What role does the exhaust tip shape, diameter, and length play in things like performance, back pressure, and noise?
The reason I ask is because every clubman exhaust comes with a giant 3"-4" exhaust tip and I have a strong distaste for giant exhaust tips. Would there be a downside to hacking them off and installing a smaller diameter tip?
The exhaust in question runs 2.25" pipes throughout, but then turns into a 4" tip

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Should the tip be equal to or larger than 2.25" or could you go a little smaller like 2"?