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An Important Driving Lesson Learned

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  • An Important Driving Lesson Learned

    While running the tests for the ďCornering SpeedĒ article, I started testing a few of my faster cars to see what the maximum cornering speed could be.

    The Jaguarís exit speed in the 38.5Ē diameter turn, the largest turn on my track, was 10.3 f/sec. The car with the fastest skid pad times, a Ferrari 312, went 10.4 s/sec. The car with the second fastest skid pad times, the Sauber C9, went 10.6 f/sec.

    In the process of running these tests I noticed how much over-driving a car costs in exit speed in the turn.

    Running multiple laps with the C9, in the 6.650 lap time range, the exit speed was always 10.6 f/sec. Any over-driving, either entering the turn or exiting the turn killed the exit speed and the overall lap time.

    The position of the car in the photos shows how far the car over-steered, at that point, either in the braking/transition to the turn, or accelerating, either to soon or to hard.

    Photos 1, 2, & 3, depict were the car stopped over-steering and began following the proper line through the rest of the turn.

    Photos 4 & 5 depict where the car first broke loose when accelerating, and continued to over-steer.

    These are the exit speeds for each position

    Photo #1 9.6 f/sec. exit speed
    Photo #2 8.4 f/sec. exit speed
    Photo #3 6.5 f/sec. exit speed
    Photo #4 9.1 f/sec. exit speed
    Photo #5 9.5 f/sec. exit speed
    Photo #6 The dark grey area is the two foot speed trap.

    I had learned from previous tests on the skid pad that driving through a turn with the nose of the car exceeding more than 90į to the slot, or the inside rear tire on the inside track tape, the car was losing speed in a turn.

    This has always made me wonder why a slot car driver would want to make a car fishtail. To me, doing this only slows a carís lap time.

    When anyone on my track turns their fastest laps, it appears as if the car has a rear guide.

    Link to the cornering speed article.

    http://slotcarillustrated.com/portal/forums/showthread.php?t=24240

    Dave
    Last edited by davejr; 09-22-2008, 06:12 AM.

  • #2
    Good observation and is very true. But Dave, I don't see pictures 5 and 6.

    The only reason I've heard folks want a car to fishtail is the car tends to be "tippy". In this case, a top heavy car may actually benefit from a greater slip angle, therefore actually increasing cornering speed and ease of driving. More so ease of driving than actual cornering speed really. I've seen many times where a driver driving a tippy car actually increased his absolute cornering speed just by installing less grippy tires in the rear. This is because some drivers have a tendency to back off with a tippy car in fear of just that, tipping over. But, if the car gives the driver confidence, he/she sometimes increase cornering speed when in reality, the car's absolute cornering speed capability has been decreased. The car's cornering speed relative to other cars is slower, but to the driver, it's faster.

    Like you said, it's a false sense of going faster which only the driver can fix.

    Comment


    • #3
      Taken from another point - we all know that a "magnet car" can zip thru a turn way faster than a "non-magnet car" so any deviation does slow down the lap times by the amount of drift/slide in the corners.

      I know any sliding in say the first 2/3rd's-3/4qtr's of the turn is not a good thing, but I've always wondered if the rear-end kicking out (somewhat like Picture #5) just before the exit of the turn as the throttle is pushed down sets the car up for more exit speed into the straightaway (assuming one has held the proper line till that point)...if not, it still looks cool doing so...LOL


      Da Vols - Bruce & Harriet & Kali

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      • #4
        I recently re-installed narrower EJ's rubber rear tires on this car, resulting in slower lap times, but a complete elimination of rollovers. It had the wider EJ's on for a while, and while cornering speed increased due to better grip, it would roll over without warning when driven too fast. With the narrower tires, the car is extremely stable, and can be thrown around without de-slotting or rolling over. If it were a racer, it would probably be faster over a longer race, as it can now be driven without errors. The reason I went with the narrower tires was to slow it down to its intended speed-class, and to keep it in the style of a pre-wide-tire racer (1950's).

        Last edited by Robert Livingston; 09-22-2008, 07:42 AM.

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        • #5
          Dave, don't make the mistake of equating 'fishtailing' with 'sliding'.

          Nuvolari was the first to perfect the four-wheel drift, and he was blazingly fast because of it. Fishtailing is when the back of the car swings back and forth. Nobody wants to do that -- not if they're trying to be fast.

          Comment


          • #6
            When driving the Scalextric GT2 cars or the Scalextric Stock Cars, with the factory rubber tires, the 90į angle doesnít hold true. Most of the rubber tires on my track need at least a 110 to 120į slip angle for their best performance.

            The rubber tires are quite a bit slower than the S1 tires on my track, this helps keep these cars at a reduced speed.

            Dave

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            • #7
              ElSecundo

              In photo #5 the rear of the is car is sliding, when the guide gets to the straight the car will start fishtailing. The greater the slide, the greater the fishtailing on the straight, unless power is reduced to straighten out the car.

              In photo #5 the car isnít sliding all that much and has already lost some of itís exit speed, 10.6 down to 9.5 f/sec.

