Explaining timing system issues.

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Explaining timing system issues.

Postby sandaltered » Fri Jul 24, 2015 7:18 am

It's been somewhat popular conversation recently, so I thought I'd try to clear up some questions about timing systems and how they work. Also explain some issues with the timing systems related to sand drag racing and why they are happening more and more frequently.

Thanks to Damian Bowers for taking these photos, that show the setup perfectly.

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Most everybody understands the pre-stage and stage beam's primary function. They are there to show you when you are staged up properly at the beginning of the race. Obviously they trigger the lights at the top of the tree when your tire (or some vehicle part) breaks through that beam.

What most people don't completely understand is the guard beam. Most people think it's function is only to serve the purpose of determining a red light. That's not entirely true. In the early days, the guard beam didn't even exist. To understand it's function, you have to know how the timing system operates.

1) Stage Beam Starting.

Stage beam starting is used on asphalt tracks. After the stage beam is activated the tree drops. When you launch, at some point your tire is no longer breaking the beam. At that point, the timing system activates. Obviously, if the beam is re-connected prior to the green light being illuminated, you will get a red light.

That seems simple enough. So why would you need a guard beam? At some point drag racers got smart and figured a way to bend the rules a bit. They started to offset the front tires to maximize the amount of time their tires stayed in the stage beam. Thus increasing their rollout. By the time the beam had re-connected the car was quite a few inches further down track. It lowered their ETs and allowed them to leave earlier on the tree to get a starting line advantage over their competitor without a redlight. This photo of an old front engine dragster model, shows what I mean.

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When this got too far out of hand, the rules started to dictate the amount of front tire stagger you had, and the guard beam was introduced. The function of the guard beam at that time was to protect against extremely large rollouts. If the stage beam has not re-connected and the guard beam was broken by the front edge of the tire, that would trigger a red light also. That kept people a little more honest on the tree.

Hopefully that's easy enough to understand. Unfortunately, that's not how most sand drag tracks operate. In order for a stage beam starting system to operate properly, the beams need to be set extremely low, so that only the tires are breaking the beams. Not body parts or other external devices. That's why there are minimum body height requirements on asphalt tracks.

Because of the nature of a sand drag track surface, the starting line holes, etc, the beams need to be raised much higher. If they are too low you start running into issues with clumps of dirt interfering with the beams. If you ran a stage beam start system, you run the risk of false times because of body panels not allowing the stage beams to re-connect or dirt flying from the front tires causing the same issue. For that reason, most sand drag tracks use guard beam starting system.

2) Guard Beam Starting.

This system activates the timing system once the guard beam is broken. Again, if that beam is broken before the light is green, a redlight occurs. Therefore you have about ~16 - 18" of vehicle movement before you redlight. It also gives you a little time to get some speed going before tripping that beam. It helps reduce ET. Obviously the greater the distance between the stage beam and the guard beam, the lower the ET potential is. That's why shallow staging can help lower ETs when trying to reduce that ET for a qualifying spot.

That works fairly well with most sand drag tracks. But there are two issues. First, if you have a lot of overhang on the front of your vehicle (fenders, spring shackles etc) you can have guard beam issues. Especially if the track hasn't been groomed in a while. You may roll in and trigger both the pre-stage beam and stage beam with your tires, but due to the holes, you're sitting at an angle large enough to have the front of your vehicle breaking the guard beam. You'll never know it, until the tree activates and the red light comes on instantly. That's due to the guard beam being broken.

The second issue is the one occurring more frequently the past few years. That's known as "jumping the beams". It happened a little bit in the past. It wasn't widely known. People would get a strange time ticket and not understand why.

In these pics, you can see that the vehicle has launched. The front wheels are clearly over the stage beam. The guard beam is still connected and has not been broken. Therefore the timing system has not activated. The vehicle now has the entire wheelbase of the car to accumulate speed before breaking that beam with the rear tires and activating the timing system.

