hmm going to be trial and error then acid, but if you are developing yer own stuff i would suggest not going witht he jonda chassis, you need to give yourself an edge over yer opponent, so maybe go for better tyres or engine than him instead.
also when developing yer own suff develop i tto the same level i.e
20/20/20/16
on all parts then move up so the best thing to do is look at how much you can upgrade each part by per race then decide on what you want it to be.
then upgrade all 9 car parts to the same level and start again. the reason for this is stability. if you develop one part that is way better than the others it can reduce the stability of the car. the other option you have is to work out what the parts are on the toyo chasis now and improve them all slightly to make the car 100% stable. this would also give you an edge over the jonda chassis as that might only be 75% stable in comparison.
my first advice ont his would be to write down what each of the 9 parts of the toyo chasis are, then add them up. i.e 20/17/14/14 = then when upgrading make them all equal the same that will give a 100% stable chasis.
so if 8 parts - 43 and one is 37, upgrade the part thats 37 to 43 and boom improved stability
if you dont get any of that ill try and explain better however im only just grasping it myself lol