[jluetjen]

Both T-bars and Coil springs work by twisting. In fact the formula to calculate the spring rate is fundimentally the same, except that the length of the coil spring is coiled while for a T-bar it is straight. As a result of the coil spring twisting, it changes height which is where the formulae defer. While with a T-bar, the swing arm just indexes around the center of the t-bar.

Yes, F1 cars use T-bars. Notibly Ferrari who combines them with rotary dampers (shocks) to create a very compact rear suspension system.

As far as stiffer being better -- not necessarily. If that were true we'd all be replacing our shocks and struts with steel beams and pitch the springs (coiled or not) to save weight. But we don't do that because the great thing about suspensions is that they suspend the car, and isolate the sprung portion of the chassis from variations in the road. Furthmore (from a performance perspective), having springs which move allows the designer/tuner to adjust how the load is distributed on the tires when turning and breaking. Being able to do that is what separates "the men" (such as Colin Chapman) from the boys when it comes to using the suspension to get a car around a course quickly.

That being said, Chapman did once observe that it was possible to make any piece of junk suspension design function passibly well by just preventing it from moving. Which brings us back to stiffer bars...

It was either the RSR's or the 934 that were the first 911's to use coil springs. In that case they were technically "helper springs" since the T-Bars were still in place. The problem was that because of the cornering forces generated by the huge slicks, it was not possible to increase the T-bar's rate enough while still maintaining the stock length (shorter = stiffer given a constant diameter). You could make them bigger, but the diameter is limited by the diameter at the splines since the bar will only be as strong as it's narrowest part. Porsche eventually did away with the T-bars on the race cars when they were raced in classes that didn't require the original style springs to be used.

The T-bars in the F1 cars are only about 4 inches long.