Pitstop set up adjustments during the race

During most races we see the mechanics make adjustments to the car during pitstops. During each stint radio communications between the driver and his race engineer will discuss the cars balance. Whether the car tends to oversteer or understeer. Since the ban on active technologies there’s little the teams can do to alter the car during the race. Currently only front wing adjustment, rear wing gurney removal and tyre pressures are easily changed during the hectic 3-4s pitstops.

Front wing adjustment

Front Flap Adjuster (arrowed)

This is the most flexible and simplest adjustment, during the stop the mechanics can raise or lower the front flap, via threaded adjusters in the mountings. Known as FFA (front flap angle), a greater angle will reduce aero induced understeer and less FFA similarly reduces oversteer. The race engineer will call for the mechanics to make so many ‘turns’ of wing. A ‘turn’ is quite simple a 360-degree rotation of the adjuster screw. One teams ‘turn’ will not necessarily be the same as another teams, as the wing\adjuster geometry will be different for every team.
Teams have historically used a cranked handled wrench for this purpose, although teams have recently been using cordless drill type adjusters. The collar of the drill modified to quickly deliver a specific number of turns, which are pre-set into the collar mechanism.
Between 2009 & 2010 drivers had the option to use the adjustable front wing flap mechanism. Allowed in the rules in 2009 as a pre-DRS overtaking aid. Although the idea did not really aid overtaking, teams did use it for the driver to alter balance during practice and in race stints.

Rear wing adjustment

A 'taped-on'Gurney flap (arrowed)

Although common in US single seat racing, rear wing adjustments are not common in F1. No team runs a threaded flap angle adjustment mechanism, preferring multiple ‘holes’ in the endplate to screw the flap into or machined inserts providing similar adjustment. In rear wing parlance, a ‘hole’ is also one unit of wing adjustment, similar to a turn of FFA. Clearly unfastening, repositioning and re-fastening a rear flap is impractical in a pit stop. However rear downforce is also tuned via the gurney flap, an “L” shaped strip along the trailing edge of the rear wing. By switching the gurney for a taller or wider strip, downforce can be increased. These strips are attached simply by tape, so are quickly removed. However fitting one does take time, requiring the wing surface to be clean and often heat guns are used to ensure the adhesive tape is sticking properly. Due to this, in the race teams are largely faced with the only option of removing a gurney and not adding one. Typically teams will add a more powerful gurney for a wet race, if the race dries then the teams will remove it. Less gurney will also decrease drag slightly and hence boost top speed.  Removing a gurney is a relaiutrvely simple process, as the strip is taped to the wing only via its leading edge.  The mechanic standing behind the wing pushes the gurney forwards and then rip sits off at an angle, taking the tape with it.
In the 2011 Suzuka Grand prix Felipe Massa was reporting understeer and his race engineer Rob Smedley radioed “Ok, we will do that rear wing thing”. At Massas subsequent pitstop, the rear wing gurney was removed. Reducing rear downforce to balance the car.

http://www.f1talks.pl/?p=11461&pid=5892

A Ferrari mechanic attaching a gurney with tape (via F1talks.pl & sutton images.com)

Tyre pressure adjustment

Wing adjustments are largely affecting medium to fast turn performance, at lower speeds the wings are less influential and the mechanical grip needs to be altered. Since the 1994 ban on active technologies, the drivers have no ability to alter the cars suspension. Before that drivers typically had the option to alter anti roll bar stiffness from levers in the cockpit.
So now the teams are left with just the option to alter tyre pressures in the race. Just as with wing adjustments, tyre pressure changes at the front or the rear alter balance. Again ahead of the pitstop the driver and race engineer will agree the change and the new set of tyres will be prepared in advance, pressurised to the right PSI.
During the 2005 season with no tyre changes teams had the mechanics with back pack mounted nitrogen cylinders, as the car stopped for refuelling, the mechanics would rapidly alter the tyre pressures to change the balance of the car.

Other changes during the race
While major balance changes are possible with wing and tyre pressure changed only at the pitstops, the driver does have some other methods to alter the cars balance, from the cockpit. Brake bias is a common adjustment allowing the driver to alter the brake bias front to rear. This can alter the turn-in to corners, as well as tune brake temperatures and locking wheels.
KERS harvesting (charging the batteries under braking) will also have a similar effect as brake bias. Drivers can alter this setting from the steering wheel.
More influential is the differential; this will alter the car at all three points in a turn; entry\mid\exit. A tighter differential will aid traction out of turns, but induce understeer going into them. Drivers will be altering each of the three settings to get the correct, mechanical set up to balance the car.
One area that’s been much talked about this year is the engines overrun settings. But these settings have been used for much longer to manage corner entry balance. How the engine behaves when the driver is off the throttle going into turns affects the rear tyre grip. A stronger overrun setting will create more engine braking, dragging the rear axle slightly on turn in. Which can make an oversteering the car more stable. Conversely softer overrun setting will suit an understeering car.
Lastly throttle and engine maps will affect the car on corner exit. Intuitively fiercer maps will make a car want to oversteer out of turns, offsetting understeer.