A rare Harley-Davidson built in 1908 has become the most expensive motorcycle ever sold at auction in the US, according to data compiled by a website that tracks vintage motorcycle sales.

The Strap Tank Harley-Davidson was recorded on vintagent.com as being sold for $US935,000 ($A1.4 million) after auction fees last month at the Mecum Auction in Las Vegas, The Milwaukee Journal Sentinel reported on Friday.

The bike was named Strap Tank because its oil and fuel tanks are attached to the frame with nickel straps. The bike is believed to be one of only 12 such models in the world.

A 1907 Strap Tank sold for $US715,000 ($A1.0 million) after fees, but didn’t go for as much as the record-setting 1908 Strap Tank because it was never restored.

The record-breaking bike had many of its original parts, making it even more rare, said Greg Arnold, Motorcycle Division Manager at Mecum Auctions.

“We marketed the bike well and Harley is by far the most famous American motorcycle brand so we had a feeling it would do well in auction, but obviously you are surprised anytime you sell the most expensive bike ever,” he said.