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## Re: Wacko Speedo/Tach?

 To: Ron and Angie Re: Wacko Speedo/Tach? Jerry Tue, 22 Sep 1998 23:32:40 -0400 Charles Ackerman , triumphs_list <018f01bde68c\$1534be70\$0102c883@boss.turbo.ron>
 ```Did I happen upon a learn-at-home course in Mathematics here! :) Jerry - 1968 GT6 MK1 Ron and Angie wrote: > Charles, > > Here's the formulae: > > mph = (rpm * tire_diam) / (gear_ratio * 336) > rpm = (mph * gear_ratio * 336) / tire_diam > gear_ratio = (rpm * tire_diam) / (mph * 336) > tire_diam = (mph * gear_ratio * 336) / rpm > > And if you don't know your tire diameter: > > tire_diam = 2 * ((section_width * aspect_ratio) / 2540) + rim_diam > > And the gear ratio is overall gear ratio, which would be transmission gear > ratio times the final drive ratio. > > Ron > Dalton, GA > 62 Triumph Vitesse Sports 6 77 Triumph Spitfire 1500 > 84 Nissan 300ZX Turbo 92 Ford Tempo GLS > > -----Original Message----- > From: Charles Ackerman > To: triumphs_list > Date: Tuesday, September 22, 1998 12:40 AM > Subject: Wacko Speedo/Tach? > > > > >Hi everybody, > > > >Recent posts about incorrect speedo/tachs got me wonder'in. > >So I got the TR on the road with a pen and paper. (Tire size 195/65R15) > >MPH RPM RPM (OD) > >30 1500 1300 > >40 2000 1600 > >50 2400 2000 > >60 2800 2400 > >70 3300 2700 > >Is there a formula to determine if the speedo/tach. is wacko? > > > >Charles Ackerman '70 TR6 CC51493LO North Bend WA > > > > > > > > > > > > ```
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