think of it this way....if you could launch your car with stock wheels on it and not spin you would probably be within a half second of advertised or closer yet. add in the factor of what you are using to time it with and you are right there. IMO it is probably fine. You just have to learn to launch your car on smaller tires and not spin. Also, if your friend was in the car with you that could slow you down a little bit too.