Mercedes MGP W01 – Spanish update predictions

Even from the cars early days in testing, Mercedes have had problems with the MGP W01 and Ross Brawn himself has been candid with the cars problems.  Fundamentally the car has the wrong weight\aero bias, with it being too far to the front.  Last year one of Brawns strengths was its extreme forward weight bias, typified by the large slab of ballast in the front splitter, when the wider front slicks rewarded a +49% bias towards the front.  This year the tyres changed, the front tyres being 25mm narrower with a 20mm narrower tread, the rear tyres were also stiffened to cope with the heavy fuel loads.  Most teams perceived the loss of grip from the rear tyre change would not offset to loss in front end grip from the narrower front tyre.  Perhaps Mercedes (nee Brawn) felt the tyres would still favour a high percentage of weight towards the front, indeed the car still sports a significant slab of ballast in the front splitter.  At the last race the cars inherent weaknesses were exhibited by Michael Schumacher, who had both understeer and a chronic lack of rear grip, leading to poor traction in the wet and overwork rear tyres in the dry.  In Schumacher’s case his driving style tends to favour oversteer, while Rosberg is able to better cope with lack of turn-in and understeer the Bridgestone’s provide.  This trait of the Bridgestone front tyres has been present since the shift to a single tyre supply, which has only worsened with the move to slicks and now narrower slicks. 

Tyres work within a window of ideal vertical load.  This load comes from weight distribution and downforce, simplistically the former affects low speed grip and the latter higher speed grip.  Teams need to balance the static weight distribution and downforce front to rear to suit the tyres.  A graph of load versus grip for a tyre will see significant drops either end of the scale as the tyre fails to work when either over or under loaded.  It seem that Mercedes have too much load on the front tyres which will see them give up grip as the tyres gets too heavily loaded, this induces understeer.  Conversely they have too little load at the rear which will compromise traction off the line and out of slow turns, but also induce oversteer.  Having both ends of the car with incorrectly loaded tyres loads, will produce a car lacking in balance. The team could reduce grip at the rear to balance the car, but will then have a car lacking in grip. 

Although drivers favour certain degrees of understeer or oversteer depending on their driving style, both prefer this to with consistent balance and grip.  The differences in car set up between drivers are very subtle, its unlikely that one driver will have a significantly different weight\aero balance front to rear compared to another, certainly not to the level where one driver runs a different layout or wheelbase.  the changes will be in small differences to; suspension, wing angle and\or ballast placement.

In Mercedes case, they have tried to shift weight rearwards; this is limited by the team’s ability to find areas to house the slabs of tungsten\densamet within the tight confines of the gearbox.  An area now compromised due to the packaging of the double diffuser.  To shift weight distribution 1% needs a shift of 10Kg from one axle to the other, obviously space at the axle line is limited, and so potential a greater weight within the wheelbase may be needed to achieve the same effect. 

If ballast placement is not going to do the trick, which appears to be the case with the W01.  Then the team are facing a layout change.  Which means the front and\or rear axles will need to be shifted forwards relative to the chassis.  Something that could be done either by new front suspension moving the front wheels forward, or the same at the rear.  The rear option could also be achieved with a shorter gearbox.  Gearbox lengths have extended in previous years to push weight forwards, thus there is scope to reduce their length without having to resort to all new gear and internals.

According to the informed rumours, Mercedes will opt for a blend of front suspension changes mated to a shorter gearbox.  In the process extending the wheelbase.  Many in the media have highlighted the changes as a wheelbase change as the solution to the balance problem, but the extended wheel base is largely a function of the shifting the axles. It is not in itself the primary solution to their problems.

Shifting weight also demands a shift in aero balance, for Mercedes this means more rear downforce.  this cannot come purely from more rear wing angle as the drag that produces will slow straight lien speeds.  So ideally greater diffuser development is needed.  the team have been quick to get a passive F-duct running, this will certainly aid the ability to run more rear end downforce, but they must be careful its benefit is not eaten up by the need to run more rear wing or sales they will lose the advantage it gives other teams.

It now transpires that the F-duct rear wing on the W01 in China was passive device.  There remains the development of the ducting towards the cockpit and a tip-off suggests this is tied to a reshape of the roll structure.   How the ducting then reaches the rear wing may be either via a shark fin or up through the rear wing support.  Although Brawn tested a sharkfin briefly in 2009 on the BGP001, the team have yet to race a version of it, making them somewhat behind the times and lacking experience in how the taller bodywork reacts on track.

At least one area not a concern for the team will be their mirrors, which are already cockpit mounted and not subject to the repositioning facing some of their rivals (RBR & Ferrari).

We can expect a very different W01 to appear for the next race, we will cover the developments as soon as the car breaks cover in the days preceding the race.