Heavy Duty Fork Spring Kits / 39mm Forks

Progressive Suspension's heavy duty spring rate for 39mm forks, sold with the preload spacers to set it up properly.

Stock Harley-Davidson fork springs are wound soft so the first inch of travel feels plush, and the price of that is everything after the first inch: dive under braking, wallow in a corner and a hard hit at the bottom of the stroke. Progressive's springs are wound at a rising rate, so the fork still moves easily over small stuff and gets firmer the deeper it goes. The heavy duty version takes that further for a heavier rider or anyone who wants a genuinely firm high performance front end. The preload spacers are included because spring rate without correct preload only moves the problem.

Features of the Progressive Heavy Duty Fork Spring Kit

• Heavy duty version of the Progressive Suspension fork spring
• Progressive rate springs supplied with preload spacers
• Improves front end stability and brake dive control
• Suited to heavier riders or anyone wanting a firm, high performance fork
• The cost effective route to a substantial gain in front end ride quality

Fitment

For 39mm forks. Grouped by family below.

• Harley-Davidson Sportster, '88-'19. Sportster 883 and 1200 XLH, 883 Hugger, 883 Deluxe, 883 and 1200 Custom XLC, 883 and 1200 Roadster XLR, 1200 Low and 883 Low XLL, 883 SuperLow XLL, SuperLow 1200 XLT, Iron 883 XLN, Nightster XLN, Forty-Eight XLX, Seventy-Two XLV, 1200 XLCP and the XL 50.
• Harley-Davidson Dyna, '91-'05. FXDL Low Rider, FXDB Sturgis and Daytona, FXDC Dyna Glide Custom, FXDS-CONV Convertible and FXDX Super Glide Sport.
• Harley-Davidson FXRT Sport Glide, '88-'93.
• Harley-Davidson Street, '15-'19. XG500 and XG750.

Before You Order

Check your fork tube diameter before ordering. This kit is cut for 39mm forks, and measuring the tube is the only reliable check on a bike that may have had a front end swap.

Works With

Sorting the front end out often shows up a tired rear. On a Sportster, the 412 Cruise Series 12.5 inch Shocks are the matching rear upgrade, and they lower the stance without costing you the ride.

Common Questions About the Fork Spring Kit

Do I need new fork oil?
Yes. The forks have to come apart to fit springs, so fresh oil at the correct level is part of the job and it affects how the fork feels as much as the spring does.

Standard or heavy duty?
Heavy duty suits a heavier rider, a bike that carries a passenger and luggage, or anyone who wants a firm sporting feel. If your complaint is only harshness over small bumps, the standard rate is the better answer.

Are the spacers necessary?
Yes, and they are included. Preload sets the ride height and where in the travel the spring starts working. Fitting springs without setting preload gives you half the benefit.