Renaults are an exception in that their maximum permissible gross train weight is less than the sum of the maximum weight of the caravan and the maximum weight of the car. It is therefore quite possible that if the car is fully laden, you may not be able to tow 85% of the kerbweight (I am assuming you are asking about the kerbweight for this reason).
The first thing you need to do is to check the manufacturer's specification what you are allowed to tow if the car is at its max. GVW. Only then is there any point in comparing that value with the kerbweight.