I thought I had 3.73's... maybe I don't?

[colemanitis]

I went out yesterday to confirm my gear ratio using my new C2 tach and one of those signs along the road that tells you how fast you're driving. I don't have a speedo right now, it's at Brother's Performance being calibrated for my new 140mph face. Anyway, I was told my car has 3.73's, but after running the numbers it seems as though I may have 4.10's. Here's the results from yesterday's test:

Here's the gear ration calculator I used: http://www.corral.net/tech/gearcalc.html

2nd gear: 30mph: 3,000rpm: 4.096 gear ratio
3rd gear: 38mph: 2,500rpm: 4.032 gear ratio
4th gear: 50mph: 2,500rpm: 3.952 gear ratio

What do you guys think? Do I have 4.10's, or should I jack up the car and count the driveshaft revolutions to be sure?

 

[Look Its Aaron]

or should I jack up the car and count the driveshaft revolutions to be sure?

Should have just done that in the first place. Would have saved you a lot of time...

 

[PhLoBuS]

sounds like 4.10s

 

[colemanitis]

 

[colemanitis]

Should have just done that in the first place. Would have saved you a lot of time...

My floor jack is broken... that's why I used the calculator first. I guess it's time to buy a new one.

 

[Michael Yount]

Counting revolutions is the only way to be certain. Tachs and speedos aren't always accurate, tire sizes may be changed, and ID tags/serial number disemination fails if the rear end has been swapped, or the gears changed. Counting shaft revs to tire revs always works though.

 

[colemanitis]

I'm gonna borrow a floor jack from a friend after work today. I guess I'll jack it up from the rear differential. Do I need to put anything in front of the front tires... will the car try to roll forward when I jack the rear up?

 

[Michael Yount]

ALWAYS chock in front of and behind the tires that are on the ground; ALWAYS use jack stands before you crawl under something that's heavier than you mind falling on you (one end of a car qualifies for most people). Mark/count carefully. The difference between 3.55's and 3.73's or 3.73's and 4.10's is only about a 1/4 of a driveshaft turn.

 

[cevtv]

I went out yesterday to confirm my gear ratio using my new C2 tach and one of those signs along the road that tells you how fast you're driving. I don't have a speedo right now, it's at Brother's Performance being calibrated for my new 140mph face. Anyway, I was told my car has 3.73's, but after running the numbers it seems as though I may have 4.10's. Here's the results from yesterday's test:

Here's the gear ration calculator I used: http://www.corral.net/tech/gearcalc.html

2nd gear: 30mph: 3,000rpm: 4.096 gear ratio
3rd gear: 38mph: 2,500rpm: 4.032 gear ratio
4th gear: 50mph: 2,500rpm: 3.952 gear ratio

What do you guys think? Do I have 4.10's, or should I jack up the car and count the driveshaft revolutions to be sure?

Aren't you running 245/60/15 tires? If so, they are about 1 inch taller than the stock tires, and that will effectively change the gearing......






.

 

[colemanitis]

Aren't you running 245/60/15 tires? If so, they are about 1 inch taller than the stock tires, and that will effectively change the gearing......

Yes, i'm running 245/60/15's. I entered this into the gear ratio calculator.

 

[cevtv]

Yes, i'm running 245/60/15's. I entered this into the gear ratio calculator.

Ooops - I should have looked at the calculator brfoe I posted.......

 

[Michael Yount]

25.7" stock vs. 26.5" for the 245/60/15 - only about a 3% difference. That tire would make 4.10's act like a 3.98 gear; 3.73's act like 3.62's.

 

[colemanitis]

UPDATE: They're definitely 3.73's. I jacked up the rear and spun the tires. The driveshaft spun exactly 3 3/4 turns. Thanks everyone for the help and advice!