Tuesday, November 10, 2015

Part One of a Trilogy on Flat tires: First, what causes them. Second,how to fix them. Third, how to prevent them.

There are three givens in life: death, taxes and if you ride a bike....FLATS!  Flat tires never happen at a good time, but the chance of having a flat while cycling can be greatly reduced with some careful attention paid to your bike's wheels, inner tubes and tires.

cycling through thorns causes flat tire due to punctures
So, what causes bicycle tires to go flat?  If you have the tire in the picture to the left it is an obvious answer, but there are at least four distinct types of flat tires.  Each type has its distinct personality and appearance.  Full anointment in the brotherhood of cycling happens when you have had the joy of experiencing them all!

First is the puncture/cut flat, which is the one we think of most often when we think of a flat.  A thorn, a piece of wire, glass or other sharp object on the road punctures or cuts through the tire and inner tube leaving you on the side of the road disassembling your bike so you can fix the flat.  This flat can take some time before it is noticed if the puncture is small, or it can be as long as a day or two before it goes flat.  Sometimes the hole is so small it is hard to find.  I have had to resort to dunking the tube in a bucket of water and watching for air bubbles to find these holes.

cycling rim tape spokes cause flat tiresThe second type, the pinch flat is the scariest flat because it often occurs when you are going fast, there is a loud pop and the tire goes flat immediately!  It happens when you hit a pothole or other sharp edge and the tube gets pinched between this edge and the two side of the rim.  For this reason this flat typically looks like a snake bite on the inner-tube with two punctures spaced apart from each other by the width of the rim.

Another type of flat happens when the rim tape moves over enough to expose one of the spoke holes in the rim.  This one can happen while riding, or even when the bike is just sitting there!  Notice in the picture how the green plastic rim tape has moved over and exposed the hole for the spoke nipple where the screwdriver tip is pointing.  That small amount of spoke hole showing was enough to cause me a flat!  This flat occurs because the rim tape fails to support the tube over the spoke nipple hole and the tube ruptures in a blowout.  It will be a large enough hole that you can't pump the tube backup with a floor pump.  The air will leak out as fast as you pump it in and the hole will be on the rim side of the tube.

The fourth type of flat is related to the cut tire, only this time the tire wall is weakened enough that the tube pokes out through it and ruptures.  This could be caused by a brake pad pivoting and rubbing on the tires sidewall until it gets so thin that it give way, or a piece of glass or metal on the road side. With this type of flat, if you don't have a spare tire you will have to line the tire with something in order to get home.  You can use a section of old inner tube, a large patch, a pre-trimmed piece of thin cardboard, a Park Tool emergency tire boot or a dollar bill placed inside the tire so you can get home.  The Park Tool emergency tire boot takes up very little room in your emergency kit, see below for a link to buy or check with your local bike shop for availability.

What should you carry with you on your ride?  At a minimum you should carry a spare tube, a tire lever and a CO2 inflator.  This can fit in you jersey pocket or in a saddle bag and will be enough to for shorter rides, group rides where people are willing to share, and supported rides that have spare tubes and flat repair as part of the ride service.  If you go out on longer rides by yourself, then you may want to include two tubes, a patch kit and either multiple CO2 cartridges or a frame pump. Crank Brothers makes a great CO2 inflator and the Topeak Road Morph G is a road pump that actually works as a pump.  There are smaller and lighter pumps but I highly recommend actually trying them before buying to see if the amount of work it takes to pump up the tire to a ride-able pressure is acceptable to you. You should also consider the emergency tire boot mentioned above.  If you are really out on your own a chain break is also a good idea.  This can be a separate Park Tool chain break or one that is part of a multi-tool such as the ones made by Crank Brothers.  Examples of both are listed below.

In my next post I will talk about how to fix the tires, and then I will follow that up with another post giving you some tips from the bike shop pros on how to prevent the flats in the first place.  Please comment on this post.  I would love to hear from you about the kind of flats you have experienced and what is in your emergency kit.


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