How to Repair a Sidewall Gash in a Bike Tire

How to Repair a Sidewall Gash in a Bike Tire

sidewall gash bike tire
Bike tire with a gash in the sidewall. Photo credit - Rob Anderson.

Getting a split in the sidewall of your bike tire is a common problem. But fixing it is easy, allowing you to keep your tire and save you money by not having to buy a new one.

Keep in mind we're not talking about merely patching a tube here, or changing a flat tire. This is a repair you do when you have a full-blown split in the sidewall of your bike tire, usually caused when a sharp rock edge rips into it, creating a sizable gash or tear which often causes the tube to bulge out. Sometimes the bike may still be rideable, but it is a tenuous situation and you can't count on going far with it like this.

To start the repair, first clean the site of the split, both inside and out. Gently wipe it with a damp cloth and also remove any debris that may be there, such as leaf parts, grit, whatever. We need this to be clean so that glue to be applied in later steps can adhere properly.

The gash in the accompanying photo was caused not by a rock but by a broken beer bottle. It happened on the Missouri's Katy Trail to my friend Rob Anderson, who is famous for doing a solo ride 167 miles from St. Louis to the Lake of the Ozarks in a single day.

Stitch Up the Gash in the Bike Tire Sidewall

Using a needle and dental floss to repair a gash in a bike tire sidewall
David Fiedler

This next step will have you feeling like a doctor or a seamstress. Gather a stout sewing needle and about 12-18" of dental floss.

Using a criss-cross pattern and starting from the inside of the tire, sew stitches across the gash, pulling the rubber of the sidewall together to replicate its approximate original position.

Before starting, tie a knot at the far end of the floss, away from your needle. This is what will anchor the floss inside the tire. Leave extra at the end (about 2-3") that we'll use to tie off the floss later.

Make sure that you run the needle in and out of your sidewall where it is intact and far enough away from the split that the stitches will hold. Saying it another way, if the stitches are too close to the split, the damaged sidewall may not hold the stitches in place.

Finish your Stitches to Repair the Split

Using a needle and dental floss to repair a gash in a bike tire sidewall
David Fiedler

Once you've finished with your stitches, you'll tie a knot using the two ends of the floss. The first end comes from the knot at the end of the floss you made when we first started; the other end is simply what's left from the front end where the needle was. Tying this off is important to keep the stitches in place and prevent the floss from unraveling. A simple square knot will do the trick; make this knot inside the tire and use a scissors or fingernail clippers to trim off any excess length.

Apply a Patch Inside the Tire

bike tire sidewall split patched with a car radial tire patch
David Fiedler

The next step is to apply a car tire patch inside the bike tire. These are available at auto supply stores and are generally called "radial tire patch" or something similar. Again these are not patches like you'd use on a bike inner tube. They are not stretchy. Their purpose is to hold the sidewall together and provide an extra layer of support against the high pressure of the inner tube that will be pressing against the bike tire side wall.

Apply the radial tire patch according to package directions. Typically this will involve putting down a layer of rubber cement, then pressing the patch down onto that.

Final step: Paint the Dental Floss Stitches with Rubber Cement

Rubber cement paste over dental floss stitching helps hold sidewall split repair intact
David Fiedler

For the final step, take rubber cement and liberally paint the stitches with the glue. This will both protect the stitches from getting snagged or damaged as you ride and will also help with yet another layer of adhesive that helps hold the sidewall together.

After you've done this (allowing a couple hours to make sure all the glue is fully dry inside and out) inflate your tire slowly. The sidewall may expand and bulge slightly and very likely will not be the same as it was before. However, your effort will extend the life of the tire and should allow you to continue riding it for some time. Do however check this spot in your tire before every ride, just as another part of your five-point safety check that you should always perform before you head out on the bike.