gravel king sk 38c tires blowing off 25 mm internal rim at 55 psi??

60 replies · 2,747 views

spectastic
43 posts
#1Mar 22, 2019, 2:54 AM
it's my first time going tube less. I got the tire to seat without a compressor first time, but instead of going for a ride, I let the wheels sit there, and they lost air over a couple of days. today, I as I pumped it up again to go for a ride, the rear tire blew off at 60 psi. I was going for a higher pressure to get the sealants to seal the hissing that I was hearing, likely from the valve stem.

I went to the bike shop, and they told me it's usually the rim tape that gives people problems. the tape i was using was slighter thinner than stans and narrower than ideal, but I did two layers, one hugging each side, and the mechanic said I did a good job. and we can't come up with a good explanation for how the tire can just blow off at 60 psi, when the max rated pressure on the gravelkings are 75..

the bike shop did help me put more sealant in there. we sealed it with a compressor, and I went for a ride to slosh the sealant around some more. It held air just fine at ~50 psi, which is what I rode at on the road. however, when I got home, I hooked it up to a floor pump to see if it held air, and wanted to see if it'll hold 55 psi over night. as soon as I got to 55, boom. another blow out, same region, other side from the valve stem, this time on the other side of the beads than the first time..

the rim I'm using is mercury g3 xc. 25mm internal 30 mm external, 24 mm deep. tubeless compatible. I can't wrap my brain around why it's not holding even 55-60 psi. faulty tire, faulty rim, bad rim tape job, any ideas?
0
cpark
46 posts
#2Mar 22, 2019, 6:24 AM
Looking at the spec, I personally wouldn't any higher than 40 psi for 38mm tire since it's a hookless rim. Don't pay attention to the psi on the label, as there are a lot of variables - the rim (hooked or hookless), dimension of the rim, rider weight, terrain you ride and etc.
0
Koyote
288 posts
#3Mar 22, 2019, 6:48 AM
You're putting in way too much psi.
0
spectastic
43 posts
#4Mar 22, 2019, 8:52 AM
it's not a hookless rim, and I was not planning to ride on 55, only to see if it would hold air. max pressure is 75. 55 should be nothing, even for a mtb tire.
0
Koyote
288 posts
#5Mar 22, 2019, 9:13 AM
spectastic wrote:it's not a hookless rim, and I was not planning to ride on 55, only to see if it would hold air. max pressure is 75. 55 should be nothing, even for a mtb tire.

Well, you've gotten the same advice from two people...So if you choose to dismiss it, the only other thing I can offer is that you might need to use rim tape of the appropriate width -- and perhaps 2 or even three layers. And then pump your tires to a reasonable level, like 40psi.
0
chas
1,305 posts
#6Mar 22, 2019, 9:50 AM
Tubeless is such a friggen mess – there are no standards. Some tire-wheel combos fit tight (and are impossible to mount), and some just fit loose. It sounds to me that you have a loose combo.
Personally I use skinny stripper inserts to keep things clean, neat, and minimize blow offs and burping.

Either way, 60psi is right at the limit (or beyond) for a tubeless tire. I ride at 60 sometimes (on a 32mm tire), but that is pushing it. There is no tube to press the tire onto the rim, so they will blow off.
If we can’t convince you, read this article on the Trouble with Tribbles:
https://janheine.wordpress.com/2017/05/29/the-trouble-with-road-tubeless/
Spoiler alert: "For tubeless, we recommend a maximum pressure of 60 psi (4 bar)."

0
cpark
46 posts
#7Mar 22, 2019, 10:31 AM
spectastic wrote:it's not a hookless rim, and I was not planning to ride on 55, only to see if it would hold air. max pressure is 75. 55 should be nothing, even for a mtb tire.

Interesting....
I checked the specification of your wheels on Mercury website, and the diagram shows no hook.
0
Koyote
288 posts
#8Mar 22, 2019, 10:36 AM
cpark wrote:

Interesting....
I checked the specification of your wheels on Mercury website, and the diagram shows no hook.

Hookless rim + 60psi = blowoffs

Run it at 40psi or lower (which is where you want to be anyway with these tires) and you should be fine.
0
SWGraveler
247 posts
#9Mar 22, 2019, 10:56 AM
Thanks Chas; there is a lot of info in that article you linked. I'm a newby to gravel & tubeless so it really offered some insight for me.
0
SWGraveler
247 posts
#10Mar 22, 2019, 10:57 AM
In the link above, it says that tubeless tires that have blown off of a rim should not be used as the bead is possibly damaged.. May explain the OP's story/on-going problem..
0
spectastic
43 posts
#11Mar 22, 2019, 3:18 PM
cpark wrote:

Interesting....
I checked the specification of your wheels on Mercury website, and the diagram shows no hook.

i called mercurycycling. they have a hookless version but it's carbon. mine is aluminum and is hooked.

the tire has become super easy to mount though, idk if i should call it manufacturer defect at this point
0
spectastic
43 posts
#12Mar 22, 2019, 3:20 PMedited
chas wrote:
Tubeless is such a friggen mess – there are no standards. Some tire-wheel combos fit tight (and are impossible to mount), and some just fit loose. It sounds to me that you have a loose combo.
Personally I use skinny stripper inserts to keep things clean, neat, and minimize blow offs and burping.

