3.73 & 4.10 RPM's @ 70MPH
3rd Gear Member
Joined: Aug 2007
Posts: 670
From: Tulsa, OK
RE: 3.73 & 4.10 RPM's @ 70MPH
2nd Gear Member
Joined: May 2007
Posts: 233
From: RI
RE: 3.73 & 4.10 RPM's @ 70MPH
this is the ultimate mustang gear calculator. it should be a sticky.
http://www.svtoa-atlanta.org/cgi-bin/trans.cgi
http://www.svtoa-atlanta.org/cgi-bin/trans.cgi
3rd Gear Member
Joined: Jun 2007
Posts: 717
From:
RE: 3.73 & 4.10 RPM's @ 70MPH
Videos, opinions, guesses and what some folks are seeing are a waste of time. You need the calculator if you want it to be accurate. Most people don't tell you what tire size and gearbox they're running when they respond with their inputs.
5th Gear Member
Joined: Jun 2006
Posts: 4,355
From: Eureka, Mo
RE: 3.73 & 4.10 RPM's @ 70MPH
ORIGINAL: MrChubs1
Videos, opinions, guesses and what some folks are seeing are a waste of time. You need the calculator if you want it to be accurate. Most people don't tell you what tire size and gearbox they're running when they respond with their inputs.
Videos, opinions, guesses and what some folks are seeing are a waste of time. You need the calculator if you want it to be accurate. Most people don't tell you what tire size and gearbox they're running when they respond with their inputs.
3rd Gear Member
Joined: Feb 2007
Posts: 899
From:
RE: 3.73 & 4.10 RPM's @ 70MPH
ORIGINAL: jEEd
(RPM) x (60 x 27.1 x 3.14159) / (.68 x 3.55 x 12 x 5280) == 70MPH
therefore... RPM=(Desired MPH x 68 x Gear Ratio x 12 x 5280)/(60 x 27.1 x 3.14159)
Gears: 3.55s
(RPM) == (.68 x 3.55 x 12 x 5280 x 70) / (60 x 27.1 x 3.14159) == 2095.95 RPM
Gears: 3.73s
(RPM) == (.68 x 3.73 x 12 x 5280 x 70) / (60 x 27.1 x 3.14159) == 2202.22 RPM
Gears: 3.90s
(RPM) == (.68 x 3.90 x 12 x 5280 x 70) / (60 x 27.1 x 3.14159) == 2302.59 RPM
Gears: 4.10s
(RPM) == (.68 x 4.10 x 12 x 5280 x 70) / (60 x 27.1 x 3.14159) == 2420.67 RPM
Gears: 4.30s
(RPM) == (.68 x 4.30 x 12 x 5280 x 70) / (60 x 27.1 x 3.14159) == 2538.75 RPM
(RPM) x (60 x 27.1 x 3.14159) / (.68 x 3.55 x 12 x 5280) == 70MPH
therefore... RPM=(Desired MPH x 68 x Gear Ratio x 12 x 5280)/(60 x 27.1 x 3.14159)
Gears: 3.55s
(RPM) == (.68 x 3.55 x 12 x 5280 x 70) / (60 x 27.1 x 3.14159) == 2095.95 RPM
Gears: 3.73s
(RPM) == (.68 x 3.73 x 12 x 5280 x 70) / (60 x 27.1 x 3.14159) == 2202.22 RPM
Gears: 3.90s
(RPM) == (.68 x 3.90 x 12 x 5280 x 70) / (60 x 27.1 x 3.14159) == 2302.59 RPM
Gears: 4.10s
(RPM) == (.68 x 4.10 x 12 x 5280 x 70) / (60 x 27.1 x 3.14159) == 2420.67 RPM
Gears: 4.30s
(RPM) == (.68 x 4.30 x 12 x 5280 x 70) / (60 x 27.1 x 3.14159) == 2538.75 RPM
On the way home from work I noticed my instrumental panel RPM reads 2500 and my auometer gauge reads 2200, and I was doing 70mph.
can some one tell me what rear i have and which gauge is more accurate.
thanks.
5th Gear Member
Joined: Aug 2006
Posts: 3,287
From: same as you.
RE: 3.73 & 4.10 RPM's @ 70MPH
ORIGINAL: euromay
I'm running on 3.73s and i at roung 2200-2400rpm @ 70mph. in 5th gear. The 4.10s should run around 200 over these numbers.
I'm running on 3.73s and i at roung 2200-2400rpm @ 70mph. in 5th gear. The 4.10s should run around 200 over these numbers.
brought up a 4 month old convo 
3rd Gear Member
Joined: Jan 2008
Posts: 732
From: Houston TX
RE: 3.73 & 4.10 RPM's @ 70MPH
a simplified version, assuming 245/45-17 tires, 5 speed trans...
RPM = MPH x Gear Ratio (rear end) x 8.7696
if you're running 275/40-17 tires, it's:
RPM = MPH x Gear Ratio (rear end) x 8.7762 (very small change in tire circumference)
EDIT: this is using a calculated tire diameter... calculated from the aspect ratio, tread width, and rim diameter. it WILL vary from tire to tire though, because not all tires are the exact same diameter, nor are they always the same diameter as "advertised". these formulas should be good to within + or - 50 rpm though. of course the tach isn't always dead on either.
RPM = MPH x Gear Ratio (rear end) x 8.7696
if you're running 275/40-17 tires, it's:
RPM = MPH x Gear Ratio (rear end) x 8.7762 (very small change in tire circumference)
EDIT: this is using a calculated tire diameter... calculated from the aspect ratio, tread width, and rim diameter. it WILL vary from tire to tire though, because not all tires are the exact same diameter, nor are they always the same diameter as "advertised". these formulas should be good to within + or - 50 rpm though. of course the tach isn't always dead on either.
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