swapping out gears.... what to get for my tire size???

[PUR PONY]

I run 275/55/17 (28.75" tall) tires on my lowered X with stock 3.73 gearing.

Right now I have a set of 245/45/17 (25" tall) tires on my X still with the stock 3.73 and it is much quicker.

I have decided to change gears..... but not sure what i want.

anyone know how to calculate this out.... Im looking for something close to a 245/45/17 (25" Tall) and 3.73 gear ratio

but with my 275/55/17 (28.75" tall) tires.....

will 4.10s give me what Im looking for or maybe higher like a 4.30 or something???

 

[Jefe]

www.4lo.com - Use their 'Change Tire Size' calculator

I put in 25" as your old tires
29" as your new tire
and 3.73 as current ratio
and it calculated it out to 4.33

If its 2wd you could go up to 4.10 or 4.27 or 4.56
however if its a 4WD or AWD your only choices are 4.10 or 4.56
With a 29" tire I'd go with 4.10's. I'd worry about severly limiting your top speed with anything numerically larger.

 

[CoryL]

I think where you are at with 3.73s is about right for a ~29" tire.

4.10s are do-able but severly pushing the bounds of limiting your highway speeds by having your RPMs sky high.

But hey, your choice.

 

[Sandy]

Going by the calulation: "(old tire OD, divided by new tire OD), multiplied by the old gear ratio, will equal the new gear ratio" Jefe is right, 4.33 is the ratio to go for.
BUT, Cory L is right in saying that you will have to look at your needs and use of the vehicle.
You need to determine where you want the rpm to be on the highway, where the power band is for your engine (where it make the best torque/HP) and use that rpm as your guide line. Then you can decide what is the best gear ratio.

I am running 35s with 4.56s and the rpm on the highway, fifth gear OD and 60 mph, is approx. 2300, this isn't bad. When in the lower gears it pulls really well and on the trail in first/second it really runs well.

So find out the best cruising range for the 4.0L and call a gear manufacturer tell him the tire size, the rpm you want and the weight of the vehicle, the manufacturer will give you the best ratio to use.

If that sounds like preaching, sorry bout dat.

Good Luck,

 

[punkbek3886]

where can i find the code for the stock axle gearing on my car? ive heard that different ratios were used very randomely in the early years.

 

[Robb]

Originally posted by punkbek3886
where can i find the code for the stock axle gearing on my car? ive heard that different ratios were used very randomely in the early years.

SMACK!....................as my palm hits against my forehead

Robb

 

[Alec]

Pur Pony has a wildly modded 5.0, not a 4.0. I'd stick with the 3.73s personally. Why spend the money for a dual axle gear swap just to 4.10s? I think you have enough torque down low to keep the 3.73 ratio, and this way you'll have plenty of RPM room on the highway. You may feel an initial loss in power with the 29" and the same gearing, but I think overall the 3.73 ring gears are perfect for you. Think mileage, too

punkbek, the axle code is on a sticker on the edge of your driver door.

EDIT: I didn't realize that Pur Pony's issue has most likely been resolved and punkbek revived the thread.