Optimum Drive: Paul Gerrard series (Pt. 3) Downforce, drag and grip

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What better way to highlight the upcoming release of a new book on driving than to have the author, Paul Gerrard, do a series of pieces and a podcast interview for FBC discussing some of the finer elements of driving? In a new series, we are calling Optimum Drive with Paul Gerrard, we will focus on some intriguing parts of Paul’s new book coming out this April. You can pre-order the book right here from Amazon. If you’re a fan of the art of driving, this book is a must-have and we are very honored to be working with Paul on this special series just for our readers/listeners.

Imagine the Wright brothers on their first flight, all the testing with kites and models had reassured them that lift was a real thing but testing a model is one thing climbing aboard an actual aircraft yourself for the first time, that’s a different level of believe altogether. It’s an amazing thing to realize that the idea of flipping the wing over to create downforce would take an additional 60 years to really stake its claim in motorsports.

Downforce & Drag

That tardiness to the party didn’t diminish the impact. It changed the sport forever, cars didn’t just need to be streamlined they also needed to make downforce and do it efficiently (there’s that word again). Downforce is not free, it comes with a negative attached called drag. Drag is aerodynamic friction or resistance, drag slows the car down as the downforce attempts to make it faster. The idea, obviously, is to have the downforce gain be greater than the loss from drag giving a net increase of speed around the track.

I say net increase because the downforce will lower the cars top speed on the straights, the net gain comes from it being faster everywhere else. It also increases at a square of the speed so the faster you go, the more downforce (and corresponding drag) you get. Generalizing a bit, measurable downforce starts being really noticeable at a bit under 100kph (62mph) and starts getting serious soon there after reaching the amazing “stick to the ceiling” numbers above 160kph (100mph) in top tier aero car.

Grip & Load

Downforce makes the car faster due to another relationship: grip and vertical load. This is of course directly describing the load sensitivity of tires. Everything about the setup and driving of the car is derived from understanding load sensitivity—more load, more grip. That’s why the drivers main job is dynamically and continually balancing that load as they drive and if the car produces downforce its invisible hand is also pushing down on the tires (through the car) as well.

Downforce adding load is really cool because it doesn’t add weight to the car, now this is kind of interesting to imagine. You might be sitting there thinking if adding load gives me more grip I should just strap manhole covers to the floor of the car and I’ll have more grip and not just when the car is going fast. I hate to be the bearer of bad news but it’s not the same due to the extra weight the car has to carry vs. downforce. Downforce is load, not weight and that means that when you brake, corner and accelerate the downforce doesn’t add mass to the car (like the manhole covers would) and that means downforce doesn’t add inertia or momentum like the weight does. Other than the associated drag it is just free grip.

The ideal then is maximum efficient downforce with the lightest car possible. Wait… I think I just described a Formula 1 car. Chuck in a 900hp power unit and you have then most capable land based G machine on the planet.

They could actually pull more G’s though and even though we shall probable see those 2004 lap records fall this year, the cars are still extraordinarily restricted, just like a 10,000+ HP Top Fuel dragster is restricted. It only seems like these sports are at the very limit of what can be technologically done but that is not even close to being true.

It is typically a balance of safety, budget and spectacle. This year’s considerable bump should produce more physically demanding racing which will test the driver’s fitness (as we talked about in Pt. 1) and the tire construction should allow the cars to be pushed (not babied) for their entire life. It is definitely a move in the right direction as long as the disparity between the teams has not gone the wrong way.

Why the 2017 regulations may work

The tires will actually play a crucial role in determining if the increased downforce of 2017’s rules package will be effective. If you’ve been watching the broadcasts for any amount of time you’ll have heard the word “graining” used by the teams, drivers and commentators. It is usually caused by pushing a tire that you can’t (or haven’t) got up to optimum temperature yet. Driving through understeer on a cold tire. The old tires where very susceptible to graining because Pirelli intentionally made the tires overly sensitive and delicate (at the request of the FIA) in a questionable effort to control disparity and improve the racing. These tires also grained in another situation that is very important to any hope of real racing, the ability to follow closely.

