Convertible T-top

Nope. Remember that air will also be pulled into the cabin from other sources, like the vents - regardless if you have them closed or not. Looking at the physics point of view - true that fast moving air outside of a the cabin will draw some air out, lowering the pressure slightly, but a majority of the air in the cabin will be largely uneffected by the air outside. Now depending on the car itself, the buffeting from all the wind can make breathing difficult. The design of the T-Tops is more critical in determining how much overall air disturbance will be. Even driven at exceptionally high speeds -there will be plenty of air available, no real chance of asphyxiation possible. Now if someone had limited breathing to begin with - asthma, emphysema, etc. - then it may become a problem. But in cases like that, they would also be troubled by any case where pressure is reduced - like flying or high altitude trips, vacation spots.

Can a convertible t-top suck the air out of your lungs or prevent you from breathing when driving at high speeds? I would think so because there is such a huge pressure difference (low press. in cabin / high press. outside) at high speeds....say 65> mph.

Absolutely not.

My first car was a convertible and since the time I got rid of it, I have driven several Trans-Ams and Camaros with T-tops as well as several convertibles. I've driven every of them at freeway speeds (80 Mph) with the top down or T-tops out. Even though it is incredibly loud and there is a lot of buffeting, there is no problem breathing.

Like Fish said, there is air entering the car through the vents. The act of driving at high speeds coupled with the air entering the cabin through the vents creates a bubble of air inside the cabin, which helps to keep the buffeting to a minimum and certainly gives you plenty of air to breathe.

...and legislate a ban on all those dangerous convertibles.

Actually, back in the 1976, the last convertible rolled off an assembly line in America. It was a white Cadillac Eldorado with a white top and interior.

It was the last factory produced convertible sold in the US until the Chrysler Lebaron debuted in 1982.

The reason for the demise of the convertible in the US: fear that Congress would pass a new FMVSS that was under consideration. This particular FMVSS in question would require cars to conform to roll over standards. As the American Car Manufacturers saw it, there was no way to build a convertible car to meet the proposed standards.

Fortunately the FMVSS was not considered important enough by Congress and was never enacted. In 1982 Chrysler released the Lebaron, the top range car built on the K-Car platform. It was available as a Convertible or Coupe.

Unfortunately for Chrysler, no one in their engineering department knew how to build a convertible and the cars were plagued with top problems and other more serious problems like the doors swinging open when you made a sharp turn. Chrysler quickly worked these issues and by 1995, the last year of production for the Lebaron GTC, they had made the car perfect.

I had the 10th from last Lebaron GTC sold to the public. My car represented 13 years of continuous improvements for that car, and it showed. Had mine not lived the first 7 years of its life in Florida, I'd probably be driving it still. The salt air killed the electrical system and the car met an untimely demise. It was a shame because it was in every way as nice and in some ways nicer than my Solara.

Now we have convertibles galore and it makes me glad. They are such carefree and fun cars. Despite the opinions of many who have never owned a convertible, they are not crappy cars. Virtually no convertibles leak anymore and they are approaching quietness levels of hard tops. While they do require eventual top replacement and there is a mechanism to break, todays vinyl tops can easily last 10 years and cars there are still 1990 Mazda Miatas on the road with the original top mechanisms (many of which have never even needed adjusted, let alone repaired.) Manual tops on smaller cars are so simple that there just isn't much to break. Power soft tops are pretty much perfected. The new hard top convertibles are too new to determine how well they'll hold up. From what I've seen of them though, some of them will have issues, particularly the Pontiac G6 and Volvo C70.

The main problem of building convertibles is that they have to be designed as convertibles, from the ground up. The frame, or unibody, needs to be stiffer in order to account for the lack of an integrated roof structure to give the body it's overall integrity. This is probably the thing which plagued the K-car convertibles built by Chrysler.

You are correct on all points.

The best convertibles (the ones that absolutely do not leak any water or air, are quiet and exhibit no rattles, squeaks or flexing of the body) are designed from the start as convertibles. The Miata, Honda S2000, Pontiac Solstice/Saturn Sky, and the Mercedes SLK are good examples of such cars. I've driven a 17 year old Miata with over 200,000 miles on it. It was on its second top, but it exhibited no issues even with the top down.

In contrast, the Mustang, 2000 and later Thunderbird, Solara, Mercedes CLK, old Camaros and Firebirds are conversions of Coupes. I've driven Mustang convertibles, test drove a Solara Convertible, and ridden in a couple of Camaro and Firebird convertibles. The cars I drove all exhibited the shakes. The shakes is a condition in convertibles where the subframe or frame vibrates at a different frequency than the body, which vibrates at a different frequency than the upper part of the car, mainly the windshield. This is not a feeling that most people associate with a high quality car. Usually the shakes can only be felt over railroad tracks or when driving the car hard. The Thunderbird, Mercedes and Solara may not get driven hard, but the Mustang and F-body cars do. Of course, people don't expect a perfectly tight convertible Mustang or F-body car. Honestly though, the Mercedes gets such extensive changes to its structure that it might as well be a factory, purpose built convertible. I can not say that it exhibits the shakes, top up or down. I've never driven one, but drivers at Motor Trend and Car and Driver say so.

The Lebaron was designed as a convertible, but it was not on a unique platform and compromises had to be made. Every other car built on the platform was a hardtop and so the platform lacked some things necessary for a good convertible. In the original model, they didn't understand exactly how much lateral bracing was necessary, so too much was left out to save weight. While this made the car faster it came at a price. The lateral bending on the car was so bad that it made the frame become out of square so badly around corners at speed that the doors would not stay latched. Eventually rails and lateral bracing had to be added to the car and the problem was fixed. After 13 years, they had made the car so tight that it exhibited virtually no shakes.