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I'd like to go from 16" tires down to 195/65r15's on my 8th gen civic LX for fuel economy reasons and less load when accelerating; and my desired wheel covers for 15" steelies would be an esthetic plus.
would doing this mod, if possible, affect speedometer accuracy? I have read similar posts, but none that definitively answer my specific questions. Thank you!!

 
Rep Power: 125

I can't find anything non-Si related that I can rely on, but I don't believe the LX would have different brakes to an EX.

So long as the wheel diameter stays the same, speedo accuracy won't be an issue.

 
Rep Power: 366

speedo accuracy depends on tire OD, not rim size

 
Rep Power: 223

Looks like tire diameter is the same as the stock 16" wheels. EX and LX calipers and rotors are all the same. I don't know if 15" wheels came stock on any of these or not. As long as it clears the caliper, it should work.

 
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The Hybrid, GX and DX trim came stock with 15" rim and tires. They're 195/65r15's. My LX came stock with 205/55r16's

 
Rep Power: 223

Should work fine then.