omegus

So, I recently had to patch my front wheel's inner tube due to a needle piercing the tire thread. I patched it up using a tire patch kit, but I noticed that the front wheel is never fully inflated anymore. It doesn't lose air completely, but it is much softer than the rear wheel. Within an hour or so, some of air escapes and the tire doesn't feel hard anymore, but doesn't fully deflate.

Is it possible the patch failed and needs to be redone or should I just replace the inner tube?

exmechanic89

Could be the patch didnt take, or maybe there's a another hole. Btw when you patch a tube, always check the inside of the tire with your fingers to make sure whatever caused the flat isnt still stuck in the tire, or you'll just put another hole in your tube.

omegus

In general, when an inner tube is patched, will it ever work the same as it did before it became damaged? I don't think it's another hole because the tire would completely deflate within a few minutes, right? I noticed this when the needle was stuck in the thread. It deflated the tire completely within a few minutes.

SquidPuppet

A properly patched tube will hold air just as well as a new tube.

Slow leaks can be mysterious. If the hole is tiny, often times the tube will only partially bleed out.

DeadGrandpa

If the patch seals completely because you did everything right, the tube should hold pressure just like a new tube. I always run my fingers inside the tire the whole way around, to make sure I don't have an additional problem. Either your patch didn't seal completely (do it over) or you have another hole in the tube. You should carry a spare tube with you and do the patching at home. Use a pail of water and look for bubbles to find small leaks.

Gresp15C

I consider a correctly patched innertube (using a good kit such as Rema) to be equivalent to a new tube. I've taken apart wheels that I've used for years, for instance to replace a worn out tire, and found that the tube was something I had patched and forgotten about.

I know it's possible to screw them up, because I've done it. I've also damaged tubes upon installing the tire.

All's you can do is re-test the tube under water and see if it's still leaking around the patch, or somewhere else. Keep note of the tire and tube orientation, so you can follow the leak in the tube, to the suspicious location on the tire.

Kapusta

A proper patch is pretty much good as new.

However, a botched patch is hard to fix.

Best way I know of to find a slow leak is to inflate the tube, then hold it under water.

omegus

Ok I'll re-check it. One more question: can I dunk the tube into a bucket of water once it is patched? Will this weaken the rubber cement adhesive on the patch if it goes inside water?

Kapusta

Water will not affect the glue.

JanMM

Yes and No.

exmechanic89

As the others have said, a patched tube will hold air just as good as a new tube - I'm using a couple in my road bike at this very moment. And no, putting the patched section under water will not affect the glue. Btw, you can have a tiny hole that will keep the tube pretty soft, a hole wont necessarily let all the air out quickly - depends on the size of the hole.

I would re-do the patch if it were me. And you could always put the tube in some water as well to see if you can spot the leak. Good luck!

Happy Feet

Sometimes the "needle" that poked through one side of the tube goes on to poke the other side too.

a1penguin

You have a slow leak someplace. These can be difficult to find. Dunking in water is sometimes the only way to find these miserable slow leaks.

I only use put new tubes in my seat pack, but I do carry a patch kit as well. When you get a flat on the road, you should carefully remove the inner tube, inflate and look for the source of the leak. Inspect the tire for a small piece of metal or glass that is still in the tire. Running your fingers along the inside of the tire (do it slowly so you don't cut yourself) for remaining bits of stuff. I have always been successful finding the source of flats and have had to remove a metal shaving, a screw and a small cotter pin from my tire. The metal shaving was very small and not particularly visible.

I will put patched tubes in tires at home and ride around for a while to make sure the patch is OK. This is after I inflate the tube and leave it for a day to see if it has a slow leak.

This approach balances cost vs being caught on the road with a bad patched tire. Patch kits are $3 and I can patch 5 flats while a new tube is $6.

rm -rf

Did you use the patch kit with a tube of glue? Or a peel-and-stick instant patch?

I consider an instant patch to be temporary, just to get me home. And I've had some not work at all.

The glued on patches are permanent, and I never worry about them after I verify they've held pressure overnight.

If your patch is leaking, it'll be difficult to impossible to re-patch it -- you can't pry off the old patch, and another overlapping patch doesn't work very well.

Patching at home
I patch a few tubes at the same time, keeping them until I have a few to do. I use up a whole tube of glue that way -- it dries out otherwise. A silver sharpie marker makes it easy to keep track of the hole. Scuff the rubber carefully, smear a thin layer of glue, then let it dry completely for at least 5 minutes. Stick on the patch, and press it down thoroughly with something rounded, like a screwdriver handle.

Water test
I've had a very tiny puncture, too small to hear or feel the air escaping. I dunked the inflated tube in the bathtub, and wiped off the small air bubbles that cling to the rubber. Then I looked for new bubbles, wiped them again to verify they were reappearing. It took 5-10 seconds for a new tiny bubble to show at the puncture location.

dabac

When you do the water test, don't be shy when you inflate the tube. Pump it up to double thickness before dunking it. It'll make small holes easier to spot.

BobbyG

Check the valve stem. Over 25 years of commuting I have had two instances where the valve stem developed a breach that only leaked air when the stem was deflected in one direction past a certain point.

I found these leaks accidentally while handling the partially inflated tube to rotate it in the sink to find the mysterious leak.

My guess is that the inner tube and valve stem were not sufficiently centered in the hole in the rim, and the edge of the hole eventually wore away at the stem where it meets the rest of the inner tube; or perhaps just the pressure exerted on the off-kilter stem was enough to tear the joint.

What ever the cause, I surmise that it is possible that a small breach where the stem meets the inner tube is opened slightly when the tire is inflated past a certain pressure (possibly due in part to an angle of deflection of the stem). When the air pressure drops below a certain point the breach closes enough that it holds air.

It is possible that after patching the original puncture the inner tube was seated in such a way to put pressure on the valve stem and cause this type of problem.

This may not be the case, but I wanted to share what happened to me. When I discovered it both times I replaced the inner tube.

VegasTriker

Even the cheapest patches sold 48 for a little more than a dollar by overseas sellers Sport 25mm Cycle Tyre Tube Bike Tire Repair Piece Tool Puncture Rubber Patches | eBay will bond permanently to the tube if you clean it thoroughly before applying the glue. One way to really clean the surface is to use a Q-tip and apply a small amount of solvent to the tube (paint thinner, Coleman fuel, or other hydrocarbon solvent) and wipe it off with cloth or paper towel. Works way better than trying to clean and roughen the tube with that little object found in repair kits.

One thing not mentioned by others who replied is to carefully inspect the inside of the tire casing for some other source for the hole. I check the site of the hole first for something to puncture the tube after I re-inflate it but also carefully run a finger around the inside of the tire feeling for anything else that may cause a hole. Out here where we have tumbleweed and goatheads if you hit one, you may have hit more so checking for thorns both inside and out is recommended.