I assure you, its not a single speed. The speed is variable by adjusting how far up you pull the lower bail, and is done with fingertip control. According to the tech support at exmark, they are not slipping the belt to change speed, but its not a hydro either. I dont have any other specifics, but what i wil do is call the dealership tomorrow and find out more. The service dept mechanic went to a school on this particular mower recently, so maybe i can pick his brain for abit more on the specifics. I gotta get to work (my other job), but more info to come. ill try and keep this post going, by providing updates on this mower as I use it. That way others can reference it as time goes by. If others are using this mower, feel free to post your comments on it here as well. We can turn this into an exmark 30 blog, and try to help others with how well this new design performs over the course of time (which is the true test) time will tell...later.