My LR4 (5.0L V8) gets somewhere between 12-15 (offroad) to 17 (highway without bad wind) and ~240-340 miles with the 20 gallon tank. I generally feel like that is enough for most trips, but it does require that you have that range number in your head all the time and it can occasionally mean you have to specifically alter plans for fuel or your risk profile can be different if a fuel stop doesn't work out.
So I think having some way to carry fuel can be nice just for piece of mind. Like all things though it is a tradeoff. Weight being a big one and usually it balances with water carry capacity which I generally think is even more important to carry. I really dislike putting fuel on a roof rack, not just for weight but leaks would freak me out. Also how you plan to get the fuel into the tank. I feel like a simple siphon hose can be the least messy. I love Wavian jerry cans but it can be kinda messy to pour one gracefully into a filler neck.
I decided to bite the bullet on a long range america tank in January. I think they won't build it till May and I need to send some measurements to them so they can build my dual filler neck with the right sized pipe.
Should give 50 gallons of fuel and up to 730+ miles of range, which is crazy.. but that means more options for when I fuel up.. what routes I take and opens up some fun options in canada to alaska or just skipping suspect fuel in mexico. (I actually just noticed one place said it was 29 gallons and one says 38 gallons.. so im not sure what I am getting...)
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