[Tuor of Gondolin]

As to references to orcish wolf-riders, in Unfinished Tales,
"The Battles Of The Fords Of Isen":

Saruman's eastern force came down with unexpected speed; it was much smaller than the western force, but more dangerous. In its van were some Dunlending horsemen and a great pack of the dreadful Orcish wolfriders, feared by horses. Behind them came two battalions of the fierce Uruks, heavily armed but trained to move at great speed for many miles. The horsemen and wolfriders fell on the horse-herds and picketed horses and slew or dispersed them.

And later in the chapter, about the second battle of the Fords of Isen:

More than half of Saruman's force had actually been sent down east of Isen. They came on more slowly than the western division, for the land was rougher and without roads; and they bore no lights. But before them, swift and silent, went several troops of the dreaded wolfriders. Before Elfhelm had any warning of the approach of enemies on his side of the river the wolfriders were between him and Grimbold's camp; and they were also attempting to surround each of his small groups of Riders. It was dark and all his force was in disarray. He gathered all that he could into a close body of horsemen, but he was obliged to retreat eastward. He could not reach Grimbold, though he knew that he was in straits and had been about to come to his aid when attacked by the wolfriders. But he also guessed rightly that the wolfriders were only the forerunners of a force far too great for him to oppose that would make for the southern road.

And in a footnote:

They were swift and skilled in avoiding ordered men in close array, being used mostly to destroy isolated groups or to hunt down fugitives; but at need they would pass with reckless ferocity through any gaps in companies of horsemen, slashing at the bellies of the horses. [Christopher Tolkien note]

Also note the interesting note of Dunlending cavalry.

I picture Tolkien's wargs not as the ridiculously-sized PJ whatevers, but
more as wolfs on steroids, big and mean, but still recognizably wolfish.