the outside diameter of the tip on the 3.0si is almost 3 inches... i think it's actually 2.9... then it tapers a few inches down to about 2.6...

i noticed it when i removed the chrome tip covers that came with the vehicle...(i was also looking to replace these tips with hartge or something else..)

the actual exhaust tips do not come off... you would need to cut and weld something else on if you want to change the tips... (or get a muffler/tip kit)

i also went through a number of bolt-on tips to see if i could slide something over the stock exhaust... (nothing would fit..and the stock exhaust sticks out thus preventing any other tips to completely slide over and become flush with the bumper)

after a few weeks of trying different options i decided to go with a semi-full exhaust kit...(everything but the headers)

still in delivery so i haven't installed it yet..but hopefully soon...

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2012 X5 50i M-Sport
2014 X3 35i M-Sport