Sy Reene

Yeah.. what I'm realizing is that Enve changed this chart sometime recently.. I know that the 80psi rating that I originally referenced used to be in red type and part of my frustration in this convo, since Enve does have this mention under the chart as well that red type = max. Either some webpage formatting error, or curiously Enve (unlike Hed, Zipp, or most other wheel makers) decided to do away with max inflation ratings?
"Red = Maximum Recommended Tire Pressure for Given Rim & Tire Volume Combo on Paved Road Surfaces"
Anyway.. we all agree that tire sidewalls max psi ratings don't mean much, and hopefully we agree that often these can be in strong misalignment with what (most) rim makers indicate as safe.

boozergut

OK, so where does pinch flatting come into play here? As a fat rider I was always told to inflate to the maximum pressure listed on the sidewall. So for my 40X700 Clements I ran running 80 psi last year. After 3 blow outs I dropped down to 70 psi and I stopped having problems. My local LBS also advised that the quality of tubes isn't what it once was..... Thoughts??

base2 

The quality of the tube has absolutly nothing to do with whether or not the tire bead blows off the rim.

Tubes come in all variety of thicknesses from ultra-thick thorn resistant to ridiculously thin latex ultra-lights. Even no tube at all in some cases.

Blow-off (in most cases that are not heat related) is a result of fitment of the tire to the rim and the construction/quality & particular combination of each.

boozergut

Heya base2. Im just trying to figure out what pressure I should ride my tires at. 80 caused me issues. How low can I go without getting a pinch flat on a 40mm gravel tire??

HTupolev

Depends on your weight, what surfaces you're riding on, how you carry your weight on the bike, what sort of suspension the bicycle has (or doesn't have), and even the designs of the particular tire and rim and inner tube.

To get some sense for a baseline, though, what's your bike+rider weight? What's your gravel like?

base2 

As I said above, they (Knarly 700'c x 41) were way faster at 45 or 50psi than at 80 IME...That being said, last winter I mostly ran them at or above 40 or so. Above ~35 if I took it gravelling, about 45-ish for on road. I weigh 200 pounds.

The above poster is correct. Conditions matter. If you're running hardcore on all tree roots & rock the likelyhood of a pinch is greater. I tend to run a bit higher just because I don't like mush & I don't like walking. How much time is lost walking back to the car? A lot! So I've made it policy to never find out how low I could go. I've always took the minimum to mean "lowest you could go to ensure the tube or tire doesn't walk around the rim" & left it at that.

So maybe a touch higher (50-ish) is better when you leave the house, then you can let some out when conditions dictate what you should do. There is no shame in looking at your own contact patch, seeing how much your sidewalls deflect or feeling how rough the ride is through your hands/sitbones and adjusting accordingly. Some gravel roads can be remarkably smooth & well packed others can be pretty rocky. I did a gravel century on 700x32's at 65psi & it worked out fine. I just (an hour ago) did 20 miles on ice with 559x60 studded snow tires at 35psi. The studs were like velcro, so It must've been right enough. The only pinch flat I ever got was a skinny 23c at 80psi when hitting a curb. So, you've got plenty of wiggle room to go down, for sure.

Sorry, there isn't a better answer in the form of a specific number....If I set off in the car & drive to a ride I keep a track pump in the car/truck & decide when I get there.

If 80 (!) is causing issues, go less. If it feels mushy or draggy go more. No need to overthink. Assuming you have 41's & good roads like me you could start at 50 psi & see what happens. I never go below 35, I just haven't seen any reason to. I hope this helps.

Sapperc

I’ve discovered that Silica’s pressure calculator chart provides a good starting point for finding good tire pressure. It is worth checking out and comparing against what you might be currently doing.

Another thought, I think for most of us the 105% rule is an overstated rule. There aren’t many road bike wheels in actual use that are wide enough for anything wider than a 25mm wide tire and still stay within the 105% rule, yet many of us are riding 26, 28mm tires with no real depreciation in actual speed. I’m not saying there isn’t a trade off, I’m just suggesting that the fraction of aero lost is less important than the gains from wider tires.

Happy cycling!