I would have to say it's 22psi

I’m gonna have to agree, that wear shows signs of heat damage and slippage. If you are looking for improved ride quality, get rid of the bargain shocks that Suzuki put on the back of the bike.

Rather than running the tires under pressurized on dirt/gravel/fire roads , I find the bike handles well simply by running it in the next higher gear than actually needed, and rock ,dips ,puddles encountered can demand your full attention (steering) as any sudden movement of the throttle will have small effect on speed (will not cause the rear tire to brake loose) .    There is little need to ride it like a dirt bike (lower the pressure for off road use) ,you're not going to be jumping a Savage over downed trees etc.  at least you shouldn't be trying , it's not a dirt bike , it doesn't begin to have the ground clearance or suspension  .

Hey thanks for all the great feedback and tips guys!

It seems I have a full set of contributing factors to that kind of wear:

1. Tire age
2. Under-inflation
3. Some necessary riding on gravel (taking it easy though)
4. Heat - We've had a heat wave here with temperatures in the high 30s to low 40s Celsius
5. Heat again - I've been riding country highways this last couple of weeks (good quality surface) but the sweeping curves allow for a pretty sweet lean at 80-100 kms per hour

@Gary_in_NJ, Thanks for the advice on the suspension. I read your excellent tutorial on upgrading the suspension some time ago. It's on my list of mods for the future. I did a bit of reading on shocks last night too and will definitely prioritize replacing the shocks.

@batman, that's good advice about the higher gear on gravel. I avoid grave where possible, but sometimes it's unavoidable. I had noticed just how easily the bike can lose traction even at low speeds (that's due to the low end torque, I assume). And boy does the bike get heavy quickly when it gets across the centre of gravity.

@Dave, thanks for the link to the article. It was very informative. Yep, I'd say the tires have 'heat tears'. I had a good look at the tread this morning. I noticed that the tread design has varied depth at different points in the tread. The depth varies along the length of each groove, and the walls of the grooves are different heights on each side of the groove, to the point that one side of the groove can be 6mm deep and the other side is 11mm deep. It looks completely like a manufacturing design and not some strange wear. This is especially along the contact band where the radius moves across to the 'lean zone' of the contact patch. I'd guess that recommended inflation is probably an important factor in maximising the design.

It's been really informative.

I'm off now to pump up my tires and read more about springy things!

@Batman, thanks for your concern. I really appreciate the advice. Your last comment prompted me to take the bike to a bike shop this morning to get the rear tire assessed. Yep, wear due to underinflation was the diagnosis. Tire age was also an issue but not to the same degree.

As for my previous post about the tread being different heights on either side of the grooves (I assumed it was manufactured that way because it was even) ... well no ... I've managed to halve the tread depth one side of the grooves due to heat and wear.

He told me it's not an emergency and it's fine for riding around town for the moment, but change the tire soon.

So, a new tire has been bumped up to number one on my list.

At the end of the day, being a newbie, I never took the factor of tire pressure all that seriously.

It's been an education.