issue with laser is that you don't have a flat front profile - I would assume that your bumper height's are all over the place with bumps and different car makes. Maybe 4 inches doesn't make a different for what you're doing. In bike, house and car racing (and others) they use high speed slit camera's for that reason because it does - you could also use rfid - you measure off the front x distance for each car with the transponder. Or use contact strips on the ground to pickup the tire contact.