Join Date: Sep 2007
Drag coefficient is used for marketing, and it is pretty much a useless number for consumers. Example was the big change in the Chevy Caprice from angular to bulbous body. The drag coefficient improved but I'd bet the drag losses were not reduced at all. GM just increased the frontal area cross section number by making the car body fatter all over. By making it organically rounded it looked "smoother" and more aerodynamic but it wasn't.
For different models of the same car body, however, the difference in coefficient is meaningful in that the lower coefficient version definitely produces less total drag. The efficiency difference however is not indicated by the delta in the coefficient. Only the fact that it is better for the version with the lower number. This results from the formula: higher cross sectional frontal area with no increase in drag will produce a lower coefficient but no savings in fuel economy. In the case of the Giulia it is clear the QV version develops significantly more drag than the normale. The TI will develop more drag than a version with smaller tires. The QV will develop more drag if only due to its wider tires. Various aero appendages will make that worse. I very much doubt the QV version generates any true downforce. Any reduction in lift is likely irrelevant to actual performance except at very high speeds. Even then back to back comparisons between the QV and the TI if fitted with the same power would be needed to establish that reduction in lift compensated for reduction in top speed. Maybe the aero effects just make the QV easier to drive at very high speeds rather than actually improving performance.
Returning to the brake upgrade issue it is critical for safety that you look for a brake upgrade package from a supplier who is competent to design one. Brakes are a system and any changes must be effected as a system even if you upgrade only one part. Buying brake upgrade parts you choose yourself is a very bad idea and potentially dangerous. You can very easily make the brake system worse.
For example, fitting bigger front brakes changes the brake bias. That changes weight transfer which can actually increase stopping distances (before the sceptic experts leap in you should recall that tire grip is related to load but not in linear fashion and, no, ABS cannot compensate for all brake imbalances). Changing just the rotor size without matching the compound to the heat requirements can result in a brake that develops less brake torque than stock because the temperature rise in the pad is insufficient. Counterintuitively, bigger brakes on the same car benefit from softer pads, or, looking at it the other way fitting more heat resistant rotors means your stock pads will likely work better than a set of harder pads. Just changing the pads to more heat resistant pads is the most common and worst amateur error because on the street you can substantially increase stopping distances when the brakes are cold, which they almost always are. If you can touch your wheels after a spirited drive your brakes are fine as they are.
The most egregious effect of fitting unnecessarily large brakes is unsprung weight. Car makers now fit the thinnest brake discs they can get away with for reasons of weight. Many modern cars wear out their discs as fast as their pads.
Holes and slots reduce weight a little but also reduce heat absorption capacity. There are zero proved benefits to holes or slotting in brake discs for road use, btw. This unsprung weight issue also arises if you fit bigger calipers, not just if you increase rotor size. Those four piston calipers you lust after can be heavier than the supposedly inferior sliding calipers your car maker fitted.
Like wheels and tires, brakes should be the smallest and lightest components you can find that perform to requirements. Going larger than you need is purely an aesthetic choice and one that I do not understand, frankly. Brakes become ugly after the first very hard stop.....
1991 Alfa Romeo 164L 5 spd
White on grey leather 230K km, owned from new
Last edited by Michael Smith; 05-05-2019 at 06:41 AM.