Narrow 5/8 x 1/4 pitch chains

Not many Harley-Davidson motorcycles originally had a 1/4-inch rear wheel chain. Specifically, it was the 1912-1914 models (with the clutch on the rear wheel hub and only if they weren't have belt equipped anyway) and the new single-cylinder models from 1926 and 1927.

When you customize your Harley, and when space is limited, a narrow chain is of course also an option. After all, a 520 chain (5/8“ x 1/4”) saves about 4.5 mm of space compared to a 530 equivalent. This can make the difference between a rasped tire sidewall and smooth performance. However, there is a catch: the tensile strength is usually lower that that of a 530 chain. This means that, with comparable driving style, it will stretch faster than the 530 equivalent.

But you state, for example, that the Alpha 520 from Tsubaki can withstand 120 hp!

Yes, it does. However, this should not be (mis)understood as a longevity statement. The longevity of a chain does not only depend on how much horsepower is pulling on it, but also on other factors: how much torque it has to transmit and whether the driver likes to pull the throttle grip all the way all the time. When it comes to torque and tension on the chain, tensile strength is clearly the deciding factor. And, of course, regular care!