Indianapolis vs Sugo: Does the Road Course Actually Have a Point?

You may have noticed that around here we tend to look at circuits somewhat differently from a simple “venue” column in the results sheet. If you have not, we shall now attempt to explain.

Let us be perfectly clear. Your Chief Pest - our less-than-respectful name for the editor-in-chief – can’t stand the Indianapolis road course - or, for that matter, most other modern contraptions belonging to that peculiar subspecies of circuit where somebody takes an oval and decides to coil an “infield” road course inside it. In the overwhelming majority of cases these things make about as much sense as a petrol generator with a built-in LED flashlight. And Indy, being the most heavily promoted specimen, is the most gloriously swollen example of the breed.

The brilliant counter-example is Sugo. A thoroughly authentic Japanese circuit, unlike either Fuji or Suzuka. And not because it lacks a mile-long straight or a self-crossing layout. The reason is simpler: it is as natural as the forest, fog and mountains surrounding it.

Why bring this up?

Because on Sunday IMSA will hold the penultimate round of its season on that thoroughly detestable Indianapolis road course, while Super GT heads to Sugo for Round 6. IMSA has 44 cars from four classes entered on 3.925 km of circuit; Sugo gets 14 GT500s and 29 GT300s on 3.586 km. So the average “population density” is actually higher in Japan: roughly 83 metres of circuit per car against 89 at Indianapolis. Obviously the cars are not spaced at equal intervals, but the order of magnitude tells us enough about the traffic problem.

This does not make the Indy road course any more likeable.

The big Speedway opened in 1909. The modern road course only appeared ahead of the 2000 United States Grand Prix: the Formula 1 deal was agreed in 1998, after which a new section was built inside the existing legendary facility. The current 3.925 km, 14-corner configuration came after another redesign in 2014. There is, admittedly, one historical wrinkle: the original Speedway plans did include an internal road circuit, but the idea was abandoned almost immediately, and there is no meaningful design lineage between that concept and the 2000 layout.

Aha, you say. And you would be right. If you mean Daytona.

The Daytona comparison simply does not work. Daytona International Speedway opened in 1959 already as a complex incorporating a road course. Bill France deliberately included it because he wanted international sports-car racing there; in 1962 it hosted the first three-hour Daytona Continental, the ancestor of today’s 24 Hours of Daytona. The oval and the road course were parts of the same concept from the outset, and together formed a vicious test of maximum speed, precision on the banking and sheer endurance through the cumulative number of corners.

Indy is the reverse. Ninety years later somebody had to bolt an attachment for an entirely different discipline onto a legendary name.

Phew. Let’s try to remove the emotion from this and approach it logically. Forget where the place came from and look only at the physics. Is the resulting circuit really quite as pointless as it seems?

Not entirely.

Two straights on a billiard table

The current “Euro-napolis” has 14 corners, a front straight of roughly 875 metres and a back straight of about 763 metres. The circuit is almost flat. The front straight ends in a major braking event into Turn 1; after the infield section the cars accelerate through the quick Turns 5–6 onto the back straight, hit another major braking zone, negotiate another internal section and return to a comparatively long acceleration zone.

When the present layout was created in 2014, the organisers openly stated that one of the aims was to provide more braking zones and more overtaking opportunities. Spectacle, shame on it, simply refused to harness itself to this silly contraption of its own accord.

So the impression that somebody “just wound a road course around inside the oval because there had to be one” did not appear from nowhere. The terrain did not tell the architect where the asphalt should go. The asphalt was arranged so that straights, braking zones and corners could be fitted into an existing facility.

Now let’s assume an improbable scenario. Suppose the audience is genuinely interested in what all this does to the engineering. That turns out to be rather more specific than the aesthetic peculiarities of those who actually enjoy this road course.

Euro-napolis separates the lap very sharply into longitudinal and lateral modes. First the car needs low drag and good acceleration. Then it needs to stop efficiently. Then it must turn at comparatively low speed, where aerodynamic load has already fallen substantially. Then it needs traction off the corner - after which the problem becomes drag all over again.

That creates a very specific setup problem. Additional downforce helps through the fast Turns 5–6 and several medium-speed corners, but much of the slow infield section cannot exploit it fully because aerodynamic force increases approximately with the square of speed. Double the speed and you get roughly four times the aerodynamic load.

