First you should have mentioned "using car motor oil in motorcycles" since not everyone knows what a JASO-MA application is.
I would strongly advise against it.
Here is a short answer why:
Car oils in Bikes ?
A lot of people have used engine oils meant for cars in their bikes and claim that there is absolutely nothing wrong in doing so since they cannot find any damage .
The damage is certainly not perceptible to you , but such engine oils undoubtedly damage the internals . A brief intro for those who don't want to read the lengthy post-
Most car oils are rated as API SF, SG, SL and the latest being SM (not yet avail in India)
These ratings are given once in three years and each new rating is an improvement over the previous one . The ratings are in the same order as the english aphabets . The newer is better . so SM is better than SL and SL is better than SG etc.
Car engine oils have friction modifiers in them . Motorbike engine oils - specifically four stroke engines with a wet clutch multiplate setup do not require oils with friction modifiers . Modifiers can increase or decrease the friction , but most of the modifiers used are to reduce friction.
In my earlier post wrt to synth oils I have already explained why synthetic oils sometimes cause the clutch to slip .
The complete answer can be found at:
Using Car oil in Motorcycles