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Date:         Tue, 7 Mar 2000 14:23:24 EST
Reply-To:     FrankGRUN@AOL.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Frank Grunthaner <FrankGRUN@AOL.COM>
Subject:      Re: Spacers
Comments: To: edevinney@bigfoot.com
Content-Type: text/plain; charset="US-ASCII"

Agreed!

The stress applied to the stud or bolt is related to the force at the capture surface dissipated over the thread surface area. There is a minimum number of threads to take the applied torque before stretching the thread stock. This minimum is related to thread pitch and diameter but is of the order of 3 or 4 threads. I typically use a value in number of threads equal to the diameter of the bolt/stud. So 12.5 mm OD, 12.5 mm of thread. At 1.5 threads per mm, the math works out to about 8 threads - overkill! Unless the spacer is flexible or compliant (very bad) the thickness of intervening material between the top of the thread capture surface and bottom of the bolt/nut face is irrelevant to any questions of strength, or wheel retention.

Offset, bearing load, scrub radius etc are all important factors and not impacted by stud strength discussion.

Aluminum is more than adequate for a spacer given its negligible compressibility and, as noted has been used by Porsche at stunning stress levels. Flexure or the wheel hub to rim probably occurs long before any issue related to the spacer. This only applies to spacer inserts (stud goes through wheel then spacer then into thread retainer). For wheel adaptors (stud threads into adaptor which bolts to hub, I would only use steel because of the annealing requirement to maintain strength of Al alloys.

As to the machining of cast or forged suspension components - I would never do this without bead blasting and annealing equipment access.

My two centimes as a Physical Inorganic Chemist.

Frank Grunthaner


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