Contour Enthusiasts Group Archives Forums General Autocross and Open Track Speaking of hairpins...

Yesterday in Tallahassee, they had this 45' slalom leading into a wide open throttle mild turn forcing a shift to third (with my tiny tires) and leading to a single cone hairpin. Your natural momentum from the turn led to the left side but I thought I could get back to the right to have the advantage of driver weight in my favor doing the 180.

Well, I'm out working the corner with several others who had just completed a novice driver's school the day before. So now I was surrounded by experts who said I should go to the right instead. As it turned out, unbeknownst to me their is a gentle slope in the lot that is in effect banking. My question is it better to have the banking work for you coming out of the corner or going in?

I was in third so it is important to maintain speed as long as possible going in but that would mean an off camber turn on exit at the bottom of the slope. The compromise was to hug the cone fairly close, exploit the slope on braking and turn-in and then finish the turn on the opposite downward slope near the parking lot edge. I'm sure the nearby workers did not like that idea. Then decisions, decisions, should I shift to 1st. I did, but probably wrong answer given my new gearing caused by shorter tires.

Opinions. Do you normally take hairpins to the left given the option? Do you downshift to 1st.

The decision on where to take a pivot cone (that's what we call a single cone turn here in SoCal) depends on where the course goes after the pivot and what kind of car you're driving. If in your example above there was a long straight after the pivot then you are much better off maximizing corner exit speed. On the other hand, if there was another slow corner just after the pivot then you're better off extending the slalom stright by going fast into the pivot.

Other considerations:

1. Traction - if it looks like a first gear pivot then proper corner exit is much more important because traction wil be a problem.

2. Momentum - if your car is horsepower limited then carrying speed through the pivot is very important so a wider line maintaining your speed will usually result in a faster time.

Just the kind of info I'm looking for John C. I never know whether to go tight or swing wide. Momentum vs. distance. Swing wide: greater distance but also greater speed. Keep tight less distance,less time in turn, and get on with it. You see the formula boys doing the wide 180s and they certainly have ample power, but also ample grip. Then you see the classic go to the inside pass, followed by an immediate repass by the guy who stays wide, late apexes, and passes on the inside on subsequent straight. I guess it's six of one, half dozen of the other.

This one was made interesting by a very slight V in the pavement for water runnoff, with the single cone on the much larger left side of the V and a small counter slope on the right. So if you turned right from the left side of the cone it was hunky doory until you got all the way around where you were then on an off camber slope. I fixed that by trying to get over onto the other right side slope but that meant crossing the hump in between. Anyway thanks for info. Anybody else? I hate 180 tight turns. Tire and brake eaters.

Well put John. In a front wheel drive car, I tend to alter my line to avoid downshifting to first and try to carry more momentum.. The transaxle motion tends to make this downshift dificult at times and the ability to gain traction under acceleration in first gear is iffy with the FWD because of the weight transfer taking weight off the driving wheels.

Respectfully,

Andy Hohl

I guess we can use this post to begin an early SZ driver's school with multiple contributors. At the event I attended last weekend they took several typical autocross training venues from Saturday's novice school and assembled them into a Sunday course. After the slalom and 180 degree turn, they had a 100 degree left hand turn going from a wide unrestricted area into a narrow area. Thus you could pick your own line into the left hand turn but if you swung too wide, you would hit a wall of cones paralleling the subsequent very short straight.

This is a typical scenario for choosing a late apex. The single inner cone you are going to place your left door next to as you pass by is the apex point in this turn. You want as much of your turn completed prior to passing that point so that as you enter the constricted area you don't swing wide plowing through a row of cones with the right side of your car. In a late apex you wait to turn into the turn beyond the time you normally feel you should. It has been said that all men are early apexers. That is we tend to want to turn too soon. The result is a tendency to swing too wide at turn completion as you exit and accelerate. By waiting and completing the bulk of the turn early before the apex, you can straighten the car and accelerate sooner on turn exit.

In addition, the late apex sets you up properly for the right hand 90 degree turn that shortly follows because you don't want to swing too wide from the left hand turn and end up all the way against the right side of the track for the subsequent right. You have all seen the formula boys come out of the turn on one side and then drive across to the opposite side of the track for the next turn going the opposite way. It is the same way in autocross. You must set up on the outside and turn into the apex. Problem is many autocross turns are closer together than road course turns requiring even more concentration on getting the line right for the preceding turn in order to not screw up the subsequent one. Enough of my rambling. John C and SVTSTS, Dave, Mark, Vern, Hawaii etc....your turn.

Nobody else wants to play? OK, more of the blind leading the blind.

