FrontEngineDragsters.Org Forum
Technical => Jon's Wheel House => Topic started by: Guido on May 25, 2019, 06:19:21 AM
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Looking into light shields , are they needed? I see them on some FED's
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Depends, If your car runs/has overhang in front, then no , because that is what trips the down-track timers. If there is no overhang and the front wheels trip the timers, then a wheel guard is added insurance . Avoid polishing anything used to stage or trip the timers/beams as the reflection can mess with the signal
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Most of my light shield customers buy them for the starting line, to prevent red lights , the shield gives you a bit more roll-out, and of course with cars with no nose, the front wheels will click the ET stop.
But keep in mind the start line light beems are on the track [lower] and the finish lights are about 3" above the track.
For years we did not run a light shield on our JF car with 18" wheels with low profile tires , 2.00x18, but the rims had a lip , like Akront or Borrani , and we had no issues of red lighting, UNTIL we raced at a Heritage race in Phoenix, where we had a redlight for the 1'st time . When I checked the other JF teams they also had red lights with the cars that did not have light shields , but no red lights with the cars that had light shields. So yes we have been running a light shield since.
When I get a call for light shields I ask if they are having red lights because the front end is jerking the front end up at the hit, if so just add another 20 lbs on the nose, because a light shield will not help if the wheels are pulling out of the start line lights.
I hope this helps,
Jon
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Jon--- stage inferaed beams are on the deck(or close to it)and the old photo-cells were a little higher (but had shields to lower the beams) so the light guard has no influence on roll-out using a standard wheel/tire combo. Down track timers are 6" up from the track, a 12" square foam block has the reflector in the middle, so covering the spokes of a car without O-H, increases the target area for the beam. We had an issue at one track where the sun was at the right angle where the refection bounced off the rim and into the beam causing it not to register. The other guy was pissed at us for trying to burn him down, but it was just one of those things, we were well past the line and the stage lights never came on
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Bruce, then nobody needs light shields ? Then why when we raced Phoenix did ALL of the cars without shields red light and all that had light shields not red light ?
I witnessed a red light problem at a national event at Vegas with a Comp Elim A/AP when it red lighted without moving [ video] , not even tire wringle, NHRA tested and tried to doublecate, and NHRA decided that a photographer standin shooting at the startline, outside the K rail , was the cause of the flash camera reflecting off his front wheel because the photgrapher was actually shootting his competitor because they left 1'st. That's why NHRA does not allow photos at the start line now. Allan Ellis has since blacked out his wheels.
How's Dennis Murphy car coming along ?
Jon
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Jon, I had a similar "shiny wheel" experience at Indy when I was in the beams for four seconds (as timed on a video replay) and went red with the trans brake set. Years later I related the story to a local Indy racer and he said he'd seen it a few times in the right lane. I was in the right lane that day.
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There is 2" of tire above the track surface before the rim edge, add another 3/4" before the light disc starts, So in no way does the disc have any effect with todays starting systems with the beams mounted so close to the racing surface. As to why there was a problem in PHX.? don't know maybe the extra weight of the disc kept the front end down longer??? but its the 3rd (guard beam) photo cell that determinds red lights
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I thought a red lite is triggered when you roll past the "staged' beam before green. Only two lites at my tracks.
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Some tracks use 3 to deal with offset front ends, pass thru the guard beam while still in the regular start line beam and the tree goes red. If your track only uses 2 beams (pre-stage and stage) then blowing thru the stage beam early will go red
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Bruce, I have built a few tall 21" wheels, with 28" tall tires, that they race full tree classes, Comp Elim, Top Dragster, with legal offset axles, which of course gives them great 60' times, and reaction times, because they are blocking the beams longer. I compared two cars roll out , one with 17", and one with 21" , the 21" has a 4 1/2 " head start on the start line. No red light because of 3'rd beam problems.
No advantage with a pro lite tree.
Jon
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You lose consistency with off-set unless you stage very shallow or go in deep. If there is no index/breakout, shallow to qualify (run at the tree) and deep for race (to shorten the track). 60' times will differ on cars with overhang vs cars without even if the both leave the line at exactly the same moment. Reaction times are the function of the driver only (in the type of cars we run) If the driver is a consistent .123 light, there is nothing on the car(providing the car is set up properly) that can be adjusted to change that