Mileage is not the reason why I switched to a passenger tire, as I have posted before the single biggest improvement with handling that I have made was when I changed from the Kenda to a passenger tire. When I would come up on a tractor trailer on the interstate I would get a lot of wiggle from the Spyder and in/out sway going around curves. When I changed to the passenger tire the wiggle was reduced significantly and the rear end dip when going over bumps or dips in the road. At Spyderfest I had a set of Elkas put on my Spyder and it did improve the smoothness of the road, but unlike some I definitely would not say that it was like having a new bike. I have a 2010 RT-S and had put on the 2011 shocks prior to putting on the Elkas, so I have went through a progression of changes on the Spyder, passenger tire on the rear then 2011 shocks then Elkas. My sentiments are echoed by the wife being a passenger on the back of the bike and rider. The other thing of course that most of us see on our 2010s (I can't speak for the later model year Spyders) is the in/out going around curves with our Spyders. As said above with the progression of changes that I have made the tire being the first change that was made and the cheapest by far gave me the biggest change and eliminated the in/out, the 2011 shocks help to reduce the front end dive, and the elkas all but eliminated the front end dive.
I appreciate what you feel, but if you never try other options then how do you know what positives or negatives are gained or loss by changing the OEM tire:dontknow:? I have owned my fare share of cars in my life time and have never kept the same tire on my car that it came with from the manufacturer. I know that others have changed their rear tire to a passenger tire and are getting better mileage out of them, even if I did not gain any additional mileage with the passenger tire compared to the OEM tire, I am still paying less money so I don't know how that could be the wrong choice?
Order of changes in 33,000 miles:
2010 shocks changed from 3 to 5
Rear tire changed from OEM to passenger tire
2011 shocks installed and settled at 4
Elkas installed at Spyderfest 3
The next change that I will probably make is changing the front tires from OEM to passenger tires. Here is what I have found or experienced to this point concerning them. As others have reported the front end can develop a wobble in the front end at a particular speed and changing the front tires to a new set of OEM tires have helped to eliminate front end wobble, which I have experienced. The problem comes later as the tires wear in that the wobble comes and goes or changes the speed range that it occurs at. If you watch the front tires while going down the road (please be careful if you do so), you can see the tire going in and out. I am meticulous about my maintenance and torque the wheels to 77 ft lbs and re-torque by loosening and re-tightening to the desire torque rating to help to reduce it. The second thing that I have experienced is during a curve, this is with all changes mentioned above with suspension components, as I enter or continue in a curve the front tires tend to give to much or weaken as the curve is maintained. I truly feel that this will be improved when going from a softer sidewall tire to a firmer sidewall tire.
I do ride the Spyder hard going around curves, but I feel that being it is modeled per say after the 4-wheeled open air Spyders of yesteryear that is exactly what it should be able to handle! I love my Spyder, but like with any vehicle or bike I have owned I want it to be the best it can be. I have a philosophy that what ever vehicle I buy I am going to treat it like what it is made to do (eg. sports car like a sports car, truck like a truck, luxury vehicle like a luxury vehicle).
I hope that I have not rambled, but I for some reason I felt like putting it out there.