Which of the two makes less wake behind the car? I would assume tunnels, but wasn't sure.

Ground effect tunnels create much less turbulence aka "dirty air." Ideally, the next IndyCar will get most of its aero grip from ground effect tunnels instead of large wings.

The undertray and diffuser created downforce with less drag.

The DP01 made great PR about the "ground effects" and 60% of the downforce at 200mmph coming form underneath the car. But understand that on road couses that level of efficiency happened maybe twice a lap. And on oval's where that number makes more sense there were other issues to contend with. In the 90's, CART was reducing the size of the diffusers (continued evolution that started with the first full ground effects Indycar in 1980). On ovals, turbulence from cars ahead would disrupt airflow underneath the cars and make it difficult for cars to run nose to tail (the following car would become loose).

Anyway, those who ignore history are destined to repeat it. Point is mechanical grip and aero grip from wings and diffusers are all tools to refine a racing car's performance. But each have their positive and negatives.

tunnels generate downforce much more efficiently. however, there are two things to consider.

first is that it is really hard to 'adjust' tunnels. while for a given underbody you can play with rake, spring rate, and ride height, you do not have the ability to adjust them on the fly in a pit stop, for example.

second is that generally, by the shape of the tunnel forced by the realities of oil/water cooler placement, etc., tunnels tend to be mid- and high- speed devices. primarily on street courses (but slower road courses as well), you still need wings to provide a lot of downforce in slow and mid speed corners.

but on the superspeedways, if you recall the cart days, the front wings were essentially vestigal and used just for minor trim adjustments. the cars probably could have qualified without them.

VNAF Ace - 11 June 2009 06:43 PM

Ground effect tunnels create much less turbulence aka "dirty air." Ideally, the next IndyCar will get most of its aero grip from ground effect tunnels instead of large wings.

I beg to differ... The tunnels create MUCH more wake turbulence than the wings. The wings can only compress air and then expand it within the laminar flow area of the surface of the wings. At best, this take place in an area where there are three sides to control and channel this air. The tunnels have a small area where air can evacuate (i.e., between the bottom of the chassis and the roadway itself) but ad hoc, they produce a four-sided captive tunnel that is much more effecient in moving air, compressing air, expanding air, changing air pressure than that of an open wing. More efficiency means more 'action' taking place. More 'action' means more of a by-product produced by the elements working on the car -- by-products meaning turbulence.

Now, if one was talking about what has more effect... ...the wings might win out because their turbulent airflow will pass through to directly engage a car exactly behind the lead car whereas the tunnels stay relatively close the surface of the track and have less of an area to engage another car and have a negative effect on the trailing car.

I would imaginer the tunnels would work about equally well in still or turbulent air because they are dramatically compressing and accelerating the air anyway.

Wings need laminar flow and without it, simply do not function.

Tyhe real issue isn't, which creates less turbulence, but which works better with turbulence.