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The Longer You Run The Better The Lap Times

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  • The Longer You Run The Better The Lap Times

    I've recently installed Trackmate on my 1/32nd 4-lane routed track. I'm learning how valuable its running statistics are in practicing and tuning.

    Yesterday I was practicing with a set of four pretty much identical IROC slotcars, all with foam rubber tires. I ran each car in its own lane, originally just to get some track time on each.

    But what I observed was on my first lap or two my lap time would be a bit north of 6 seconds, but after maybe 15 or 30 laps I could get each car down to about 5.1 seconds. Doing that four times in a row was pretty convincing evidence that something was causing the lap times to drop, and doing it consistently.

    Now this was not anything new. I learned long ago that lap times will improve after a bit of running. But doing it with four IROC cars with the real-time feedback from Trackmate sort of rubbed my face in it.

    So the question is, why? Why do those lap times fall? I have some theories. Five to be exact.

    The first theory is that I just drive better given a few laps to accustom myself to the car and track. That theory doesn't hold up so well because going from one car to the next my lap times started off above 6 seconds, and the cars were so similar. If it was just me warming up my slotting reflexes my initial lap times should have fallen too.

    The second theory is that the track was 'rubbering in'. That theory isn't so convincing either. The track had seen quite a bit of running previously, and not been cleaned. Also, I tend to practice on the yellow lane a lot, but there seemed to be little difference in the lap times on all four lanes. If it was a matter of rubbering in there should have been noticeable differences among the lanes.

    The third theory is a bit more credible -- the tires were warming up. Warm rubber does stick better than cold. There has been a recent post here describing how a cold track results in slower lap times. There is good reason to believe that the tires will warm up a bit due to friction. So this theory seems to indeed be credible.

    The fourth theory is the tires wear a bit, exposing fresh rubber which has a bit more stick. Foam tires do wear significantly. In enduro racing fresh sets of foam tires have been known to wear out. If wearing off the old surface and exposing new improves traction then this theory should hold water. Not so much, however, in the case of solid rubber, silicone and urethane tires. They wear much slower. But they too exhibit this business of falling lap times.

    The fifth theory is a bit wonky. There is such a thing as 'surface energy'. It is important in how well paints and inks stick. Materials with high surface energies bond really well to coatings. Materials with low surface energy -- like polyethylene and polypropylene -- are awfully hard to coat successfully. Bu there are ways to increase the surface energy of materials. Brief exposure to a flame or a corona discharge works well. That is how plastic syringes -- commonly made out of polyethylene -- can be printed with volume markings and manufacturer logos.

    So, is surface energy a factor here? Do slotcar tires start out with a low or modest surface energy, but after rubbing around a track for several laps does their surface energy increase, also increasing grip?

    I kind of like this theory, if for no other reason that I've seen the effects of surface energy in my engineering career. Proving it may not be so easy. There are special pens you can use to measure surface energy. They come in sets, with inks that are less or more strongly attracted to a surface. The more inks coat the material well, the higher that material's surface energy. So if I had a set of those pens I could measure the surface energy of tires before and after a run. Increases in surface energy don't degrade quickly. A material that has had its surface energy increased may take days to return to its original energy.

    Doing such a test on foam tires would be difficult or impossible, just due to their porous nature. On solid rubber, silicone or urethane it should work. They all have smooth surfaces.

    Problem is, now that I have retired, to access surface energy pens I'd have to buy a set. McMaster.com has them, but they cost US$25 each. I'd have to be super extra good this year to find a set in my stocking. Dang.

    Ed Bianchi

    HO RacePro
    HRW Forum Veteran
    Last edited by HO RacePro; November 24, 2021, 09:53 AM.
    Ed Bianchi
    York Pennsylvania USA

  • #2
    It must depend on your tyres and track surface.

    We allow tyre treatment (oil, naptha, home brew...) as long as the tyres are dry on the track. I always find lap times get worse as the tyres wear during a race, as the ryres run over the braid either side of the slot scuffing the tyre surface. Sticky shiny tyres = FTD
    Kevan - Isle of Man
    Print It, Build It, Race It, Improve It, Repeat...

