New HUGE tires, Speedo Re-calculation Needed

I am soon going to get my new 31 X 10.5 tires installed on my 1997 Explorer XL 2 Door 2WD.

I read all the treads, out found out that my axle is 3.73 open. (Axle code 46 on the sticker) I currently run 225 70r 15.

I punched all this into the gear ratio change selector at http://www.therangerstation.com/Gear_Tire_RatioChange.html

This gave me the following results;
Actual Ratio 3.33
High Ratio 3.8
New Ratio 4.18
Low Ratio 4.56

Am I correct in thinking my new ratio should be 4.18, with the closest available ratio being 4.1? (ie. Code 42 - Open)

As well, does anyone know what speedo gear I have, and which one I need to go to? (I have an automatic trans.)

Which one below should I pick?

Automatic Transmission:

16 tooth blue(D0AZ-A)
17 tooth green(C7SZ-A)
18 tooth gray(C7SZ-B)
19 tooth tan(C7VY-A)
20 tooth orange(C8SZ-B)
21 tooth purple(D0OZ-B)

Thanks,

 

[olivesman]

yeah, that is saying your new gear ratio should be 4.18 for your truck to be like stock again. although, with the 3.73's you have now, you should be just fine. if anything, you'll get better interstate gas mileage. -russel

 

[Robert]

Originally posted by pmassche
I am soon going to get my new 31 X 10.5 tires installed on my 1997 Explorer XL 2 Door 2WD.

...snip...

As well, does anyone know what speedo gear I have, and which one I need to go to? (I have an automatic trans.)

Which one below should I pick?

Automatic Transmission:

16 tooth blue(D0AZ-A)
17 tooth green(C7SZ-A)
18 tooth gray(C7SZ-B)
19 tooth tan(C7VY-A)
20 tooth orange(C8SZ-B)
21 tooth purple(D0OZ-B)

Thanks,

Since you in all likelyhood have the 5-speed automatic, none of these will work. You need to pick one with one more tooth than the one you pull out from this chart:

Manual Transmission:

16 tooth wine(C0DZ-A)
17 tooth white(C3DZ-C)
18 tooth yellow(C0DD-B)
19 tooth pink(C0DZ-B)
20 tooth black(C1DZ-A)
21 tooth red(C4OZ-A)

I know it say's "Manual Transmission" however the chart was posted on a Ranger board before the 5-speed automatic was developed. My '97 5-speed automatic came with a 19 tooth pink gear and I needed to buy a black one. The Ford parts department first brought out a 20 tooth orange gear and it was a slightly different length than mine was. I had them go back and bring me a 20 tooth black one and it matched up perfectly. The only way to know for sure what color your current gear is is by removing it and looking at it yourself. It takes a 10mm socket and about 5 minutes to pull it out. Make a note of what color it is and how many teeth are on it. Go down to your Ford parts department and select a gear from the same chart that your current one comes from that is one more tooth.

 

[pmassche]

Thanks guys,

i do have the 5 speed automatic,

i'll take your advice,
i guess i better open it up and see.