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.Suppose we continued driving all the way around the corner at constant speed and then accelerated out the exit chute at 0.5 g? This is the dummy line.We won't really drive this line after the apex, but discuss it nonetheless to provide a reference time.It's very easy to compute and provides a foundational intuition for the more advanced exit computation to follow in the next instalment:ExitTotal Timespeedtime(sec) Time for from TimeCombinedInscribed (sec)inentrance chuteinpost-apexCorner up to cornerand(mph) exit Combined time andRadiustheafter complete @ g/2 chute segment exit-chute(ft)apex apexcorneraccel (sec)timetime150 11.8720.000 11.872109.091 5.67017.541 5.670152 10.9120.860 11.773107.857 5.52817.301 6.388154 10.5441.209 11.754107.422 5.46017.213 6.669155 10.4011.348 11.750107.260 5.43017.180 6.779160 9.8721.88111.753106.697 5.30817.061 7.189170 9.2082.60011.808106.101 5.11616.924 7.716180 8.7623.12611.888105.806 4.95516.844 8.082190 8.4243.55611.980105.666 4.81316.792 8.369200 8.1503.92712.077105.627 4.68216.760 8.609So, we see that, driving the dummy line, the widest line yields the slowest time from the entrance up through the complete semicircle, but the quickest overall time when the exit chute is included.The widest line has lower (better) times than the tightest line in• the entry straight by about half a second, because h is large and the entry straight is shorter for wider circles• in the braking zone by about three tenths because the cornering speed is higher and less braking is needed• and in the exit chute by almost a second, again because is h large and the exit chute is thereby shorterThe widest line has higher (worse) times by about a second in the circle itself because the wider circle is also longer.When the balances are all added up, the widest line is about eight tenths quicker than the tightest line, but it's all because of the effects of thecorner on the straights before and after.Recall once again that the dummy line is not a line we would actually drive after the apex.But, with that as a framework, we're in position to introduce the nextimprovement.Everything we do from here on improves just the post-apex portion of the 79corner and the exit chute.We will actually drive the dummy line up to the apex.So, from this point on, we need only look at the last column in the table above, where we are shocked to see that there are almost three seconds' spread from the slowest to the quickest way out.A good deal of this ought to be available for improvement byaccelerating and unwinding.80Physics of Racing,Part 18: "Slow In, Fast Out!" or, Advanced RacingLine, ContinuedBrian Beckman, PhD©Copyright August 2000In the previous instalment, we did exact calculations for a dummy line down a 650-foot entry straight, a 180-degree left-hander, and a 650-foot exit chute.Cornering radii vary from 150 feet to 200 feet, and the track is 100 feet wide all the way around.This dummy line carries constant speed around the entire left-hander.We did thosecalculations to provide reference times to compare against this month's moresophisticated calculations, in which we unwind the steering wheel and accelerate at the same time.The baseline times for the dummy line over the whole course, as a function of cornering radius, are in the second-to-last column of the following table:TotalExittimeTimeTime forspeedCombinedInscribed (sec) (sec) in entrancefromTimepost-apexCornerup to cornerandchute in exit Combined time andRadiustheaftercomplete (mph) @ chute segmentexit-chute(ft)apexapexcornerg/2 accel (sec)timetime150 11.8720.000 11.872 109.0915.67017.541 5.670152 10.9120.860 11.773 107.8575.52817.301 6.388154 10.5441.209 11.754 107.4225.46017.213 6.669155 10.4011.348 11.750 107.2605.43017.180 6.779160 9.8721.88111.753106.6975.30817.061 7.189170 9.2082.60011.808106.1015.11616.924 7.716180 8.7623.12611.888105.8064.95516.844 8.082190 8.4243.55611.980105.6664.81316.792 8.369200 8.1503.92712.077105.6274
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