DBS Anti roll bar upgrade for DB9. There was a variety of anti roll bars fitted to the DB9 and DBS as listed below. A good upgrade is to use DBS Anti roll bars for the DB9 which uses both DBS anti roll bars to upgrade the handling of the DB9.
DB9 Coupe 2004-2012
The DB9 coupe used 25.4mm Anti-roll bars at the front and rear of the car
DB9 2004-2012 Front anti roll bar Part No. 4G43-5494-AB
DB9 2004-2012 Rear anti roll bar Part No. 4G43-5A771-AA
DB9 Volante 2004-2012
The DB9 Volante uses a slightly thicker anti roll bar (26mm) than the coupe but does not have a rear anti roll bar, it does have the same mounting points though, See here for fitting a DB9 coupe anti-roll bar to a volante
DB9 Coupe 2006 – 2010 Sports Pack
In 2006 the DB9 coupe came with the option of a Sports Pack, this came with lighter (same size) wheels, stiffer front and rear springs, a front stiffening plate under the car to make the chassis stiffer (see here for details on upgrading) and a larger 26.5mm diameter front anti roll bar
DB9 Coupe Sports pack 2006-2010 Front anti roll bar Part No. 6G43-5494-AB
DBS 2007 -2012
The DBS, Coupe and Volante came with stiffer front and rear stiffening plates, see here for fitting to a DB9, and upgraded front and rear anti roll bars, the front bar is 29mm and the rear 29.8mm diameter. The DBS bars can be retrofitted to a DB9. The mounting points, straps and drop links are the same for all DB9s and DBSs. But a spacer plate is used when fitting the rear DBS straps
DBS Rear Anti roll bar 8D33-5A771-AA
Rear Spacer Plate 8D33-5A493-AB
DBS Front Anti roll bar 8D33-5494-AB
Stiffness Calculation for Anti Roll bars
Simplified (and appropriate in this case) the stiffness of an anti roll bar is a function of the diameter to the fourth power.
i.e. 29.4^4/25.4^4 = 1.8, so the DBS sway bar is 80% stiffer than the DB9 bar
Bushes
The Straps for fitting the anti roll bars are identical between the different models, but the bushes are different to allow for the different diameter bar to pass through. DBS rear bushes are particularly expensive and its cheaper, for all sizes of bushes, to purchase polyurethane bushes
Driving
The result of upgrading to DBS anti roll bars from DB9 bars is a far more control, the car corners much flatter and feels more neutral with a better turn in. The change from a DB9 Volante to a Volante with DBS anti roll bars front and rear is a huge improvement with seemingly no downside.