Overall crawl ratio?

[ld50]

Okay, you guys might hate me for this, if you don`t already! I just can`t get my head around this stuff.

transfer case has a ratio of 2.69:1
I change my stock diff gears to 4.10s and add 33 inch tires.
What is the overall ratio from engine to tires, and how the heck does a guy figure this all out?

Also, if a guy got an Atlas t-case, which comes with 3 choices, how do you decide what is best? AND, will the Atlas change the ratio to my rear tires without engaging 4x4, or does it just send the same ratio straight through?

I`m thinking of blowing a bunch of cash this spring, and need to chose something to do first.

 

[Jason_25]

http://www.4lo.com/

There's the calculator.

You can do pretty much what you want with the atlas. You can run in 2-low with just the front axle getting power if you want. And no, it won't modify the ratio going straight through, "high range" is still 1:1.

 

[Brian1]

Your crawl ratio is tranny 1st gear x t-case low range gear x axle gear ratio. For example on my rockcrawler, 7.01 x 2 x 5.13 = 72:1. If you have a manual tranny a low crawl ratio is good. If you have an auto, you dont need that low of one. As for atlas choices, go with what you think you would need. I would do the 4:1 if I had a manual tranny or a 3:1 for an auto.

 

[ld50]

Jason, that calculator is awesome, I think I got it figured but:

Your crawl ratio is tranny 1st gear x t-case low range gear x axle gear ratio. For example on my rockcrawler, 7.01 x 2

-using brians info as a test here-
the 2 would mean you have a 2:1 tcase then?

so All I need is to find my 1st gear ratio and I`m set after that right?

thanks guys the info is probably here somewhere else and I couldnt find it.

 

[ld50]

I got all my info now, thanks guys.

One thing tho` that calculator isn`t affected by changing your tire size input. What`s up with that?

 

[DesertSpive]

I think the FX4 manual has a CR of 34.6:1...

--Sean

 

[ld50]

Okay desertspive, I got a ratio figured at 37.5:1
with my setup.
lots of different info here but the #s I settled on were:
-Mazda 5-spd. has a 3.4:1 first gear
-BW T-case is 2.69:1

And then I noticed all that info is findable on that calculator site- Doh!

 

[Paul Gagnon]

The B-W 13-54 transfer case has a 2.48:1 low range not 2.69

 

[ld50]

Ah thanks Paul, I see the error now, the calculator site says BW-1356, I just saw BW and thought that was it.

Great, I should have it now!

That makes it 34.57:1

Call the papers! I`ll be at the mall tomorrow for autographs
thank-you

 

[TarHeel085]

what do you guys put in for RPM and MPH? nevermind figured out you dont need it ok WTF my crawl ratio is 25.11:1 thats with 31.5" tires, 4.10 gears, 2.48 L range, 2.47 1st gear.

 

[DesertSpive]

Originally posted by ld50
That makes it 34.57:1

See, 34.6:1 .

--Sean

 

[TwoToneX]

What's the first gear ratio for a '91 automatic? I'm hoping it's higher than what I think it is because I've got a real crappy crawl ratio... I need to get those 4.56's in...

 

[ld50]

See, 34.6:1 .

lol, oh yeah, sorry, I was thrown by the "FX4". What does that mean?

 

[TarHeel085]

Originally posted by ld50
lol, oh yeah, sorry, I was thrown by the "FX4". What does that mean?

its the offroad ranger package

Standard 4.0L V-6 engine
5-Speed manual transmission
Standard heavy duty premium shocks, Skid plates, front tow hooks, all-terrain tires, and limited slip axle
Mach AM/FM Stereo MP3/CD Player
Bold two-tone bucket seats in Ebony/Red and Ebony/Blue
Bilstein shock absorbers and Torsen rear differential
BF Goodrich KO 31x10.5 tires, ALCOA forged aluminum wheels

some of those are repetative but its from Fords website. why in the hell is mine 25:1? is that good or bad, cause if i think im right, that SUX doesnt it?

Jared- i think its 2.84:1

 

[ld50]

Aha! FX4

Yours should be same as mine, is your ratio for the transfer case correct? looks like I found a different number.

 

[TarHeel085]

Originally posted by ld50
Aha! FX4

Yours should be same as mine, is your ratio for the transfer case correct? looks like I found a different number.

what number did you use, cause i used 2.48:1

 

[ld50]

I used same but used 3.4:1 for first gear, can`t remember where I found that here, but it also says that on the calculator site when you click the transmission ratio link.

So is my number wrong?
Yeesh, so many #s flying around!

 

[DesertSpive]

My ratios are the same as you guys...

--Sean

 

[TarHeel085]

i still wanna know why mine is SOO bad?

 

[SteveVB]

Originally posted by TwoToneX
What's the first gear ratio for a '91 automatic?

2.47:1

With the auto you can add another multiplier for the torque converter - most likely around 2 or 3 to one. The added multiplication only applies when the converter starts from a stop though- but thats where you need the extra ratio.

So for my 91 Auto with 4.10 rear its:

2.47 x 2.48 x 4.10 x 2.5 = 62.78:1 as I start rolling, once going its around 25:1 in first gear with no torque converter multiplication( in reality there is some but not as much once rolling).