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Re: How do I calculate final gear ratio?
[Re: Cab_Burge]
#1173563
02/07/12 01:11 AM
02/07/12 01:11 AM
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Joined: Nov 2007
Posts: 1,522
Orleans, Ontario
moparcanuk
OP
pro stock
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OP
pro stock
Joined: Nov 2007
Posts: 1,522
Orleans, Ontario
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I was trying to find out what the actual gearing is with a 3.23 gear and 28 inch tires. Since the F70/14s (24.6 inch diameter) that came stock from the factory are smaller in diameter than my 28 inch tires, the final gear ratio on the road has to be higher than 3.23. I now know that it's equivalent to a 2.84 gear.
Last edited by moparcanuk; 02/07/12 01:15 AM.
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Re: How do I calculate final gear ratio?
[Re: Twostick]
#1173569
02/07/12 01:58 AM
02/07/12 01:58 AM
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Joined: Dec 2010
Posts: 12,375
SoCal
MuuMuu101
I got lucky at Woodward!
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I got lucky at Woodward!
Joined: Dec 2010
Posts: 12,375
SoCal
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I like this calculator. Plug in numbers and have fun. Idk what you are trying to do. I think you are reverse thinking this just for curiosities sake. Instead of finding the change in rpm with the new tires you are looking for the change in gear ratio, if I understand you correctly. Well, here it is: http://www.csgnetwork.com/rpmcalc.html
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Re: How do I calculate final gear ratio?
[Re: moparcanuk]
#1173573
02/07/12 06:34 PM
02/07/12 06:34 PM
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Joined: May 2011
Posts: 4,489
northern,Ohio,USA
Clanton
master
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master
Joined: May 2011
Posts: 4,489
northern,Ohio,USA
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Quote:
I found this equation which answers my question:
http://www.4lo.com/calc/geartire.php
Which gives me a final gear ratio of 2.84.
(28/24.6)x3.23 = 2.84
and that is what i have read that every 1" tire change will change the gear .10 like you did.dont let them get in your head and mess thing up. 
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Re: How do I calculate final gear ratio?
[Re: Dodgem]
#1173574
02/08/12 02:35 AM
02/08/12 02:35 AM
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Joined: Nov 2007
Posts: 1,522
Orleans, Ontario
moparcanuk
OP
pro stock
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OP
pro stock
Joined: Nov 2007
Posts: 1,522
Orleans, Ontario
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Quote:
Well if it took 2650 rpm to go 60 with 24.6 tires it will now take 2277
if you were going 60 with the 28 tires you will now be going 68 ??
At 2650 rpm with 28" tires - Yes!
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Re: How do I calculate final gear ratio?
[Re: moparcanuk]
#1173575
02/08/12 03:10 AM
02/08/12 03:10 AM
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Joined: Feb 2009
Posts: 982
W. Sacto CA. USA
phantomx
super stock
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super stock
Joined: Feb 2009
Posts: 982
W. Sacto CA. USA
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The rpm with your 28" tire is the same as it would be with your stock tires and a 2.84 gear. A 28" tire doesn't magically make your 3.23s into 2.84s, it just makes your 3.23s feel like you kept your old tires and swapped to 2.84s. All you are doing is calculating the effective gear ratio difference due to your change in tire diameter.
Travis..
70 GTX project, orig 440-4, 4 spd, track pack, FC7, stripper/street racer special.
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Re: How do I calculate final gear ratio?
[Re: phantomx]
#1173577
02/08/12 10:02 AM
02/08/12 10:02 AM
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Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
70Cuda383
Too Many Posts
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Too Many Posts
Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
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Quote:
The rpm with your 28" tire is the same as it would be with your stock tires and a 2.84 gear. A 28" tire doesn't magically make your 3.23s into 2.84s, it just makes your 3.23s feel like you kept your old tires and swapped to 2.84s. All you are doing is calculating the effective gear ratio difference due to your change in tire diameter.
Travis..
Guys, I am pretty sure the original poster is well aware of this fact, and he simply wanted to know what his new tires would FEEL like in terms of rear gear ratio.
we all talk about "going from 3.55s to 3.91s really wakes up your car and gives it a stronger off the line punch" well...what DOES that mean, really? how do you put a number on a feeling? all the OP is trying to do, is put a number on a feeling.
Most car guys will talk about what their rear gear ratio is when in casual conversation. For example, I say my Dakota has 3.92 gears in the rear axle. I don't bore the person to death in a casual conversation by saying "my dakota has a 3.92 gear ratio in the axle, I'm running a 28.3" tall tire, and my first gear ratio in my transmission is a 3.48, my second gear ratio is a...."
because what use is the rear gear ratio, when you can have a 3.55 gear set in the axle that drives like a 3.92 simply by having a transmission with lower gear ratios.
by trying to put everything in terms of "effective rear gear ratio" it's just a way to standardize what everyone is talking about.
**Photobucket sucks**
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Re: How do I calculate final gear ratio?
[Re: phantomx]
#1173579
02/08/12 10:22 PM
02/08/12 10:22 PM
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Joined: Nov 2007
Posts: 1,522
Orleans, Ontario
moparcanuk
OP
pro stock
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OP
pro stock
Joined: Nov 2007
Posts: 1,522
Orleans, Ontario
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Quote:
The rpm with your 28" tire is the same as it would be with your stock tires and a 2.84 gear. A 28" tire doesn't magically make your 3.23s into 2.84s, it just makes your 3.23s feel like you kept your old tires and swapped to 2.84s.
D'uuuuuuuuuuuuuuhhhhhhhhhhhhhhhhhhhhhhhh. I'm not so stupid to think that my gear 3.23 gear would magically turn into a 2.84. C'mon guys, a little thought before posting.
Quote:
All you are doing is calculating the effective gear ratio difference due to your change in tire diameter.
Travis..
That was my question in my first post!!!!!
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What are you trying to find out, engine RPM lost at a steady tire speed, or distant traveled with the taller tires for the same engine RPM or what?
