One of my tyres on alloy rims continues to lose air. This is despite being checked by a tyre specialist for leaks and nails in the tyre (tyre removed and checked internally). They fitted a new valve and cleaned and resealed the rim. Could it be porosity through the alloy rim or other problem?

Octavia II blue estate

Stephen A

Your best best is to totally submerge the wheel in a container full of water (a decent tyre fitter should have one) and look for where the bubbles are coming from.

Agree that the wheel/tyre should be water tested first . If the bubbles are coming from the junction of the tyre and wheel rim then this should be checked.

Sometimes the tyre rubber bonds itself to the inside wheel rim .When the tyre is removed some of the rubber is left stuck/bonded to the wheel. If this is not cleaned off properly then it prevents the replaced tyre from sealing properly.If this is the case get the tyre fitter to remove tyre and examine the inside rims. If there is some rubber left there get them to scrape it off ( not with an angle grinder that some garages use !). Any decent tyre fitter should have checked for this.

Edited 14 August, 201015 yr by vwcabriolet1971

Your best best is to totally submerge the wheel in a container full of water (a decent tyre fitter should have one) and look for where the bubbles are coming from.

Thank you.

The wheel and tyre were submerged before changing the valve and resealing. No bubbles were found. I was watching as well.

Agree that the wheel/tyre should be water tested first . If the bubbles are coming from the junction of the tyre and wheel rim then this should be checked.

Sometimes the tyre rubber bonds itself to the inside wheel rim .When the tyre is removed some of the rubber is left stuck/bonded to the wheel. If this is not cleaned off properly then it prevents the replaced tyre from sealing properly.If this is the case get the tyre fitter to remove tyre and examine the inside rims. If there is some rubber left there get them to scrape it off ( not with an angle grinder that some garages use !). Any decent tyre fitter should have checked for this.

Thank you.

All the items you mentioned: submerge in water (no bubbles), clean old rubber with wire brush, re seal with new sealant was done. I will try inflating to 3 bar and submerging again. I have been told that some alloy wheels develop porosity over time, so I am thinking that the inside of the wheel needs spraying with a sealant, or use an inner tube.

I'd say check your alloys for cracks. My dad had a similar problem on his old Alhambra. All of a sudden the front near side wheel was flat, took it to the local tyre place who replaced it. Couple of days later it was flat again, so we took it back and they noticed a crack on the inside of the alloy which was causing the air to leak out.

We then had to buy a whole new alloy as it was cheaper than repairing and it was fine.

Thank you.

All the items you mentioned: submerge in water (no bubbles), clean old rubber with wire brush, re seal with new sealant was done. I will try inflating to 3 bar and submerging again. I have been told that some alloy wheels develop porosity over time, so I am thinking that the inside of the wheel needs spraying with a sealant, or use an inner tube.

The coating on the inside rim should prevent porosity leaks. But if that coating is broken / scratched / cracked down to the raw Aluminium alloy then it is possible that ,if is it is a poor quality casting , porosity leaks can occur.It would have been better if the tyre fitter had carefully used a scraper rather than a wire brush. I hope he didn't use an electric drill with the wire brush !