Tyres, not F-ducts, provided the talking point in the Canadian Grand Prix. Guest writer John Beamer reviews the technical developments in the last round.
At Montreal conventional wisdom was proven right. McLaren’s straight-line speed advantage, driven by a fully working F-duct and the Mercedes engine (worth up to 30bhp) allowed it to secure a one-two on the Gilles Villeneuve circuit.
Before the race weekend many believed F-duct efficiency would be the main technical talking point and specifically whether how effectively Red Bull adapted the device to its car.
In the event Red Bull didn’t even bring an F-duct to Montreal deeming that the downforce cost was too excessive for the small saving its wind tunnel figures were showing. And after FP1 one thing was abundantly clear – tyres were going to be talk of the paddock.
Why were tyres so important?
Remember Montreal 2008? If so you’ll recall the constant breaking up of the tarmac around the hairpin. Repairs had to made before the race despite which the cars continued to rip up the tarmac.
To prevent similar problems this year the organisers re-surfaced the track with finely-grained asphalt. Finer aggregate allows the bitumen to bond much more tightly, making it less likely to break up under the strong lateral forces of 96 F1 tyres every lap. This is a particular problem in Montreal because of the extreme temperature variations between winter and summer which loosens the surface.
To understand why this is an issue it’s important to know how tyres grip the road. There are three main friction forces acting on a tyre: adhesion, deformation and tearing/shearing. A soft racing tyre is designed to be sticky (at race temperature) and to deform so it ‘digs’ into the asphalt. In short finer-grained tarmac reduces tyre deformation and therefore grip.
Last week the surface adhesion was lower than expected, making life more difficult for the teams. As with all non-permanent tracks the tarmac wasn’t rubbered-in. Typically the asphalt has a layer of sticky rubber on it put down by many hundreds of race cars. Normal car tyres are far less visco-elastic than racing tyres and don’t put down rubber. In addition temperatures were lower and heavy rain on Friday night washed away what rubber had built up. These factors combined to produce an ice-like surface.
This was all compounded by the long straights and tight corners demanding a low drag-downforce set-up. The more downforce a car runs, the higher the tyre load, and the more likely it is to get to the right operating temperature.
The consequence of all these was extreme graining even on the medium tyre. Drivers couldn’t get heat into their rubber. As a result it was slipping over the asphalt creating a shear force. As the tyre shears over the tarmac the rubber collects in balls on the surface of the tyre. This temporarily reduces the contact patch between the road and the tyre as well as reducing the coefficient of friction – and grip falls off massively.
Previously at Montreal teams have run low-drag set-ups similar to those seen at Monza.
As a result many teams brought revised front and rear wings. Drag increases as the square of speed so a steep wing leaves cars susceptible to overtaking on the straights. Traction out of the hairpin is also key and may necessitate some (relative) softness in suspension set-ups as it isn’t uncommon for cars to slide on exit.
However, the tyre grip problems led to many teams increasing downforce for qualifying – this was done by ratcheting up the wing angle. If you look closely at the rear wing of each of the major teams you’ll see that McLaren ran substantially more angle (see picture). However, the wing was still shallower than at previous races so McLaren opted for a narrower outlet slot for the F-duct in the wing.
The Woking-based outfit is the only team that has perfected the F-duct – its competitors see an unacceptable fall off in downforce when the duct is ‘off’. The other clue was that the MP4/25 wasn’t the fastest car through the speed traps. To keep the balance right the steeper rear wing also meant that McLaren ran a slightly more aggressive front wing. It was this extra downforce that allowed McLaren to secure a 1-2.
The other feature of Montreal is the need to large brake ducts. The long straights with sharp corners mean that the brakes do a lot of work. To compensate teams bring oversize ducts to ensure the get enough air to cool down. It is a fine balance as the expanded ducts significantly increase drag, which on a low downforce track needs to be avoided at all costs.
Ferrari even went as far to change its brakes to Carbone Industrie, which uses a harder material to withstand higher temperatures. Every team on the grid without exception ran with larger ducts.
