Hi
I went for a couple of bumpy rides (more little jumps than usual) on my full suspension Giant Trance and started running the tyres at a much lower pressure than before (they were previously at the stated max).
I now have the feeling that the suspension is a lot harsher at the front and back.
Does anyone have any good advice about learning to tune a suspension for an absolute beginner?
I have a suspension pump – but haven’t used it yet – and just had the bike tweaked in the shop in the past, so I am starting from scratch.
Thanks!

Have a quick look here as a starter: http://locotuning.co.uk/tech-info.html

started running the tyres at a much lower pressure than before (they were previously at the stated max)

😯 that must’ve felt horrific

I have a suspension pump – but haven’t used it yet – and just had the bike tweaked in the shop in the past, so I am starting from scratch.

Make one change at once and ride the same track. Best advice I had was ride something with your 3 key elements in drop, fast hits and tech climb (modify for your riding).
Adjust what you have one at a time (pressure, rebound.climbing) and learn how the changes feel. Work out what fast and slow rebound is and how it effects you.
Then you will understand your suspension, then you can get it right.

This is one of the better guides I’ve found online:

Bikerumor Suspension Setup Series: Full Series PDF – Free Download!

Well, you’ve learned lesson 1. Your tyres are part of your suspension system, so keep them consistent if you’re experimenting… 1-2 psi tyre pressure difference can be noticeable, so check them every ride.

EDIT – tyre pressures are tyre dependent too, so don’t assume a psi value on one tyre will act the same on another.