HJC F 31 LUDI MC-1SF
The F31 is HJC's fibreglass open-face — an AFC composite shell in three shell sizes, so the small sizes aren't carrying a large helmet's outer dimensions around.The HJ-43 shield seals... Read More
The F31 is HJC's fibreglass open-face — an AFC composite shell in three shell sizes, so the small sizes aren't carrying a large helmet's outer dimensions around.
The HJ-43 shield seals better than the outgoing design, is Pinlock-ready and blocks 99% of UV, and HJC's DMS sun shield steps down behind it. The moisture-wicking liner and cheek pads come out for washing, and the shell is SMART HJC 2nd Generation ready with a boom-mic cover moulded in.
Features
- DOT FMVSS 218 certified
- AFC (Advanced Fiberglass Composite) shell in three shell sizes
- HJ-43 face shield with improved sealing, Pinlock-ready, anti-scratch, 99% UV protection
- DMS (Dynamic Multi-Step) internal drop-down sun shield, anti-fog coated
- ACS Advanced Channeling Ventilation — three intakes, one exhaust
- Moisture-wicking removable, washable interior; interchangeable cheek pads
- SMART HJC 2nd Generation ready with integrated boom-mic cover (50B / 21B / 11B)
Specs
- Certification: DOT FMVSS 218
- Shell: AFC (Advanced Fiberglass Composite), three shell sizes
- Shield: HJ-43, Pinlock-ready
- Sun shield: DMS internal drop-down
- Ventilation: ACS — 3 intakes / 1 exhaust
How to measure
Wrap a cloth tape measure horizontally around the fullest part of your head, about 1 inch (2.5 cm) above the eyebrows. Repeat a few times and use the largest measurement. The chart is a starting point — always try the helmet on for final fit.
HJC size chart
| Size | Head circumference (cm) | Head circumference (inches) | Hat size |
|---|---|---|---|
| 3XS | 50-51 | 19 3/4 - 20 1/8 | 6 1/4 - 6 3/8 |
| 2XS | 52-53 | 20 1/2 - 20 7/8 | 6 1/2 - 6 5/8 |
| XS | 54-55 | 21 1/4 - 21 5/8 | 6 3/4 - 6 7/8 |
| S | 55-56 | 21 5/8 - 22 | 6 7/8 - 7 |
| M | 57-58 | 22 3/8 - 22 7/8 | 7 1/8 - 7 1/4 |
| L | 58-59 | 22 7/8 - 23 1/4 | 7 1/4 - 7 3/8 |
| XL | 60-61 | 23 5/8 - 24 | 7 1/2 - 7 5/8 |
| 2XL | 62-63 | 24 3/8 - 24 3/4 | 7 3/4 - 7 7/8 |
| 3XL | 64-65 | 25 1/8 - 25 1/2 | 8 - 8 1/8 |
| 4XL | 66-67 | 26 - 26 3/8 | 8 1/4 - 8 3/8 |
| 5XL | 68-69 | 26 3/4 - 27 1/8 | 8 1/2 - 8 5/8 |
Youth sizes
| Size | Head circumference (cm) | Head circumference (inches) |
|---|---|---|
| YS | 48-49 | 18 7/8 - 19 1/4 |
| YM | 50-51 | 19 5/8 - 20 1/8 |
| YL | 52-53 | 20 1/2 - 20 7/8 |
One official HJC chart covers all models (full-face, modular, open-face, half); size availability varies per model. cm values are canonical (verified on both official US and EU HJC sites); inch values follow the mathematically consistent EU print where the US page conflicts with its own cm column (M and L rows). Note: many retailers still publish HJC's LEGACY chart (XS 53-54 … 3XL 65-66), which disagrees with the current official chart — do not mix them. Youth chart is the official Y10 chart (EU site).
Manufacturer sizing data · verified July 8, 2026