GM-11 Decima Helmet
This GMAX® dual sport helmet is truly an all purpose helmet. The GM-11 is just as comfortable on your favorite fire road as it on the interstate. With the sun-blocking... Read More
This GMAX® dual sport helmet is truly an all purpose helmet. The GM-11 is just as comfortable on your favorite fire road as it on the interstate. With the sun-blocking peak, it can be a commuters best friend as well. The GM-11 helmet is loaded with features and designs normally found on other high priced helmets, but delivered to you at a true GMAX® competitive value.
Features
- DOT Approved
- Can be quickly converted from a visor configuration to a visor-less configuration
- Side shield plate covers come as standard equipment in the box to use when configuring to a visor-less set-up
- Outer flip shield is completed hidden under the visor, and out of line-of-sight, when in the fully raised position
- Large eye port that accepts large goggles
- Visor is designed to allow airflow to pass uninterrupted across the helmet to virtually eliminate helmet-lift at highway speeds
- Shield can be fully raised or lowered when using goggles
- Plush removable/washable COOLMAX® interior
- Intercom compatible with integrated speaker pockets
- 100% UV400 protection
- Optional cold weather kit available P/N - 72-3348 (dual lens shield, breath deflector, chin curtain)
How to measure
Measure the circumference of your head one inch above the eyebrows and across the largest portion of the back of the head, then find the matching range. The crown should apply snug, even pressure and cheek pads should be snug (they break in with use). If the helmet moves on your head it is too loose; if it causes pain it is too small. If between sizes, size down.
GMAX size chart
| Size | Head circumference (cm) | Head circumference (inches) |
|---|---|---|
| YL / XS | 53-54 | 20 7/8 - 21 1/4 |
| S | 55-56 | 21 5/8 - 22 |
| M | 57-58 | 22 7/16 - 22 13/16 |
| L | 59-60 | 23 1/4 - 23 5/8 |
| XL | 61-62 | 24 - 24 3/8 |
| 2XL | 63-64 | 24 13/16 - 25 |
| 3XL | 65-66 | 25 5/8 - 26 |
| 4XL | 67-68 | 26 3/8 - 26 3/4 |
Youth sizes
| Size | Head circumference (cm) | Head circumference (inches) |
|---|---|---|
| YS | 49-50 | 19 5/16 - 19 11/16 |
| YM (= XXS) | 51-52 | 20 1/16 - 20 7/16 |
| YL (= XS) | 53-54 | 20 7/8 - 21 1/4 |
One universal GMAX chart covers the whole lineup (street, dual-sport, snow). Youth and adult small sizes share shells and are dual-labeled: a Youth Large is the same fit as an adult XS.
Manufacturer sizing data · verified July 8, 2026