Bolt on suspension kit for increasing vehicle payload

1. A vehicle suspension system comprising:

a first suspension assembly operably coupling a first wheel to a chassis of a vehicle;

a second suspension assembly operably coupling a second wheel to the chassis, the first and second wheels forming a pair of front wheels;

a third suspension assembly operably coupling a third wheel to the chassis;

a fourth suspension assembly operably coupling a fourth wheel to the chassis, the third and fourth wheels forming a first pair of rear wheels; and

a payload extension kit that is attachable to the chassis non-permanently,

wherein the payload extension kit includes a fifth suspension assembly operably coupling a fifth wheel to a sub-frame extension of the payload extension kit, and a sixth suspension assembly operably coupling a sixth wheel to the sub-frame extension, the fifth and sixth wheels forming a second pair of rear wheels,

wherein the chassis comprises a first longitudinal frame member, a second longitudinal frame member, and a transverse frame member extending between the first and second longitudinal frame members,

wherein the sub-frame extension comprises a first longitudinal sub-frame member, a second longitudinal sub-frame member, and a transverse sub-frame member extending between the first and second longitudinal sub-frame members,

wherein the first longitudinal sub-frame member is non-permanently fixed to the first longitudinal frame member, and the second longitudinal sub-frame member is non-permanently fixed to the second longitudinal frame member via both a vertical fixing member and a horizontal fixing member,

wherein the first and second longitudinal frame members each include a first bracket on a lateral side thereof,

wherein the first and second longitudinal sub-frame members each include a second bracket corresponding to the first bracket, and

wherein the first and second brackets are affixed to each other via the vertical fixing member.

2. The system of claim 1 , wherein the vertical fixing member and the horizontal fixing member are each bolts.

3. The system of claim 1 , wherein a portion of each of the first and second longitudinal frame members is received in a sleeve bracket that is affixed to a corresponding one of each of the first and second longitudinal sub-frame members,

wherein the horizontal fixing member operably couples the sleeve bracket to the corresponding one of each of the first and second longitudinal frame members.

4. The system of claim 1 , wherein the third and fourth suspension assemblies include a first leaf spring assembly and a second leaf spring assembly, respectively, and

wherein the fifth and sixth suspension assemblies include a third leaf spring assembly and a fourth leaf spring assembly, respectively.

5. The system of claim 1 , wherein the third and fourth wheels are operably coupled to a first rear axle, and

wherein the payload extension kit includes an electric motor powering a second rear axle, thereby converting the vehicle to a plug-in hybrid electric vehicle (PHEV).

6. A vehicle suspension system comprising:

a first suspension assembly operably coupling a first wheel to a chassis of a vehicle;

a second suspension assembly operably coupling a second wheel to the chassis, the first and second wheels forming a pair of front wheels;

a third suspension assembly operably coupling a third wheel to the chassis;

a fourth suspension assembly operably coupling a fourth wheel to the chassis, the third and fourth wheels forming a first pair of rear wheels; and

a payload extension kit that is attachable to the chassis non-permanently,

wherein the payload extension kit includes a fifth suspension assembly operably coupling a fifth wheel to a sub-frame extension of the payload extension kit, and a sixth suspension assembly operably coupling a sixth wheel to the sub-frame extension, the fifth and sixth wheels forming a second pair of rear wheels,

wherein the third and fourth suspension assemblies include a first leaf spring assembly and a second leaf spring assembly, respectively, and

wherein the fifth and sixth suspension assemblies include a third leaf spring assembly and a fourth leaf spring assembly, respectively,

wherein the first and second leaf spring assemblies support a master axle at a middle portion of each of the first and second leaf spring assemblies, and

wherein the third and fourth leaf spring assemblies are operably coupled to the master axle at a first end thereof, and operably coupled to a slave axle at a second end thereof.

7. The system of claim 6 , wherein a middle portion of each of the third and fourth leaf spring assemblies is pivotally supported by a support bolster extending away from the first and second longitudinal sub-frame members, respectively.

8. The system of claim 6 , wherein the slave axle is operably coupled to an electric motor.

9. The system of claim 6 , wherein a rocker ratio of the first and second leaf spring assemblies relative to the third and fourth leaf spring assemblies establishes a selected load split between the master axle and the slave axle.

10. The system of claim 6 , wherein the third and fourth leaf spring assemblies are operably coupled to the master axle via a bolt-on coupler.

11. The system of claim 6 , wherein the fifth and sixth suspension assemblies each further comprise a damper operably coupling the slave axle to the first and second longitudinal sub-frame members, respectively.

12. A payload extension kit that operably couples to a chassis of a vehicle having a front pair of wheels and a first rear pair of wheels to increase a payload capacity of the vehicle, the payload extension kit comprising:

a sub-frame extension;

a pair of suspension assemblies operably coupling a second pair of rear wheels to the sub-frame extension,

wherein the chassis comprises a first longitudinal frame member, a second longitudinal frame member, and a transverse frame member extending between the first and second longitudinal frame members,

wherein the sub-frame extension comprises a first longitudinal sub-frame member, a second longitudinal sub-frame member, and a transverse sub-frame member extending between the first and second longitudinal sub-frame members,

wherein the first longitudinal sub-frame member is non-permanently fixed to the first longitudinal frame member, and the second longitudinal sub-frame member is non-permanently fixed to the second longitudinal frame member via a removable fixing member,

wherein the first and second longitudinal frame members each include a first bracket on a lateral side thereof,

wherein the first and second longitudinal sub-frame members each include a second bracket corresponding to the first bracket, and

wherein the first and second brackets are affixed to each other via a vertical fixing member.

13. The payload extension kit of claim 12 , wherein the fixing member is a bolt.

14. The payload extension kit of claim 12 , further comprising a sleeve bracket that is affixed to a corresponding one of each of the first and second longitudinal sub-frame members,

wherein a portion of each of the first and second longitudinal frame members is received in the sleeve bracket, and

wherein the horizontal fixing member operably couples the sleeve bracket to the corresponding one of each of the first and second longitudinal frame members.

15. The payload extension kit of claim 12 , wherein the first pair of rear wheels are supported by a third and fourth suspension assembly, respectively, the third and fourth suspension assemblies including a first leaf spring assembly and a second leaf spring assembly, respectively, and

wherein the first and second suspension assemblies include a third leaf spring assembly and a fourth leaf spring assembly, respectively.

16. The payload extension kit of claim 15 , wherein the third and fourth leaf spring assemblies support a master axle at a middle portion of each of the third and fourth leaf spring assemblies, and

wherein the first and second leaf spring assemblies are operably coupled to the master axle at a first end thereof, and operably coupled to a slave axle at a second end thereof.

17. The payload extension kit of claim 16 , wherein a middle portion of each of the first and second leaf spring assemblies is pivotally supported by a support bolster extending away from the first and second longitudinal sub-frame members, respectively.