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Old 09-21-2016, 12:13 AM   #1
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Default DIY alignment observation

I’ve​ ​been​ ​playing​ ​around​ ​with​ ​my​ ​alignment​ ​lately.​ ​As​ ​anyone​ ​who​ ​has​ ​fiddled​ ​with​ ​their​ ​alignment knows,​ ​you​ ​can​ ​use​ ​the​ ​pythagorean​ ​theorem​ ​to​ ​calculate​ ​your​ ​toe​ ​or​ ​camber​ ​pretty​ ​easily​ ​by comparing​ ​your​ ​wheel​ ​to​ ​a​ ​straight​ ​reference.​ ​I’ve​ ​been​ ​using​ ​the​ ​string​ ​method​ ​and​ ​a​ ​carpenter's
square​ ​as​ ​my​ ​references.​ ​I​ ​found​ ​it​ ​annoying​ ​to​ ​have​ ​to​ ​calculate​ ​the​ ​angle​ ​every​ ​time​ ​i​ ​made measurements,​ ​and​ ​it​ ​got​ ​me​ ​thinking:​ ​what​ ​is​ ​the​ ​optimal​ ​hypotenuse​ ​length​ ​(e.g.,​ ​the​ ​diameter​ ​of your​ ​wheel,​ ​or​ ​length​ ​of​ ​your​ ​alignment​ ​stick)​ ​to​ ​get​ ​a​ ​10:1​ ​ratio​ ​between​ ​changes​ ​in​ ​distance
between​ ​your​ ​reference​ ​&​ ​wheel,​ ​and​ ​changes​ ​to​ ​your​ ​alignment​ ​in​ ​degrees?
It​ ​turns​ ​out​ ​the​ ​optimal​ ​length​ ​for​ ​an​ ​alignment​ ​stick​ ​is​ ​just​ ​about​ ​exactly​ ​573mm,​ ​or​ ​22​ ​9/16”.​ ​With an​ ​alignment​ ​stick​ ​this​ ​length,​ ​you​ ​can​ ​move​ ​the​ ​top​ ​of​ ​your​ ​stick​ ​inboard​ ​1mm​ ​from​ ​the​ ​reference, and​ ​it​ ​will​ ​lower​ ​your​ ​camber​ ​by​ ​.1.​ ​​ ​Here’s​ ​where​ ​it​ ​gets​ ​funky:​ ​the​ ​OD’s​ ​of​ ​our​ ​more​ ​common wheel/tire​ ​combos​ ​are​ ​very​ ​close​ ​to​ ​this​ ​number:
195/50/15​ ​on​ ​15x7’s​ ​=​ ​576mm
205/50/15​ ​on​ ​15x8​ ​=​ ​586mm
225/45/15​ ​on​ ​15x9​ ​=​ ​583mm

All​ ​three​ ​of​ ​these​ ​will​ ​get​ ​you​ ​within​ ​a​ ​gnat’s​ ​***​ ​of​ ​.1​ ​change​ ​in​ ​alignment​ ​for​ ​every​ ​1mm​ ​of
movement​ ​at​ ​the​ ​outside​ ​edge​ ​of​ ​the​ ​tire.

Now​ ​obviously​ ​this​ ​doesn’t​ ​take​ ​into​ ​consideration​ ​sidewall​ ​deflection,​ ​tire​ ​inflation,​ ​tire​ ​wear,​ ​or
any​ ​number​ ​of​ ​other​ ​factors.

I​ ​don’t​ ​know​ ​if​ ​this​ ​is​ ​common​ ​knowledge,​ ​but​ ​I​ ​thought​ ​it​ ​was​ ​worth​ ​sharing.
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