Your math looks right, have you checked your speedometer?
Larry Hoy; Denver, CO. USA
1969 MGB Roadster
1987 Jaguar XJ6 VDP
"It's not how fast you go, it's how fast you go fast"
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> -----Original Message-----
> From: owner-mgs@autox.team.net [mailto:owner-mgs@autox.team.net]On
> Behalf Of Michael Graziano
> Sent: Tuesday, June 23, 1998 8:39 AM
> To: MGList
> Subject: Differential Calc Update
>
>
> OK. I sat at home with my manuals, and my MS Excel and did
> the math.
>
> My tires are P155/70R13's. The wheel radius is 11.050
> inches (and therefore, the wheel circumference is 5.79
> feet. So at 4000 rpm, the car should run the following
> speeds:
>
> 3.72 differential: 70.70 mph
> 3.90 differential: 67.43 mph
> 4.22 differential: 62.32 mph
>
> So, I'd have to have a 5x to 1 gearing in my differential
> to explain 50mph at 4K rpm. Definately not the case. Where
> to next?
>
> BTW - when doing the calc, using the 3rd gear ratio of
> 1.433:1, I'd be doing 50 mph @ 4K rpm. BUT I KNOW I'M IN
> 4TH.
>
> Can it possibly be a tranny problem?
>
> Mike
>
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