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ASTM's F1952 Downhill Standard

Summary: ASTM's F1952 Downhill Mountain Bicycle Racing helmet standard is significantly more stringent than the CPSC bicycle helmet standard. A helmet needs much more coverage to meet F1952, and is tested at higher impact levels. Chinbars are not required, but are tested if they are present.


ASTM developed F1952 because downhill mountain bike racing has more crashes than street or road riding. The standard does not require a chinbar, but if the helmet has a chinbar (even one that is removable) then the chinbar is tested. Helmets with removable chinbars are tested both with and without the chinbar. Test lab impacts are more severe than the CPSC/ASTM F1447 standard, and the test line is significantly lower in the sides and rear, so the impact performance is tested in the added area. Helmets certified only to CPSC may have extra coverage in the rear, but it is not tested, and must be presumed not to meet either CPSC or the downhill standard. Note that F1952 helmets are heavier than road helmets and their harder foam to meet the more severe impact requirements may affect performance in lower level impacts. Even without chinbars the helmets resemble light motorcycle helmets.

Test Line determines coverage

The table below shows where the test line is drawn on a bicycle helmet tested to CPSC or downhill helmet tested to F1952. The distances are above the reference plane, a line drawn around the headform at the ear level. Lower numbers are better, putting the test line closer to the reference plane and further down the helmet.

Standard Front Middle Rear
CPSC Bicycle 41 41 27
F1952 Downhill 50.5 25 0

Note that any helmet sold as a bike helmet in the US must meet the CPSC standard. That guarantees testing on the front of a downhill helmet down to 41mm above the reference plane. But the downhill helmet does not have to meet the more stringent impact requirements of F1952 in that 9.5mm area, just the CPSC impact requirement. We have a page up with test lines from other helmet standards.

Impact performance

The table below gives the drop velocity in meters per second for impact testing. Higher is more severe. The hemispheric anvil is approximately the shape of a grapefruit. The curbstone anvil looks like a section of 90 degree curbstone tilted back so that the rounded edge is upward. Downhill mountain bike racers are much more likely than road riders to hit a non-flat surface.

Standard Flat Anvil Hemi Anvil Curbstone Anvil
CPSC Bicycle 6.2 4.8 4.8
F1952 Downhill 6.2 5.6 5.6

Note: 6.2 m/s corresponds to a 2 meter drop. 5.6 m/s corresponds to a 1.6 meter drop. 4.6 m/s corresponds to a 1.2 meter drop.

In addition to the drop height difference, CPSC uses separate samples for the curbstone test and only impacts them in one location. F1952 mixes one curbstone, one hemi and two flat anvil impacts on all samples. Since the curbstone anvil impact is much more severe than the other two, that is a significantly more rigorous testing sequence.

Partial Utilization Prohibited

F1952 has a statement: "1.3 Partial utilization of this standard is prohibited. Any statement of compliance with this specification must be a certification that the product meets all of the requirements of this specification in its entirety. A product that fails to meet any one of the requirements of this specification is considered to have failed this standard, and should not be sold with any indication that it meets parts of this standard."

If you see a manufacturer saying that their chinbar meets the F1952 downhill standard, but the helmet is only certified to CPSC, it means that the manufacturer is violating that prohibition. The prohibition is designed to prevent them from confusing you about the helmet's level of performance. A product is certified to meet a standard in its entirety or the manufacturer is not to reference that standard in their advertising. It is hard to respect a manufacturer who violates that provision, either out of intent or ignorance.