              Dave

              Comment


              • #8
                Originally posted by davejr View Post
                ElSecundo

                In photo #5 the rear of the is car is sliding, when the guide gets to the straight the car will start fishtailing. The greater the slide, the greater the fishtailing on the straight, unless power is reduced to straighten out the car.

                In photo #5 the car isnít sliding all that much and has already lost some of itís exit speed, 10.6 down to 9.5 f/sec.
                Photo #5 shows a fishtail in progress. The car has slid beyond the point where the longitudinal axis of the car is tangential to the curve. As the car powers out of the corner, the tail will oscillate. All fishtailing is sliding, but not all sliding is fishtailing.

                When the slide does not get beyond the point where the longitudinal axis is tangential to the curve, the car will exit quickly. The car you're showing has lost at least 0.05 seconds by sliding as much as it is.

                Comment


                • #9
                  A seemingly small slip beyond the angle of tangency to the slot will result in a noticeable increase in lap time on the clock. I can observe it, but I can't always control it. I think the ability to judge the speed of a car on the track separates the really good drivers from the merely-OK drivers. Too much entry speed can result in a slide part way through, which scrubs off speed. As a (mostly) proxy competitor, I try to build cars that are both fast and forgiving. That means they can recover from a slide without going off. This seems to be based on grip as well as longitudinal CG (weight bias forward vs rear).

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                  • #10
                    Races are won and lost in the corners.

                    Thats a saying, right?

                    I still set my fence back to give me more tail sliding room in the corners after long straights. Just in case. Nothing worse than a wing hanging on the top of a fence leaving the wheels high and dry while the competition blasts right past you and gets to kiss the trophy model.

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                    • #11
                      ElSecundo

                      My understanding of the term fishtailing, is that the rear of the car slides back and forth across the center of the lane in both directions. I have never seen a car fishtail in a turn. The only fishtailing I have ever observed is a car being overdriven entering the straight.

                      I donít understand where the 0.050 seconds loss came from that you are using. If you calculate the difference between the two times for the 10.6 to 9.5 f/sec of the two foot speed trap, the difference is only 0.020 seconds.

                      The car in photo #5 didnít start sliding more than normal until past the last foot of the speed trap. The loss for this car in the photo would be less than 0.010 seconds for this turn's exit speed.

                      Dave

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                      • #12
                        It helps if I read things thoroughly - so given my posted example I'd expect to lose about 1/100th or so if my exit was like #5 vs #1 - but it would look lots cooler...LOL

                        By the way, do you think there needs to be better/new wordage rather than "understeer" & "oversteer" as to how a slot car goes through a turn since there is no "steering" involved...I would think "tight" & "loose" would be better...???


                        Da Vol - Bruce

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                        • #13
                          I call it slide-out vs. tip-out. If the car rotates too far around the guide it is a slide-out. If the car's rear stays planted, and the car rises up on two wheels and rolls over, or just deslots and drives off the outside of the turn, I call it tip-out.

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                          • #14
                            Originally posted by davejr View Post
                            ElSecundo

                            My understanding of the term fishtailing, is that the rear of the car slides back and forth across the center of the lane in both directions. I have never seen a car fishtail in a turn. The only fishtailing I have ever observed is a car being overdriven entering the straight.

                            I don’t understand where the 0.050 seconds loss came from that you are using. If you calculate the difference between the two times for the 10.6 to 9.5 f/sec of the two foot speed trap, the difference is only 0.020 seconds.

                            The car in photo #5 didn’t start sliding more than normal until past the last foot of the speed trap. The loss for this car in the photo would be less than 0.010 seconds for this turn's exit speed.

                            Dave
                            Dave -- All fishtailing starts in the corner. Once the car gets beyond that tangent line, preventing a fishtail condition is difficult, and like you said, it manifests at the entrance to the straight.

                            The 0.050 second loss is just a rough number I use for a slide that far. I've spent literally thousands of hours observing the effects of driving mistakes on lap times. More often than not, I can predict a car's lap times based on the mistakes made (within about 2/100ths). The mistake in #5 looks very much like a 0.05 second loss, but that's just empirical observation on my track. Mind you, that much slide has a different time penalty associated with it depending on the grip available. If you are driving on ice, that particular slide can cost you a full second or more. If you have fantastic tires on a fantastic surface, that mistake may only cost 2/1000.

                            I don't do that so much any more -- haven't had the lap timer hooked up for about 2 years.
                            Last edited by ElSecundo; 09-22-2008, 08:28 PM.

                            Comment


                            • #15
                              All fishtailing starts in the corner.
                              No it doesn't, not necessarily, I disagree.

                              Even with the solid rear axle we use in slot cars, and our best attempts to balance them, grip will invariably be better on one side than the other - and in an inline setup, there will be the concomitant issue of torque exacerbating the problem.

                              What am I driving at here? Simply, that if you nail the power on a straightaway, with the car perfectly aligned to the slot, it will still step out to one side or the other.

                              (In 1:1 cars, fishtailing is usually caused by overcorrecting the steering to combat this, instead of using finesse with the throttle and steering wheel - but that's another issue, and almost irrelevant with modern stability control systems.)

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