Originally Posted by
treadtread
Tire quality? If you have the patience, you could try swapping tires.
That would be my guess as well. Just because both have tires of the same size (622mm diameter, 28mm width) doesn't mean they are of the same quality or performance. A tire with an inefficient tread design and stiff sidewalls can have far more rolling resistance than one with smooth tread design and supple carcass.