Gearing Advice

[Drizit]

Just an FYI for the next time you are using the calculator. Your tcase on a tj is an NP231 or a NP241OR (for rubi only) and you would leave the under drive blank as you don't have one.

—
There must have been a time
when we could have said no.

 

[jchadscud]

View attachment 36942 Recorded this data on scanner on way to work.

Those numbers seem to line up spot on with 4.10 gearing.

 

[dimension12]

Those numbers seem to line up spot on with 4.10 gearing.

What I thought when using the calculator. If I drop the tire size to 31 it is closer with 3.73.
Not sure I trust this calculator. Grimmjeeper.

 

[jchadscud]

Well it matches my actuals on 4.10’s as well. I think that calculator has been proven pretty solid so I’d say it’s likely that your gearing isn’t 3.73.

 

[dimension12]

Well it matches my actuals on 4.10’s as well. I think that calculator has been proven pretty solid so I’d say it’s likely that your gearing isn’t 3.73.

Tonight I will crawl under and count revolutions to be sure and let you know.

 

[greenliftedtj97]

yeah, I have 4.0, 32rh,33" w/ 4:10's and I turn around 3300 @ 70 mph....

 

[dimension12]

Ok. I used the formula @Chris posted and physically measured from the ground to the hub center and doubled it. At 60 mph according to my scan tool I am at about 2600 rpm. 31x2600 is 80600. Divided by 60x336(20160) gives me 3.998 or 4.0.
So if I air my tires up to be at 32” it comes out to be 4.126.
Now my iphone gps app and scanner vss are identical. I bought the speedo gear for 33” tires with 3.73 gears. I think it is safe to assume the gear chart on Quadratec is wrong. What do you think?
Oh, I have a 31 tooth gear and the actual speedo is 2 mph slower than vss and gps from zero to 80. Haven’t checked beyond that.

 

[jchadscud]

Ok. I used the formula @Chris posted and physically measured from the ground to the hub center and doubled it. At 60 mph according to my scan tool I am at about 2600 rpm. 31x2600 is 80600. Divided by 60x336(20160) gives me 3.998 or 4.0.
So if I air my tires up to be at 32” it comes out to be 4.126.
Now my iphone gps app and scanner vss are identical. I bought the speedo gear for 33” tires with 3.73 gears. I think it is safe to assume the gear chart on Quadratec is wrong. What do you think?
Oh, I have a 31 tooth gear and the actual speedo is 2 mph slower than vss and gps from zero to 80. Haven’t checked beyond that.

You said previously you had 33” tires, but now you are talking 31 and 32. What’s your tire size?

 

[dimension12]

You said previously you had 33” tires, but now you are talking 31 and 32. What’s your tire size?

They are 33x10.50 R15 Dick Cepek extreme country. I run them at 35psi and measuring from the ground to the hub center I get 15.5” which is 31”

 

[jchadscud]

They are 33x10.50 R15 Dick Cepek extreme country. I run them at 35psi and measuring from the ground to the hub center I get 15.5” which is 31”

That’s gotta be the difference then. I knew that the tire size wasn’t always the actual measurement, but seems crazy to be off by a full 2 inches.