewall tires just handle completely differently than a vulcanized rubber tire. Tire Rim interface is the limiting factor for tubeless tires as well as some clincher setups and there is some serious voodoo and trial and error involved in running low pressure clinchers.
The situation I have seen roll clinchers off of rims usually involves a good rider who is used to tubulars and is running sub 25 psi pressures on clinchers and hits a root on an off camber or cuts a tight 180 off camber. I have see the tube hemorrhage out the side clearly showing that a flat had not yet occurred. I personally have had less issue with this when running a narrower rim and praying to not pinch flat.
I don't think anyone who hasn't run properly setup tubulars has a perspective of what handling should be with a clincher or tubeless setup. There is no savings in the tubular wheelset vs a clincher and the tires might cost $125 vs $60-75 for a raceable clincher but you are going to burn through $20 worth of sealant over the course of year per tire assuming 2 oz/month per tire should you go tubeless. I can tell you that not running enough, or not topping off sealant is a huge issue with tubeless tires. Then you get into the issue of do you break the bead loose to add sealant or gum up the valve core with an injector. I can also say that I ruined 2 sealing rim strips getting properly seated tubeless tires off in the field to fix sidewall cuts. I have no doubt that tubeless works as I had success with Kenda Small Block 8's and American classic TCX tubeless wheels for gravel racing, but I would never run that terrible hard rubber, mud clogging OEM mess of a tire during an actual cross race. Certain good clincher tires with supple rubber sidewalls just don't hook up tightly enough to be an idea cyclocross race candidate. Michelin Mud2's were probably the best compromise of good bead seal and general handling for a tubeless setup if I went forward.
I don't deny that its possible to make tubeless setups work, it just takes the right tire/rim combo and having a compressor around. There is still a lot of voodoo involved, and if mountain bikes are any indication, no one wanted to race the super thick side walled "tubeless ready" tires for quite a few years because they never handle as well just the same way that a race car driver isn't going to race run flat tires because they don't handle well for the 1% of the time they save you.
Having read article from pro's that race tubeless they admit they aren't as good as tubulars, just easier to switch tires on so that your pit wheelset has the correct tire for the conditions.
Most of the tubeless interest I have seen was firmly from the 4/5 riders with one wheelset, hoping that tubeless was a magic bullet to save them more wheelsets and money who had never actually dealt with tubulars. I do think that tubeless is the future for the sport, but it doesn't involve garage hacking as much as standardizing in pairing rims and tires from scratch.
If you look at the Clement line of tubulars, you will find they are actually tubeless as they are a single bonded piece of rubber with glued on base tape instead of the hand glued Dugast/FMB/Challenge cotton/silk sidewalled type of tire with a latex inner tube. Tufo is also a tubeless tubular as well.
Thanks Kurt. Certainly some valid points in there. What I am still confused about is "pinch flatting is the #1 mechanism to flat a clincher and a wider rim will help that for sure". Are you saying a wider rim helps increase the chances of a pinch flat or the opposite? Maybe I am just reading your comments wrong. If I recall you seemed to allude that a wide rim would be more pinch flat prone in one of your last comments. With the above quote, I can interpret your comments to be either pro or con wide rims. The wide vs. narrow rim comments are definitely what piqued my interest. As again, everything I've seen, read, etc. pretty clearly points to wide rims decreasing the chances of a pinch flat (more air volume, less tire hanging over the rim, etc.). I can see how a wide rim might increase the chance of rolling the bead, as the reduction of the "light bulb" profile will put less force on the bead and reduces the angle needed to potentially separate bead from rim hook.
As for tubeless vs. tubular - I don't think anyone has said tubeless is on parallel performance wise with tubulars. Tubs are still king in the performance arena. I guess the big thing with tubeless is how much performance are you letting go to gain other advantages (cost, easier changes, etc.). By many accounts the performance loss is relatively minor, given a strong set-up. But you are probably right, tubeless is more appealing to the lower level racers working on a confined budget and looking to avoid the hassle of multiple tubular set-ups. You could also argue the performance gap between tubs and tubeless for this audience is probably less noticeable.
Wider rims help prevent pinch flats and allow a lower psi as such, but I think they are easier to roll an open tubular type tire off of since the tire doesn't neck down as much at the rim interface. My experience points towards those tires holding better on narrower rims, but being worse with regard to pinch flats.
I still think running a mud style tubular as your only race tire isn't out of the realm of most users as you can build a wheelset with tires for $500-$600. Look at a set of Stans, the cheapest wheelset is $550 without tires. If you buy used you can get a ready to race tubular set for $300 on rim brakes. That's a good value for 1 second gained around every corner of a cross course.
"Wider rims help prevent pinch flats and allow a lower psi as such, but I think they are easier to roll an open tubular type tire off of since the tire doesn't neck down as much at the rim interface. My experience points towards those tires holding better on narrower rims, but being worse with regard to pinch flats."
Thanks Kurt, totally on the same page now. Thanks for clarifying.
Great advice: I am curious, what are your top 3 "mud style" tubular tire favorites? It seems you prefer a rubber casing vs a higher TPI soft cotton tire.
Clement PDX for my top pick based on reliability, forgiving PSI range and availability.
FMB Supermud with the Latex Sidewall as a really great more expensive, hard to get option.
Clement MXP as a do all tire that takes a lot of mud to really clog up.
I can't really recommend the Dugast Rhino as I got burned when one of their tires wouldn't hold air brand new for more than 10 minutes, but we didn't know that until after we glued them up and they wouldn't refund or replace them.