shoota 

I have a set of Iron Cross wheels that have a rim PSI limit of 45psi. What are our options for a ~32mm tubeless tire that is suited for mostly road with the occasional 1-2 mile gravel road thrown in per ride, that works well at 40-45psi?

Marcus_Ti

How much do you and your bike weigh? Tires that low a pressure and narrow I'd be very concerned about bottoming out and damaging rims on pavement debris or potholes or speedbumps.

shoota 

All in combined weight would be around 210lbs.

I mean what were these wheels designed for in that they can only handle 45psi???

ThermionicScott 

I just watched the Stan's video on BST rims. They're designed to allow "nearly any" tire to be run tubeless. I wonder how much of the 45 psi limit goes into ensuring that non-tubeless-ready tires don't blow off the rim. So I'm curious if that 45 psi limit could be pushed a little if you have genuine tubeless-ready tires that fit snugly on the rims, perhaps with an extra layer of tape to make it extra-snug.

https://www.notubes.com/technology/bst

Marcus_Ti

Note the name "cross" in their name...In regulation CX you (used to) never run tires much more than 33mm or so, and you'd almost never ride more than 45PSI for the sake of traction as you'd want more tire "drop". Riding on, at best, hard earth and at worst a mudpit it didn't matter too much WRT damaging a rim (caveat--the odd tree root or barrier bunny hop). But using them on pavement makes for bottoming out (AKA rim damage) problems with tubeless, or pinch-flat problems with tubes.

Per @ThermionicScott that pressure limit is conservative and can be pushed. When you mentioned such a low max PSI I envisaged an MTB width rim at first blind guess, without looking. But, being a sub-400g alloy rim with a max of 930N spoke tension they're not hurly burly rims suited for pushing the envelope. And remember that pneumatic tires, and more so tubeless, cause spoke tension drop in the wheel when inflated. Following a 15% tire drop model, you'd be way over that limit in the back and right at it on the front...OTOH 15% is not the be all end-all.


This afternoon was Telenet CX World's up in Waterloo....and it was an absolute mudpit for both the men and women ...of course being pros they're riding tubulars, but they're using 33mm tires at all of 15-20PSI max.

shoota 

Wow that's amazing info dude, thanks. You know what's bizarre to me is that these were stock wheels on the 2017 Warbird. A gravel bike designed for wide tires, but using a lightweight, narrow cyclocross wheelset. Bizarre.
Additionaly, if you read the internet the 45psi limit is pretty hard and fast. Several reports of blowoffs after going just over, and my own friend swears he blew off tires at 46psi a couple. Needless to say I don't feel comfortable going over 45psi.

And for my intended purpose I'm not confident they'll work. I need something fast on the road, tubeless, and right around 32mm. I'm thinking Vittoria Terreno Zero 32, Terreno Dry 31mm, or something like the Hutichson Sector 32mm, GravelKing slick 32. I just don't know if 45psi is enough for those tires though. Grr.

chas58

Well, wrong wheel then for your application.

I have hook-less rims that are rated to 70psi. I don't really run my 32mm tires above 60psi. For gravel its more like 40f/45r.

i would think that "tubeless" tires would not stretch and could take 60psi. Tires designed for tubes might be able to be run with a max of 45psi (i.e. "any tire can be run tubless"). But that is with my wheels, not yours. Either way, when in doubt, I use skinny-stripper rim strips to help seal the air chamber and reduce the chance of blowoffs. Still - a blow off could easily put you in an ambulance - so personally I would stay within the rim specs.

Either run 40mm tires, or get different rims for your 32mm tires.

shoota 

You don’t think 45psi is enough for 31mm Terreno Drys set up tubeless?

Marcus_Ti

Stock wheels...what can I say? They're usually the place OEMs cut corners. Note how cheap those rims are: $25 a piece. In CX you break stuff and that is a wonderful sacrificial rim. I almost want to say back in MY2017 the Warbird was adverted as a CX racer

There really aren't any tires that will solve your quandry, mi amigo ....other than non-pneumatic ones.

chas58

Its good for gravel (I ride 40F/45R on gravel with 32mm). Its kinda low for pavement. Doable, but the steering will suffer a little (and to a minor degree rolling resistance)

shoota 

Thanks guys. I know I'd be fine with 40mm tires at 35psi but I already have that covered with my Warbird. I guess I'm looking for a different wheelset

redlude97

I blew a tire off a stan's arch right at the psi limit of ~50psi when seating a tubeless gravel tire. I wouldn't try to go much beyond the max listed tubeless. They are lightweight rims that aren't meant to be the most robust

unterhausen

some rim manufacturers spec higher pressures for narrower tires. I'm pretty sure the PSI is related to a structural limit, and narrower tires put less of a load on the rim.

Having said that, 31mm with 45psi = either pinch flats or dented rims

shoota 

Thanks everyone. I'll be passing on these wheels.

chas58

True - Take a look at enve's chart at the bottom of this page: https://www.enve.com/en/lp/g-series/

They do a good job of matching rim width, tire width, rider weight and riding type (gravel/road). Best chart I have seen.

That said - 32mm, 23ID, 170lbs, gravel = tire pressure in the 30's (with tires from 32mm - 45mm). I'm running 40-45psi on gravel (so, I agree with them). But of course, I'm not running 32mm tires on terrain where I'm gonna bang the rim. If it is that chunky, I'm on a bigger tire.