How do I know what rear end gears I am running?

burg65

New Member

Mar 2, 2004

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Charles City, Iowa

Apr 23, 2004

#1

• Apr 23, 2004

• #1

Is there a way to check, if there is how? At 60 mph going down the road in 4th it is winding pretty high. I don't have a tach, so I can't tell you an rpm. I would like to change them to something a little better for the Highway but not loose a whole lot off the line too. This is just a daily driver not a racer!
Thanks

 

6

65shlbycln

Founding Member

Aug 24, 2002

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Atlanta

Apr 23, 2004

#2

• Apr 23, 2004

• #2

I don't have a tach in my car yet either. And i thought my car was running high @ 60 too. But I took my car to a guy who has over 20 mustangs in his garage, he told me that i was running 3.00 gears, possibly 3.25. So the sound can decieving unless you REALLY know your stuff. That said, I believe if you take out your gears and look at the edge of it, it should have the number written on it. If you dont wanna take out the gears, then get a tach. Thats what i have to do.

 

MustangPaul

Founding Member

Jun 20, 2002

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South East Louisiana

Apr 23, 2004

#3

• Apr 23, 2004

• #3

What about counting drive shaft rotations vs. tire rotations? That'll tell, too, right?

 

65fastback2+2

New Member

Aug 4, 2003

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Louisville, KY

Apr 23, 2004

#4

• Apr 23, 2004

• #4

jack the back end of the car up.
put it in neutral.
either count how many times you have to turn the driveshaft to get the wheel to turn once or
count how many times the driveshaft turns as you turn the wheel.

This ratio will tell you your rear gear ratio.

I knew mine was running way high at 70mph so I counted mine, and i got pooey 4.11's on a c4 =/

 

burg65

New Member

Mar 2, 2004

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Charles City, Iowa

Apr 23, 2004

#5

• Apr 23, 2004

• #5

Thanks guys, I will spin the drive shaft tonight!

 

Pakrat

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Aug 6, 2000

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Currently: NH Originally: Rhode Island (and all po

Apr 23, 2004

#6

• Apr 23, 2004

• #6

So doesn't he need to know the ratio or the formula to calculate it still? Or do you simply divide the driveshaft rotations by the wheel ones? Maybe I am just not understanding it exactly.

 

O

Ozsum67

Too much thin air

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Jan 6, 2002

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Eastern Colorado

Apr 23, 2004

#7

• Apr 23, 2004

• #7

Pakrat said:

So doesn't he need to know the ratio or the formula to calculate it still? Or do you simply divide the driveshaft rotations by the wheel ones? Maybe I am just not understanding it exactly.

Click to expand...

No math needed. One tire rotation, count how many times the DS turned. Since there will probably be a part of a turn in there on the DS, you will need to keep close watch to the last partial turn to get the Point something.

 

Pakrat

Founding Member

Aug 6, 2000

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Currently: NH Originally: Rhode Island (and all po

Apr 23, 2004

#8

• Apr 23, 2004

• #8

aha, so one tire turn gets you either 2.79 turns or 3.25 or 3.5 or 4.11 etc and so on. I see now, very simple. Me so stupid. It seems so logical but it never dawned on me for some reason that you could verify it that way.

 

RajunCajun

New Member

Nov 26, 2003

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Apr 23, 2004

#9

• Apr 23, 2004

• #9

Just wondering, but is there by any chance a data tag on the rear housing? if so you can easily decipher it if not you can get really close to what it is by using this formula
Gear Ratio = TIRE RADIUS x RPM / 168 / MPH
Ex. = 14 x6500 / 168 / 120
=4.51

 

66stangmeister

New Member

Apr 14, 2004

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Lafayette, LA

Apr 23, 2004

#10

• Apr 23, 2004

• #10

well, say you have a tach...how do you tell then? cuz i have a tach and i ain't about to jack the back of the car up just yet lol

 

69stanger

Founding Member

Oct 20, 2002

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CA

Apr 23, 2004

#11

• Apr 23, 2004

• #11

66stangmeister said:

well, say you have a tach...how do you tell then? cuz i have a tach and i ain't about to jack the back of the car up just yet lol

Click to expand...

try this calculator

http://www.f-body.org/gears/