One surprise of the season has been Renault’s development rate. After being sold by its parent company after the Singapore scandal many predicted the demise of the Enstone-based outfit.
Instead the aero team has upped the ante and produced new parts at every race. Montreal was no exception with a more extreme M-shaped rear wing and a more obvious cascade-less front wing.
In addition to the loss of the cascade the lower flap grew out and a third vertical vane sprouted just inside the endplate to condition flow around the tyres. The genesis of the endplate design gives insight as to what the cascade is doing.
If you look closely at the cascade (compare it to the wing they used in Turkey) you’ll see it has a twist that directs air through the suspension. Although removing the cascade will reduce drag it messes with the carefully-crafted airflow characteristics. The addition of the vertical vane corrects this.
The more extreme ‘M’ rear wing reduces the effective angle of attack of the wing which reduces load and cuts drag.
Williams also brought a significant update to Montreal, albeit one that was overdue after development was disrupted after both cars crashed heavily at Monaco.
The most obvious change was the addition of Red Bull style vanes under the nose. These prevent dirty air from the wheels polluting air under the nose, which allows the floor to be fed with cleaner air, which in turn results in a more consistent diffuser. More consistent air flow to the diffuser means it is less likely to stall during cornering when the airflow may slow or change direction. Any stall at this critical moment will result in less rear downforce.
Also the endplates were updated with the addition of second, small outboard vane attached to the footplate. This works in tandem with the larger footplate vane to twist air away from the wing and around the outside of the wheel.
Interestingly Williams abandoned the semi-circular footplate venturi, which is designed to create a vortex that prevents air above the footplate spilled underneath – it effectively seals the wing. This is likely because the outermost section of the wing has more to do with tyre management than downforce generation. Look just inside the endplate and a venturi channel is evident on the lower side of the wing.
The Scuderia’s rate of development has been disappointing so far this year. That’s partly because it got distracted with its F-duct development, which still isn’t working as well as intended.
As a result Ferrari was over a second a lap off the pace in Turkey. For Montreal Ferrari produced a revised low-drag front wing. It had visibly less angle but supported a surprising number of subtle additions such as the fence on the inner most part of the flap to prevent airflow spilling onto the main place compromising downforce. Even in low-drag mode efficiency is important and this fence effectively allows the wing to run more efficiently.
The next races
Expect the major teams to produce some significant updates at Valencia and Silverstone. In particular, watch for Red Bull’s rivals adopting their low exhausts that blow into the diffuser. Many aerodynamicists now believe the RB6 gets its high downforce from its unique exhaust system. The exhausts blow gasses into side channels in the diffuser. Since diffuser downforce is highly dependent on volume of air flowing through the device the exhausts naturally increase grip.
However, engineering this correctly is a challenge. For a start exhaust gas velocity is dependent on throttle. As drivers lift the throttle through the corners the diffuser could stall if airflow isn’t consistent. In addition it’s also important to manage the lag between the exhaust gas and exit. Finally exhaust gasses are super hot and can damage the suspension of tyre unless the gas flow is well managed.
Blowing exhaust gasses through the diffuser isn’t new. Teams used to do it in the 1990s but ultimately couldn’t handle the inconsistent downforce. McLaren also tried to achieve it on their un-raced MP4-18 in 2003. Red Bull has found a way, perhaps by feeding the exhaust gasses into the coke-bottle zone. We’ll see if the other teams can replicate its advantage.
Retrofitting new exhausts and suspension will not be easy. The failure of teams to get the same kind of performance McLaren have from their F-duct is a case in point. Also, Red Bull is likely to understand the airflow characteristics at the rear of the car much better than its competitors so will be in a better position to refine and optimise the solution.
The noises coming from McLaren and Ferrari are encouraging. Wind tunnel tests are apparently very good and it is believed the low exhausts could be worth up to half a second a lap, which would cut Red Bull’s ever-diminishing advantage. In addition Ferrari is thought to be moving to a pull-rod rear suspension to try to create a tighter coke-bottle zone and improve flow over the floor and diffuser.
With the banning of double diffusers next year blow exhausts could be a fleeting development and potentially another example of poor cost control in the sport.
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