Burped about 10 PSI
 

This past weekend, I had more fun on the gravel bike than any other gravel ride. 85% dirt - 5,000' of climbing... and 5,000' of descending!

I weigh 178 lbs. I was on 40mm Schwalbe G-Ones with fresh sealant. I usually run them at 38 and 35 PSI (tubeless). Because the ride started with a couple hours of climbing on mostly maintained dirt/gravel roads, I started at a much higher PSI than I usually do. I went up to 45 and 43... which SUCKED as soon as we started coming down after the first peak. I dropped to 38ish PSI.

Note: I've got a BMX and MTB background - so, I do pay attention to how I clear or absorb ruts, rocks, etc. I was having a *@#^$ing blast! Some bunnyhopping, some manuals... some Bigfoot video-like blurred rattling (if you're over 45, you'll get that reference) over rocky sections. Sooo much fun.

But, after bombing down a fast, not-so-well-maintained road, both tires had burped their way into the 20s. I aired back up to close to 40 PSI.

So, should I chalk this up to tires that needed to be better sealed (on other rides, I've not lost any pressure)? Or, chalk it up to "Dude, it's not a mountain bike, slow the $*#& down."? Oh... I did break one spoke.

Take the MTB next time.

Tires and rims aren't a good match I'd say. Bead might not be tight enough. Though was there sealant everywhere? if not maybe not enough of that?

tubeless tires on tubeless rims shouldn't burp. Unless you dented a rim. I have some maxxis tires that are a little loose on the rim, I should probably add some tape.

I've had burps with tubeless tires on tubeless rims. psi was too low, and terrain was too rough. It happens.

Were you riding hookless or rims with a bead?

a tire shouldn't burp if it is matched well with the rim. It really needs a good bead seat in the rim bed. If it is matched well, you can ride the tire when it is flat, much like you can a tubular tire.

But like Koyote says, it happens. There are no real standards for gravel tires and wheels. I have some "smallish" diameter rims and some non super tight tires and they are super easy to mount. I also have some super tight beads and some slightly oversized rims, and they won't mount at all. Tire/wheel interface is a **** show.

In your case (with a loose or uncertain bead set), I use something called "skinny strippers." Basically a latex rim strip, but it bonds to the tire in essence making the tire kind of a tubular tire. The tire will hold (a little) air even when off the bike. So burping is basically impossible. But, if you have a well matched tire/rim combo you shouldn't need anything like that.

And for gosh sakes, don't slow down!

When I read about your ride, I'm reminded of this video. So, do you have a hipster beard and a dropper post? ;-)
https://bikepacking.com/news/easton-...-dropper-post/

Ha! No - no beard, no dropper post. But, I do those little cross-ups when I jump on the gravel bike. Maybe I'd get more air if I grew that beard. ;-)
I have done some fast, not-so-technical single track on the gravel bike and thought it was awesome - more fun than expected. I've found the gravel bike to be really good in the woods... as long as the trail is smooth(ish). Even with 40mm tires at 35 psi, it doesn't take much to remind you you're not on a mountain bike.

Did you just install these tires? Sometimes fresh tires take a couple days to hold air and seal completely.

I love my gravel bike on single track. Coming from a MTB background, there are a lot of trails that are just too tame (for me) to ride on a mountain bike. But on a gravel bike, "tame" trails are a ball. Anything that is appropriate for a fully ridged MTB can be a ball on a gravel bike - besides my bike (at 17lbs) climbs like a mountain goat. I just have to pick my lines with more care (like we did in the early days of mountain bikes).

tdilf The tires came on the bike - a 2018 Canyon Grail. They're probably 50% spent, worn in but not worn-out... just added some Stans via the stem. I suspect the culprit may have been dropping the PSI too much.

But you're right about tires often needing time to seat... I raced this bike the first time I rode it off road. I'd ridden it 4 or 5 times on the street using another wheel set with road tires. My race went like this...
Friday evening: Pull the tubes, set up tubeless on the 40mm Schwalbes... Saturday - still holding pressure. Race starts at super high pace (24 mph ++) and 7 miles in, I'm thinking I'm gonna blow up - but thinking the bike is awful comfy... then realize why I'm blowing up AND the bike is so comfy... back tire is at about 10 psi. Race over for me.

However, even after TWO tube swaps - in the rain - and the race blown, I had so much damn fun the rest of that ride. I was hooked!

chas58 Exactly! The beginner to intermediate trails that are boring on the mtn bikes are perfect for the gravel bikes.

Your mistake is the part I put in bold font, as you probably are aware. Don't do any significant fiddling with your bike the night before a race, when there is no time to test it out.

No doubt! I violated Rule #1 . I fell victim to "Hey, what are you doing tomorrow?" I couldn't imagine doing a race with tubes... should've done the race with tubes.

Okay, so here's my story: Tough gravel race, with muddy nasty trails (lots of rain that week), and my bike was shod with 37mm tires. Since I didn't have wider tires (and no time to ensure they were set up and sealed properly), I figured that I would just drop the psi in my 37s in order to get more traction.

About seven miles into the race, over the first rough patch, the rear tire started to feel all sloppy and soft...I had dropped the psi too much, and most of the air had burped out. I had to get off the bike and pump it up - which gave me a chance to watch plenty of other riders sail past me.

Live and learn, as they say.

True. I think typically the problem is getting the valve core to seat with the rim. Usually after a few days it will fix itself, but I find it often takes most of a week for things to stabilize with tubeless installs.

Nothing quite as frustrating as being in shape then tweaking something on the bike to make things worse or having an equipment failure. I once trained in the lower alps for 10 days (~100 miles a day) and then did a mountain bike race. In practice I had shaved about 20% off my time - easy first place. Then on race day, half way through the race my seat fell off...

from your description, had you done the race with tubes you would have had pinch flats.

10 psi in a 4" wide fat plus tire?

Man, I beat the heck out of my my tubeless gravel rig - I ride it like a mountain bike in rocky SoCal - and I've never had burping like that. I weigh a bit less than you but I run in the 20's psi offroad. Any slow leak after adding sealant, etc always sorts itself out the first ride.