Acceleration of more than 1g is probably not possible for 0-60; there isn't much of that speed range that would allow for downforce (downforce would only start

Acceleration of more than 1g is probably not possible for 0-60; there isn't much of that speed range that would allow for downforce (downforce would only start have a tangible effect after approximately 50mph (80kph)), and there is no other appreciable way for the car to generate more friction with the road that doesn't scale with vehicle mass. I suspect what the OP was trying to get at is the vector addition of gravity plus the forward acceleration of the car means that the apparent scalar force feels substantially higher than normal (i.e. 1g downwards); it's just poorly worded.