Bahrain: Petrovs Renault retirement

In this weekends race Petrov retired with e a suspension problem, it transpires the ride height adjusting shim fell out between the carbon pushrod and the titanium end fitting,  Here James Allison explains “On lap 11, Vitaly reported that the car wasn’t behaving normally and he began losing a lot of lap time to Barrichello. We called him into the pits for a precautionary check and found a problem with   the   right-front   suspension   pushrod   that   forced   us   to   retire   the   car.   Upon   further investigation, it transpired that the pushrod had been touching on the chassis when running on very heavy fuel at the start of the race. This damaged the bolt that attaches the pushrod to the car, and meant we lost a shim from the suspension, causing the DNF. Robert preferred a slightly different ride height and was fortunate not to encounter the same problem. We are, of course, disappointed  that  we  did  not  discover this  problem  during  pre-season  testing.  The  parts  in question will be modified for the next race to ensure that it cannot recur.”

At the top of the pushrod You can see where it splits to allow the shim to be inserted


Pushrods: these are normally used to adjust ride height, adding shims between the carbon pushrod and the metal top section

Ride height changes with fuel level

Pushrods: these are normally used to adjust ride height, adding shims between the carbon pushrod and the metal top section

The ban on refuelling was originally envisaged as a method to liven up the show, forcing drivers to overtake rather than wait for pitstops.  Making the cars fuel tanks big enough to house the 170+ kg of fuel for a race distance has been a well publicised challenge.  But there’s another facing the teams brought in by the rule change. How the cars handling changes with the ever lightening fuel load.

Its been a long time since F1 cars had to run without refuelling.  Since then the car have raced with 60-80kg of fuel on board, burned it off over 20-30 laps and then take on another tankful. Now teams will start with 170kg of fuel and burn it off over the course of the entire race.  With F1 cars dry weight just 610Kg this is now a substantial proportion of the cars weight.  This extra weight will press down on the cars suspension pushing it closer to the ground.  Thus the cars ride height will alter considerably from the start of the through to the end.  Ride height is critical for two reasons; the overriding issue is aerodynamic.  Firstly the front wing and diffuser work in ground effect, so they work better the closer to the ground they get.  Thus the wings will work better at the start of the race and diminish as the fuel load lightens. Secondly ground clearance, the plank and titanium skid blocks will be prone to wearing when the car is heavy, excessive wear on the skid blocks will render the car illegal in post race scrutineering.

The teams will need to set the car up to work over a wide range of ride heights, this will mean compromises somewhere, making the car better at high or low ride.

Making matters more complicated will be the return to low fuel final qualifying, the cars wil enter Parc Fermé on Saturday all but empty, then they will be fully fuelled before the race.  Again do the teams make their set up favour low fuelhigh ride height qualify or go for heavy fuel low ride height for early race pace, or pick a point somewhere in between?  Every track will favour certain compromises.  Monaco is the classic example of a set up compromised towards qualifying, so teams will focus on the lighter fuel settings, but remain conscious that plank wear can be high over the principalities bumps and kerbs.

One solution put forward was ride height adjustment made during the race.  Since the ban on active technologies in the nineties, the rules are clear, there can be no adjustment of the cars suspension while it is moving, equally parc ferme rules prevent any changes between qualifying and the race.  But teams could have a mechanic adjust the ride height during the pitstops.

This would be legal and feasible, as the pushrods or torsion bar mounting could be fitted with a quick adjustment mechanism.  Even within a sub 3 second pitstop, this could be completed accurately.  But as the car will start the race with qualifying (low fuel) ride height settings, this could not be adjusted until the first pitstop, thus the opening stint would be compromised by the wring ride height.  Of course the balance of the race could then follow the ride height with the decreasing fuel load, but adjusting at the second and subsequent stops.

How could this be done?

Teams generally adjust ride height with shims fitted to the pushrods.  The pushrod is split between the main shaft and the metal end fitting, by loosening the bolts that tie them together a shim can be added into the gap.  Thicker shims mean more ride height and the shims need to be added to each of the four pushrods (two front two rear) to gain a balanced ride height.  Adjusting via this method is impractical during a rapid pit stop.  The pushrods could have a threaded adjuster as used on the front wing flap, a turn of the adjuster drops ride height by a fixed amount, this would be quicker to adjust, but still all four relatively in accessible (during a hectic pitstop at least ) would be difficult.

More likely would be to rotate the fixed ends of the torsion bar springs, by fitting the torsion bars on each axle to a common mechanism, they could be quickly adjusted by a single adjuster (two in total for the car) accessible through the top of the chassis or gearbox. Although the latter would be still hard to access shrouded by the rear wheels and rear wing, plus the associated wheel change and jack mechanics.