As Phil says, it’s basically a wider chain. The pitch and roller diameters are identical.

520 chain: Pitch = 15.875mm, roller diameter = 10.160mm, roller width = 6.350mm, sprocket thickness = 5.766mm

525 chain: Pitch = 15.875mm, roller diameter = 10.160mm, roller width = 7.938mm, sprocket thickness = 7.214mm

A 525 will last longer as the load will be spread over a wider area and less prone to lateral flexing. The minor down side of a wider chain is that it will cause slightly greater drivetrain power losses, but not so much as you'd notice on an the road, you might see a fraction of a horse power drop off on a dyno.

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