Either way, 60psi is right at the limit (or beyond) for a tubeless tire. I ride at 60 sometimes (on a 32mm tire), but that is pushing it. There is no tube to press the tire onto the rim, so they will blow off.
If we can’t convince you, read this article on the Trouble with Tribbles:
https://janheine.wordpress.com/2017/05/29/the-trouble-with-road-tubeless/
Spoiler alert: "For tubeless, we recommend a maximum pressure of 60 psi (4 bar)."

they inflated their tubeless setup to 108 psi, way beyond the max. 60 was thrown in there conservatively because it was way below the max of 90 psi. i'm blowing off at 60. thats shouldn;t happen

i can try to double up tape. but if the tire was already seated properly, and there was no load on it, i don't see how it can just pop off

as mentioned above, i think bead is compromised. but idk how. i never even rode on them before they blew off
0
chas
1,305 posts
#13Mar 22, 2019, 4:00 PM
I'm not comfortable going beyond 60, and even then I know that there is a lot of tolerance variation just in my tires and wheels.

I don't think most hookless tires are rated for beyond 60 either. If you are not using a tube, the hook isn't doing that much. There is no tube pressing against it.

You are not the first person to have a blow-off in that range.

0
chas
1,305 posts
#14Mar 22, 2019, 4:03 PM
SWGraveler wrote:Thanks Chas; there is a lot of info in that article you linked. I'm a newby to gravel & tubeless so it really offered some insight for me.

Glad it helped. This post inspired me to read this one:
http://g-tedproductions.blogspot.com/2019/03/a-promise-of-better-fit.html

In a swift and somewhat surprising move, both ETRTO and ISO agreed that the standards needed to be updated and there was a quick move to set the rim manufacturers straight to the point that any tire manufacturer could then build a tire which not only would safely fit any rim, but be mountable and removable by hand. However; in the tubeless realm, there was a fly in the ointment, and that came from Stan's NoTubes.
...
"It is clear tire companies cannot test and assure that tires based on a 622+-0.5mm bead seat and other agreed wall height and channel width and depth parameters, especially for high-pressure applications like Road and Track, can be mounted comfortably and still safely maintain proper tire fit with Stan’s 623 +-0.3mm BSD design parameters without high risk of failure." - from Morgan Nichols' letter to "Bicycle Retailer and Industry News"

0
spectastic
43 posts
#15Mar 22, 2019, 9:44 PM
after another trip to bike shop, it appears there's 2 max pressure, 75 is for a tubed wheel, while 60 is the max for a tubeless setup. my mistake.

still. I'm considering the forces being exerted on the wheel during riding, especially on rough terrain. can a bump against a large rock cause a blow out, if I run a sensible pressure of say 40-45 psi?
0
Koyote
288 posts
#16Mar 23, 2019, 7:32 AMedited
spectastic wrote:after another trip to bike shop, it appears there's 2 max pressure, 75 is for a tubed wheel, while 60 is the max for a tubeless setup. my mistake.

still. I'm considering the forces being exerted on the wheel during riding, especially on rough terrain. can a bump against a large rock cause a blow out, if I run a sensible pressure of say 40-45 psi?

The Gravelking SK is one of the most popular tires (perhaps THE most popular tire) in the gravel cycling scene. If used properly, it will be fine. And by "properly," I am mainly referring to reasonable air pressures. 45psi, as you suggested, is safe but too high. You'll get more comfort and traction (with no real increase in rolling resistance) at 40psi or even lower pressures. If you want to run such high pressures, you might as well stick to tubes.

In your initial post, you reported hearing "hissing," likely from the valve stem. That indicates that your rim tape job was likely insufficient. So, rather than re-do it, you pumped up the tires way beyond normal psi, and blew one off the rim. As SWGraveler noted, that blow-off may have compromised the tire, which would perhaps explain why (1) it became easier to mount and (2) it blew off the rim a second time. (Though it blew off at 55psi, which is still too much pressure.)

At this point, you can re-use that tire if you are willing to take a risk; otherwise you should replace it. (And no, it's not a warranty issue, as you abused the tire.) If you just follow the mounting instructions that are all over the 'net, and don't overinflate the tire, it should work just fine. Or perhaps you should just pay your shop to mount them for you.

