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Subject: Thorns aka Puncture Vine
From: Jobst Brandt
Date: September 21, 2000

Those who suffer from thorns should become familiar with the plant before spending much effort selecting tires that will survive thorns. Recognition is a large step toward avoiding flats. The plant is not mobile and does not propel its seed pods away from its tendrils. However, some riders think nothing of pulling thorns from their tires and throwing them on the road for other bicyclists to encounter. This practice seems to be part of not understanding avoidance. In my experience, riders who suffer most from thorns, have no idea of the plants appearance or its habitat. Most, think the yellow star thistle is puncture vine. It is not and is also incapable of causing a flat.

Flat tires are caused by beer in winter and by cigarettes in summer. As odd as this may seem, there is a direct link.

Glass is visible on roads by its shiny splinters and shards as well as not being the same color as the road. When wet from rain, these characteristics vanish and leave glass looking like any bit of gravel. Not only is it "invisible" but it is lubricated and cuts through rubber effortlessly. A convincing experiment is to cut a thick rubber band with a razor, first dry, then wet.

In summer flats are caused by puncture vine thorns, a plant that grows only on barren soil. There isn't much of that around except peculiarly on roadsides that have been sprayed to prevent grass from growing, grass that when dry presents a fire hazard for cigarettes discarded from cars. Puncture vine grows on these barren roadsides that have been created for safer cigarette disposal. If roadsides were not sprayed, puncture vine would be a rare occurrence along roads where bicyclists most often ride.

Puncture vine, known as tribulus terrestris, grows mainly on barren soil, typically on roadsides that have been sprayed with herbicides to prevent cigarette initiated grass fires. It germinates in early summer after the first hot days, and grows, radiating with flesh colored tendrils, from a central root to a radius of about 30 to 50cm, having 1 x 3 cm filigree dark green leaves that follow the sun. It has five petal yellow blossoms 1 cm in diameter that produce seed clusters of five tetrahedral pods with a heavy base and two 3 mm thorns, one of which preferably points upward when breaking from the clusters that the plant produces throughout its annual growth.

Previously, this page had links to some examples, but clueless webmasters at and broke the links. Life is too short for me to deal with this sort of incompetence.

Jobst Brandt

Spoke Divider

See also Sheldon Brown on Flats

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