exact
#s aside, maybe squeeze them with your eyes closed? the front should feel softer. I like to look at the rear tire as I roll, to see how much it is deforming under my weight. I don't want a pinch flat but I also want some strength & weight bearing. plus if the trail is a harder pack variety I can go a little faster if the rear is a little harder than what I would use on softer ground. it's been surprising for me to see how low I can ride w tubed 29x2.25 Riddlers. I think they're at 21 front 25 rear