BMW R1100 fitted with K&N Intake system, the installment is very easy, inclds instructions that  are clear and very helpful for those not mechanically inclined. You will feel the extra power gained from the kn motorcycle filter intake and gas mileage improved as well.

Part BM-1199 Product Specifications
Product Style: Panel Air Filter
Height: 1.313 in (33 mm)
Outside Length: 5.625 in (143 mm)
Outside Width: 4.313 in (110 mm)
Filter Material: Cotton Gauze
Filter Re-Oiling Amount: 0.31 oz (9 ml)
Weight: 0.52 lb (0.24 kg)

Cross reference BMW Air Filter / KN BM-1199
BMW 13717650976
BMC FM23404

K&N BM-1199 fits the following:
2005 BMW R1100S 1100 - All
2005 BMW R1100S ABS 1100 - All
2005 BMW R1100S Boxer Cup Replica 1100 - All
2004 BMW R1100S 1100 - All
2004 BMW R1100S ABS 1100 - All
2004 BMW R1100S Boxer Cup Replica 1100 - All
2003 BMW R1100S 1100 - All
2003 BMW R1100S Boxer Cup Replica 1100 - All
2002 BMW R1100S 1100 - All
2002 BMW R1100S ABS 1100 - All
2002 BMW R1100S Boxer Cup 1100 - All
2002 BMW R1100S Sport 1100 - All
2001 BMW R1100S 1100 - All
2001 BMW R1100SA 1100 - All
2000 BMW R1100S 1100 - All
2000 BMW R1100S Sports Boxer 1100 - All
2000 BMW R1100SA 1100 - All
2000 BMW R1100SA SE 1100 - All
1999 BMW R1100S 1100 - All
1999 BMW R1100S ABS 1100 - All