Bajaron gives good advice here. The Spyder rear tire is a light duty tire, 2-ply is like a 2-layer construction in simple terms. Most any other "car" tire we use is going to be a 4-ply. This does many things, including giving us a "stronger" tire that has a higher speed rating (safer at continued high speed rotation) and a higher load rating (able to handle more weight and heat). Anyone who pulls trailers should be able to tell you what happens when you install a tire with less plys (plies) as they will have more punctures and more failures. Granted, the Spyder is a lighter machine so a 2-ply might be "acceptable" but many of us want higher quality, reliability and durability.
The car tires can be found in so many treads designs and rubber compounds, one needs to be careful here. A longer lasting car tire is almost always going to use a harder rubber compound, which is generally a reduction in traction. Even a car tire with a "low" tread wear rating of only 300 is going to last longer than the OE tire, but will also be sticky and work very well from a traction standpoint. Only those who push their machines to their traction limits will be truly qualified to make statements as to a certain tire working like the OE tire. During casual riding one might not notice much of a difference, but get real familiar with your nanny and you can soon find out the differences between the various tires in various conditions.
The comment was made that riders switch to a car tire because it is less expensive, that is just one consideration. We can save money, we get a longer lasting tire, we get one that has a higher speed rating, we get one with a better load rating that is more resistant to damage/puncture. We get one that wears more evenly, instead of ballooning out in the middle at high speeds. As for the front tires, we have on many occasions found the cheap OE tires to be barely acceptable in terms of roundness and balance, they cause all sorts of wobbles and shakes. So many times it is simply a cheap tire, get rid of it and the front end runs straight and true. Assuming good alignment, of course!
There have been volumes on these subjects in this forum over the years, please use the search function to review all of the great posts many have made on these subjects. From my personal experience of 73,000 Spyder miles on three machines, I can tell you BRP has changed their rear tire compound several times and the latest one is a softer stickier tire that doesn't last as long. I burned up the new OEM tire on my 2013 ST-S in 2,500 miles, replaced it as 3,750. I only run car tires, have for years. Have used several Kumhos, Maxxis, now running Toyo Proxes 4. Me personally I will get about 7,500 miles per rear tire, on average, all due to speed, weight and driving habits. Like last week, 960 miles in three days, typical. 300-400 miles per day is normal, zero four-lane roads, all back roads.
Funny thing, most of the tire stores no longer have the Kumho in our size, not sure if it has been discontinued or what. The Toyo Proxes 4 is also discontinued, but we are talking only the OEM size. There are many very similar sizes that will work, so there are plenty of options. Again, many posts on this over the years. But right here and right now, I for one will never run a cheap OE 2-ply tire on any of my Spyders ever again. Hope this helps.
