If a car can't do 100km, then don't go on a road that has a 100km/hr speed limit. If your car cannot do the speed limit on ANY road while taking into account the yellow triangle signs that suggest a speed to take a particular corner at, then take the car off the road! Make it road worthy and return it to the road and do the speed limit. A manufacturer will not bring a car into the market that doesn't have those capability's.
If a car can do all of these things while the weather is at least 85% clear and the driver does not go the speed limit then the driver is the problem.
The best thing that I will do after giving my children a driving education is ensure there car is fitted with good shocks and springs, good bushes all round the suspension system, good brakes, a wheel alignment, proper inspection of tyres and I will not buy the cheapest tyres if the shelf.
Give every other driver a break and take a taxi.