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How Do You Find a Leak From Wheel Porosity or a Cracked Rim?

If the bead, valve, and tread test clean, spray the wheel itself: barrel, spoke roots, and face. Porosity seeps tiny bubbles; a crack shows a line

3 min read CHAOS Moto

If the bead, valve, and tread all test clean, spray Bubble Check on the wheel itself: the inner barrel, the spoke roots, and the face. Porosity shows as tiny bubbles seeping out of the metal away from the bead and stem. A crack shows as a line of bubbles along the crack. A porous spot can often be sealed from the inside; treat a cracked wheel as a replacement, and follow the wheel maker's guidance.

Find your leak in 3 taps: Leak Lab →
Wheel diagram: tiny bubbles seeping from one spot on the wheel metal, and a line of bubbles along a short crack near a spoke Porosity or crackSPRAYInner barrel, spokeroots, wheel faceLOOK FORPinpoint seeps, or aline along a crackNEXTSeal porosity inside;replace a cracked wheel
Wheel porosity and cracks: tiny seeps from the metal itself, or a line of bubbles along a crack.

How does it show up?

  • A slow leak that keeps coming back after the bead has been cleaned and resealed.
  • Cast alloy wheels, where porosity in the casting can let air through.
  • A leak after a pothole or curb hit, from a crack near the bead seat or a spoke.
  • Corrosion pitting on the barrel of an older wheel.

Where do you spray Bubble Check?

  • The inner barrel. With the wheel off the vehicle and the tire inflated, spray it and turn the wheel slowly.
  • The spoke roots, where the spokes meet the barrel.
  • The wheel face and the area around any impact mark.
  • Keep this until last, after the valve, bead, and tread test clean.

What do the bubbles look like?

  • Porosity: tiny bubbles percolating from a patch of metal, sometimes from several pinpoint sources.
  • Crack: a row of bubbles along a line, often near the bead seat or a spoke root.
  • Both can be slow. Give each area time.

What do you do next?

  1. Mark the spot on the wheel.
  2. For a crack, take the wheel out of service and replace it.
  3. For porosity, demount and seal the area from the tire side with a sealer made for wheel porosity, applied per its maker's instructions, or replace the wheel.
  4. Remount, inflate, and spray the area again to confirm.

How to run the check

  1. Inflate the tire to its specified pressure. A soft tire may not push enough air to show a slow leak.
  2. Spray Bubble Check on the area and give it time. A slow leak can take a little while to show.
  3. Watch for bubbles that keep forming at the same point. The first light foam from the spray settles; a leak keeps building.
  4. Mark the spot with a tire crayon before you wipe the area dry.

About Bubble Check

Bubble Check is the CHAOS Moto spray-on tire leak detector. It comes in a 32 oz bottle with a trigger sprayer, so you check the tire on the wheel with no dunk tank needed. Shops use it to pinpoint valve and bead leaks and for TPMS stem checks. See the Bubble Check page or where to buy. Bubble Check is not currently sold on Amazon.

Common questions

Can a porous wheel be sealed?

Often, from the inside with a sealer made for wheel porosity, applied per the sealer maker's instructions. If it keeps leaking, replace the wheel.

Can you see a wheel crack without a leak test?

Sometimes, but hairline cracks on the inner barrel are easy to miss. A leak detector makes a leaking crack visible.

How do I check the inside of the barrel for leaks?

With the wheel off the vehicle and the tire inflated, spray the inner barrel and turn the wheel slowly, watching each section.

More leak types in the Leak Lab. Related: bead leaks and when you cannot find a slow leak. Questions: sales@chaosmoto.com or 480-829-7888.

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