2

I just got 2 new Panaracer Gravelking SK tires and mounted them tubeless on WTB i21 rims with the correct width rim tape from WTB. I inflated them to 60psi to set the bead and the rear blew off the rim before even taking it off the stand.

The rim is now way out of true. In fact, I think it has to be replaced now.

After this happened, I trued the rear wheel as best as I could and re-installed the rear at about 40psi. I went for a test ride and 2 minutes in, the front blows! It was between 50-60psi at the time. And now the front wheel is severely out of true as well.

  1. Is that normal for a rim to be ruined from a blowout?

I realize that I should not have inflated them to their max rated psi (60psi max for tubeless and 75psi for tubes). But, in my experience, I have never had a tire blow out right at the max psi. Most tires can go way beyond that for a short period, especially for just setting the bead.

  1. Is this rim/tire combo just incompatible?

  2. Should I just run tubes with this combo? (I have trust issues now).

Update (8/8/2022)

Ok, so 60 psi is a little insane to ride on for a gravel tire. I get that now. I talked with WTB about this and they see no reason the tire should have blown off. They did give me crash replacement pricing for new rims. I have since rebuilt the rear wheel with the new rim and I am now running the same tires on the old front wheel and the new rear wheel. I will be rebuilding the front wheel soon, once some more parts arrive. I have been running this setup for about a month now at 35-40 psi with absolutely no issues.

Here is my theory of what happened. I think my floor pump gauge was starting to fail when I originally pumped up the tires and it was reading much lower psi than it actually was. I think this because just recently, the gauge completely failed and reads all over the place. Who knows how high I actually pumped them up to when they blew.

Update (11/1/2023)

Just an update on where we are at with this. After rebuilding the wheels with new WTB i21 rims, I have now run this rim/tire combination with zero issues for over 2800 miles. I have had to re-seat the tires a handful of times as well. I have been consistently running 35-42 psi. I don't plan on going any higher due to trust issues. However as a recent answer mention, it's possible the older rims were build out of spec. Unfortunately, I don't know how old they were, but they were the exact same make/model.

Side note: Gravelkings wear very well and I haven't had a single puncture that I am aware of! After 2800+ miles, I probably have another 500-1000 miles left.

7
  • 1
    what size and model of the Gravelking SK did you use?
    – Andy P
    Jun 17, 2022 at 20:43
  • Hi, welcome to bicycles! The correct size tire shouldn't blow off the rim at the rated pressure, not even max pressure. Even running them with tubes won't fix that because the pressure on the bead will be practically the same. The first order of business should be to make sure you got the right size tires.
    – DavidW
    Jun 17, 2022 at 20:47
  • @AndyP I used the Tubeless Compatible Clincher
    – Geo242
    Jun 20, 2022 at 21:07
  • 1
    What pressure are the rims rated to? Perhaps their limit is lower than the tire's, although really there should be a margin of safety.
    – MaplePanda
    Jun 21, 2022 at 1:39
  • 1
    There's a good chance that you did not have the tires properly seated on the rims. Jun 21, 2022 at 16:46

3 Answers 3

6

Recently, an understandably irate user posted a YouTube video of a Continental GP 5000 tire blow out on an Extralite wheel when installed according to manufacturer instructions. The user contacted both companies, and he sent the wheel to Continental, who examined it.

enter image description here

I don't believe that the WTB i21 rim, which I think is this one was made outside of the new (2020 or 2021) ETRTO specs for hookless rims. So, I am more posting this for general information on why a tire might blow off.

That wheel was made quite a bit out of ETRTO specs. The rim was measured at 4 points, and the ETRTO spec is listed in the rightmost column. Conti's analysis (screenshot below) shows that the actual bead seat diameter (measurement D1) was about 621.0mm or a bit less, versus an ETRTO spec of 621.95mm, +/- 0.5mm (last column). The G-height (measurement G, which is the distance from the bead seat to the top of the rim sidewall) was 5.0mm versus a spec of 6 +/- 0.5mm. Extralite said that they made the wheel like this to ease mounting. Perhaps this was not a good idea. That said, this sort of non-standard rim might have been OK if it had bead hooks.

So, the easy solution for consumers is: don't buy wheels that are out of ETRTO spec. But how do you know which rims are made to the ETRTO specs? We don't know which year rim the OP has. I suppose it's possible that they had an older, non-ETRTO spec version of the rim. The ETRTO spec is mentioned on the WTB page, so I think the current model year is in spec. Basically, even if a consumer knows they should be buying something conforming to the ETRTO specs, it's not always obvious where to check the information. I don't think there's a standard "ETRTO" sticker to put on the rims. For hookless rims, an in-spec rim will probably have a warning that the max pressure is 72 PSI. So that warning label may be an indicator. Also, I think that compliant rims might be labeled TSS (for hookless) or TC (means crochet, i.e. hooked).

