Marshall Pruett’s Racing Tech Mailbag for March 6

First off, I want to say thank you for doing this mailbag. Being fascinated with car technology is what led me to study engineering, and it can be difficult to find straight answers on racing technology.

I wanted to ask about the third spring/damper system used in (at least) F1 and IndyCar, as I still don't fully understand it. I understand a spring/mass/damper system, and I understand how roll bars work, but I still don't get third springs.

Aaron Foster, West Lafayette, IN

MP: Thanks for the kind words, Aaron, but don’t thank me too quickly. I might disappoint you before this first one is done…

The conventional damper system with two shocks up front and two in the back worked just fine until downforce started having a major influence on performance. With air pushing cars lower and lower as they go faster and make more downforce, teams used the one option they had to combat the problem by stiffening the suspension with heavy coilover spring rates.

The big, stiff springs kept the downforce cars from bottoming out and also helped to maintain the correct ride heights to make optimal downforce– especially in the fast corners. But in the slow corners, those heavy springs provide very little suspension movement, which hurts mechanical grip. If you’ve ridden in a car that’s so stiff it rattles your teeth over every bump, this is essentially what teams had to do to keep from burying the floor of their car into the racing surface at high speeds.

Think of Long Beach and the hairpin leading onto the straight. With big springs on an Indy car or a prototype, that car is going to struggle for grip turning in at the hairpin and again when leaving the corner as the driver tries to put the power down. It won’t turn and it will light up the rear tires when you touch the throttle.

I’m exaggerating, but in the hairpin, you want the thing to roll around like an old Cadillac, yet the big springs make it handle more like a tank. Then, while accelerating down Shoreline Drive, a massive amount of downforce is piled onto the car, and in that situation, the big springs keep the ride height – and the underside of the car – low and under control.

Engineers want the best of both worlds for their drivers – supple handling in the slow corners without giving up solid and stable handling in the fast stuff – that will produce the fastest lap time. The first evolution came with limiting shock travel, but it had its drawbacks.

Hard plastic shims cut to various thicknesses (known as packers), along with softer bump rubbers, were attached to the exposed portion of the shock’s shaft to limit ride height once it was compressed a certain amount. It allowed softer springs to be used, but once the shocks were compressed enough to hit the shims and/or bump rubbers and could compress no farther, the suspension went solid. Crashing over curbs, hard landings and other big movements could mean all of the cornering forces were being managed by the tire sidewalls instead of the shocks and springs. That might work for karts, but not for heavy cars with gobs of downforce.

The solution was the third spring system, which attaches through links on the bell cranks that connect the suspension pushrods to the shocks, and acts as a friendlier ride height limiter.

Instead of using the main coilover springs to control ride height or a mix of springs and packers, the third spring system took over that responsibility, allowing teams to use softer coilovers, which improves mechanical grip.

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As you can see in the photos above, teams have their own take on the best method – for some it’s a small spring with packers and bump rubbers, while others go for a series of packers and bump rubbers. Even hydraulic ride height control is used in some series.

It’s all done to keep the front and back of the car from going below the engineer’s desired height, and with the t-swivel in place, the inter-linked suspension is allowed to work independently.

Engineers will call for adjustments to the shim stack on the third spring as they make ride height adjustments, leading mechanics to pick from bins to find the exact thickness needed.

Some teams rely on third springs more than others, and at some tracks, they may only be used up front. Running without them is also an option. And stiffer springs are still used at certain tracks…

I don’t mean to be vague, but the third spring system isn’t a magic cure-all. It works great at tracks where low speed mechanical grip is needed and high speed cornering is also crucial. Like the rest of the suspension and aerodynamic tuning options, it’s an important tool, but not the only one for teams to consider.

Curious as to your thoughts regarding relative safety of carbon vs. tubeframe cars in IMSA. Clearly, Memo Gidley's accident at Daytona was huge, but hopefully educational for the series and constructors. I think we all want spectacular and fast cars, but safety must always come first.

