10 mm is less than half an inch. I'm sure there will be posters who tell you it makes a huge difference to them but certainly not me. I once agonized about ordering a 175 mm crank when I was used to 172.5 mm and when it came I couldn't tell ANY difference.
Sometimes 1 measurement is worth 1,000 beliefs. I'd suggest measuring your BMX crank. I doubt it's 180 mm.
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