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
|