Tech
FXR Forks: 35mm vs 39mm
Every FXR had a 35mm fork until 1987.
For 1987 the FXLR Low Rider Custom and the FXRS-SP got a new 39mm fork. Every other FXR, the FXRT included, switched for 1988.
From then on every FXR ran 39mm, through 1994 and on the 1999 and 2000 CVO bikes.
By year and model
| Years | Models | Fork | Source |
|---|---|---|---|
| 1982 to 1983 | FXR, FXRS (Shovelhead) | 35mm | H-D fork brace instructions |
| 1983 to 1986 | FXRT; FXRD (1986) | 35mm long tube, air fork with anti-dive | H-D 1984-86 FXR parts catalog; Rider, Feb 2017 |
| 1984 to 1986 | FXR, FXRS, FXRDG, FXRC | 35mm short tube | H-D 1984-86 FXR parts catalog; H-D fork brace instructions |
| 1985 to 1986 | FXRS with the Sport package | 35mm long tube | H-D 1984-86 FXR parts catalog |
| Late 1984 to 1987 | FXRP police | 35mm long tube | H-D fiche, late 1984 to 1987 FXRP fork |
| 1987 | FXR, FXRS | 35mm short tube | H-D fiche, 1987 FXR and FXRS fork |
| 1987 | FXRT | 35mm long tube, air fork with anti-dive | H-D fiche, 1987 FXRT fork |
| 1987 | FXLR | 39mm short tube | H-D fiche, 87 FXLR, FXRS-SP and 88-later fork; H-D fork brace instructions |
| 1987 | FXRS-SP | 39mm long tube | H-D fiche, 87 FXLR, FXRS-SP and 88-later fork; H-D fork brace instructions |
| 1988 to 1994 | FXR, FXRS, FXLR | 39mm short tube | H-D fiche, 87 FXLR, FXRS-SP and 88-later fork |
| 1988 to 1994 | FXRT, FXRS-SP, FXRS Convertible, FXRP | 39mm long tube | H-D fiche, 1988 FXRT fork; H-D fiche, 1988 and later FXRP fork |
| 1999 to 2000 | FXR2, FXR3, FXR4 | 39mm Dyna length tube | H-D fiche, 1999 FXR2 fork; H-D fiche, 2000 FXR4 fork |
Long tubes go on the taller touring and sport models: FXRT, FXRD, FXRP, the Sport package or SP, and the Convertible. Short tubes go on the rest.
Why it changed, and the traps
Stiffer, and it came with a second disc
Hot Rod tested the 1987 FXRS-SP. The SP package cost $150 more and added a second front disc, more cornering clearance and the new fork (Hot Rod, Jan 1987). Their take on the old one:
The old fork used flexy 35mm tubes to hold the front wheel to the bike, which occasionally allowed the wheel to take its own sweet time about turning and stopping.
The 39mm unit, they said, “takes much of the approximation out of steering” (Hot Rod, Jan 1987).
FXRs got it before Sportsters
Harley's own fork brace sheet lists the 39mm brace for the 1987 FXLR and FXRS-SP, then all 1988 and later Sportsters, FXRs except the FXRT, and Dyna Glides except the Wide Glide (H-D fork brace instructions). So the 39mm fork showed up on two FXRs a year before the Sportster got it.
The short FXR tube, 45381-87, is the same tube aftermarket catalogs list for 1988 and later Sportsters (V-Twin fork tube listings). That is why so many Sportster 39mm parts bolt onto an FXR. The CVO FXRs went the other way: their 24.25 inch tube sits in Dyna (FXD) sliders in Harley's parts fiche (H-D fiche, 1999 FXR2 fork; V-Twin Forum, FXR tube lengths).
The 1987 FXRT trap
The 1987 FXRT kept the 35mm air fork with anti-dive. Harley's fiche for it lists the 35mm tube 45392-86 (H-D fiche, 1987 FXRT fork). The FXRT got the 39mm fork for 1988 (H-D fiche, 1988 FXRT fork).
Some owners report 39mm forks on a 1987 FXRT, and some parts listings say FXRT 39mm from 1987 (V-Twin Forum, FXR vs FXRT fork oil). Going by the factory listings, a 1987 FXRT with 39mm forks has most likely had them swapped. Check before you order parts.
The change halfway through 1986
Harley's 1984 to 1986 parts catalog lists new slider tubes and new tube caps for late 1986 on every FXR: 45407-83 to 45407-86 on the short forks, 45392-83 to 45392-86 on the long ones, and caps 45993-73 to 45993-86 (H-D 1984-86 FXR parts catalog). It is still a 35mm fork.
Aftermarket charts call it a change from fine thread to coarse thread caps, so early and late 35mm parts don't mix (HD Timeline fork size chart). Some say it was also a change of supplier from Kayaba to Showa. We could not confirm that, and Rider describes the 1983 FXRT fork as a Showa (Rider, Feb 2017).
Fork tube part numbers
| Part number | Size | Length | Stock on |
|---|---|---|---|
| 45407-83 | 35mm | 23.25 in | 1984 to early 1986 FXR, FXRS |
| 45407-86 | 35mm | 23.25 in | Late 1986 to 1987 FXR, FXRS |
| 45392-83 | 35mm | 25.5 in | 1984 to early 1986 FXRT, early 1986 FXRD, 1985 to early 1986 FXRS Sport, FXRP |
| 45392-86 | 35mm | 25.25 to 25.5 in | Late 1986 to 1987 FXRT, FXRD, FXRS Sport, FXRP |
| 45381-87 | 39mm | 23.375 in | 1987 FXLR; 1988 to 1994 FXR, FXRS, FXLR; 1988 and later Sportsters |
| 45393-87 | 39mm | 25.375 in | 1987 FXRS-SP; 1988 and later FXRT, FXRS-SP, Convertible, FXRP |
| 45395-92 | 39mm | 24.25 in | 1999 FXR2 and FXR3, 2000 FXR4 |
Fitment comes from Harley's parts catalog and fiche (H-D 1984-86 FXR parts catalog; H-D fiche, 87 FXLR, FXRS-SP and 88-later fork; H-D fiche, 1988 FXRT fork; H-D fiche, 1999 FXR2 fork). Lengths come from aftermarket catalogs and a forum list (V-Twin fork tube listings; V-Twin Forum, FXR tube lengths), and listings for 45392-86 differ by a quarter inch. Measure yours before you order.
Where sources disagree
- Who made the 1987 SP fork. Hot Rod's spec box says “39mm Kayaba” (Hot Rod, Jan 1987). Cycle World's 1987 FXLR test calls its fork a 39mm Showa (Cycle World, Jan 1987).
- The 1987 FXLR. Cycle World's spec box says 35mm and its article text says 39mm (Cycle World, Jan 1987). Harley's fiche says 39mm (H-D fiche, 87 FXLR, FXRS-SP and 88-later fork).
- Sportster year. Some guides say Sportsters went 39mm in 1987. Harley's brace sheet says 1988 and later (H-D fork brace instructions).
- 1987 FXRT. Some listings say 39mm. Harley's fiche says 35mm (H-D fiche, 1987 FXRT fork).
- Kayaba or Showa on the early 35mm forks. Not confirmed either way.
More
More chassis detail: FXR Frame and Chassis and the year by year model guide.
FXR Archive | Tech | October 2026