As soon as the cornering speeds get aerodynamic, the ability to follow closely is hugely effected by the wake of the car you are trying to follow. If their wake causes your front wing to lose downforce it makes your car understeer and when it understeers the tires are susceptible to graining. Graining basically sheers the rubber off the tire without the adhesion the tire needs to get into operating temperature range. That is why the tires in 2017 are not just bigger their compounding and construction will resist graining by being more tolerant of understeer.

The other way the FIA is trying to close the field up, besides tire improvements, is that they are actually adjusting the wake of the leading car. Race cars make downforce in two distinct ways; air going over the car and air going under it. Remember when we were talking about how the FIA restricts everything earlier(?), well one of the big adjustments they made in the rule book is the shape of the floor under the car, along with the ride height and the size/position of the wings, it’s another ratio they can play with. The air under the car (which exits the diffuser) leaves a relatively “clean” wake while the wings leave a relatively “dirty” wake.

In 2017 by increasing the diffuser size the teams will hopefully run less wing front and rear therefore even though they have increased cornering speeds considerably, the wake the following driver needs to drive through to pass or follow should be cleaner and provide more downforce to their front wings while the tires are now better at coping with potential graining.

Just like Orville and Wilber continuously refined their aerodynamics and adjusted lift to drag ratios depending on available power as their experience base grew, the FIA and the teams are furiously competing on the world’s stage that is Formula 1. Over the course of the Winter they have simulated and modeled countless combinations hoping to “out efficiency” the other guys. They have had their wind tunnels working 24/7 since the 2017 rules package was released and ran the cars on “shaker” rigs simulating every track on the calendar while the drivers drive every possible variant on the driving simulators. Just a little bit less efficiency in the aerodynamics can mean a losing season for the team especially if it is a fundamental flaw in the shape of a part of the car that cannot be altered once the car has been FIA crashed tested (for example).

If the culprits are little trim bits and pieces, then the season can be salvaged but if the package is fundamentally inefficient or unbalanced they are in trouble. Fortunately, they have at least unlocked the engine development which could help level the playing field (assuming Mercedes does not simply progress at the same rate).

Horsepower!

That brings up my last point: Horsepower is downforce. I am not talking about blown diffusers and the like, I am referring to the well proven fact that if you have more horsepower you can set the car to run with more downforce and drag. The straightaway speeds will be around the same but your braking cornering and accelerating will be improved as will relative tire wear…it is the sneaky and smart way to win races and championships.

Whether you are a fan of aero or not, there is no denying the influence it now has in any form of racing, now that we know the benefits of downforce no matter the rules, teams will shape the car (within those rules) to maximize the downforce to drag ratio and produce the optimally efficient car that basks in the winner’s circle at the end of the race.

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jakobusvdlSalvu BorgNegative CamberAre Buntz Recent comment authors

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Are Buntz
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Are Buntz

I hope he turns out to be correct about the lead car aero effect on the trailing car… I am still looking for full ground effect, no wings spec.

Negative Camber
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indeed. It’s been one of the more discussed issues with the regulation changes. Why dial in more mechanical grip but then undo that with more aero but as Paul’s ays above, perhaps that is not taking into account the new regulations concerning the under floor restrictions and maybe this will pan out…I hope it does.

Salvu Borg
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Salvu Borg

agree, I too hope he is correct about the aero effect of the leading car on the car following behind.

jakobusvdl
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jakobusvdl

Great article, lots of useful insight on how the 2017 regulation changes may affect the show. I hadn’t heard about the change in the balance of over wing and under floor air flow, or the understeer tolerant tyres.
Now, I need to read parts 1 and 2.
Great stuff Paul, much more of this please F1B!

jakobusvdl
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jakobusvdl

Back again, been through parts 1 and 2 now. The story is building well. 60 years between the wright brothers and the Lotus 47, we could never uninvent all thats known about aerodynamics but how do you envisage a modern Formula 1 series that didn’t use high down force would be like? What would top speeds be? Could they be made stable at super high speeds? I’d imagine the demands on tyres would change completely – high traction to enable up to 1000bhp and mega torque to be put onto the road, high strength to cope with the high speeds… Read more »