I think it can be said that front spoilers and rear wings dont influence downforce much at 80 kph, which is the speed from where aerodynamic aid is starting to work. So not much to expect in everyday traffic. However in countries where there is no speed limit like in Germany, where you can go over 200kph, the spoilers and wings can make some difference. Then also in racing at higher speeds.
The size of the difference is hard to say without comparing a car body without the aerodynamic aids with the same car with the aids. A help comes form a German Magazine Sport Auto which in their Super Test on Nürburgring also measures the downforces on the test cars in windtunnel and lists up these values at 200kph. Its interesting to see what values we can expect from sport and sporty cars for the market.
Some examples.
Audi RS 3 Sportback......F/R...21kg up/1 kg down
Opel Astra OPC.....................7Kg up/ 1 kg up
BMW M135i..........................7kg up/ 13kg up
BMW 1 M Coupe...................5 kg down/ 37kg up
VW Golf R............................17kg up/ 29kg up
Subaru WRX STI...................64 kg up/ 14 kg down
Mercedes A45 AMG...............43kg up/ 15 kg up
Ferrari 458 Italia..................32kg up / 31 kg down
This should give an idea of size of aerodynamic forces on cars at 200 kph. At normal road speeds it will be much lower of course.
One could also notice the Subaru cannot be so much fun with 64 kg lift at the front at 200kph, while the BMWM1 Coupe actually generates a small downforce and should be quite stable at 200kph in comparison.
Have not seen figures for the Alfa Giulia Q, which would be interesting.
The size of the difference is hard to say without comparing a car body without the aerodynamic aids with the same car with the aids. A help comes form a German Magazine Sport Auto which in their Super Test on Nürburgring also measures the downforces on the test cars in windtunnel and lists up these values at 200kph. Its interesting to see what values we can expect from sport and sporty cars for the market.
Some examples.
Audi RS 3 Sportback......F/R...21kg up/1 kg down
Opel Astra OPC.....................7Kg up/ 1 kg up
BMW M135i..........................7kg up/ 13kg up
BMW 1 M Coupe...................5 kg down/ 37kg up
VW Golf R............................17kg up/ 29kg up
Subaru WRX STI...................64 kg up/ 14 kg down
Mercedes A45 AMG...............43kg up/ 15 kg up
Ferrari 458 Italia..................32kg up / 31 kg down
This should give an idea of size of aerodynamic forces on cars at 200 kph. At normal road speeds it will be much lower of course.
One could also notice the Subaru cannot be so much fun with 64 kg lift at the front at 200kph, while the BMWM1 Coupe actually generates a small downforce and should be quite stable at 200kph in comparison.
Have not seen figures for the Alfa Giulia Q, which would be interesting.