[Armchair Spaceman]

Someone among you must know...what's the difference between campagnolo 10sp cog spacing & shimano 10sp cog spacing?

 

[C-40]

Campy 4.12, Shimano 3.95..

Someone among you must know...what's the difference between campagnolo 10sp cog spacing & shimano 10sp cog spacing?

Although .17mm (.0067 inch) doesn't sound like much, this difference accumulates after every shift, if you have the wrong cassette on either brand of drivetrain. In the worst case, you could find the derailleur 39% off it's intended location, but careful tuning can split this in half, each way from the middle.

Using a shimano cassette with a campy drivetrain is likely to produce better results, since the RD will overshift, not undershift.