Are these LEGO pieces original? How can I be sure?
For the rim I would say its original. 


LEGO made this part in Transparent. 
It has the correct mound ID 88517
And contains the LEGO logo + copyright symbol


Only this part comes in 2 sets which doesn't contain a tire.

The tire you have looks like Motorcycle Tyre Ø 100,6. Based on photos I cannot see any visible markings on the outside of the tire. I do own a couple of these tires myself but don't have access to them at the moment. So I can't check if there are any markings on the inside of the tire. 

If I check for example the Bugatti or the Harley-Davidson tire, all the id stuff that is not mentioned on the outside, is on the inside. See picture below of the small tire used in the Harley-Davidson.

So you can check the inside for any markings telling you if its an original part or not.