Above, I referred to the tolerances around the ETRTO spec (the +/- values). Speaking of this, it's possible that the original rim was built to ETRTO specs but out of tolerance. Even in high-quality manufacturing processes, you should expect to see a few duds, and the manufacturer will have quality control processes, but it's always possible to miss some duds. The problem is that I don't think the equipment to measure the rim precisely is widely available. The YouTuber had to send his wheel to Continental, who may have used some sort of CT imaging technology to measure. So it's hard to verify this aside from incurring multiple blowouts - but then maybe the tire batch was out of tolerance or defective. Also, the OP blew out tires on different rims, and you would expect it to be rare for one purchaser to get two duds - unless there was a systematic process problem.

Users in this situation could ask the wheel manufacturer or tire manufacturer for assistance. The problem is that they could both point fingers at each other. You could call the rim manufacturer for advice. The bike manufacturer and/or the store where you bought the bike may also be able to provide input. However, these aren't guarantees of useful information.


Daniel Hicks mentioned in a comment that perhaps the tires weren't seated properly. That's possible. Check that there's a line visible above the bead; the tires are deliberately made that way. The line should not dip below the top of the sidewall. Additionally, be careful if you use tire levers to mount the tire. It's possible to damage the bead if you go way too hard; the Geek Warning podcast (Escape Collective) speculated that this could have been one reason the tire failed before we got Continental's response.

The larger the tire, the higher the amount of tension on the casing at a given pressure. I think the difference may grow non-linearly as well. So, it may be better to avoid putting 60 PSI in a gravel sized tire. I believe that you should not need to overpressure the tire by a lot just to seat the bead. To seat beads, we need a big volume of air moving into the tire. Various tricks can help you achieve that, e.g. remove your valve core when seating, borrow the gas station's compressor and use a schrader to presta adapter, borrow the bike store's compressor, use a CO2 cartridge to seat.

1
  • 1
    While it's true that tooling to take those measurements aren't widely at hand in bike shops, you could do it with means less sophisticated than X-ray/ultrasound/etc. G and D1 you can do with the depth gauge of a vernier caliper with a 123 block laid across the top surface of the rim and the pointy bit going through a hole in the block, to keep the caliper pointed straight down. Getting point-to-point OD measurements to that accuracy would take more doing, but wrapping something around it and dividing the circumference by pi sounds pretty feasible if one was content with an average. Nov 2, 2023 at 5:20
4

I'm afraid there might be no good answer that is going to put your mind at ease and guide you what to do next, but i'll have a go based on the information we have available.

From the information you have given, you didn't do anything wrong. 60psi in a 38c tyre is certainly not a crazy amount on a hooked rim, and from looking at the WTB website there is no maximum pressure listed for the rim. Your procedure of inflating to the max pressure to seat the beads was certainly a very normal thing to do a few years back when tubeless was new and products weren't designed quite so well.

  1. I wouldn't say its normal, but its certainly not unheard of for a blowout to severely damage a rim. In addition to re-trueing the wheel i'd also very carefully inspect the rim hook area for signs of damage before attempting to reuse the wheel.
  2. It's extremely unlikely that this rim/tyre combination is incompatible.
  3. You are wise to have trust issues. I would be trying to investigate more into what caused this issue before using this combination again.

One area i would investigate would be the pressure gauge on your pump, it wouldn't be the first time i've heard of a gauge being 10-20psi out. Accidental overinflation would explain what is otherwise quite a strange case.

2
  • 1
    60 PSI on a gravel bike with 38C??? I normally ride around 35, sometimes it drops to 20 when I forget to inflate (a non-TLR rim). Why would one do this to themselves? It must ride almost like a solid tyre. Jun 23, 2022 at 8:33
  • 2
    @VladimirFГероямслава 60PSI isn't intended to ride on, its intended to get beads seated, you let it down again afterwards. But in terms of holding pressure and not blowing off the rim 60psi is quite reasonable
    – Andy P
    Jun 23, 2022 at 8:39
4

My experiences with Panaracer tyres and WTB rims have been at both ends of the spectrum.

I first set up my Gravelking SK 43mm on WTB KOM Light i23mm rims at 45PSI. I left them for two days with no issues and then set them at 35PSI for riding. About 10km in the first ride the rear blew off both beads while stopped at a traffic light. I used a tube until I could set it up tubeless again. Around ~40km of tubeless riding later it blew off both beads from the rear again while doing 30km/h, which resulted in trashing the rim on the road. I replaced it with a Spank Flare 24 rim.

I sent a report to Panaracer stating that it was operating within pressure guidelines, so they sent me a replacement tyre. I was out of pocket for the rim.

I've since run several sets of Gravelking SK 43mm and a set of Gravelking+ slick 38mm on the original WTB i23 front rim and the replacement Spank rear rim for thousands of kilometers without issues. I've used the same pumps and gauges all the way through.

At the time of my tyre's blowout I read of several other reports of blowouts with the same tyre/rim combo. It seems to mostly happen on the rear.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.