If you are running 37s it is my opinion that you should regear to 4.88s or even 5.38s. The 10% underdrive gives you a final ratio of 4.56 and IMO not low enough for 37s or larger.
I do like the low range 2.9 to 1 and recommend it especially with 33 inch and larger tires. It gives you a real improvement in low end crawling, greater control, greater power, and increased slowing when you let off the gas meaning not having to ride the brakes on a steep grade.
For 285s, the 4.56 would bring you just about back to the original gear ratio with maximum power and torque regained. I would do the transfer case low range and overdrive.
The larger the tires the less horsepower gets to the rear wheels (unless you gear much lower). I do not recommend 37s or larger unless you have increased first increased your braking, RCV installed axles, modified your steering, and have turned your Cruiser into a Rock Crawler. You also need a strong savings account. 35s will get you through most Moab trails, and many of the lighter Rock Crawling trails in Johnson Valley etc. Unless you have built your Cruiser well, including 5 point seat harnesses, you need to accept the fact that your Cruiser is NOT a Rock Buggy. It can be built to be a Rock Buggy but putting 39s on it would be the last thing to do. 37s only give one more inch of ground clearance.
I run my Cruiser with 35s, I run my Rock Crawler Jeep with 35s ( I used to run 37s but found that they really didn't help, and caused me to increase the lift more than I liked). I do run my Ultra 4 Buggy on 42s but it was built for them, 700hp , race built, including Full Racing Axles etc. (FYI I use the FJ80 as a chase car).
I do like the low range 2.9 to 1 and recommend it especially with 33 inch and larger tires. It gives you a real improvement in low end crawling, greater control, greater power, and increased slowing when you let off the gas meaning not having to ride the brakes on a steep grade.
For 285s, the 4.56 would bring you just about back to the original gear ratio with maximum power and torque regained. I would do the transfer case low range and overdrive.
The larger the tires the less horsepower gets to the rear wheels (unless you gear much lower). I do not recommend 37s or larger unless you have increased first increased your braking, RCV installed axles, modified your steering, and have turned your Cruiser into a Rock Crawler. You also need a strong savings account. 35s will get you through most Moab trails, and many of the lighter Rock Crawling trails in Johnson Valley etc. Unless you have built your Cruiser well, including 5 point seat harnesses, you need to accept the fact that your Cruiser is NOT a Rock Buggy. It can be built to be a Rock Buggy but putting 39s on it would be the last thing to do. 37s only give one more inch of ground clearance.
I run my Cruiser with 35s, I run my Rock Crawler Jeep with 35s ( I used to run 37s but found that they really didn't help, and caused me to increase the lift more than I liked). I do run my Ultra 4 Buggy on 42s but it was built for them, 700hp , race built, including Full Racing Axles etc. (FYI I use the FJ80 as a chase car).
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