Mavic Cosmic Carbon UST

Everything about building wheels, glueing tubs, etc.
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Paperboy
Posts: 24
Joined: Tue Jun 04, 2019 5:38 pm

by Paperboy

I just switched over from a tube/tire setup to these tubless wheels and I ran into an issue. It seems air is leaking from the bead in multiple spots. The wheels are brand new and came with the tires mounted. I set them up as as per usual (inflate to seat bead, take out valve core, add 30-40ml of sealant, replace valve core, inflate).

Upon initial inflation (pre sealant), I pumped it up to 80 psi. The bead must have already been seated because I did not hear anything; same went for the other wheel. The tires appear seated from factory. The rear wheel is holding air fine. It's the front that's leaking. I pumped it up to 90 and it drops to 60psi. Hopefully the sealant does it's job and seals any leaks overnight.

Has anyone else encountered such issues? Could it possibly be leaking from the rim tape? I picked the wheels up off ebay so I'm SOL with warranty.

jlok
Posts: 1200
Joined: Tue Jun 30, 2015 3:30 am

by jlok

Points to check:
Tubeless Valve rubber base / tubeless tape interface (if any). Is the punched hole on the tape too big?
Valve Core. I got a bad valve core before and it will leak.
Tubeless tape around the rim. Properly taped the whole rim bed?
Litespeed T1sl Disc / BMC TM02 < Giant Propel Advanced SL Disc 1 < Propel Adv < TCR Adv SL Disc < KTM Revelator Sky < CAAD 12 Disc < Domane S Disc < Alize < CAAD 10

by Weenie


Paperboy
Posts: 24
Joined: Tue Jun 04, 2019 5:38 pm

by Paperboy

jlok wrote:
Wed Jul 24, 2019 9:48 am
Points to check:
Tubeless Valve rubber base / tubeless tape interface (if any). Is the punched hole on the tape too big?
Valve Core. I got a bad valve core before and it will leak.
Tubeless tape around the rim. Properly taped the whole rim bed?
Thanks for the checklist. I took the bike into the lbs. I didn't know that, aside from spinning the wheel, after applying sealant you need to shake the wheel so that the sealant is able to migrate to the bead. After shaking the wheel a bit, it just sealed up. I thought that with Mavic's UST system sealant is more of an option than a necessity. I guess I had too much faith in their system tolerances :noidea:

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bikerdan
Posts: 151
Joined: Thu Dec 02, 2004 4:03 pm
Location: Germany

by bikerdan

So this was with the Mavic tyres that come with the wheels? I also would have expected that to seal without sealant

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zefs
Posts: 439
Joined: Sat Aug 05, 2017 8:40 pm

by zefs

I run mine without sealant currently but using Ksyrium Elite UST that don't need tape but it should work on Cosmic's too.
What tires and valves are you using? If the tire has play when you move the wheel by hand it probably hasn't seated correctly, try 100 psi?

jackalope
Posts: 21
Joined: Tue Sep 19, 2017 5:18 pm
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by jackalope

I would also suggest the valve itself it tight on the rim. I've gotten wheels where the valve is just loose enough that it leaks air. When inflating also make sure you are not exceeding the limit of psi rated for the rim itself. If there is a limit it will be published on the rim. Go right to that number.

You are also correct, the tires come seated from the factory. You could try a different sealant too. If it's just a matter of a little leakage of air, something like Orange Seal would take care of it over the Mavic sealant by Hutchinson.

Paperboy
Posts: 24
Joined: Tue Jun 04, 2019 5:38 pm

by Paperboy

The wheel/tire combo came setup together. It's their Yksion Pro UST tire. The max psi rating for the wheel/tire is 87psi. I went for a ride today and everything worked fine; no loss in pressure. I pumped them up to their max psi (87); even at that pressure I could tell there's more compliance and less rolling resistance. What an eye-opener UST tires are! I'm never going back.

jackalope
Posts: 21
Joined: Tue Sep 19, 2017 5:18 pm
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by jackalope

Mavic has an app called My Mavic to help calculate ideal tire pressure. It's been pretty eye opening when it comes to the width of the tire, the width of the rim and the weight of the rider to see how the pressure differs.

Paperboy
Posts: 24
Joined: Tue Jun 04, 2019 5:38 pm

by Paperboy

I used the app. I plugged in 25mm tire, 19mm internal width, 160lb rider+17lb bike, performance. It came out with 86f/87r. My guess is that once your weight exceeds a certain threshold it's going to be max pressure no matter what for performance riding.

by Weenie


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