RE: here is the roto start for .18 truck & buggy
it is optional to add to the order to put on another nitro so that if you have 2 or more with .12, .15, .18 motor you can install/buy only the back plate instead of buying the whole kit ie 16.95 instead of spending another 39.99 to have on another car.
btw tower hobbies does has a typo in the stock # go to site using prompt in the above post then click on last hilighted st# at bottom of page and it will take you to the page fot hpi st #87121 (the optional part which is the same part included in the kit)
+1