I’ve seen all types of flats and the sometimes crazy reasons that cause them. I’ve even seen a flat caused by a bullet. Most flats are obvious, some are not, and sometimes you get stuck in the “frequent flat” routine. Let me first start by saying that under inflated tires are often the cause of many flats. Low pressure makes your tire more susceptible to thorn type punctures as well as pinch/snakebite flats where the tire bottoms out against the rim thus pinching the tube. Ideally you should check your tire pressure before each ride.
If you’re getting frequent flats you really need to get methodical about discovering the cause. The first thing I suggest you do is go buy a paint pen, I like silver. Now, when you install the tube, put a big X on a specific SIDE of the tube. Anywhere you like is fine. This “keys” your tube. Now, install the tube with the X facing the DRIVE SIDE of the bicycle. The drive side is the crank side of the bike. Line the X up with some identifying feature on the tire (most tires have logos). If the tire has no identifying feature or too many logos, make one on one sidewall with the silver pen. If your tire is directional make it on the drive side of the tire. Now, with the X on the tube lined up with the identifying feature on the tire, install it so that they both line up with an identifying feature on the rim. This can be a sticker, a scratch, a mark with your paint pen, the rim seam, anything you can identify. Wheels are directional too, if your hub has a logo you should always install the wheel so that you can read the logo when sitting in the saddle, again paying attention to how you install the tire onto the rim if the tire is directional.
Now next time you get a flat you can identify the EXACT spot on the rim, tire and tube where the flat occurred. Take your tire and tube off the rim and begin an inspection. Inflate the tube to figure out where the puncture in the tube is located. If the puncture is on the tread side of the tube, line the X on the tube up with whatever identifying feature of the tire you used and inspect the area of the tire that coincides with the puncture in the tube. Run your fingers along the inside of the tire feeling for anything sharp. Push the tread inwards and use a headlight on the inside of the tire so you can get a good look. I’ve seen cases where a small metal thread (from a blown out car tire carcass) can get embedded into a tire. Those little strands are nearly invisible and can cause repeated flats. Be prepared to get your fingers pricked and have a nice pair of needle nose pliers to grab any offending objects in the tire. Inspect the entire tread area of the tire for embedded objects, remove these too as over time they can work their way through to the tube.
If the puncture is on the rim side of the tube, line everything up and start looking at the rim in the location of the puncture. Rim punctures can be caused by many things. Often times it’s a rim strip issue or a metal burr on a spoke or spoke hole. It’s important to use a quality rim strip. The cheap rubber ones are not really acceptable except for single wall rims. If your rim is double wall use a quality high pressure rim strip of the proper width. The strip should cover the spoke holes but not be so wide as to interfere with the seating of the tire at the bead. I regularly install KORE, FSA, Origin8 and Velox tapes. In rare cases poor engineering of the rim can cause flats. A few times I’ve had to install thin rubber tubing into a groove in the center of the rim and then cover it with rim tape because the tube was thinning out so much when filling into the groove that it would fail simply from friction.
If you’re just getting regular pinhole type punctures in the tread area and there’s nothing embedded in the tire it’s just dumb luck. Investing in better tires is one way to reduce flats. There are many tires on the market that have some type of built in puncture protection, some are better than others and those often come at a higher price. When it comes to tires you really get what you pay for. For puncture resistant performance road tires I often recommend Continental Gatorskins. For relaxed commuting and touring I recommend Schwalbe Marathons or Michelin Pilot Sports. There are of course other choices but I don’t have much experience with them. Vittoria’s Randonneur line, Michelin City Proteks and the uber bargain CST Selecta which are actually pretty decent albeit with limited size choices.
If you can’t afford puncture resistant tires or can’t bear to replace your perfectly good barely worn tires, consider tire liners. They work but I would avoid using them in narrow road tires. Mr. Tuffy used to hold the trophy for best liners but now I have to recommend Rhinodillos for the best protection. A tire liner goes between the tube and the inside of the tire. It deflects objects that pierce the tire. They do reduce flats but as the saying goes, there’s no such thing as “flat-proof”. Tire liners do add weight, the Rhinodillos are hefty and they do not make a “light” version like the Mr. Tuffy Ultra-Lites.
Another option is a tube sealant. Slime is JUNK. It eats away the bond between rubber and brass so eventually you get a bubble around the valve stem and you flat. I’ve seen it many times. We use an alternative at the shop. Flat Attack. It uses fibrous material versus the rubber chunks in Slime and it doesn’t cause the valve stem separation issue as far as I can tell. Personally, I use Stans NoTubes in my tubes. Stans works wonderful, the only downside is that it dries out quicker and you must add more in as little as 3 months depending on the atmospheric conditions in which the bike is used and stored. Stans is actually a latex rubber based product and when it cures it cures as a latex rubber. Slime and Flat Attack don’t cure, they just clog and dry up in the puncture. Stans is also intended for tubeless applications. The thing to remember with sealant is that it doesn’t always seal the hole the first time. With Slime and Flat Attack if you get a puncture and can hear air escaping you need to get that puncture facing the ground so the sealant can flow and be forced into the hole by air pressure. If the puncture seals and you park the bike with the puncture at the top of the tire the sealant can run away from the puncture and allow it to leak again. If this happens, re-inflate the tire and ride the bike so the sealant is distributed along the inside of the tire. Alternatively face the puncture towards the ground and let gravity get the sealant there. With Stans NoTubes you shouldn’t have this issue once the puncture is sealed as when the Stans is exposed outside the tire it will cure up to rubber.
Lastly, I feel it pertinent to include some thoughts on “airless” or “solid” tires. I would avoid these entirely unless you’re riding through something akin to a warzone and absolutely need to eliminate flats. Solid tires offer no pneumatic cush and will destroy your rims and hubs quite quickly. Your spine and kidneys may also suffer from the bone jarring ride of solid tires.
I hope I’ve covered all the situations that cause frequent flats and there are many ways to reduce flats significantly. If I’ve missed something please contribute in the comments!