If you have been following my build then you know that late last year I started fitting the new 39s on bead locks. I now have enough seat time to give a honest review. First I spent a lot of time to keep a low COG, it sits at the same height as it did with the 37s, has close to the same up travel and rides better on and off road then it did with the 37s and the old suspension.
To make the 39s fit the front axle had to be moved foreword, for whatever reason I moved it 11/8" foreword plus the 1" bigger in radius tires = a much better approach angle. It's was a very noticeable difference when approaching ledges on my recent trip to Sand Hollow.
It now has 1" more clearance at the Diffs makes a noticeable difference on Rocky trails like the Dusy Ershim.
The Kanati mud Hog M/Ts hook up really well, They run smooth on the Highway at 70 MPH with no balancing, They were one of the only tires I could find that are taller then a 37 and 12.50 wide. I did not want to go wider then a 12.50, The price point made them a winner. I got them at Tires - easy .com for 271.70 each delivered to my door Tax & shipping included.
I mounted them on Battle Born bootlegger bead locks, The wheels have 31/2" back space and are 17x9s this give the Reg a 3" wider stance at the center of the tire, makes it more stable on the the road and in off camber situations on the trail another win. I got them on a black Friday 20% off sale sweet !!
With out a doubt the new tire and wheel combo with all the modifications I did to make them fit at the same ride height made it a better trail Reg, but at the same time there was noticeable loss of power, on my first trail ride I noticed it was much harder to get the front tires to climb up a obstacle and after I aired down it was hard to get up to speed on hard packed roads or pavement. This was never a issue with the 37s.
I was already running 5.29s and low range transfer gears. I needed more power in hi & low range so I had Shoppy install a set of the 10% under drive gears. This has brought it back to what it was power wise with the 37s except for in hi range in the sand dunes I still feel a loss of power over the 37s.
I am very happy with the new set up it works well and I am not going back to 37s. That being said I think that 37s are the sweet spot for a 80, minimal effort to make them work. Yes the 39s have improved its abilities on the trail, But it took a lot of time work and CASH to make it happen.
And they look SWEET !!!
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weather was perfect. 