Image

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In these cases an ET will be much quicker than a normal run for that vehicle. In the case of our car, it's been on the order of about 0.4 - 0.5 sec. Your reaction time will also be very slow, and your 60' time extremely quick. Unless, you carry your front wheels over the 60' beam as well. On nitrous we've seen ETs as quick as 2.7's with our car. That happened in the first round of Gravelrama for us last year. It does look cool to the fans when it pops up on the scoreboard, but it's frustrating when you'd like to know your real time. It's one of the reason you'll see some sort of rag or strap hanging from the front of a lot of the cars that tend to wheelie. The rag is there to break that guard beam.

The moral of the story with guard beam starting on a sand track is have the beams high enough that it's difficult to jump, while not so high that it interferes with the full body vehicles.

To confuse the issue even more, there is a 3rd way to start that a lot of the tracks are switching to.

3) Stage or Guard Beam start.

This is simply a combination of the two. That means whichever event occurs first (stage beam reconnects, or guard beam breaks) the timing system will activate. So that appears to solve all problems, correct???? Unfortunately not. I think it solves the problems for most vehicles. Unfortunately, it creates a new problem for very few. Our car is one of them. It's the reason I've been researching this, and asking some questions of some of the tracks and people controlling the timing systems.

The new issue for us has been inconsistency. If the timing system is setup on Stage or Guard beam start and our car launches hard with the front wheels lifting straight up, it'll typically reconnects the stage beam first. She gets great reaction times of course. If for some reason we spin the rear tires a little harder and the car moves forward without lifting the front tires we'll actually activate the timing system with the guard beam. The reaction time slows down because of the 16 - 18" of forward movement I spoke of earlier, but the ET will quicken up by about the same amount.

We ran into this at Cleves and WMSD this year so far. Cleves realized about halfway through Friday test-n-tune that a lot of cars were jumping the beams. They switched from a guard beam only start to a stage or guard beam start. We made our first pass off the trailer with a good reaction time and a 3.52 ET. That was more than likely a stage beam start. In the following run, we may not have wheelied as hard on the launch and tripped the guard beam to start. We had a higher reaction time and ran a 3.39 ET. At that point we were a little concerned because we were actually trying to dial the car in for a 3.50 index class. I pulled some timing out of the car on launch to try to slow the car down and we went back up for a 3rd pass. We ran a 3.49 so I felt like we did a decent job with the tuning. On our first round run the timing being pulled must've been enough to calm the car down on the starting line to not wheelie out of the stage beam. We had a slower reaction, great 60' and broke out with a 3.43, lifting and dropping 6mph at the finish.

Anyway, that scenario got me investigating and learning what I've shared here. The same thing happened at WMSD back in June. We had a couple occurrences where the ET picked up over a 0.10 for no reason and the reaction slowed down. We think the same thing was happening. Like I said, this is probably only effecting very few cars. I just have to work it out with our car to get some consistency for bracket and index racing.

If you have any questions post them up. I'm not sure I covered everything, but I think I typed more than enough for now.
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Re: Explaining timing system issues.

Postby Dreher Race cars » Sun Jul 26, 2015 1:29 pm

Very good info Mike. And lots of good pictures of Kerr trying to beat the system. :lol:
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Re: Explaining timing system issues.

Postby sandaltered » Mon Jul 27, 2015 6:49 am

:lol:
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Re: Explaining timing system issues.

Postby Sebastian Lindau » Mon Jul 27, 2015 1:43 pm

Good posting Mike - very interesting!

Best regards, Sebastian.
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Re: Explaining timing system issues.

Postby sandaltered » Mon Jul 27, 2015 2:50 pm

Moral of the story from these pics.

I hope IOK can check to see if they can raise the beams to the proper height within the next month.
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Re: Explaining timing system issues.

Postby sixpak » Mon Jul 27, 2015 3:21 pm

Well done Mike!
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Re: Explaining timing system issues.

Postby 357Bronco » Sat Aug 15, 2015 10:53 am

We've shared this with our racers, great information, thanks.
someone go back and get a shit load of dimes
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