Re: [CR]RE:TIRES

(Example: Framebuilders:Alex Singer)

From: "Jon Schaer" <jschaer@columbus.rr.com>
To: "Bob Freitas" <freitas1@pacbell.net>, "CLASSIC RENDEZVOUS" <classicrendezvous@bikelist.org>
References: <40BA3323.2000601@pacbell.net>
Subject: Re: [CR]RE:TIRES
Date: Sun, 30 May 2004 16:39:05 -0400


----- Original Message ----- From: "Bob Freitas" <freitas1@pacbell.net>


> Anyone want to tackle an explaination of " TRAIL" and tire
> sizing?
>

Just think of it as basic right triangle. The vertical through the hub axle makes one side, and identifies the contact point of the tire. The ground is the other side of the right angle. Where the extended axis of the steerer/head tube hits the ground is the point that the tire contact point "trails" with any forward movement. That distance along the ground is the trail figure.

So, anything that changes the wheel radius changes the size of the triangle. A larger tire makes the contact point further away from the hub axle (increases wheel radius), and since the vertical line and the steerer axis line are diverging, the horizontal line between them will be longer (greater trail).

Generally I think the variations in trail due to tire size are considered fairly insignificant. You could do the math to compare wheel radius variations vs trail to head angle or fork rake variations vs trail. I never have.

Jon Schaer
Columbus, OH