First off are they 35 or 40 series profile and have you done a calculation on the rolling diameters compared to your back tires.

Second, I would make sure that the 295's are load rated for the BMW. The Cayenne is a heavy beast so I would assume that they would be.

Third, are you getting any rubbing?

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2012 X5 50i ZAP(2VA, 336, 465), ZTP, ZPP, ZPS(6VC), ZCW, ZRC, 322, 4UB, 4NC, 610
2011 ///M3 Silverstone II
2011 X5 50i(lemon)
-- SOLD --
08 550 Msport
07 X5 4.8I sport
04 545i sport
02 4.4i sport
01 540I M/sport
00 SL500
97 SL500