My newish back wheel losses about 20psi during the week and the front one about 5-10. Took the inner out of the back one and checked for puncture with the old bubbles in the water test. Nothing?

Pumped up for two longish riides over past two weekend and fine, but still will be down a lot by next weekend.

Is it just the warm temperatures? Never goes totally flat, but seems odd.

Schreader or presta?

Valves.

Presta

Checked the valves under the water. Would it be that they are just not done up enough?

If they are removable , pop em out and a wee bit of grease, refit.

Or, alternatively, this is justification for you to join the 21st century, tubeless.

Tubeless??? I’ve only just moved up to a FS… 😉

Still the same tyres, and same problem. Pump them up for a ride and no problem. Including a 31/2 hour ride yesterday. But next day, back tyre always totally flat and front one -15psi.

Really odd. If there is a problem, why do they not deflate under my weight on a ride?

pump tube up, and imerse in bowl of water, then gently while holding tube underwater, wiggle the tube valve stem from side to side, looking for bubbles, common problem with tubes is a leaking joint between tube and valve stem

You have punctures. Assuming the tubes aren’t really old and a bit perished, aren’t latex and you’re not filling them with co2.

Change the tubes for new and see if they go down overnight. If they do someone’s winding you up.

I’ve tried the bubble test and nothing – I’ll just replace the tyre probably but seems really odd. Why would the tyre not default during the ride and under my weight?

You have not got latex tubes in have you ?

They probably do but you don’t notice as you ride for perhaps two hours and then leave them for 18 hours. During your ride they deflate 10% ish of the amount they deflate in total

Have this on the CX bike

Essentially you have punctures there can be no other cause [ unless someone in the house is messing with your bike].

It does deflate when you ride and if you used an accurate enough pressure gauge I am sure you could prove this

As its a [very] slow puncture IME you need to pump the tube up really really hard to find the little blighters. I also squeeze to increase the pressure of the bit underwater- it possibly only one bubble but always n the same place- tbh it might be easier to change tubes and be done with it.

I agree about testing the valves with wiggle as I have had that happen as well. Dont try and repair these. DOn’t get frustrated when your initial attempts to repair the valve and design ever more elaborate fixes either as it wont work…not that i would be this foolish 😳

has the presta valve got a removeable core ? if it has squirt a syringe of stans* in…. should seal any slow leaks.

*other products are available.

You could have something sharp embedded in the tyre, running your fingers around the inside won’t find it but if the wheel and tyre press on something at just the right point then the sharp will be pressed into the tube and cause a very small puncture.

Take the tube out, inflate (carefully) and immerse in a bowl/bucket of water and you should see where the problem is.

All inner tubes will lose pressure over time as the rubber compound isn’t completely air tight but overnight suggests a puncture.