Can I put slightly larger diameter tire?
 

Hello,
My car originally needs 225/70R16. A friend could give me a set of alloy rims with 225/75R16. This is 3.12% diameter increase. I read 'stay within 3%'. Can I take these 225/75R16 or should I avoid them? Main concern - can this much of an increase do any harm to transmission?? I know about the speed / odometer reading, that's not an issue really. The real issue is transmission. Maybe there are other serious concerns in this given case? Please suggest if you are knowledgeable. Thank you.

it affects many things, not just transmission
abs, traction control, speedo/odo, braking performance, fuel economy, etc.
It's a good rule of thumb. Try to stay within the 3%