You're going to LOVE the fit. Try it on and experience our perfect fit. If you don't love it, send it back in new and unused condition within 30 days for an exchange or full refund*. Risk free.
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Key Features
Modular Functionality
Simply lift the chin bar for full-face modular access
Inner Sunshade
Easily drop-down inner sun shade with left hand helmet trigger
Shuttered Venting
Adjustable shuttered venting in key areas of helmet
Fidlock Magnetic Chin Strap
Comes standard with Fidlock® easy-open magnetic strap clasp
Aerodynamic
Aerodynamic shell design with durable ABS construction
Drag
Take a breather in our Mach IV MOD Helmet. This fully modular helmet offers our classic 509 graphic stylings in an aerodynamic shell so you can easily chat with your riding buddy, cool off at a stoplight or take a sip of coffee on your morning commute. With adjustable venting in the top of the helmet and chin bar, and a drop down sun shade, dare we say this will become your favorite everyday commuter helmet.
Key Features
- Three configuration modular design: dual sport, full face, or open face
- Poly Alloy Shell
- Climate Control Ventilation system with two stage front chin vent, adjustable forehead vents, and exhaust vents.
- Moisture wicking removable Liner & Cheek pads for custom fit adjustments and easy to wash → Shop Cheekpads for Mach IV Mod Helmet
- Fidlock® The Fidlock System is a cutting-edge magnetic chinstrap buckle used in motorsport helmets ensuring quick, secure, closures with one hand and is DOT and ECE compliant.chinstrap strap closure for easy in and out
- Interior drop-down sun shade
- Multiple shield options (technologies including polarized, mirror, and photochromatic available)
- ITO (Indium Tin Oxide) shield coating to prevent surface scratches and fogging
- Universal camera mount capable
- WARNING for California residents
Specs
- Helmet Certification: DOT & ECE 22.05
- Starting Weight: 16800 grams
- Best Head Shape: Intermediate oval fit
- Size Range: XS - 2X
- Shell Breaks:
Small shell - XS, SM, MD, LG
Large Shell - XL, 2X - Included items: 509 helmet drawstring bag, breathbox, 509 Sticker
Size Guide
Not sure about your size? Try on at your local dealer!
*Street Helmets are a tighter fit due to cheekpad compression, however, they do pack out over time/use.
How to Measure
When measuring your head, use a cloth tape. Start it just above your eyebrows and circle it around the thickest point in the rear of your head and then reference the size guide below.
Scroll to the right to see more sizes
| Size | US Hat Size | Inches | Centimeters |
| X-Small | 6 5/8 - 6 3/4 | 20 7/8 - 21 1/8 | 53 - 54 |
| Small | 6 7/8 - 7 | 21 5/8 - 21 7/8 | 55 - 56 |
| Medium | 7 1/8 - 7 1/4 | 22 1/2 - 22 5/8 | 57 - 58 |
| Large | 7 3/8 - 7 1/2 | 23 1/4 - 23 1/2 | 59 - 60 |
| X-Large | 7 5/8 - 7 3/4 | 24 - 24 1/4 | 61 - 62 |
| 2X-Large | 8 | 24 3/4 - 25 | 63 - 64 |
| 3X-Large | 8 3/4 | 25 1/4 - 25 3/4 | 64 - 65 |
| 4X-Large | 9 | 26 - 26 1/4 | 66 - 67 |
| Youth Small | 6 | 18 1/8 - 18 7/8 | 47 - 48 |
| Youth Medium | 6 1/8 - 6 1/4 | 19 1/4 - 19 5/8 | 49 - 50 |
| Youth Large | 6 3/8 - 6 1/2 | 20 - 20 1/2 | 51 - 52 |
Pressure Points
When trying on a helmet, take note of any pressure points on your forehead—a sign that the helmet is too round. Pressure points on the sides of your head indicate a helmet is too oval for the shape of your head. After you buy a new helmet, try wearing it for 30 to 45 minutes to check for pressure points before using it on a ride.
Pressure Points
When trying on a helmet, take note of any pressure points on your forehead—a sign that the helmet is too round. Pressure points on the sides of your head indicate a helmet is too oval for the shape of your head. After you buy a new helmet, try wearing it for 30 to 45 minutes to check for pressure points before using it on a ride.
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