Where the Rubber Hits the Road

May
15

Posted by Coach Adam Sczech

photo by Heather Sczech

 

Tires offer possibly the easiest free speed out there, but not without tradeoffs. 

What is a tire? The answer is simple. It's the rubber part of the wheel. But, like much in the world of triathlon equipment, it is more complex than most realize.

Here are the basics of a bicycle tire, starting with the three general types:

 

  1. Tubular (a.k.a. sew-up) - The original tire option for bikes, a tubular consists of a tread on a casing that is sewn together with a tube inside making the tire/tube one piece. It is glued onto a concave rim. 
  2. Clincher - A tire that has a tread on a casing between 2 beads.  The bead can either be steel or Kevlar.  It is held onto the rim by a bead hook.  A tube is placed inside the tire during installation.
  3. Tubeless - A clincher tire with a specially shaped bead that when used with a tubeless rim, creates an airtight seal making the tube unnecessary.  It is important to remember that all tubeless are clinchers but not all clinchers are tubeless.

from http://www.betterbybicycle.com/2014/04/a-simple-guide-on-essentials-of-wheels.html

 

The most important parts of the tire are the rubber and the casing

Rubber

The Rubber is what the tread of the tire made of, and determines the “gripiness” and longevity of the tire. The rubber used in tires is identified by its Durameter, which is a measure of the rubber’s hardness. The higher the number the harder the rubber in the tire. A harder (higher durameter) makes for a good training tire because it wears down more slowly and is more resistant to punctures, but is not as grippy or comfortable because it cannot conform as well to small changes on the road surface. A softer tire makes for a more grippy tire but it will wear out faster.  Some tires use multiple durameters of rubber in the tread, using a harder rubber in the middle for longevity and a softer rubber on the sides for better grip.  Different durameters can make a huge difference depending on the weather.  In hot dry conditions a harder tire works just fine, but in cold or wet condition a softer tire will out perform a hard one.  This is because as rubber cools it naturally gets harder, so a softer tire will perform in cold conditions like a hard tire in hot conditions. 

Casing

The casing is the base of the tire and biggest determiner of how a tire is going to ride. A tire starts out as a casing then layers of tread are added. Casing is made of nylon (in less expensive tires), cotton (in higher end tires), or silk (in super high end tires). Just like bed sheets or other textiles, TPI (threads per inch) is listed for a tire. The higher the TPI the better and more supple the tire. A higher TPI means that the casing is made of smaller, more tightly wound fibers that allows the tire to be more flexible.

A more flexible tire is ideal for a few reasons, the most important for free speed is that it allows the tire to deform more easily to little bumps and cracks in the road. That allows it to act like a tiny shock absorber, keeping the bike from bouncing up and down -- and that bouncing causes a loss of forward speed. The deformation of the tire also saves calories because when a rider rolls over a bumpy road he or she will use more muscles to hold to the body off the saddle, allowing the bike to bounce up and down more than the body. This why a dual suspension mountain bike is capable of being as fast as, and a rider is less tired after riding, a lighter hardtail bike. 

The other main benefit of a high TPI casing is that is less likely to puncture. It is more difficult for a thorn to go through a tightly wound casing than a looser casing, much like it is easier to push a pin through a knit scarf than a silk scarf

Not all casing is the same, so it is important to pay attention to how the TPI is listed.  A good supple tire is made with a single high TPI layer of casing. Some companies will list a TPI of 300 for a tire but use three layers of 100 TPI casing on top of each other. This produces a less supple tire. A good way to test the suppleness of a tire is to pick it up and try to flatten it out.  The flatter the tire can be from bead to bead, the more supple the tire.

Notice the the strands casing of these tires above. The left is 127 TPI and the right is 220 TPI.  it can also be seen at the top of the picture the tire on the left does not lay a flat as the one on the right, this is means the tire on the right is the more supple tire.

An entire book could be written about tires on everything from sidewall sealing to siping (for increased traction and braking). I like to geek out on this stuff so I am more than happy to talk tires with anyone, just send me an email at adam@teamMPI.com.


 

Coach Adam is an IRONMAN Certified Coach, USAT Level I Certified Coach and a certified Bike Fitter based out of the Western Slope of Colorado. Adam has years of experience coaching beginners, juniors, elites, and clubs as well as a year focusing specifically on special needs athletes. Adam's expertise with bike fitting is extensive with over 15 years and 8,000 fits for athletes that include two world record holders, a national champion, several IRONMAN Pro/Age Groups winners and an ITU winner. He has completed several full and half Ironman races, as well as numerous Olympic and Sprint races. Adam grew up competing in speed skating and hockey in the midwest before playing football in high school and college.  After an injury in college football he took up road cycling, and competed on the road and track until making the switch to triathlon in 2009.

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