Any advice on stopping Burping on tubeless wheels

New wheels for my son (13 3/4) and on the first race, they were perfect until 5 laps to go when it “burped”. He still finished though. Wheels are Parcours Rondes designed for 28mm tyres. Tyres are 28mm Continental GP5000TL. He still managed to finish 12th nursing soft back tyre.

I had put about 55 psi in the back and about 53 in the front. He is 61kg + bike, water bottle and kit - a system weight of about 70kg. The roads were typical Belgian concrete and rough (you should see that on the second photo - that is one of the better bits of road. It is concrete with a joining strip. I had thought that pressure to be optimum considering the rough road and 30mm width (actual) of the tyre and the system weight. Silca tyre pressure calculator suggests about that weight for standard tyres and I thought that would be ok for tubeless. Sealant was about 55ml. I had seated the tyre with a Milkit pressure booster and schwalbe easy fit and pumped it to 85 psi and left it overnight before adding sealant and pumping up to about 85 psi again to make sure it was seated. He doesn’t remember hitting anything hard, but it was in the heat of racing with 5 laps to go so who knows. On normal tyres previously in another race, he did hit an object and pinch flatted, so at least this did not happen and he finished.

Do you have suggestions for preventing burping? We had done short rides Tuesday/Wednesday and Thursday and a tune up session Saturday, some with some speed and rough roads and cobbles, without any issues. We had used cycle paths and had been up to 45kmh and had not issues on the cycle paths and one session with sharp bends as “crit training”

Is the sealant too much?
Was the pressure too low? (I’m thinking so??)
Do I need to use more pressure for the initial seating?
Could it be variability in Continental GP5000 TL production?
Could you have variability in production tolerances for rims?
Should I buy another Continental GP5000TL?
Or try another brand?

When pumped up back up to 80psi it appears fine and there is no “bump” when riding, so I am assuming it is seated correctly afterwards.

Any advice greatly appreciated. At least he managed to finish and finish 12th in only his 4th race in Belgium.

Wheel photo

Rough roads

Not sure I can be much help here but I have run tubeless on my MTBs for years on low pressures, bouncing off rocks, and have never experienced a burp.

I’ve also never managed to seat my road tyres tubeless so always run with tubes.

There seems to be a lot of leakage around the rim. Aside from the large one, which is presumably the burp, was any of that present before the race? I wonder if the tyre was properly seated.

Mine can sometimes take 3 or 4 days of slow seepage before they settle in and hold tight.

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Judging by the colour of the sealant, can I guess you’re using MucOff?
Change it for Stans Race… I’ve seen just too many people have problems with MucOff and without a word of a lie, on other forums I’m on, if someone is having problems with a tubeless setup there’s a better than coin-toss chance they’re using that (which, considering the volume of options, is ridiculous).

I also know other people who use it without trouble at all, but I’ve seen just too many people struggle with it to not recommend against it.

That said, tubeless wheels can sometimes misbehave for a short while. My newest wheels were fine for their first ride, then dropped most of their pressure overnight, then were mostly okay on their second ride but slowly went soft and behaved like that for about 5 or 6 rides, then suddenly stopped and since then have held pressure perfectly.
Road wheels are worse for it than gravel which are worse than MTB too, presumably because of both the pressures and the tyre to wheel interface.

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It could also be tire/rim combo. Some combinations are painless and seat in with a hand pump and others have you inventing new swear words even with a compressor, extra rim tape, etc.

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This is what I was wondering - how long between setting up tubeless and doing the race? If it was just a few days, with not much riding, then the sealant may not have had time to fully seal the tire/rim interface.

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The wheels are designed to be run with tubeless and I used schable easy fit and a tyre booster. Pumped up and left overnight which is why I’m confused.

Thanks for the reply Jon, I’m using Milkit sealant but with the valves that came with the bike. Pumped them back up to 80psi and they seem fine. Letting them settle now.

Oh, just seen your reply, that is interesting. Installation was Monday, then test rides/race tune ups Tuesday, Wednesday and Thursday (short rides under an hour) and Friday off with another road based “Primer” on Saturday.

Funny thing is, Parcours had tested them with the Continental GP5000TL as the “go to” all round race tyre with the best mix of speed/reliability/ low rolling resistance.

Sealant seals the rim bead (if pinned not welded), tyre sidewalls and punctures, its not there to prevent burping, which is caused by the bead-rim interface not being secure enough. Although I have notice that some brands of sealant seem more slippery so could perhaps act to lubricate the bead-rim interface?

I’ve been running tubeless on my MTB, but the only issue I’ve ever had due to burping in 15 years were during hard cornering and were a result of the bead being a fraction too loose a fit on the rim.
A few wraps of tubeless rim tape helped but the problem only went away when I switched tyres, never had a problem since despite running just 20psi.

Did your son have problems with burping in just one tyre? In which case you could try swapping the tyres around to see if you 've got a tyre with an a bead that is a fraction too big?

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The rear tyre burped. There was only a couple of psi difference between the two. I checked it today after leaving it with 80psi overnight and it appears fine. I suppose I’m gonna have to test out the wheels with my not inconsiderable weight of 85kg (compared to my son’s 61) and see if I can provoke it.
It may have been a one off, but I want to try and exclude every possibility.
Cheers for the help.

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I would recommend running a higher PSI. I was running 60 front/65 rear. Felt unstable. Went back up to 70 in both and the bike feels great with a little bumpiness on larger pavement cracks. We have a road that is in serious need of a redo (we are asphalt) and it is where I test out how well tires work and that portion felt very stable at the higher PSI. Also, check if you have any weeping from the rim tape at the valve stem. If there is, replace the rim tape. It will feel like oil on the rim.

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I would think the pressure is right for such a light rider and that big tyres.

Sometimes after first installation the tyres need some time to get to work properly. had the same problem with the Schwalbe Pro One last time around. Took 2-3 rides to completely seal properly. Losing some pressure during the first rides.

The Conti GP5000TL aren’t that good either. I would switch to Vittoria Corsa Control on our awful Belgian roads (I’m really happy with them)

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