what trips end of run?

Take a walk to the "big end' of your track and try to see how high the beams are. I didn't realize they are higher than the start beams. Maybe get a good pic of your car going through.
The largest diameter front tire you can fit will give you a "roll" at the start. The clock doesn't start til you break the beam with the rear side of your front tire. You're moving faster, and are further down the track with a larger tire when this happens. It helps more than you would think.