WRC Tech: Arctic Rally aero and stability struggles

Arctic Rally Finland offered a mouth-watering challenge for every car and crew in the World Rally Championship. Hyundai upset the odds to snatch the team’s maiden win in Finland beating Toyota’s Jyvaskyla-built Yaris WRC.

Rally Insight’s technical analysis of WRC’s Arctic adventure hints at how Ott Tanak and Hyundai managed their perfect comeback from a miserable Rally Monte-Carlo.

After being tipped to be the fastest-ever world championship rally, Tanak’s Arctic average of 121 kph fell shy of Kris Meeke’s 126 kph record from Rally Finland five years ago.

The Arctic’s stereotypically Finnish sections of fast-wide tracks were offset by narrow, back-and-forth corners which demanded completely different car characteristics.

Demanding stages were complemented with new studded Pirelli tyres while below-zero temperatures forced teams to think of the effects of ice build-up on the many aerodynamic devices displayed on a modern World Rally Car.

Hyundai introduces complex dive plane

A multi-element upper dive plane was integrated into the Hyundai i20 WRC for Rally Monte-Carlo.

I didn’t cover this in Rally Insight’s previous review of Hyundai’s aerodynamic upgrades but as Hyundai triumphed in Lapland it is only fair to point out how this intricate upgrade improves the i20’s aerodynamic package.

The image above shows that there are now three slots in Hyundai’s upper dive plane rather than being one continuous piece. 

Both upper and lower dive planes generate front-end downforce and direct airflow around the side of the chassis.

The engineering challenge is to generate as much downforce as possible without creating a turbulent flow of air behind.

The slots in Hyundai’s new upper dive plane bleed some air from the low-pressure, underside to the high-pressure side which reduces the risk of airflow separation on the underside of the dive plane.

Hyundai’s new design reduces drag and maintains an efficient, streamlined airflow.

The intricate design brings WRC aerodynamics to a new level with such delicacy previously considered too much of a damage risk in rallying.

Hyundai has taken the risk and with its i20 trumping the Toyota Yaris for front-end grip on Arctic Rally Finland, its recent aerodynamic investment is paying off.

Engine bay blanking

Last weekend, teams used additional blanking plates on the front grill of the World Rally Cars as well as adding covers to the exit vents further along the bonnet.

These plates help protect the engine bay from snow and ice as well as maintaining optimal temperatures around the engine.

The cooler Arctic temperatures and higher average speeds meant less area was required for engine cooling. The blanking plates in front of the engine bay also allowed teams to cover part of the bonnet vents.

These changes also have the potential to improve airflow around the grill and bonnet with air encouraged around the car rather than entering the less efficient engine bay.

Brake ducts

The cooler temperatures also allowed teams to shut off brake duct inlets. The images below compare Hyundai’s inlet on Rally Monte-Carlo and Arctic Rally Finland.

Brake ducts are usually required to encourage airflow around brake components to avoid overheating and brake fade.

Closing off the brake duct inlets improves aerodynamic performance as well as removing the risk of ice build-up within the ducts.

With the inlets closed off the airflow travels smoothly along the bodywork in streamlines rather than being forced into a turbulent high-pressure area within the wheel arches.

A streamlined airflow is even more important when it comes to the high-speed stages witnessed on Arctic Rally Finland as it reduces drag and encourages higher top speeds.

Arch vents

Like the inlets, the WRC teams also blocked off the wheel arch outlets to reduce ice build-up which would consequently add weight to the car.

How the vents were blocked varied from car to car. And in many cases, the rear arches vents were knocked off the car following collisions with the Arctic’s endless snowbanks.

The original purpose of the vents is to remove air from the high-pressure wheel arch with vanes and louvres directing the airflow into desirable areas behind the car.

With arch inlets blocked off in the Arctic there was less air to remove from the wheel arches and the complex louvres within the wheel arch vents were likely to be blocked with snow and ice anyway.

Mudflaps were also added to stop ice collecting on the bodywork. Having a smooth surface inside the wheel arch made it much easier for crews to remove ice, snow, and gravel before the start of each stage.

Sub-optimal set-ups

In Toyota’s pre-event press release, Team Principal Jari-Matti Latvala outlined the importance of high-speed stability on Arctic Rally Finland.

