This has been said a lot already and I would think since you are asking the questions you would be aware of it, but gear ratio is important in multiple aspects. The 2 main things I think about when sizing tires to an existing engine, trans, and gear ratio, are what will my crawl ratio be, and what will my final drive RMP be at around town and highway speeds. I have not lifted my 99 XJ yet, and with the stock gears (3.07Æs), and trans (AX15), I am not sure I want to. I can speak from experience on my Æ79 F-150 though. I had driven it for a few years with 33Æs and when it came time to replace tires, I sat down with a MS Excel file, and had Speed vs RPM laid out for each gear of the transmission, and high and low range of the Transfer Case for both 33Æs and 35Æs. My Ford has stock 3.50 gears, and it does great on the highway (~70 MPH, ~2700 RPM) with 35Æs, it was like getting an overdrive, but I only have a 4 speed (NP435) in the truck. I did loose a little around town though, and I have to shift more frequently between 3rd and 4th in the 25 -30 MPH range. First gear I never used anyway around town, which I believe is around 6:1, so its intended to be a granny gear rather than a true first gear. I didnÆt feel like I lost anything on the trails either, I just use low range most all the time when wheeling, rather than using 4 high. All that being said a Ford 400 which has been mildly built (Cam, .040 over pistons, Eldelbrock performer intake, and Holley 600 Double pumper) is going to put out more HP and Torque than a Jeep 4.0 and is going to be able to ôabsorbö slightly oversized tires easier, so performance losses will be less noticeable. If I had my Ford to build ideally and not worry about money, I would go with 3.73 gears, and add in a ôdoublerö type transfer case, that would allow me to get back closer to stock gear ratio, and give me overdrive and give me an additional underdrive, but then I donÆt know if that actually exists for my application.

There is a lot to be said for gear ratio. One of the guys we used to go wheeling with back in college, had a early 80Æs solid axle Toyota, just running the 22RE, but he had very low gears, and a doubler case, and was running 35ö SSRÆs. I canÆt remember the actual crawl ratio, but it was way up there, and his rig would run through almost anything even with that little 4 cyl, putting out a whopping ~120HP. He almost never had to worry about stalling the engine either because of the crawl ratio he had, he would just idle through things.

If you want I can send you the Excel file I used, you will just have to plug in your gear ratios for your trans, tx case, axles, and tires size. It will at least give you a mathematical reference for what RPMÆs you will be turning at various vehicle speeds. Granted there will be additional losses involved in turning the larger tires, but it will be close.

The other thing I will mention too, you did say something along the lines of you were hitting trails you could not pass with your rig, and other guys you were going with could pass. There is a lot to be said for picking the right line to get through an obstacle, you can get most any rig stuck if you do not pick the right line no mater how itÆs built. Just because there is a giant mud hole there doesnÆt mean you have to go through it. Part of going wheeling is being smart, and knowing the limits of your rig. Now I am not saying donÆt modify or lift your rig, I am just saying take your time and think about your line. The only time I have ever had to park my truck and hop in with someone else was when I broke a transmission shift fork. And I have seen areas I knew I could not get through, if I just drove through the area, but when I picked my line carefully I was able to keep it so I did not bury myself in a mud hole, or drive around the mud hole. I have high centered axles, I have gotten stuck and had to dig out, but ultimately, eventually I would always find a way around and onto the next obstacle.


Sean