Originally Posted by SurferRosa

Required pressure for road tires is generally a function of total weight (bike+rider+rig) and tire width, with the latter being an inverse relation. The rear tire requires more pressure than the front.

I weigh 160lbs; my bikes are around 20lbs + rig. So ...

​​​​​​28mm rear with groceries = 90 lbs
25mm rear road = 90lbs
25mm front road = 85lbs
23mm rear road = 100lbs
23mm front road = 95lbs

Originally Posted by cxwrench

Yeah, that was a little harsh. If it's for a class it's legit. Therefore:

Road: (40mm tires) 34frt/38rr
Mountain: (2.4-2.5" tires, tubeless) 18-19frt/23-24rr