What we actually find when a slow puncture cannot be explained

• Hairline rim cracks. by far the most common cause. Pothole or kerb hit weeks or months ago, crack opened up slowly, leaks 1-2 psi per day.
• Corrosion at the tyre bead. older alloys, salt damage. Air leaks past the bead seal. Common on cars more than five years old in Slough.
• Failed TPMS sensor seal. the rubber gasket on the valve has perished. Looks fine, leaks slowly. Easy fix.
• Cracked spoke welds on multi-piece wheels. split rim wheels can crack along the spoke weld and leak through to the barrel.
• Porous casting defects. rare, but real. Tiny voids in the original casting open up over time and leak air through the wheel itself.
• Old badly-done weld repairs. someone welded the wheel poorly years ago and the weld is now leaking. We grind it out and re-weld it properly.

How the leak test runs at our Slough workshop

Drop the car at our SL3 7EW workshop. Wheel off the car, tyre off the wheel, both inspected separately. Wheel pressure washed clean of brake dust and old sealant. Dye applied to the inside of the rim, the spoke roots, the valve area and the bead seats. The wheel is pressurised through the valve and inspected under bright light. Most leaks show up within 30 seconds.

For confirmation we then submerge the wheel in a water tank under pressure. Any leak you have, no matter how small, will bubble. Once located, we mark it, log the failure mode, and quote the repair before anything else happens. No surprise bills. If it is a crack we TIG weld it. If it is bead corrosion we machine the bead back to clean aluminium and re-seal. If it is the TPMS we replace the service kit or the whole sensor. Then we pressure test again before refit.

Common cars that come to us in Slough with mystery slow punctures

• BMW 3 Series F30 / G20 with M Sport 19" wheels. inside-rim hairline cracks from London potholes. We see them weekly.
• Audi A4 / A6 B9 / C8 with 19" or 20" V-spoke. kerb damage cracks that go undetected for months. Standard fix.
• Range Rover Evoque / Velar with 20" or 21" diamond cut. corrosion at the bead seat plus the occasional hairline.
• Mercedes A / C / E Class AMG line on 19" or 20". AMG diamond cut wheels are prone to bead corrosion after three to four winters.
• VW Golf, Tiguan, Touareg on 19" optional wheels. diamond cut bead corrosion. Tyre keeps going flat. We machine and re-seal.
• Older cars (5+ years) on any alloy. winter salt eats into the bead seat. We see this on everything from Mini to Bentley.