The 1958 Harley-Davidson FL Duo-Glide motorcycle introduced a genuine rear suspension system, finally giving riders of the big Harleys smoother, modern ride.
Finally, after decades of relying only on a sprung saddle for "rear" suspension, the big Harleys adopted a swingarm with coil-over shocks in 1958. With that, the Hydra-Glide became the Duo-Glide, upping the ante in the touring market.
Two versions of the Big Twin continued to be offered: The milder, low-compression FL engine ran cooler and was easier to kick over than the hopped-up FLH, making it better suited to around-town driving.
Still sized at 1200 ccs/74 cubic inches, period Big Twins were advertised at 53-55 horsepower in the FL, 58-60 in the FLH.
Despite the new rear suspension, a sprung seatpost remained standard, providing what Harley termed "the Glide Ride." Of course, nearly 600 pounds worth of bump-flattening weight didn't hurt, either.
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