And the power required to overcome drag rises with the cube of speed. So additional wing angle has to be paid for rather dearly on the two long straights. And much of that payment is fairly pointless, because in a slow corner a large share of the work is still being done by the tyres.

Sugo mixes everything together

Sugo does precisely the opposite. The circuit is shorter - Super GT uses the 3.586 km configuration - but the elevation difference is 69.83 metres, maximum longitudinal gradient reaches 10%, and the track is only 10-12.5 metres wide. Between corners the car is almost constantly climbing or descending.

Here you can no longer sort the car’s operating states neatly into labelled boxes marked “braking”, “cornering” and “acceleration”.

After Turn 1 the car descends. After the hairpin it begins climbing through the chicane. Rainbow feeds onto the downhill back straight, at the end of which the driver has to brake for Umanose. Then come the fast SP-In and SP-Out. The final corner begins downhill and ends with the car accelerating uphill onto the start-finish straight. Even Sugo’s own circuit guide makes a point of the constant changes in gradient.

On a flat circuit, vertical tyre load changes mainly because of aerodynamics and the car’s own dynamics: braking creates pitch, acceleration transfers load rearward, cornering creates roll. At Sugo, the vertical curvature of the road itself joins the argument.

Over a crest, normal load decreases. In a compression it increases. For aerodynamically loaded GT500s and JAF-GT300 silhouettes - and to a much smaller extent conventional GT3 machinery - that means the mechanical tyre load and the position of the aerodynamic platform are changing at the same time.

Compress the suspension and ride height changes. Unload the car over a crest and the front and rear ride heights change again. With them changes the balance of the floor and diffuser.

In other words, the circuit profile itself interferes directly with the car’s aerodynamic map. Indianapolis does not indulge in that sort of behaviour.

Ten percent - how much horsepower is that?

There is a simpler and more visual piece of physics here, one any sixth-former could explain. Well, in the chief pest’s day they could, anyway.

On a gradient, a component of the vehicle’s weight acts along the road:

 

At a 10% gradient:

tan() = 0.1

so:

g sin() ≈ 0.98 m/s²

which is very nearly 0.1 g.

Naturally, Sugo only reaches 10% on particular sections. But the number gives us the scale of the effect. Take a hypothetical one-tonne car climbing a 10% gradient at 200 km/h. The climb alone - before we even include all that fashionable aerodynamic drag - requires roughly:

P = m g v sin() ≈ 55 kW

In other words, the hill is taking away about 75 horsepower per tonne at 200 km/h.

And do not forget that the effect works the other way too. Not in the sense that those horses climb politely back into the cylinders on the downhill, obviously.

The car accelerates down towards Umanose and then has to get rid of that speed. Under braking it is dealing not only with the kinetic energy accumulated under engine power, but with the contribution of gravity during the descent. For identical cars and tyres, the braking distance downhill will therefore be longer than it would be on level ground.

Indianapolis has almost none of these corrections. Its braking zones are much closer to the sort of conditions in which one might quote clean, repeatable numbers: speed, drag, downforce, tyre grip, braking capability, and energy recovery in the LMDh cars.

At Sugo, go on - try working out whether sacrificing downforce for straight-line speed is even worthwhile when gravity itself comes along asking to borrow a substantial share of the available power. Then load the rear wing up instead, crest the rise onto the start straight, and bang - there is the air wall waiting to punch you in the face.

So no, it is not entirely straightforward.

The tyres get different jobs too

On the Indy road course, a tyre goes through a fairly intelligible cycle. Large longitudinal load under braking. Corner. Large longitudinal load again under acceleration. The front axle has to remain stable under heavy braking; the rear has to survive the traction demand from slow exits.

The LMDh cars make this rather “special”. The large braking zones provide the hybrid system with convenient and repeatable windows for energy recovery. At the same time, engineers have to blend mechanical and regenerative braking so that variations in available electrical recovery do not alter pedal behaviour and vehicle balance from lap to lap.

At Sugo, the boundaries between operating modes disappear into the fog that regularly hangs over the circuit.

Braking may begin on one gradient, the corner may continue on another, and acceleration can start while the car is already climbing. Through the fast SP-In and SP-Out, most of the tyre load remains lateral; in the final corner longitudinal demand is gradually added to it, while the car first descends and then climbs.

At some point the tyre must surely cry out: “What exactly are you people doing to me?”