Randy Brink

Has the use of direct injection had a bigger impact on power and fuel economy figures as well as drive-ability in prototypes or GTE cars and what are the percentage gains for mpg and horsepower? Additionally, are the gains in GTE big enough to change how teams will plan to run a 12- or 24-hour race?

Patrick Palony, Robbinsdale, MN currently living in Ames, IA

I’ll borrow a piece I recently wrote for RACER’s GM Special Edition to answer the rest of the question that serves as a bit of an explainer and also delves into the merits of DI:

Direct-injection is a style of feeding fuel directly into the combustion chamber, which differs from port-injection where fuel is sprayed into the intake where it meets with the air and then follows its way into the combustion chamber.

DI sends fuel into each cylinder through a high-pressure solenoid valve, a fuel injector, and typically, this is done at incredibly high pressure pressures – about 3,500 psi. When you read about the benefits of DI, it’s somewhat simplified and most say it just gives better combustion efficiency. But really what happens is that injecting that fuel right into cylinder allows you to make the engine more efficient by increasing the compression ratio, which comes from cooling the air charge.

It takes energy to boil water on your stovetop and it's very similar to DI where that energy comes from the air. So by using the fuel in the cylinder to decrease the air temperature, it increases the density of the charge in cylinder. The more air you have in cylinder, the more fuel you can add, and you can make more power. It allows you to be more aggressive with spark timing or increase the compression ratio to increase the expansion efficiency of the engine.

That all translates typically into improved performance, peak torque and peak power gains.

I am missing something about how the whole shaker rig process works. A car is put on the shaker rig to work on the set up for, say, Sebring. As I understand it, the shaker rig emulates a lap around the track using data from past years (bumps, chassis roll, ride height changes due to aero downforce, etc.). The engineers no doubt try various combinations of ride height, springs, damper valving, bars (if the car has them), etc. to optimize the set up for this particular track. My question is this: how do the engineers know if the changes they have made to the car, while on the shaker rig, work or don't work? I assume that shock traces and such have something to do with it, but it seems to me it must be all guesswork until the car is actually on-track.

Richard, Flower Mound, Texas 

Engineers work on various damper builds, springing packages and a host of other handling-related items, but as you pointed out, until those items are tested in the real world by the driver(s) in mind, it’s hard to have complete confidence all that work in the lab will translate into speed and happiness. The odds improve with experience, but there’s still no guarantee.

I asked a race-winning friend and engineer with lots of shaker rig experience to take a deeper dive into the process for you:

Richard – good question and a million dollar one at that! You are correct in the assumption of a rig simulating a lap around the track. Also very true in the essence of rig work is very challenging to get exact answers. This is where it becomes difficult. In order to take guesswork out, you have to pinpoint certain parameters which correlate a rig to a track – damper velocities, load variations, and accelerations to name a few. It takes a significant amount of time to get the correlations right, and there will be false starts as you have stated. Look at it this way: a rig could be a good place to explore theories or trends rather than an outright “bolt this on the car and you will go faster” deal. It will allow you to answer questions of: Why does a driver like this particular damper? Why does he think this damper has more grip but less support?

When youTHINK you have answered the question, it allows you to further develop the topic. Then you are able to go back to the racetrack and put the final touches on the theory. The rig is where you gain an understanding of a theory, and race track is where you either prove or disprove the theory. When approaching a rig you have to have a very detailed, goal-driven test plan. All engineers want more grip you but you have to pinpoint exactly how you are going to achieve this and stick to it.

I have heard that all Indy cars start off the same, but can have some modifications made by the teams. I am curious what those changes are, as I have been unable to spot any differences.

Tom Phillips

When I got to college I was able to experience the 12 Hours of Sebring for myself and I'm looking forward to my 11th Sebring this year. As I learned more about endurance racing the technology and the technology transfer to production vehicles interested me.

