Published on June 23rd, 2015 | by Brett
How To: Selecting Tire Compounds, Casings and Beads
A lot of riders will spend considerable time selecting a saddle or grips, prioritizing their contact points with the bike. More often than not, the most important contact point is frequently overlooked. I’m speaking about tires. Tires are your contact point with the ground and make a world of difference in handling performance. It can, however, be hard to make a tire selection if you don’t understand construction methods, rubber compounds, and rating systems. To me, tires used to seem very abstract and I made selections based on price and looks. After having learned some basic tips and terminology, I feel much more confidant when making tire selections.
Art’s has published several guides with recommendations for different tread patterns and combinations based on terrain and intended use. This article will focus on construction methods of the tire rubber, bead, and casing to give you the tools to analyze a tire independent of the tread and make an informed decision between some closely matched competitors.
Tire beads hook underneath the edge of the rim hook. Tubular tires don’t have a bead, but all other tires will have wire, Kevlar (foldable), or carbon beads. Bead profiles will vary depending on intended use. UST (Universal Standard Tubeless) beads have a squared off profile with a small flap on the edge to facilitate easy initial mounting and an airtight seal. These beads are designed to hold air even without any sort of sealant.
Casings run from bead to bead and are rated in TPI (threads per inch). The casing is essentially a fabric that acts as a skeleton underneath the tire’s rubber. Higher thread count casings feel more supple and improve ride quality. Higher TPI tire casings, while providing excellent ride quality, are more fragile and not desirable for applications where the tire needs to stand up to a lot of abuse on rough trails or roads.
Tire compounds will most likely make the biggest difference in the feel of your ride compared to a casing’s TPI. Rubber compounds are rated using a Shore hardness durometer, the durometer being a device used to measure the hardness of rubbers and other similar materials. There are more than 10 different durometer scales denoted by a letter following the rating. This rating is out of 100 and is a measure of the amount of deformation of the object. So if a tire exhibited absolutely no deformation, the Shore Durometer rating would be 100A. In comparison, most tires measure at about half of that.
The Mavic Crossmax Roam XL Tire has a harder rubber in the center of the tread, measuring at 60A, while the softer side knobs measure a durometer of 50A. A lot of tires will be composed of one rubber with a single hardness rating, but higher quality tires combine multiple rubber compounds for more desirable performance across a spectrum of riding conditions. The 60A rubber in the center of the Crossmax is harder and better for faster rolling over fire roads as well as long term durability. The softer shoulder compound will grip the trail better and allow for more traction while cornering.
Soft compounds provide better performance while descending due to their grippy nature, but will wear much faster. Hard compounds offer lower rolling resistance and longer lasting tread life.
Some brands like Maxxis and Schwalbe offer triple compound tires that layer multiple compounds with a harder base layer beneath softer compounds. This results in longer lasting tires that grip better than a single compound tire with a similar tread life. Schwalbe offers PaceStar and TrailStar compounds to satisfy either end of the spectrum of riding. PaceStar tires provide low rolling resistance, while TrailStar tires have a softer compound for really grabbing a hold of the trail.
Taking all of this into consideration, you should be able to weigh the features of potential tires to best select one that will work for you. Mountain riders will first limit their selections to tubeless selections if they are already tube-free. While cross-country riders will likely select high TPI tires with a higher durometer for decreased rolling resistance, the opposite will be true of a trail or enduro rider. While high TPI provides suppleness, the enduro rider will want a more durable tire with a lower TPI and possibly some added layers of casing protection. For instance, some Continental tire models feature Apex Sidewall protection that’s simply an added layer of puncture protection. Road cyclists should also consider that softer tires with lower durometer ratings, perform better in wet conditions. So if you are doing lots of rainy season training, this is definitely something to consider.
You will be the ultimate judge as to which tire will work best for you, but hopefully the knowledge acquired here will help you to select an appropriate tire for your riding style and usual conditions. If you are looking for help with mountain tread selection, Luke has some excellent advice for front/rear tire combinations as well as tires intended for hero dirt and hard pack conditions. Each product page of the Art’s Cyclery website also gives recommendations for each tires intended use.
Rubber Side Down is a weekly column dedicated to the fledgling cyclist in all of us. Art’s Cyclery Web Content Editor, Brett Murphy is not a professional cyclist, and doesn’t try to masquerade as one either, but he does love to ride bikes. Whether you are clipping in for the first time or counting down the days until your first race, read on, learn from his mistakes, and keep the rubber side down.
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