Gearing and 37"s

[brandon mena]

Anyone have advice for me? I think a 4.88 and a posi would be good now for some 37" tires. I'm currently running a 4.10 open with 30" tires. Suggestions, how-to, someone selling anything?

 

[Bill Ellis]

To get same thrust at street [torque/radius] you would need whatever is closest to a 5:05 diff with 37" tires.

 

[Bill Ellis]

Looks like 5:13 would be the better choice if you want some speed off the line performance.

 

[brandon mena]

My only worry is the highway which I use frequently. Has anyone changed gearing like this on here. Searching has yeilded minimal info for me.

 

[Bill Ellis]

Stock Trac comes with 29" tires and 3.73 diff or bigger tires and 4.10 diff. Using the 29/3.73 as a guide, a 4.75 diff with 37" tires would result in the same engine rpm at any speed. So a 4.88 would result result in about 3% higher rpm and 3% speedometer error [it would read higher than your actual speed].

 

[Nathan Potance]

I'm running 35's with 4.88's. Everything improved with my gear change. Power/Takeoff returned to the feeling of stock. My milage even went up due to the fact that i was now within the powerband again. Cruising at 75 (adjusted speedo) results in RPM's of about 26-2700. If you have any questions about gearing, let me know. I think Johnston and I are the only people that have re-geared.

 

[brandon mena]

Oh awesome guys thanks. Nate, I have many questions for you. Do you have aim or msn or yahoo even?

 

[Yardsale]

Another consideration - even though, mathematically, the ratio may workout to coincide with the change in tire diameter, you should consider the additional weight and rolling resistance of the larger tires and wheels.

 

[Nathan Potance]

Brandon,



I am natedoggnp on AIM....hit me up whenever.

 

[tony brizag]

i wouldnt go over 4.56 with some 37's or 38's. people over gear so much. in my jeeps i run 4.11 gears front and rear locked and 39.5 x15 tires (soon to be 42's) and have no problems turning them up or going at highway speeds 70+.



just dont listen to all this 4.88 or 5.13 and up crap, its all just crap and you'll hate your life if you put in that low of a gear

 

[Nathan Potance]

Tony....while i agree with you on some level, you're speaking of 2 different engines and drivetrains. I'm guessing the jeep has a straight-6, which is an engine with ALOT more torque. Fords 4.0 is weak in comparison. With my 35's and 4.10 gearing i once had to put it in 4LOW to get up a curb....yes, a 8 inch curb. 4.10's were however fine for the highway, but since i was out of the powerband, mileage went to hell....



I went 4.88's with my 35's and i've never regretted the decision.