Trail, or caster, is the horizontal distance from where the steering axis intersects the ground to where the front wheel touches the ground. The measurement is considered positive if the front wheel ground contact point is behind (towards the rear of the bike) the steering axis intersection with the ground. Most bikes have positive trail, though a few, such as the two-mass-skate bicycle and the Python Lowracer have negative trail.
Trail is often cited as an important determinant of bicycle handling characteristics, and is sometimes listed in bicycle manufacturers' geometry data, although Wilson and Papodopoulos argue that mechanical trail may be a more important and informative variable.
Trail is a function of head angle, fork offset or rake, and wheel size. Their relationship can be described by this formula:
where wheel radius, is the head angle measured clock-wise from the horizontal and is the fork offset or rake. Trail can be increased by increasing the wheel size, decreasing or slackening the head angle, or decreasing the fork rake or offset. Trail decreases as head angle increases (becomes steeper), as fork offset increases, or as wheel diameter decreases.
Motorcyclists tend to speak of trail in relation to rake angle. The larger the rake angle the larger the trail. Note that, on a bicycle, as rake angle increases, head angle decreases.
Trail can vary as the bike leans or steers. In the case of traditional geometry, trail decreases (and wheelbase increases if measuring distance between ground contact points and not hubs) as the bike leans and steers in the direction of the lean. Trail can also vary as the suspension activates, in response to braking for example. As telescopic forks compress due to load transfer during braking, the trail and the wheelbase both decrease. At least one motorcycle, the MotoCzysz C1, has a fork with adjustable trail, from 89 mm to 101 mm.
Read more about this topic: Bicycle And Motorcycle Geometry
Famous quotes containing the word trail:
“You will trail across the rocks
and wash them with your salt,
you will curl between sand-hills
you will thunder along the cliff
break retreat get fresh strength
gather and pour weight upon the beach.”
—Hilda Doolittle (1886–1961)
“We sank a foot deep in water and mud at every step, and sometimes up to our knees, and the trail was almost obliterated, being no more than that a musquash leaves in similar places, where he parts the floating sedge. In fact, it probably was a musquash trail in some places.”
—Henry David Thoreau (1817–1862)
“And Change with hurried hand has swept these scenes:
The woods have fallen, across the meadow-lot
The hunter’s trail and trap-path is forgot,
And fire has drunk the swamps of evergreens;
Yet for a moment let my fancy plant
These autumn hills again: the wild dove’s haunt,
The wild deer’s walk: in golden umbrage shut,”
—Frederick Goddard Tuckerman (1821–1873)