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Both the (new) tyres I have bought deflate overnight: I have to pump them up again every time I want to ride them.

This happened before I even rode them for the first time, so no punctures.

Is this just because I haven't got around to adding sealant yet, or is it a serious problem with the rim/tyre? The wheel is Shimano Ultegra 6800.

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  • Yes tubeless (ready) need sealant
    – paparazzo
    Commented Oct 2, 2015 at 14:08
  • Did the old tyres/tires lose air fast? Then it may be rim damage or a leak somewhere else. If they were just worn, then your installation may be flawed. Sealant is absolutely required, and if you didn't use it, then you're dependent on air pressure alone to form a seal. If you have no sealant, take the bike to a LBS and get it done right.
    – Criggie ♦
    Commented Oct 2, 2015 at 22:45
  • The rims are only about 6 months old. Previously I used normal tyres with tubes, they did not lose air. Ok will put in sealant and report back.
    – Ne Mo
    Commented Oct 3, 2015 at 7:20
  • @NeMo its been two months now - can you give us an update on your deflating tyres ? Did the sealant help?
    – Criggie ♦
    Commented Dec 4, 2015 at 4:10
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    Sorry, yes the sealant helped. Just a case of me being dumb
    – Ne Mo
    Commented Dec 4, 2015 at 17:49

2 Answers 2

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Is this just because I haven't got around to adding sealant yet...?


Yup.

The sealant plugs the very small air leaks in the casing and between the rim and bead. The tire will leak down substantially faster without it.

Despite the fact that it's not the subject at hand, it's worth reinforcing what brendan said: make sure you're running tubeless specific road tires for road tubeless. Standard beads- both steel and kevlar- stretch, and without a tube to bind them in place they will stretch enough to climb over the rim and blow off suddenly and catastrophically. You can get away with non-tubeless specific tires at the lower pressures used by mountain bikes- Stan's made their initial mark on the industry by providing conversion kits for non-tubeless rims and tires. But you cannot get away with that at road bike tire pressures. Road tubeless tires use a carbon bead that doesn't stretch, and therefore doesn't blow off the rim. That is the critical innovation that took so long to come around and make road tubeless possible.

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Which tyres are you using? If you are using tubeless tyres (e.g. Hutchison Fusion or Schwalbe One) then they will usually seal without sealant when you install them (but don't leave them that way...). If you are not using tubeless tyres, then they will have too many holes in the sidewalls to seal without sealant.

You will need to put sealant in to seal the last few gaps on the rim and pin-prick holes in the sidewalls. The easiest way to do that is to remove the valve core (assuming you have good quality valves with removable cores?) and then use a syringe or very steady hand to pour the sealant in through the valve.

Also, using non-tubeless tyres on a road bike - even if it has tubeless wheels like your Ultegra 6800 - is a bad idea. Please don't do it. There is a good chance of having a tyre burp all it's air out while you are corning, causing a rapid involuntary dismount.

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