I installed a sidecar on my Valk about three years ago. It was a Motorvation Spyder, see pic.
When you add 300 pounds of weight off center, handling is completely different. The Valk is slower on acceleration. When you accelerate the sidecar tends to pull the rig to the right, when you decelerate, the sidecar tends to push the rig to the left. you no longer use countersteering, the rig steers like a car, you turn it. The steering becomes heavy which can be lessened by changing the trail (triple tree modification). If the triple tree is changed, and you take the sidecar off, the Valk will tend to be unstable (this , by the way, is the opinion of experienced sidecar installers). There is a lot more to adjusting the rig so that it runs true,etc. Be ready to accept a new way of driving a rig. Lots more but that sums it up from my experience. If you asked me "Would you do it again", the answer is no but that's me.
One last thought. For safety reasons. if there are three persons involved, for instance, a Wife, driver, and a small child, the wife, being heavier, should ride in the 'car. Of course, you might have others disagree with me but we did install the sidecar ourselves and learned a lot by necessity.
