"I love my 205 60 Rears, but I wouldn't want a car tire on the front."
Front darkside usually refers to running a "rear" motorcycle tire on the front wheel.
OK, now my recollection is refreshed.
Because I have never been able to get more than 7-8K on front tires (that I trust; with softer compounds), I long ago tried a rear tire on the front (reversed on the wheel, to avoid 'cord stacking' on braking). The idea being that rear tires all have more tread depth than front tires, so should last longer.
I can't remember the make and model of the one I chose, but instead of a 150-80-17, it was a 140-70-17, and while it did have a nice deeper tread, I was never happy with the handling and grip in turns and corners, and I changed back to a normal OE size front tire long before I wore it out (experiment fail). It wasn't terrible, but it made me nervous. Having and riding 2 Interstates (one with a normal OE size front tire), the difference was significant to me. But it may have been more a matter of the tire compound than the size difference that I didn't like so much.
And I'm not saying no rear on front will work, only that mine didn't to my satisfaction.
The tire size comparison that shows up in the link I provided above is the rear on front I tried compared to an OE tire.