the difference are:
http://www.amainhobbies.com/product_...ducts_id/13250
This is a rear middle conversion set for the Kyosho Lazer ZX-5. This set narrows the rear of the car slightly, and lengthens the wheel base of the car to make the car turn better, and at the same time make it more stable.
The set includes new rear lower suspension arms that are shorter than the ones included in the kit as well as a set of front arms that are the same as the original kit arms, new rear uprights (same rear uprights that are used on the RB5) with low height ball studs, new rear swing shafts to match the shorter suspension arms, new front shock shafts that are 2mm longer, a set of rear shock shafts that are the same as the ones that came with the kit, and new improved shock cartridges front and rear including e-clips, and o-rings (same shock cartridges that are used on the RB5).
anda conversion kit to make the rtr an SP:
http://www.amainhobbies.com/product_...ducts_id/20007
* Shock Plastic Parts Sets (2) KYOW5194-01
* Steering Knuckles (2) KYOLA254
* 7 Degree Hub Carriers (2) KYOLA254
* 10 Degree Hub Carriers (2) KYOLA254
* Front Dish Wheels (2) KYOW5201W
* Rear Hub Carriers (2) KYOLA252
* Lower Suspension Arms (4) KYOLA255 x 2
* Front Swing Shafts (2) KYOLA257
* Rear Swing Shafts (2) KYOLA258
* Shock Cap Nuts (4) KYOW5189-01BL
* Steering Knuckle Spacers (4) KYOLA256
* Blue Aluminum Collars (2) KYOW0144
* 4.8mm Ball Studs (2) KYOUM128
the SP has different front wheels too, I'm not sure of the difference though. i'm running HB Cyclone D4 wheels though.