Hey guys, I’ve been driving around the Costa Rocosa roundabout trying to find out what maximum speed I can maintain without leaving the centre lane, or losing grip.
In the 2020 Toyota GR Supra and 2008 Mitsubishi Lancer Evo X GSR on stock tyres, that speed is exactly 74mph (for a body G-force of 0.95). With semi-slicks the maximum speed is 79mph (and a body G-force of 1.1), again for both cars. This is fine, and expected.
What isn’t expected is the effect of front and rear aero on these values. I would expect that with maximum downforce, both front and rear, I should see an increase in the maximum speed for some given rate-of-turn, or body G-force, but it doesn’t. That maximum does not change, regardless of aero settings.
I would have thought that at over 70mph the effect might not be that significant, but it would at least be noticable. I don’t see even 1mph difference. Am I missing something?
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It’s possible that it doesn’t work, some of my best cars have no Aero.
Some cars already have aero. You just can’t adjust it. I prefer mechanical grip, but it definitely helps my Elise on circuits. 
Both those cars have rear aero by default, I just replaced it with adjustable Forza version, and added adjustable aero at the front too, and used the roundabout to see what actual cornering benefits they would give. Which is none, apparently.
Could be an issue with front/rear aero balance, causing the front or rear tires to lose grip due to the opposite end having too much relative downforce. Usually is accompanied with over or understeer.
Could also be that the corner you’re testing on isn’t fast enough for the after-market aero to make an effect difference over stock.
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I would say go for a test in wider curves at higher speeds
Its tough to test aero effect when going in any circle. At some point there is a max speed the car can go and maintain control to hold a driving line.
Tighter circle like a round abouts will produce lower speeds when compared to say the inside track at the stadium.
For a quick test of this I ran an upgraded A Class AMC Gremlin with max front aero and no installed front aero at all. With aero I could maintain the inside line at 137 mph and with aero mods removed I could maintain the inside line at 137/138 mph, but this required slightly more effort.
I think to obtain better test results you would need to run several different cars in various configurations one circuits and record the best lap times for each different build.Also keep in mind, lower classes do not require aero at all, B and below do not require aero modifications and in A class there are some cars that dont require aero and can still perform well while others may benefit from aero mods.