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Thread: 2in of "independent" travel - rule interpretation

  1. #1
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    2in of "independent" travel - rule interpretation

    Many teams barely use .5in of travel, yet they have 2in based on damper travel and ratio - making it rule compliment. Independent? I guess a de-dion/live axle allows at least some independence (although it is considered a "dependent" system). Anti roll bar would mean dependence, but if it can be disconnected, that complies then. But what if it's, lets say, torsion (trailing) arms? I guess what I'm trying to understand is if it is even possible to be disqualified on the basis of one of these 2 (as far as I remember, that was it) vague suspension rules.
    Ryerson Formula Racing Suspension Co-lead
    Ryerson Baja suspension Designer
    2nd year Mech

  2. #2
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    I'm quite sure the rules don't mention anything about being "independent". Has the rule recently been changed?
    ex-UWA Motorsport

    General team member 2013-15, Vehicle Dynamics Team Lead 2012
    Project Manager 2011, Powertrain minion 2009/10

  3. #3
    Straight from the fresh 2017-2018 rule book which is exactly identical to the 2016 rules.
    No mention of 'independent' suspension travel.
    T6.1 Suspension
    T6.1.1 The car must be equipped with a fully operational suspension system with shock absorbers, front and
    rear, with usable wheel travel of at least 50.8 mm (2 inches), 25.4 mm (1 inch) jounce and 25.4 mm (1 inch) rebound, with driver seated. The judges reserve the right to disqualify cars which do not
    represent a serious attempt at an operational suspension system or which demonstrate handling
    inappropriate for an autocross circuit.
    T6.1.2 All suspension mounting points must be visible at Technical Inspection, either by direct view or by
    removing any covers.
    Typical example of not actually reading the rules yourself and just relying on what some dude on the team told you.
    Read the rulebook. Learn the game before you play it.
    Funny how you call something 'vague' without reading.
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  4. #4
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    The T6.1 suspension rule is the original 'Anti GoKart Rule', written many years ago after some teams brought what were effectively gokarts to the competition.
    The rules makers decreed that all cars needed suspension.
    So, "what should 'suspension' be"? was asked.
    The answer? "Oh I guess a minimum of one inch movement in either direction would suffice", was the answer.
    So, the rule has always been vague and it certainly does not preclude beam axles.
    There is no rule about wheel rates etc, so suspension on FSAE cars is often 'virtual', assessed by the tech inspectors by inspection rather than measurement.

    However, remember, excitation at the contact point is the enemy of grip.. and stiff suspension excites the contact patch!

    Pat Clarke
    The trick is... There is no trick

  5. #5
    Quote Originally Posted by Pat Clarke View Post
    The T6.1 suspension rule is the original 'Anti GoKart Rule', written many years ago after some teams brought what were effectively gokarts to the competition.

    There is no rule about wheel rates etc, so suspension on FSAE cars is often 'virtual', assessed by the tech inspectors by inspection rather than measurement.

    Pat Clarke

    On more than one occasion have I had a tech inspector insist that a team member stands in or on the car and jounce the car to prove that we could travel 2" with the springs we had installed while they stood there with a tape measure to check travels.

    "Oh, dear that only looked about 1 7/8 inch of travel... do yo have anyone heavier?"
    "Sir, that student is 150lbs. I'm pretty sure cornering forces are going to do more than that..."
    Kettering University Vehicle Dynamics
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  6. #6
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    Onemaniac - I have read the rules last year, and re-read a few sections recently that were relevant at the moment.
    Honestly, I was just thinking about some idea, and that bit of the rules came to my mind. I thought I remembered it perfectly, and that it was all there was to it - guess not, lesson learned. The anti-gokart rule mentioned answers my question, pointing me in a different direction (from that you may guess what I was thinking about)
    Ryerson Formula Racing Suspension Co-lead
    Ryerson Baja suspension Designer
    2nd year Mech

  7. #7
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    The problem is that it is quite hard to measure what the actual wheel travel of a car is. Especially if the team is using very stiff springs. The method I know from the European competition is that you put a tape measure next to the car and one is bouncing down the car trying to push it into the bump stops. If it seems that the wheel travel is in the right ballpark it is considered ok. At some occasions I also saw scrutineers just move it up and down a bit to see if it is a "functioning suspension" and that's it.

    Of course it is not ideal that this is one more example for using different methods to check a rule, but as long as you make sure you have enough suspension travel, you should be fine at comp.
    Rennteam Uni Stuttgart
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  8. #8
    One assumes that the rule means +/-1" of wheel travel relative the the sprung mass of the car, but this is not clearly stated. +/-1" of wheel travel relative to the ground would be easily proven by lifting each wheel of the ground (something you want to AVOID happening while driving round a bend).

    Bouncing up and down on the car is also a poor test. Depending on tire wall design, pressure, and condition, it's not infeasible that half of you travel could come from tire deflection.
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