Re: [CR] Nail catchers: Automatic Tyre wiping

(Example: Production Builders:Tonard)

In-Reply-To: <>
Date: Thu, 14 Jul 2005 15:34:17 -0400
To: "Kahrl, Michael" <>, <>
From: "Sheldon Brown" <>
Subject: Re: [CR] Nail catchers: Automatic Tyre wiping

At 3:00 PM -0400 7/14/05, Kahrl, Michael wrote:
>I believe Jobst Brandt, whose essays can be accessed from Sheldon's site, m
>ade the claim that punctures occur on first contact.

Yes, he does.

I don't agree with him on this, one of the few technical issues where we don't see eye to eye.
> This debate will never rest until some enterprising researcher
>conducts a series of tests to see how effective each method was.
>A bicycle with a rider of consistent weight (no eating or drinking or sweat
>ing during the test) will ride a bike through a passage of broken glass equ
>al to one circumference of the tire.
>Multiple passes with a nail-puller, a glove wipe, and with nothing at all w
>ill be made.
>The bike stops five wheel rotations after the end of the glass where the ti
>re will be inspected for leaks.

I don't think it is possible to create a truly controlled test for this, because the orientations and configurations of the glass shards, as well as the tire's actual path, will vary chaotically.

If you grant Jobst's premise that the shard goes in as deep as it's going to go at first impact, rather than being driven in by successive blows as a nail goes into a board, there are still issues that support wiping:

Road surfaces are not perfectly flat. Tiny objects, including glass slivers, will tend to settle into low spots. As a tire rolls over a glass sliver in a low spot, the sliver may go part way into the tire. On some succeeding revolution, the glass sliver may hit a projecting bit of the road's surface texture, driving it in farther.

Then again, a glass sliver may stick into a tire at some point not on the tire's centerline. It may not penetrate fully until the bike banks into a turn, bringing the sliver into firmer contact with the road.

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