What size tire height and width was used in that calculation? I just put on a new set of Firestone Destination a/t 265/75/16. They are supposedly 31.7" but I can confirm they are ALOT bigger then my 31" tires, like 1.75" "bigger not 0.7". With that said I absolutely love them. When calculating RPM you also take the tire design and things like wind resistance into account. An aggressive tread heavy tire will require more rpm for the same given spead as well as things like roof racks and such that increase wind resistance. I always ask the question "what will you be doing with the vehicle 90% of the time?" if you answer this question honestly and build accordingly you will love the results in the end. It is very hard to get the "best of both worlds" with a homebuilt budget, heck its hard to get in brand new vehicles.

 

Here's my build goals.
6.5" lift custom 3 link long arm with 37" tires. I will be stretching the wheel base 6-8" front Dana 44 rear Dana 60 and according to grimjeepers gear ratio calculator 5.89 gears. I can go deeper in gearing with those axles though.

 

It will be 50% on road and 50% off road if anything more on road time but when I do wheel it will be wheeled hard. I don't plan on using an aggressive tire like pitbulls or tsl or anything like that probably gonna go with courser mtx 37s

 

Even with gearing thats alot to ask out of a 3L anything especially one with a short stroke. I'm not trying to discourage you but sometimes when you try to biuld a rig good or great at 2 things it ends up bad at both. Based on my experience this engine would not be a good candidate for your needs. Torque is what's needed and this engine just doesn't have enough. I'd biuld a 4 cylinder Perkins with turbo (just like a 4bt but smoother) and a 5 speed, I have wheeled one personally. I'd encourage you to find a 300d with one of these engines and drive it, you should expect the same performance after transplanted.

 

The tire you mentioned IS an aggressive tire.

 

I bought the car and drove it 2 hours home I know its a slug. I've never heard of a Perkins I'll check it out. My original plan was 35" tires with the same lift set up. I believe the jeep 2.5 l4 is close to the diesel as far as power goes and I know there's people out there with 4 cylinder jeeps on 37s. I might stick with 5.89s and my original plan of 35s

 

I am also running the 5 SPD ax15 in my rig not a auto aw4

 

And with my axle combo I believe I can go as low as 7.xx gears

 

I'd love to see this work. Keep us posted and keep asking questions.

 

Will do! I love the way a locog Cherokee looks on 37s but you are right that is a lot to ask of that motor. And I was wrong a d44 will only go as low as 5.89 so I have 2 choices. #1 keep the 44 and downsize tires or #2 get a front 60 and gear the living hell out of it. Option 2 is gonna have me sitting where I want but will add a lot of weight so I think I'll stick with 44s f/r and run 35s with 5.89 gears