So you survived the late apex left hander leading into a narrow short chute. Now you are bearing down on a 80 degree right hand turn. Because of your late apex on the prior left turn you have time to set up for the coming right turn by swinging to your left along the edge of the short chute. You clip the apex with a little left foot trail-braking, staying on the gas.

Now you are approaching a 130 degree right turn into another narrow chute. Again, it calls for a late apex and there is plenty of room to the outside so you swing wide to set up for turn-in. You watched plenty of folks stay too tight and clip the inside cone or end up plowing through the ouside cones on turn exit.

After completing this turn there will be another left hand turn leading into the final curved "straight." At 60 mph you travel 88 ft/sec versus just 44 ft/sec at 30mph. So straight speed is extremely important to a fast time. Faster turn exit onto the straight pays off big.

Normally you would opt again for a late apex to allow you to straighten the car and accelerate early. But the course designer has been generous and allowed wide gates for the final gently curved straight. This means man can follow his natural inclination and apex a little earlier allowing a wider turn permitting harder acceleration to carry him out to the edge of the gate. It's a good thing, too, because the previous 130 degree turn just would not let you set up for this turn leaving you nearly hugging the inside row of cones as you approach the left hand turn apex.

So recap. Leading from a wide area into a narrow area means late apex...i.e. turn-in later completing most of your turn before the apex. On the other hand, a narrow chute leading into wide chute allows the luxury of a early apex. This allows turning acceleration to carry you out to the edge of the track. Generally, for most turns, late apex good, early apex bad.

I remain uncertain about the best way to do a hairpin turn. So last night I did some SWAG calculating.

Picture a single-cone 180 degree hairpin. Now think of three different radius turns going around that hairpin. The first is a 20' radius, about the limit of turning radius at any kind of speed...we'll say 20mph or 29.3 ft/second. The second is 40' radius, taken at say 30 mph or 44 ft/second. The third is 60' radius taken at 40 mph or 58.7 ft/second. Dong the 2 pie r thing gives you circumference, and the half circumference distances are, drum roll:

20'radius = 62.8' distance
40'radius = 125.5' distance
60'radius = 188.4' distance

Now we apply the AVERAGE SWAG speeds to each distance (realizing that there is trail-braking going in and acceleration coming out) and we get:

20' radius half-circle @ 20 mph/29.3ft/sec = 2.14 seconds

40' radius half-circle @ 30 mph/44 ft/sec = 2.85 seconds

60' radius half-circle @ 40 mph/58.7ft/sec = 3.2 seconds

But wait, the widest diameter half-circle requires a turn-in point 40 feet earlier than the smallest half-circle. Choosing a smaller diameter half-circle still means you must traverse that distance in a straight line. Braking takes less time than acceleration, so we add .8 seconds for braking that extra 40', and 1.3 seconds to accelerate that extra 40' coming out of the turn. Add .4 seconds to brake the extra 20' for the middle diameter half-circle and .6 seconds to accelerate the extra 20'.(Wish I could draw this for you).

Results:

20' radius half-cicle + straights in and out=
4.24 seconds

40' radius half-circle + straights in and out=
3.85 seconds

60' radius half-circle (at 40 mph)= 3.21 seconds
60' radius half-circle (at 36 mph)= 3.57 seconds

I know, it looks like the smallest half-circle is the slowest and biggest half-circle is the fastest. The unknowns are who would have the higher exit speeds at the same line in space coming out of the turn. After all you can accelerate much faster in a straight line, while the car in the largest diameter turn is cornering and accelerating.

In addition, I contend you can brake later going into the tight turn because the bulk of the distance during braking is at higher speed. At slower speeds you can brake over much less distance. In other words there is not a direct distance ratio braking from 60mph to 40 mph for the wide radius turn versus from 60 to 20 mph for the smallest turn. The extra time spent at 60mph/88feet per second before braking SAVES you mucho time. But no time to discuss that here. Errors in my logic???? Help???? Off to work.

EDIT: Look at Road and Track figures for 80-0 and 60-0 braking. Think they are linear in proportion to speed? Think again. If a car requires 130 feet to brake from 60 mph, you can count on adding another 100' for the extra 20 mph. I would like to see braking figures for 40 mph and 20 mph going to zero. They would definitely be much, much less. In addition you can't just stand on the brakes to slow from 60 to say 40. You will screw up the weight transfer. The time spent transitioning, (i.e. trail-braking) at less than max pedal is lengthy and a smaller proportion of overall braking from say 60 to 20mph than say 60 to 40 mph. I contend you could brake a fraction of a second later going to the lower speed in the scenarios above.