For both Le Mans and in Formula 1, the fuel usage is going to play a critical role in who wins the races. In Formula 1, there is a set amount of fuel to be used for the entirety of the race. In the Le Mans/ACO rule, there is a specified amount of energy that is allowed to be used per Le Mans lap. Obviously in Formula 1 they can use as much fuel per lap as they want, but will pay for it later in the race. For the WEC races, they have to make any excessive fuel usage in a lap up within the next two laps. Does the fuel limit change with the track or do the cars get the same amount of energy to use per lap regardless of the track? And what do you think we can expect in terms of tactics with this new rule?

DM, Atlanta, GA

The ACO has gone in the opposite direction, placing limits on the amount of fuel than can be burned each lap. If that sounds like rules that skew the world’s biggest sports car series towards meeting self-imposed fuel standards instead of allowing balls-out racing, you’re interpreting the rules the same way I see them.

Le Mans is obviously the Holy Grail event for the ACO, and the fuel usage/lap for the rest of the WEC rounds is keyed off of the 8.5-mile La Sarthe circuit. Fuel types and fuel tank capacities vary, so the ACO came up with a formula that says: Le Mans Fuel * track distance / Le Mans track distance * 1.11, meaning teams will have 11% more fuel use allowed per kilometer at the other tracks.

Will this new fuel economy formula affect tactics? Absolutely, and that’s not a good thing. I wrote shortly after Audi’s new R18 hybrid began testing at Sebring that the team was working on “lifting strategies” to minimize fuel use each lap. If you want the simplified translation, the new rules have the most successful factory prototype team on the planet crafting a plan on when and where to have their drivers intentionally avoid accelerating each lap. We’ve gone from “who can get to the finish line fastest” to “who can get there at a reduced speed to avoid being penalized.” It’s ridiculous.

I asked a friend on another factory sports car team about how they plan on dealing with the new fuel rules, and it appears “lifting strategies” will not be limited to Audi: “This will lead to work on optimizing the engine mapping and strategies towards fuel efficiency rather than absolute performance.”

A few years ago, you posted a great Indy 500 tech update with lots of info on the shock/damper suppliers and packages the teams were using. What's the current lay of the land and who is running what?

Brett

I'm excited for the new Mailbag. To help get your creative & technical juices flowing, let's assume that IMSA appointed you "Sports Car Czar" just after announcing the sports car merger in 2012. You have complete control of the class structure for the 2014 United Sports Car Championship. What do you do, keeping in mind that the classes must make sense competitively and financially?

Kyle in Raleigh

My answer is fairly simple. Under IMSA sanctioning, sports car fans are treated to the mother of all twin-bill events. ALMS and Grand-Am go forward, no classes are axed, and where possible (Daytona, Sebring, Petit Le Mans), the two series run together earning points towards their respective classes and championships.

For the rest of the rounds, you get Saturday-Sunday sports car overload, and at some places (Long Beach and Detroit, for example), the ALMS runs solo at its SoCal date while Grand-Am does the same in the Motor City. It keeps the door open for European P1 teams to bring their cars and wow the crowds. It allows drivers, during tight economic times, to continue to earn in both series. It maintains the best attributes of both series while they continue to be divided by different types of cars.

You’re still faced with logistical issues like paddock space at the smaller tracks, but it’s not the first time two professional series have shared an event and run on different days. TV would also be an issue to sort out. I’d argue that with the demise of SPEED, North American sports car fans were never going to get the amount of desired airtime starting in 2014.

With IMSA and the ACO working on a single prototype spec for 2017, and provided the car is faster, more exciting than the current P2/DP regs allow and isn’t too expensive, combining P1/P2/DP into a single class would be a solid option in a few years.

PC is a great class for pro-am competitors and offers a chance for small business owners to make a few bucks, but if it meant increasing grid sizes, I’d rather see PC ditched and the single prototype class split into Pro and Am divisions like the ACO does with GTE. Keeping the gentlemen drivers engaged and interested in racing prototypes is vital – it has been for decades.

