The standard front tyre size on my bike is 100x90x19,I have changed it to a 110x90x19.......so do I have to change the tyre pressure? If I do, why and what to? Thanks in advance

 

I would refer to the tire manufacturer for correct pressure. Is the tire the same brand as the original? If so run that pressure until you find out differently.

 

Read the sidewall of tire itself for its max pressure.

[Then I run a few pounds under that for solo riding]

 

Same pressure as you always ran is appropiate. Your tire is just a bit wider now that's the only difference,you still need the same pressure. I run 32psi front,36psi rear solo. Loaded with a passenger I run 40psi on the rear.

 

All depends on your brand of tire.
Read the side wall.

 

Despite what many people think, the pressure listed on ANY tire's sidewall, car, truck, bike, airplane or golf cart,
is the MAXIMUM that the tire is designed for, NOT the recommended pressure. The vehicle manufacturer will
specify that in the owner's manual.

A larger tire such as you have fitted is capable of supporting a greater load at the same pressure as you have been using
so I'd start with that. The difference isn't going to be huge so I wouldn't be surprised if you just stay with what you'd been
using, but it never hurts to play around a little. In theory, you could lower the pressure a smidgen, but I wouldn't.

 

Right,plus he is talking about the front tire only. Anywhere between 30-36 lbs. psi will be fine.

 

Depending on your brands recommendation of the tire.
My Metzeler front 110/19 takes 38 psi
Metz's run hard.