Your other option is to go back to using tubes.
0
Zurichman
1,526 posts
#17Mar 23, 2019, 8:10 AM
I too was the newbie about a year and a half ago. These guys on here know what they are talking about as they have been there dun that. It was tough at my end getting the tire pressure right coming from the roadie end. My first set of tires on my Raleigh Tamland 1 weren't tubeless ready(Clement MSO xplor). I got the front sealed but not the back. I ended up running the rear with a tube for awhile. From what I have read throughout the thread if you didn't want to chuck the tires now you could try running them with tubes but I wouldn't be comfortable running them tubeless. Every rider has to find their sweet spot with riding their conditions and with their weight. I am around 200 lbs. and have found that 40 rear and 35 front is my sweet spot for rough gravel. On a more roadie course I run 45 rear and 40 on the front. You haven't stated your weight but if you weigh less you can go with even lower pressures. You want to run as low as you can to smooth out the ride of your bike. It was tough for me to get use to riding around in what felt like a 1/2 flat tire. Good luck

Zman
0
HollyBoni
333 posts
#18Mar 23, 2019, 11:15 AMedited
It says it right on the side of the tire:
Tubeless Compatible MAX 400kPa (4.0 bar 60psi)

So if you didn't exceed 60psi, you didn't do anything wrong. Actually riding them at 50-55 is a bit too much, but whatever floats your boat. I use an air compressor to seat tyres, i'm pretty sure I went up to 60psi when I mounted all my SKs, but I aired them down shortly after. Still, they didn't blow off, and they shouldn't unless you go really sky high with the pressures.
As Chas said, the tubeless world is a bit of a mess. However, this still shouldn't happen. Maybe you got a faulty tyre, maybe the rim and the tyre don't like each other. What about the other tyre? Or did you buy just one, not a pair?

At this point, I wouldn't feel comfortable using the tyre. So the only option I see is get another one, try again. I'd also tape the rim again, hissing at the valve stem is not normal. Personally i'm a fan of using wider tape, wider than the ID of the rim itself, so it goes up into the sides of the bead. Some manufacturers recommend this too. For the valve hole in the tape use just a toothpick, then push the valve through. This creates a perfectly sized hole. No messing about with cutting a cross with a knife etc.

I have the SKs in 38 and 43. For 100% pavement I run them at ~43psi at the back, 39-40psi at the front. For offroad I go down to 29 front, 34-35 back. Used them for one season so far, zero issues. I also have the SKs in 32, I use them for road riding in the winter (with some super short offroad sections), i'm usually at 50 back, around 46 front. Used them for 2 winters so far, zero issues.
0
spectastic
43 posts
#19Mar 23, 2019, 1:35 PMedited
i'm writing out a warranty request for panaracer to replace the tire. it happened again last night, after I cleaned the bead, and inflated it to 60 just to see if it'll hold air. it blew at 55.
.
0
SWGraveler
247 posts
#20Mar 23, 2019, 3:44 PM
spectastic wrote:i'm writing out a warranty request for panaracer to replace the tire. it happened again last night, after I cleaned the bead, and inflated it to 60 just to see if it'll hold air. it blew at 55.
.

Sorry, but I have to call this out for what it is; a lack of integrity. At this point, the fact that it blew at 55 psi is meaningless as the tire has clearly been damaged by your previous carelessness. This has been pointed out repeatedly.. Cleaning does not restore the integrity of something that has been damaged.. Imho, it speaks to the quality of the tire that it withstood that much pressure at this point.

We all pay more for thing because mfg's have to allow for/pay for stuff like this. How you can file a warranty claim with a clear conscience is amazing to me.. Karma will visit you; she is not always a nice girl.

I'd like others to chime-in here; if you do/don't agree with me I'd like to hear your perspectives.

Lots of love for the Gravelking here; it will continue to be my tire of choice.

1

Related threads

Gravelking SK 43 on 25i rimGravel Wheels (Wheels, Rims, Hubs, Etc) · 19 replies · Nov 23, 2018
Chiru VagusBikes · 0 replies · Feb 22, 2020
Are 30mm Rims Too Much for 650B x 47?Gravel Tires · 3 replies · Jun 19, 2021
Any reason I should run Crest mk3'sGravel Wheels (Wheels, Rims, Hubs, Etc) · 11 replies · Oct 23, 2017
Homebrew tire insertsGravel Wheels (Wheels, Rims, Hubs, Etc) · 3 replies · Jun 3, 2020

Related threads

Gravelking SK 43 on 25i rimGravel Wheels (Wheels, Rims, Hubs, Etc) · 19 replies · Nov 23, 2018

Chiru VagusBikes · 0 replies · Feb 22, 2020

Are 30mm Rims Too Much for 650B x 47?Gravel Tires · 3 replies · Jun 19, 2021

Any reason I should run Crest mk3'sGravel Wheels (Wheels, Rims, Hubs, Etc) · 11 replies · Oct 23, 2017

Homebrew tire insertsGravel Wheels (Wheels, Rims, Hubs, Etc) · 3 replies · Jun 3, 2020