I had a pain mounting my 5000tl on my Jet 6+s and I think the biggest issue was junk in my valve stems. Once I cleaned that out it worked 'like it should' have to begin with. They just weren't allowing enough air through. I use an air compressor to blast air as it seats the tires a lot easier vs. a floor pump.

I use a product similar to Stans race and the chunks of rubber get caught up in my valve stems it seems... so I remove the stems vs. the core when I'm adding sealant outside of mounting tires.

Yes that is correct.
And I am using air can pumped up to 140psi, still i can not bead to seat
Conti 5000 TL are already so tight around the wheel even if it sits in the middle

What do You mean by valve stems ? Is it the same as valve core?

I am using milkit valves with rubber at the other end of the valve

Try taking the valve core out of the valve stem try to pop the beads on without it. That will allow for a greater air flow through the valve stem, can sometimes make a difference.

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Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
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Use a tire lever and get the bead up in the channel as much as you can on both sides as shown in this video:


Then pump with floor pump. Or - use an air compressor.

Rim tape: 21mm since the internal width of the rim is 21mm.

Sealant, I don't add sealant until the bead sits and no leaks after an hour or so to make sure the bead seals, in case you need to adjust the tape so you don't have to deal with the mess. Then, add sealant through the valve hole to preserve the seated bead.

I suppose yes... I mean the valve core. My wheels have Zipp valve stems that are somewhat modular... they're essentially four parts if you count the nut and the presta valve. I guess what I was getting at was I was having a similar issue with seating the tires with the valve stem. It should have been obvious to me... so look at what you add or change to the scenario when it isn't seating and there's most likely your problem.

For me it was crap air flow in my stem.. took an hour or two before I put that one together... mounting, remounting, checking tape, etc. Ran a small bit in my stem, cleaned out the rubber and BAM, they mounted.

Tried to do as THE secret in video, but can not get the bead seated.
It is already SO tight (the tire around the rim) when it sits in the middle that I simply can not get seated as in video

(I don't know why) but I used 23mm rim tape. Might be that is what is preventing me to get the tire seated.
Just ordered online 21mm tape and will try again

Air compressor or local bike shop, 10 minutes in and out and support the little guy.

OR

Did you try installing a tube and stretch the tire a bit? I usually put the new tires in a laundry basket with a load of towels fresh out of the dryer or lay them on in the sun to heat up a bit.

i havent read the whole thread so apologies if someone has addressed this already, but i have often had trouble on various rims, including HED jet 6s and zipp 303. I get it, not everyone has space for a compressor, but man they make them so cheap and small these days and they are so handy for sooooo many other things, that i highly highly suggest getting one.
I have found that when i am having trouble normally, even with a compressor, i take out the valve core, put on an attachment that used more for just blowing air try to seal that as much you can against the now open valve stem and that has done the trick every time! just make sure to put your thumb over the valve once the bead sits in so you dont lose air rapidly and the bead pulls away. let the air out slowly or put the valve core back in quickly.
compressor are so much quieter and cheaper than they used to be. keep an eye at lowes or depot and you can find great deals. you dont need a big one. 1.5 gallon will be just fine. and they are so handy for kids bikes, car tires, blowing stuff out etc..... or go to Harbor Freight and pay half of that price but it might only last half as long and will probably be 2x as loud, but it will work!

https://www.lowes.com/...it-Ensemble/50129862 something like that works great for when you have the core removed. there are tons of stuff like that out there
https://www.lowes.com/...nflator-Gun/50126453 - then i bought this, cut off the hose and attached something like the following..
https://www.universalcycles.com/...yEAYYBSABEgJkO_D_BwE - then you have an awesome trigger pull set up with dual heads for shrader and presta and a semi accurate gauge. sure Sagan isnt trusting that gauge for riding cobbles at Roubaix, but for most of us, its plenty close.

Probably a little more than most want to spend but I am telling you, once you have this set up, you will find it so nice. sure i still use my regular pump alot of the time for my bikes .but if am airing up all my tires, or all the family bikes, grab the compressor and its done in a fraction of the time. and with the added tubeless benefit to me it was a no brainer.

Just did that
And it HELPED :)

Trend out valve was not tight enough screwed

It's not just you. I'm running this combo and needed a lever to get the tire on and a compressor to get it seated. Now - mine don't come loose once seated, but my install procedure includes sealant once it's seated and keeping them pressurized for a few days in a row at least.

Per HED :

https://www.youtube.com/watch?v=h-XFMGDO2rA