Bigger tires on a motorbike without changing the motor size makes more or less work for the bike?

I think you're talking about fitting wider tyres? (not larger diameter)

If so, then fitting wider tires would increase the contact patch of the tyre on the road and in turn this would increase the rolling resistance, making the engine work harder, very slightly.

Fitting tyres that are too wide for the wheels could also upset the handling, so be careful.

Good luck! Dave.

Fitting bigger tires will make the motor work harder as the result is the same as fitting higher gearing, another gear beyond top gear. The result is the engine revs slower but with more throttle making the motor labor harder, and so more engine heat. It is sort of like making the motor 'think' it is going permanently up a hill. The worst result would be an engine seizure, the least would be more engine wear...

Fitting bigger tires will make the motor work harder as the result is the same as fitting higher gearing, another gear beyond top gear. The result is the engine revs slower but with more throttle making the motor labor harder, and so more engine heat. It is sort of like making the motor 'think' it is going permanently up a hill. The worst result would be an engine seizure, the least would be more engine wear...

It would create more work being that the tire is bigger. Check out this website http://www.2wheelbikes.com/hybrid-commuter.html they have cool bike there.

"Handling is not a concern"

You want to make your bike worse ?