Zaskar

Okay first off, I know. These numbers are for my safety... and the safety of anyone behind me... I know. I would never exceed the max PSI on a tire. Ever.

But let's say someone did. Hypothetically. For example, if I, I mean, a rider finds that the calculated ideal PSI for the width of the hookless rim and the size of the tire is 78 PSI, and the max PSI on that tire (let's say they're 28mm Conti 5000s) is 73 PSI, do we think the engineers factored in a 6.5% margin of error, and that 78 PSI is totally fine. Hypothetically.

EDIT: Hookless... not hooked. datlas

datlas 

You mean hookless? Hooked max>hookless.

Zaskar

Yep. Typo.. dammit. Thanks datlas!

tempocyclist

Potentially yes, but for the sake of simply running 5psi less I wouldn't risk it.

choddo

Why would this hypothetical individual not want to run 70-73 psi?

tomato coupe

Maybe because the optimum tire pressure for that tire size could be higher, but Continental is capping it at 73 psi (maximum hookless pressure ala ETRTO) for legal reasons.

datlas 

I think with hookless it’s a shift from the max being based on the TIRE to the RIM.

At this stage, I would be very cautious with higher pressure on hookless. Proceed with caution. I expect with time and even greater tolerances with rims/tires it won’t be as big a concern.

6thElement

Run 30mm Conti's or eat less pies.

choddo

Sure but that’s not a reason to want to do it though. If 70 felt smoother and was as fast or faster than 80, Conti doing that wouldn’t matter. Curious why the desire to run higher pressures. It’s kind of right in the vicinity of what I use on hooked 25mm.

edit: aha skimmed past your “optimum”. ok so it’s probably slower?

base2 

If you find yourself at the maximum pressure recommended for a particular tire, it is time to run a bigger tire. It's as simple as that.

If you find the necessary pressure required of a particular tire size exceeds the maximum allowable by the rim, you need a stronger rim.
Here's a fun example of why.

Zaskar

Good point datlas - the 73 (actually, 72.5) PSI is the spec from Syncros on the hookless rim. There's always been that standard 1.5x safety margin in engineering... that a gross generalization for everything engineered. I'm looking for that real world data - you know, that "I've been running 15% over the max for 10 years and... " or "I went 76 PSI and the rim blew apart."

The hypothetical rider is at his optimal weight - eating fewer pies, losing weight isn't in the cards. Going from 28mm to 30mm tires isn't out of the question.

eduskator

Why would you need more than 72.5PSI when hookless and tubeless? Don't worry, it won't blow up under you if you go up to 80PSI. They are tested for long duration at pressures a lot higher than that.

FYI, my former hookless rims (Giant SLR1) had a 125PSI pressure limit. Not all of them are maxed out at 5 bar. However, you need to make sure to respect both your wheel and tire maximum pressure ratings.

Iride01 

I had hookless rims on my old Schwinn Varsity. Back in my less enlightened days, I'd pump them up to over 120 psi. Those were wire bead tires though.

If you are skittish and want no risk, then why even ask? Do you want to live forever?

tomato coupe

ETRTO only requires testing to 110% of maximum. Scary.

eduskator

Giant Tire Test Protocol | Giant Bicycles Canada (giant-bicycles.com)

tomato coupe

It would great if every tire manufacturer did that (or more).

terrymorse 

Doubtful. 120 psi on a hookless Schwinn Varsity rim was a blow off waiting to happen.

BITD, I repaired more Varsity bikes than I care to remember. Horrible, heavy things.

aliasfox

That's the reason I stuck with hooked rims. I'm biggish and like the ride at ~80psi on my front tire (Conti Ultra Sport 28mm, inflated to 32mm), and 90psi on my rear (GP5k 28mm, inflated to 29mm). I've tried running lower, but always found that it felt squirrelly and squishy.

At least that takes away the want/need to go hookless/tubeless - no real point at the pressures I'm riding.

So I'd throw another option into the mix. If the rider wants to try 80psi on a short section of smooth road, it's likely fine. But if that's what he/she likes, then:
- Getting a fatter tire is likely the better solution
- Going back to hooked rims to allow for higher pressures

genejockey 

RMOT. When I watch this, I always imagine someone in the back yelling, "IS THAT AN OPTION?!?"

PeteHski

Just go wider. Too many variables to know what the risk factor actually is for any individual. Let's say 73 psi is safe for 100% of normal use cases, 78 psi might be safe for only X% of use cases. The value of X is an unknown. So just go wider so you don't have to worry about it. Assuming you have tyre clearance of course. If not then just run 73 psi anyway. Running slightly under the "ideal" pressure (which is only an estimate anyway) is better than running slightly over it in terms of rolling resistance.

Note: check your pressure gauge is reasonably accurate too, especially when working close to the max limit.