Surprisingly enough, the NYC metropolitan area is blessed with fine mountain biking venues, both public trails and designated mountain biking parks.
Did you know that New York City is the closest large city to the Appalachian Trail? Well you do now. Not that it is acceptable to ride on the AT on designated hiking sections, but the AT follows some roads, the shoulders of which are the trail, so we do unknowingly ride on the AT at times.
The point is that we are within striking distance of the Appalachian Mountains on mountain bikes via Metro North and NJ Transit. Therefore you don't need a car to portage your mtn bike to these routes and venues.
This section includes trails conducive to mountain biking connected by roads, and access to specific mountain biking venues, all from railheads out of the NYC metropolitan area. Trailforks, a mountain biking website, has an app which has made navigating these mostly unmarked trail systems user-friendly. In a few short years the sport has grown, developing light and nimble machines, designing and building sustainable, diverse and challenging trails, and an increasing number of enthusiasts, many who also ride road bikes.
Consider giving mountain biking a try. It might interject a renewed passion for pedal and wheel.
That's me below, at the end of the descent of Poison Ivy at Ringwood, the only time I have successfully managed to thread my handlebar between those 2 close trees, captured on GoPro. I'll never be very good, but it is so fun I keep coming back. There are worse addictions.