I saw your comment about how the chain came off during one of the races.
Have you tried putting a chain tensioner on the car? I made one for my car with the option to take it off if needed. I usually run one now since I had a flat one time on the back wheel of all things. Without it, taking the wheel off the car would have taken much longer without it.
Another option you could do would be to put a chain guard around the wheel sprocket to keep the chain from jumping off due to lateral flexing. I know Dave Cloud has done that with his sprockets to prevent the chain from accidentally falling off.
I'll see if I can find some pictures to help you out.