Classic Mustangs List Archive

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Mail From: Pielzner (email redacted)


Hey Guys,
I am looking on the web for a tire size, RPM and Gear ratio
calculator, I found one a while back but didn't bookmark it. Does
anyone know of one?

I was just curious about approx RPM and MPH, I just changed from
205/60/15's, which read almost dead on on the speedo, to 215/60/15's.
Now the speedo is whacked, I just don't know how much.
If anyone has this combo, maybe you could tell me? its 215/60/15's,
with 2.79/2.80 rear gears. I was interested in like 65 or 70 MPH, how
many RPM's is it turning?

Thanx a lot
Marcus Miller
Formerly: (email redacted)
68 Coupe Pearl White, 306 c-4, in the body shop next week
68 Coupe Ultra Red, 289 C-4, needs chrome :-)
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This read-only message was archived from a public mail list.
Mail From: Bud Sharp (email redacted)

Here is a formula, it is accurate when the trans is 1:1. If you are running
an automatic, deduct about 5%.


(rpm x tire dia x .003)
------------------------- = mph
axle ratio
Bud
68 Coupe w/CJ
68 Conv.
90 LX

Pielzner wrote:

> Hey Guys,
> I am looking on the web for a tire size, RPM and Gear ratio
> calculator, I found one a while back but didn't bookmark it. Does
> anyone know of one?
>
> I was just curious about approx RPM and MPH, I just changed from
> 205/60/15's, which read almost dead on on the speedo, to 215/60/15's.
> Now the speedo is whacked, I just don't know how much.
> If anyone has this combo, maybe you could tell me? its 215/60/15's,
> with 2.79/2.80 rear gears. I was interested in like 65 or 70 MPH, how
> many RPM's is it turning?
>
> Thanx a lot
> Marcus Miller
> Formerly: (email redacted)
> 68 Coupe Pearl White, 306 c-4, in the body shop next week
> 68 Coupe Ultra Red, 289 C-4, needs chrome :-)
> _________________________________________________________
> DO YOU YAHOO!?
> Get your free @yahoo.com address at mail.yahoo.com
>
> ------------------------------------------------------------------------
> All the list info you'll ever want: antler.moose.to/~server/cm


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All the list info you'll ever want: antler.moose.to/~server/cm

This read-only message was archived from a public mail list.
Mail From: Jeff Rautenberg (email redacted)

>Hey Guys,
> I am looking on the web for a tire size, RPM and Gear ratio
>calculator, I found one a while back but didn't bookmark it. Does
>anyone know of one?

This site has an useful tire size calculator.

powerdog.com/tiresize.cgi

I made an Excel spreadsheet that you input your tire diameter, transmission
final drive ratio, and rear axle ratio. It then calculates RPM at various
speeds. Its a great tool to show how valuable an overdrive is. With
225/50/15 tires, and 3.89 gears at 60 MPH, your engine is screaming at 3200
RPMs with a 4spd (1:1). It drops to a comfortable 2000 RPMs with a 5spd
(.63:1). Drop me a line, and I can forward it to anyone that wants it. I'm
on digest, and I'll be gone this weekend, so it will probably be Monday that
I can send it out, unless I get your email at work today.

Jeff Rautenberg




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