This is precisely where Max Verstappen’s Madrid lectures on combined use of the friction ellipse might finally come in handy.

Add aerodynamic load changing with the square of speed, plus the dynamic vertical load imposed by the road profile, and it becomes obvious that one set of tyres sees a much less repeatable sequence of operating states over a lap. By the first few kilometres it is probably already dreaming of retirement rather than whatever this is.

Now it becomes clearer why Sugo separates cars not merely by peak coefficient of friction, but by the width of the tyre’s useful operating window. And in Super GT that is particularly interesting because the tyre war is - somehow - still alive.

Then the slow cars arrive

Indy gives the leader several places where time lost behind a slower car can be recovered fairly quickly. Both long straights end in heavy braking zones. If an LMDh catches a GT3 at the right moment, the difference in longitudinal performance allows the pass to be completed relatively cheaply. Catch one before the internal sequence of corners and you wait.

At Sugo, catching a GT300 at the wrong moment can ruin an entire sequence of corners. Alter the entry and you lose the exit. Lose the exit and you fail to carry the required speed into the next section.

Because the track is narrow and the terrain restricts the available lines, there is less scope to construct an alternative trajectory. Catching a slower car before the SP section or the final corner is particularly expensive because the lost speed propagates further along the lap, onto the start-finish straight itself - where gravity is already sitting in the bushes with a sack, collecting tolls.

Traffic at Indianapolis is therefore fairly “digital”: pass the car, forget about it.

At Sugo you can get a persistent analogue noise from the disturbance to your lap time, to the point where a driver might feel like pulling over, having a coffee, considering what precisely has gone wrong, and calming down by contemplating the scenery so attractively arranged around the circuit.

So does the Indy road course actually have a point?

As a circuit in its own right, the chief pest still does not understand it in the way he understands Sugo, Knockhill or the frankly phenomenal Road Atlanta. At those places the geometry grows out of the terrain. You cannot alter one corner without altering the approach to the next, the road profile, the braking zone and the following acceleration.

Indianapolis could quite happily have been drawn differently. And indeed it has been drawn differently. Even IMSA itself, in a post-race article in 2025, explicitly described the road course as artificial by nature - just short of calling it synthetic - and contrasted it with the elevation-rich Laguna Seca, Road Atlanta, Road America, VIR and Watkins Glen.

But synthetic does not mean physically meaningless. Euro-napolis does have a specific engineering speciality.

It is a circuit from which elevation has been almost completely removed, leaving drag, longitudinal acceleration, braking, low-speed traction, kerb behaviour and a handful of corners in which aerodynamic load still matters. That makes it rather good at separating cars according to longitudinal efficiency and the quality of the basic compromise between downforce and drag.

Sugo gives us the opposite problem.

There it is almost impossible to isolate a single quality of the car. Power interferes with climbing. Braking with descending. Suspension with aerodynamics. Aerodynamics with tyres. A mistake at the entry to one corner carries through the exit and into the next section. There is nowhere to press “Restart” button!

If you sit through the broadcasts wearing a laboratory coat, Indy is therefore particularly useful for separating braking, minimum speeds, acceleration and top speed. If one LMDh gains time in the corners but consistently loses it on both long acceleration zones, the reason should reveal itself relatively cleanly.

And that makes Indy one of the better places to continue our investigation into the Balance of Performance: separating a power/drag advantage from a downforce advantage should be easier here than on most circuits in the calendar.

(Oh dear. We may have said too much.)

At Sugo - laboratory coat still on - it makes more sense to study linked sections rather than individual corners: Turns 1–4, chicane–Rainbow, braking from the back straight into Umanose, SP-In–SP-Out, and the entire final corner together with its uphill exit. There, an advantage in a sector may appear somewhere quite different from the place where the car actually earned it.

And so the Indy road course finally receives at least one justification. Not as “another legendary Indianapolis circuit” - historically Daytona is much more honest in that respect. But as an almost deliberately simplified test rig for the longitudinal dynamics of a racing car.

Sugo, on the same weekend, provides the opposite case: there are so many interacting variables that it is difficult even to decide which knot in the causal tangle of high-level vehicle dynamics should be pulled first.

But tell us honestly: how many people still watch motor racing as a full-scale engineering experiment with an absurd number of variables?

Truth be told, even the chief pest does not always bother. And he will not be watching the Indianapolis road race at all, even if there is engineering value in it. Because he still cannot stand the place.

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