“What’s typical in Lapland are very long, fast corners where you can lose a lot of time if you’re not feeling confident,” explained Latvala. “So the stability of the car is very important.”

Toyota’s knowledge of Finnish stages combined with Rovanpera’s Finnish flair pegged them as Arctic Rally favourites, only for Latvala’s pre-event prediction to come to fruition.

“In the second stage,” Rovanpera remarked on Friday evening, “I could already see in the beginning that the set-up we had was not optimal for the conditions in the second pass with a lot of gravel coming through, and I was having a lot of understeer.”

Rovanpera’s understeering issues persisted on Saturday morning before a midday set-up change finally stablised his Yaris’s handling.

What was going so wrong?

While Toyota remained the car to beat on Arctic’s fastest stages: Kaihuavaara and Aittajarvi; Rovanpera was struggling to take Arctic’s longer corners in one sweeping slide.

It was a car balance issue also experienced by WRC 2 runner Andreas Mikkelsen.

As Rovanpera flicked his Yaris into the long corners, his powerslide gradually turned into understeer. Rather than seeing the exiting apex of the corner, he was pointing towards the ever-closing snowbank on the far side of the corner.

Instead of controlling his cornering with the throttle, Rovanpera was having to reach for the handbrake and realign his slide which disrupted all the forward momentum he had built up.

Tanak, on the other hand, seemed to have a more tail-happy i20 which had no issue powering through the long corners. The only downside for Hyundai was the continuous rear arch damage caused by regular contact with snowbanks.

An interesting reason for Toyota’s mid-corner understeer ironically could come from its impressive high-speed performance.

If the Yaris was set up for the fastest of Finnish roads then a stable rear-end was a desirable characteristic to have. Consequently, through slightly slower, longer corners the extra rear-end grip counteracted powerslides, giving Rovanpera the frustrating understeer feeling.

Tanak was having no trouble rotating his i20 as its back-end twitched threateningly towards the exiting snowbank.

Springs, anti-roll bars, differential settings, and aerodynamic features all play their part in the stability of a World Rally Car. It’s impossible to single out one particular aspect as it comes down to the front-rear balance of each area.

However, Hyundai’s recent front-end aerodynamic upgrades will have given it a headstart when seeking front-end grip that is crucial to beat that horrible understeer sensation.

Tyre wear

The potential for tyre wear was overlooked coming into Arctic Rally Finland as most WRC fans expected perfect frozen bases for the snow-covered stages.

Although I am sure Hyundai, M-Sport, and Toyota realised from pre-event tests that this was something to be aware of as 50-plus rally cars ripped up the first pass of each stage.

As gravel protruded through the snow and ice, sparks started to fly from Pirelli’s studded tyres. The extent of degradation shocked the leading crews on Friday night’s Sarriojarvi stage.

The front tyres were dead coming into the final sections of the 31-kilometre stage. The cars were visibly struggling with understeer and as drivers responded with more steering lock application it only made the wear-rate worse.

Two three-stage loops on Saturday demanded the same tyre management from crews. Again Tanak seemed to have it mastered as he extended his lead to over 20 seconds.

The Estonian described his car’s handling as “very nice” which many of his rivals could only dream of. One reason for Hyundai and Tanak’s perfect tyre management may well have been how differently their car was set up to Toyotas.

For example, Rovanpera’s understeer issues would have put even more pressure on his front tyres – front tyres that were already wearing much faster than the rear tyres.

If you think about it, the front tyres are taking the vast majority of load through braking and cornering. This is where most tyre and stud wear occurs.

So when drivers fight with understeer through a corner they are loading the front of the car for longer through the corner rather than enjoying a nice four-wheel powerslide.

It all comes back to the importance of balance as explained in the previous section. A well-balanced car will give the driver confidence to push, it will maintain forward momentum, and in-turn will prove more efficient when managing tyre wear.

In the end, with Toyota and Hyundai’s World Rally Cars an equal performance match, Arctic Rally Finland was won by Andrea Adamo’s squad perfecting a set-up that gave Tanak the confidence to push through every bend he faced around Rovaniemi.

Next up, it’s the asphalt bends of Rally Croatia which will provide a polar opposite technical challenge for rallying’s best.