oh - almost forgot, in California motorcycles are 100% exempt from the mandatory seatbelt laws so if you are worried about the risk of a helmet with a seatbelt you are free not to wear the seatbelt
I actually added a simply lap belt to my slingshot that I use instead of the factory belt because when its 110 degrees out that strap across the chest gets very uncomfortable - - I carry a printout of the law in my glove box where it specifically says that motorcycles are exempt and I have asked some LEO friends who have told me they would never ticket anyone in a slingshot for a seatbelt violation - -said its legally a motorcycle and the exemption applies
here is the first part of the CA seatbelt law: look at the third paragraph (c)
f
7315.
(a) The Legislature finds that a mandatory seatbelt law will contribute to reducing highway deaths and injuries by encouraging greater usage of existing manual seatbelts, that automatic crash protection systems that require no action by vehicle occupants offer the best hope of reducing deaths and injuries, and that encouraging the use of manual safety belts is only a partial remedy for addressing this major cause of death and injury. The Legislature declares that the enactment of this section is intended to be compatible with support for federal motor vehicle safety standards requiring automatic crash protection systems and should not be used in any manner to rescind federal requirements for installation of automatic restraints in new cars.
(b) This section shall be known and may be cited as the Motor Vehicle Safety Act.
(c) (1) As used in this section, “motor vehicle” means a passenger vehicle, a motortruck, or a truck tractor, but does not include a motorcycle.
(2) For purposes of this section, a “motor vehicle” also means a farm labor vehicle, regardless of the date of certification under Section 31401.
(d) (1) A person shall not operate a motor vehicle on a highway unless that person and all passengers 16 years of age or over are properly restrained by a safety belt. This paragraph does not apply to the operator of a taxicab, as defined in Section 27908, when the taxicab is driven on a city street and is engaged in the transportation of a fare-paying passenger. The safety belt requirement established by this paragraph is the minimum safety standard applicable to employees being transported in a motor vehicle. This paragraph does not preempt more stringent or restrictive standards imposed by the Labor Code or another state or federal regulation regarding the transportation of employees in a motor vehicle.