ALMS GT (GT Le Mans) doesn’t need to be touched, Rolex GT was a weird mix of cars that produced great racing and has been vastly improved with the new GT Daytona regulations that incorporate the former ALMS GTC class. If there’s one significant improvement to come from unifying the series, it’s GTD.

ALMS owners had more than a decade to switch to switch their allegiance Grand-Am, and the same is true for Grand-Am teams wanting to run in the ALMS. For the most part, it didn’t happen, which is telling. Going forward, in a few years, I think a combined series with what we have today – Prototype, PC, GTLM and GTD – could really take off and see new teams created to compete in the series.

How adjustable are the Indy car diffs? What changes can teams and drivers make to them?

Fernando Diaz

If you have no clue how a differential works (and trust me, you aren’t alone), Chevy made this awesome film in the 1930s to explain the concept:

Of all the current IndyCar drivers, Schmidt Peterson Motorsports driver Simon Pagenaud talks the most about the importance of diff tuning, so I asked him to share his thoughts on the topic, a bit of what he likes and how it impacts what he feels from inside the cockpit:

To me, differentials are the baseline of your setup package, the foundation. For me, you have to pick your differential setup before you pick the rest of the setup. Basically, can pick your ramps, on the coast side you have a certain angle on the ramps, and then on the drive side, you can go for the same angles or something different. In addition to that, you have friction faces in the differential, and the more friction faces, the more locked up the diff is going to be. It all depends on the ramps. The more open the angle, the more free the car will be and the more wheelspin you’ll have on drive and the more oversteer on coast.

If the diff is very tight on coast, the rear is going to push the front – it feels like the diff is locked up, basically. And so when it’s free, the inside wheel has a greater difference in speed, so it helps rotating the car. That’s the basics. The biggest thing is that when you step into the car, pick the differential setting you like because it’s such a big balance changer. If you can’t feel what the diff is doing, you could go around all year long trying to tune the car with the dampers and springs and not really know why you can’t get the balance the way you want it. The issue might be the diff the whole time. There are little tricks you can use, which I won’t give away, that you can use to tell if the diff is too free into the corner or too free on power.

If you like understeer, you can have a very tight diff on entry to get that, but then that’s going to require a very free diff on power to rotate the car. And from my experience – my theory – is that this way of doing things spins the inside too much and hurts tire wear. I like to have something that’s very equal on coast and on drive. I want it to be predictable when I turn and when I get on power. And the diff settings can change at every track because of the grip levels, engine braking can influence your settings…there are many things that go into what you ask your mechanics to do to the diff to make it right for you.

Is there an update about IndyCar's development and feasibility of using steering dampers for the upcoming season?

Rob Peterson

Rob,

We are working with Dallara's help developing a prototype steering damper which, if successful, may be an option item for the teams to use to reduce steering kick back. As yet it’s too early to say when it will be introduced. First we have to finish it, test it, and then track test it before we consider its release. Hope this answers your question.

Are the 2014 F1 engine long blocks (sans KERS, turbos, ECU’s etc.) even a little close to the IndyCar engines so they may be used permitted in IndyCar if Mercedes, Renault and/or Ferrari choose to make them available?

Donald McElvain, Polson, Montana

Not a technical question, but, is there a "code of ethics" between teams when it comes to hiring engineers, mechanics, and the like? It seems we see technical people switching teams a dizzying amount of the time. I can’t see that being helpful as far as team spirit, continuity, etc. goes.

John Vecchi

As a bit of a sidebar, one area where ethics is often missing is when data and setup info departs with key employees. (I still have most of my setup sheets and data from every team I worked for, BTW.) I was at a test earlier this year, commented to one quick driver how another driver was blindingly fast on the day, and he fired back with, “He ******* should be, one of our engineers left and took all our setups to their team!” The practice has been going on for ages, and so far, I’ve yet to come across a team that would refuse info brought by a new hire into the program.