Tripping the beams.

[The Enthusiast]

Keeping it short and simple. Eg: A car/bike goes through the timing lights. The front wheel(s) is off the ground. How accurate is the speed/et when going through the beams?

[crikey]

Speed will be accurate, et will be very slightly down. Assuming a legal launch and a full pass.

[Burndown]

The Enthusiast said:

Keeping it short and simple. Eg: A car/bike goes through the timing lights. The front wheel(s) is off the ground. How accurate is the speed/et when going through the beams?

It is accurate to 1/10'000 of a second usually and speed to two decimal places.

[The Enthusiast]

Burndown said:

It is accurate to 1/10'000 of a second usually and speed to two decimal places.

How high usually is the beam off the ground? Wouldnt it record the rear tyre if fronts too high?

[Burndown]

Or chassis or bodywork. It won't make a difference to a heads up race, it can only lose you a race really.

[hairyjester]

All beam heights except for 60' and the startline are 6" from the track surface.

[Jon C]

There have been a couple of instances I can think of when STTF bikes have crossed the first beam with the front wheel off the ground (so the back wheel or some central part of the frame starts the ts clock), and then put the front wheel down. Its a rare occurrence, and fairly transparent when it happens. I recall Per Bengstrom on "The Beast" displaying a terminal of 250 plus that was fairly easily discounted by this simple explanation...

[crikey]

Jon C said:

There have been a couple of instances I can think of when STTF bikes have crossed the first beam with the front wheel off the ground (so the back wheel or some central part of the frame starts the ts clock), and then put the front wheel down. Its a rare occurrence, and fairly transparent when it happens. I recall Per Bengstrom on "The Beast" displaying a terminal of 250 plus that was fairly easily discounted by this simple explanation...

Which, if memory serves, was perfectly legal until a rule change a couple of years back.

[PiPPl]

Timing rules are by necessity based on having the same part of the vehicle triggering all timers. So the accuracy of measurements in time and speed over an official race- and speed trap distance is impacted if you trip a start timer with the front wheel and the corresponding end timer with the rear wheel, or vice versa.

Jon C said:

There have been a couple of instances I can think of when STTF bikes have crossed the first beam with the front wheel off the ground (so the back wheel or some central part of the frame starts the ts clock), and then put the front wheel down.

Yes, it happens now and then and is sometimes a cause for controversy in post-race discussions.

crikey said:

Which, if memory serves, was perfectly legal until a rule change a couple of years back.

In UEM competition there are no rules against dropping the front wheel as per above.

Burndown said:

Or chassis or bodywork. It won't make a difference to a heads up race, it can only lose you a race really.

Yes. Keeping to the bikes, UEM rule RR10.3.3, on finish line, states that "The winner is the first motorcycle to cross this line with the front wheel."

So we have Bike A and Bike B race each other. Both bikes have 0.0 seconds reaction times and run identical speeds (real speed over ground, not timed). Bike A clocks a 6.0001 second run but with the front wheel above the finish line and in that stops the ET timer with the rear wheel. Bike B clocks a 6.0000 but stops the ET timer with the front wheel. If these are long wheel base bikes then Bike A crossed the finish line first but will be judged loser of the race since in reality it is the number on the clocks that count, not the first to cross the finishline with the front tire as defined by the rules.

Now, if "cross this line" means the same as "breaking this line" it gets worse

Regards
PiPPi
http://HarleyDrags.com

[hairyjester]

There is a solution to these kind of occurences which can and do happen from time to time and that's photo-finish technology. The cameras nowadays run at 10,000 frames per second and there's no arguing with photgraphic evidence but I can't see a provision for the technology to be used as evidence in any rule book any time soon.

[crikey]

PiPPl said:

Jon C said:

There have been a couple of instances I can think of when STTF bikes have crossed the first beam with the front wheel off the ground (so the back wheel or some central part of the frame starts the ts clock), and then put the front wheel down.

crikey said:

Which, if memory serves, was perfectly legal until a rule change a couple of years back.

In UEM competition there are no rules against dropping the front wheel as per above.

I bow to your greater knowledge Pippi I did say "if memory serves", my memory not being the most reliable of things these days !

[PiPPl]

crikey said:

my memory not being the most reliable of things these days !

Hehe, you're not alone. Of course I had to doublecheck the actual rulebook before posting...

Regards
PiPPi