I have had both tires. The Terra Grapplers on my 1 ton and the Ridge Grapplers on a K5 Blazer. I'm angry right now with Nitto and so I can no longer recommend them.
The Terra Grapplers, I bought in June 2014. Last year I had a tread separation just past 4 years of use and 15,000 miles. I bought another tire on the prorated warranty and didn't give it another thought.
This spring I had another tire separation, this time with 18,000 miles. They offered me another warranty replacement. I told them I wanted to prorate out all 4 remaining tires (I bought a spare when I bought my tires). They said no but offered me $270 in credit, the approximate cost of one full new tire. My thought was that two failed tires out of one set was a pattern and all of them needed to come off. They still refused.
I used the money to buy a competitor product (the Goodyear Wrangler All Terrain Adventure). I just got them installed last week, so I can't comment on the new Goodyears. I chose this tire because it has a treadwear warranty and the mountain snowflake symbol, which is my current standard for tire choices for the truck.
The Ridge Grapplers on my Blazer have been excellent. The off road traction isn't as great as I hoped, but they are super quiet on the road and even in the 37x12.50 size, they balance nicely and ride very smooth. I have had them for ~2 years. I rotate and balance them religiously. There has been some chunking from rock crawling but that's the nature of the beast. Overall, they are excellent. I spent a lot of time agonizing on what tire I was going to use on this rig and I really have no regrets. If I was going to buy another set of tires, I'm not aware of anything better in the 37" size. If the GY Wrangler Duratrac came bigger than a 35, I'd consider it, but it doesn't. I don't need tires this aggressive on my tow rig, though.
I am furious about the Nitto Terra Grapplers coming apart on my Ram after 4 1/2 years and them trying to claim this is normal. I am religious about checking tire pressures and I have never overloaded the tires. They failed at 18,000 miles after less than 5 years. I had hoped to get one more season out of them.
The treadwear and traction of the Terra Grapplers were excellent throughout their life, until two of them (out of five) failed and came apart on me.
I am frustrated and I do wonder if I was just expecting too much out of a set of tires. I think just about anyone should expect five years of solid service out of a tire, though.
If I were you, I would, if you're stuck on Nitto, use the Terra Grappler.
And in any event, I would NOT tow anything on P rated passenger car tires, that is dangerous. Metric sizing is fine, but LT only and nothing less than a D rated tire, even on a 1/2 ton. For 3/4 and 1 ton, E rated/80 PSI tires only, no exceptions.