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    • #3
      I certainly "suffer" from the same malady. But in my case nothing as esoteric as surface energy. My slow starting has been exhibited numerous times, the most obvious one being when running proxy rounds. In recent times I have been running proxy rounds with the same fellow club member. He is a very good, consistent, fast driver. And every heat that we run, we see the exact same pattern: he pretty much immediately gets down to low lap times while it takes me around 10 laps to settle into fast times. So he normally builds up a lead in the first laps of the heat and I then slowly whittle it down again. And I see the same thing in endurance racing and even our normal club racing: I am a slow starter.

      For me I believe it is all about gradually "absorbing" the behaviour of the car, refining my "muscle memory" with the car and lap by lap pushing the envelope slightly. And particularly with rubber tyre proxy cars, warming of the tyres over a number of laps definitely plays a very significant role.

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      • #4
        Ed - thanks for the thoughtful analysis. I record hundreds of lap times for my cars and times typically improve as a session progresses. Slowest time for a session is usually during the first few laps, then times tend to flatten out. Later in a long run times get less predictable as my racing hand and trigger finger get tired. Somewhere between 150 and 200 laps my trigger finger gets numb as though falling asleep and I have to take a 20 to 30 minute break.

        I also like the 'tires warm up theory' and think it could easily be tested using a hair drier or heating pad and a very accurate thermometer. It's also likely track friction level changes with track temperature, if that varies noticeably.

        Given that even visually 'identical' cars are never truly identical, there will be individual differences making reaching any consistent findings difficult. The experimental solution to identifying a meaningful bias or trend in the data is to do many many trials so the signal (information) can be quantified despite the noise (variance).

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        • #5
          I tend to think it is more about getting in a rhythm. I usually run my best laps after I run a few minutes. I think you just get into a "zone" for lack of a better term. You push just that little bit more and that makes all the difference. It's never speed that is faster, it's hitting a really smooth lap where you push 2 inches farther into a corner or don't slide the little bit extra. That is all it takes for lose a tenth or two.
          Matt B
          So. In
          Crashers

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          • #6
            I’m with MattB regarding getting in a rhythm. I notice after a deslot it takes me few laps to regain my rhythm and get my times back down to where they were before the “off”.
            Mike V.
            Western North Carolina

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            • #7
              Well foam tires work best once you get some heat in them and they do not have drop off once they get up to temp.. if every thing is equal,foam tire car will out run RUBBER tire car 9 out of ten times.
              THE other Vancouver aka Vancouver Washington across the river from keep Portland weird....
              Member NASTE (Northwest Association of Slot Track Enthusiasts)

              Comment


              • #8
                Originally posted by HO RacePro View Post
                The first theory is that I just drive better given a few laps to accustom myself to the car and track. That theory doesn't hold up so well because going from one car to the next my lap times started off above 6 seconds, and the cars were so similar. If it was just me warming up my slotting reflexes my initial lap times should have fallen too.
                I would say your first theory is correct. You are not going to put a car on the track and drive it the same way you drove the last car without testing brakes and traction first. If you do you are going to be doing a lot of walking putting the car back in the slot.

                Butch Dunaway
                Oxford, Ohio

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                • #9
                  I think getting into a rhythm with the car is probably the greatest factor but in my experience there does seem to be some validity to getting some heat into the tires. Certainly this is true of 1:1 cars. I can’t imagine that the temperature of a slot car tire increases much. I’m no engineer - do the effects of temperature scale proportionally to the size and weight of a slot car? Maybe a difference of a few tenths of a degree in temperature play a role in the 1:32 world.
                  Team SCANC
                  Woodland Trace Raceway - SlotZuka - Bent Tree Raceway
                  OFI - Buena Vista Motorsports Park - Slotkins Glen
                  Leadfinger Raceway

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                  • #10
                    It's been quite a while since I've been here, so, "hello" to any who have never seen my name before. :-)

                    For me, what seems to be the most best explanation is:
                    1. rhythm
                    2. warm tires (the motor heats up, so why not the tires as well? )
                    3. my arthritic trigger finger needs to loosen up before I can run consistent laps

                    # 1 and #2 also make sense to me as the same thing happens with all of my 4 grandsons (ages 5 to 11).
                    Lap times lower for each of the first 4 or 5 laps, then level off with an occasional "fast" lap.
                    I use a DS200 lap counter/timer.

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