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

[burg65]

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

 

[65shlbycln]

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]

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

 

[65fastback2+2]

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]

Thanks guys, I will spin the drive shaft tonight!

 

[Pakrat]

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.

 

[Ozsum67]

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.

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]

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]

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]

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]

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

try this calculator

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