The Baby Jogger Summit X3 has tracking adjustment on the front wheel. With the front wheel locked (not swivelling) the pushchair may veer a little to left or right if your personal style is to hold the handle to one side of centre - you are essentially steering the pushchair ! The option to have the front wheel swivelling inevitably results in a small amount of 'play'. Either way you can adjust the alignment of the front wheel to tune out the inaccuracy.
Front Wheel Tracking
When locked the front wheel tracking can be adjusted by turning the Red Knob, this moves the lock mounting block