The optimal rim width, ime, for a XR2 Team 2.2 for sidewall support is around 30mm inner. I've run that tire since 2014 on 29.6 and 30mm inner width rims on a carbon hardtail. On that width rim you can reduce your pressure to below 20psi, possibly as low as 18 for a rear. The exact psi will depend on your weight and terrain. You can be limited by the combo of bike speed and how rocky/rooty the worst segment of your ride is for rim hits. If you're not getting rim hits in the rockiest spots reduce pressure until you are. Then add a pound. Guys add a rim protector like CushCore so they can go lower in pressure on wide rims when they have higher speeds to deal with.
The XR2s are designed for Trek by Frank Stacy Testing for wide rims, low pressure and max traction from a big footprint. They are higher volume with a more rounded tread pattern profile.
https://flowmountainbike.com/features/interview-frank-stacy-bontragers-rubber-wizard/
When you put this design on a wide rim the sidewall support lets the 120tpi very flexible sidewall crinkle down instead of fold over at lower pressures when you add torque. Like when you climb or change your line in a curve.
This gives you a big conformable footprint for maximum traction. When you compare this to the same tire at 24psi on a narrower rim you can think of it like airing down your Jeep tires to go rock crawling. You're going to have more capability from your vehicle at lower pressure.
You still need good body weight positioning and smooth power application techniques. You'll still reach limits. You'll have more traction to work with.
The 2.35 XR2 Team is matched to a 35mm inner and Mikesee in Park City is running the 2.6 new XR2 Team on 40mm inner rims. You can mix rim widths and tire widths front to back, also. Most non Boost RockShox and Fox forks will take the 2.6 XR2.
I've had the 2.2 on a 30mm inner rim as a front tire as low as 11.5psi. The footprint and traction were phenominal but rim hits were too much by far so 14 is my standard for a front. You have to experiment to get what works for you.
I use carbon rims from CarbonFan for good stiff but still comfortable builds with Sapim Laser spokes. They keep wheel weight down in the reasonable range. I don't mind a few grams to gain more cornering and climbing speed. Overall I come out ahead with much better control over how my tires behave when pushed to lose traction.
If you want to test this with your current rim width air down your rear to 18 psi at the bottom of your tough climb. You'll be ok at low climbing speeds going mostly straight. When you get to the top go back up to 24 with a hand pump.
