Editor’s Note: This article was written by Art’s Cyclery web content editor Brett Murphy, who uses his mechanical engineering background to explain the latest industry advances and breakdown component design. The original post can be found here.
Most riders spend considerable time selecting a saddle or grips, prioritizing their contact points with the bike. But often the most important contact point — tires — is overlooked.
Tires are your contact point with the ground and make a significant difference in your bike’s handling performance. It can, however, be hard to choose a tire if you don’t understand construction methods, rubber compounds, and rating systems.
Indeed, tires can seem very abstract, leading consumers to choose based on price and looks. But after you learn some basic tips and terminology, you’ll feel more confidant when making tire buying decisions.
Important factors include tread patterns and combinations based on terrain and intended use, and construction methods of the tire rubber, bead, and casing, which are the focus of this article.
The tire bead hooks underneath the edge of the rim hook. Tubular road tires don’t have a bead, but all other tires 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 without 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. 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.