Every now and then it happens – you flat.  More frequently on a road bike then a mountain bike, but it happens to both at some point.  After a flat, should you patch the tube or throw it away?

As for preparation for the inevitable, well you should always carry two New tubes as spares. You should also have a ‘patch kit’ or more appropriately some ready to use preglued patches.  These are in case you flat more than twice – yes I personally have flatted 3 times on more than one occasion on my road bike (although in one case I borrowed a tube from someone else rather than patch).

When you do flat you should always take your punctured tube with your or dispose properly of it.

Thus my first rule is after clearing my tire from any debris which is poking through the tire causing the flat is to use a new tube.  Note that I specified “New” tubes earlier.  Your spare tubes should never have been previously patched. If you are using a patched tube and you flat 300yds down the road you don’t know if your patch failed or if you left debris in the tire – with a new tube you can be confident that you didn’t clear the tire correctly (and apply the appropriate expletives while changing your tire AGAIN).

Once you get back to base/home you have a damaged tube in your pocket (or are you just happy to see me Which brings me back to the question of should you trash or patch it? 

Well my preference is to patch once.  Only once, because each patch introduces another potential point of failure and so I limit myself to one patch on a given tube.

Having said that for what to do when riding where does patching fit in and why?  Well the fact is that a patch introduces a new point of failure in your tire.  No not the ability of the patch itself to withstand pressure, but the glue holding the patch down.   Applying the patch on the road is risky because depending on your skill a large number of patches aren’t applied correctly to start with not to mention on the road it’s harder to tell if you’ve gotten the hole(s).  That's why you carry two spares since

Thus for me the rule of patching is: to patch a tube and place it back on the bike at home.  It doesn’t matter whether I’m swapping that good tube back out to be a spare again or if I’m replacing a worn tire with a new one.  Along with this the goal is to patch in the evening allow the patch to hold overnight (showing it was a good patch) and then do a short ride and finally leave the patch in the sun/heat.  I bring this up because I’ve repeatedly had new patches which seemed to hold, even to support me during a short ride to suddenly fail when my bike was parked in the sun.  In some cases with more traditional patches I was able to re-inflate the tire and in the process the patch had gotten a better seal – in other cases especially with a self adhering patch, the patch was dead. 

Thus I am willing to patch a tube for reuse locally and allow it to prove itself.  However, I wouldn’t patch or install a patched tube if I was preparing a new tire for use as part of a long ride or an important ride where I didn’t want to risk a failed patch flat.