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Last Post 23 Jul 2015 05:55 AM by  sjfehr
Should cars line up at the start based on front wheel or the car body?
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madame_toussleau
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21 Jul 2015 08:03 AM
    I autocross with a local non SCCA club where 1 starter lines the front wheel of every car up at the start line. I've always lined cars up based on the front most part of the car body.

    It's a small difference so I shouldn't care, but I think the physical car breaks the light and should be used.

    Maybe I'm missing something in the SCCA rule book but I don't see it.

    I did ask our local SCCA starters who just said the car body which makes sense to me but does anyone know if this subject is covered in writing anywhere?

    drdisque
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    21 Jul 2015 10:58 AM
    If it's the same for everyone it doesn't matter but obviously the same starter isn't working the whole event. It's the car body that does break the beams so that does make sense to use the front of the body (or front wing for cars without a body). The only thing it would affect is PAX comparisons between cars who run different heats. The cars lined up using the body vs. the wheel would have a slight advantage.
    madame_toussleau
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    21 Jul 2015 01:17 PM
    You are completely right. The pax'ed classes were pretty much grouped together - so that's a good point.

    Now I can see why the SCCA book doesn't need any kind of rule talking about this.

    Thank you
    47CP
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    21 Jul 2015 04:06 PM
    How much difference in time could there be? (Not arguing too much, just wondering out loud :))

    My car has a huge front overhang with a low splitter. IIRC, it is about 48" from the axle centerline to the tip of the splitter, which is a huge, low overhang compared to almost every other car. The front tire is 25.5 diameter but you wouldn't get the radius as an advantage, but I would WAG that there might be 30" difference in launch point from front of car versus center of tire.

    It also accelerates faster than the average car when it has grip. Hitting 1.0+g accel on launch is pretty easy on concrete.

    The only cars I can think of that would have more overhang and more acceleration off the line would be the BM cars with those low forward wings.

    I can't put my brain around the math to figure the exactly number, but I can't see where 3 feet of acceleration is even measurable with what we do? I know it would be measurable on a drag strip, but we a) don't have nearly those kind of launch conditions and b) almost always have a hard turn or other element right after the start to negate acceleration advantages.

    I dunno, not arguing, just rambling out loud.

    Oh, another reason there is not a rule in the book is that the book assumes national event, running by class, and no PAX. As long as the starter was consistent during his heat, no competitor would have an advantage over another.

    DaveW
    madame_toussleau
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    21 Jul 2015 05:21 PM
    yes, all true- at the particular event, it was a straight line thru the lights, and the cone to line up from was about less than 20 feet from the start timing lights.

    I do get it - my car at the time (old C4) had a long nose, so it just looked wrong to me :)
    sjfehr
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    23 Jul 2015 05:55 AM
    It depends on the beam height. Do the beams trigger on the wheels or on the bumper?

    Car speed increases exponentially from the start, so penalizing cars with long front overhang by aligning the front wheel is a potentially substantive penalty (or vice versa for low beams). It would depend on courses design on the small speed increase 3' of acceleration brings, but I would think it would be substantial enough to show up on time slips for some courses. Our club recently started using staging lights with the staging beam set at the same height as the timing beams- takes all the subjectivity out of it, and allows the starter to concentrate on safety. It's worked out really well, actually.
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