"BRP will always recommend installing OEM tires on all Can-Am Spyder Roadsters as this has an impact on the dynamic behavior of the unit (notably, the Vehicle Stability System). "
Here's the deal. When Bosch does the VSS calibrations on their test tracks in Germany they have to do so using a baseline set of tires and air pressures. The VSS is calibrated to these specifications. They do not waste time doing alternate calibrations on other tires, yes they could, but they do not.
This is not to say that other tires are going to automatically "screw up" the VSS. But it should be safe to assume that tires with vastly different traction and sidewall flex characteristics are going to force the VSS to act differently that it would with the OE selections. To what degree we do not know. From personal experience of so many miles with so many different tires and encounters with the VSS, I am personally satisfied with how it has performed with my choice of tires, but I am very selective on what I use.
Example, a Spyder with firmer tires at higher air pressures and/or a stiffer sway bar. Instead of allowing body roll (like it would with 2-ply tires and a soft sway bar), there will be more of a tendency for the vehicle to corner flatter, to a point, and then lift more abruptly. The VSS is still going to sense this lift and catch it, but realize the VSS algorithms are optimized for the baseline specifications. Does not render the VSS useless, but BRP and Bosch can not test every possible tire out there. Their obligation is to make sure it works as delivered.
Yet another consideration to front end lift would be the rear tire. Yes, the rear tire. If it allows a slight amount of side slip it will help to keep the front end down. If the rear tire is totally glued, the vehicle will lift the inside front tire more easily. Just like a snowmobile, three-point vehicle dynamics. This can be affected by ride height, rear spring preload, tire tread, air pressure, road surface, just something else to consider.
