UKH

Its my first winter on my mountain bike.....it has 4" x 26 tyres. These say 5-30 psi on them - anybody recommend a good pressure for road/ice/snow use? Currently trying 13 front/16 back for commuting on roads but I have read that lower pressure will be better on snow?

For off road almost certainly single figure pressure.  Will also depend on tyre tpi in the sidewall?

You will need to experiment.

I ride around our local ski resorts (they do uplift on a couple of lifts) and I found this useful and stuck in my bookmark list.

https://forums.mtbr.com/fat-bikes/fat-tire-pressures-snow-1000620.html

Commuting on the roads with 4 inch tyres.

You might find it easier dragging a pulk along the tarmac.

I was thinking similar, i commute on 700X25c quite happily, but I have been considering changing to 28s.

And of course we don't know how bad the roads are where the OP lives.

Variable pressures will be needed depending on terrain, it’s firmness and what speed/performance you’re expecting! Sorry not helpful really, but that is the way it seems to be.

In my limited experience less than 9 psi.

I run mine at max of 9 psi f&r as my preference for mixed and frequently variable terrain, but that is not for doing a lot of tarmac roads, really hard aggressive stuff or really soft stuff. Always going to be a compromise if using on different mixed terrain as depends on what feel and performance your looking for unless your prepared to keep altering pressures.

At 9 psi: not great for fast hard/tight cornering as lots of side wall give causes some under steer and when coupled to soft, slippery or loose surface can cause alarming side slippage; on tarmac there is a torque over steer reaction when outer tread bites suddenly though it’s easy enough to control when you are expecting it; and on dry tar noisy as **** (don’t need a bell though to warn pedestrians   !). There can also be what I think of as the bouncy castle effect felt on certain harder undulating terrains when the tyre give can’t recover in time for the next hit.

Softer the terrain generally the lower the pressure to spread the weight and try and create more float, but it does hugely depend on a lot of variables. Carry a gauge and pump and be prepared to alter the pressures as you go.