Wouldn't the rolling diameter be less since the tire is compressed?
On 6/29/01, Ron Tebo <tebomr@cadvision.com> wrote:
All:
Could it be possible that some people are using true diameter to
calculate while others are using rolling diameter?
Ron Tebo
Thomas Wiencek wrote:
>
> Where did you get your diameters from? They seem a little high. Check out
>this site for all size tires.
> Welcome to the Turbo! Saab tire size calculator!
> Thanks to our friends at Miata.net, We've ...
> www.secret-secret.com/turbo/DIY/tirecalc/turbotire.html
>
> On 6/27/01, J Arzt <humber_snipe@hotmail.com> wrote:
> Don't forget the value of pi in the equation, Jan - there's a pretty
> significant difference in the circumference of the two tire sizes. The
> diameter of a 560x15 measures out at about 25.90", and the 560x13 at 23.60".
> That can be calculated to a circumference of about 81.35" and 74.10".
> Right off the bat, you have to increase the revs by about 10% just to make
> up for the tire change.
>
> So, if you compare percentages, the 4.55 Minx axle, less the 10% advantage
> of the 15" tire, cuts to about a 4.10, or just slightly longer-legged than
> the 4.22 Alpine. The 3.89 Alpine rear would only be about 5% better than the
> Minx, when corrected for tire size.
>
> My goal is a 4.22 Alpine rear in my 58 Minx convertible (with 15" tires),
> along with a 1494 or 1592 engine. That will give me a comparative ratio of
> about 3.80 to 1, (slightly better than an Alpine with a 3.89 and 13"
> tires), and enough power to push it.
>
> Of course, then the trick is to find a non-synchro first overdrive trans to
> put in............. after all, I DO live out here in the middle of nowhere,
> where it takes hours of interstate travel to get to anything! lol
>
> Jon Arzt
> Omaha, NE USA
>
> ----- Original Message -----
> From: "Jan Eyerman" <jan.eyerman@usa.net>
> To: <Jay_Laifman@countrywide.com>; <alpines@autox.team.net>
> Sent: Wednesday, June 27, 2001 7:48 PM
> Subject: Re: [Re: Overdrives and rpm]
>
> > I am not sure if those numbers are right, I have calculated 3500 RPM for a
> '59
> > Minx with a 4.55:1 rear with 5.60x15 tires. Even with smaller wheels, I
> would
> > assume an Alpine with a 4.22:1 rear would have to do better, and a 3.89:1
> rear
> > MUCH better.
> >
> > Jan Eyerman
> > 1959 Hillman Minx Series III DeLuxe
> > 1973 Hillman Avenger DL
> >
> >
> >
> >
> > Jay_Laifman@countrywide.com wrote:
> > Tom writes:
> >
> > >With all this talk of Overdrives, ...
> > >does anybody know how fast the Series
> > >V engine is approximately turning at
> > >65 mph?
> >
> > My speedo is completely accurate, as it was just calibrated, but my tach
> is
> > probably off. I do recall others reporting certain RPMS, etc. I do
> > believe though that before I changed to the OD (and the speedo was not way
> > off), my tach would read about 4000-4100 at 65. Now, with the OD and the
> > calibrated speedo, at 65 I'm reading about 3600. I believe others have
> > reported 3300 rpm at 65. For a long time, I've believed my tach to be
> > about 250-300 high. So, this makes sense.
> >
> > That all said, I think someone had and equation for all this, and thus had
> > the exact numbers, perhaps taking into account some tire size change too.
> >
> > Jay
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