[QUOTE=JonBoy,Jan 27 2010, 07:19 AM]Aluminum is tricky because it has a constantly changing fatigue life.

 

The Insight was a halo model (from an efficiency/engineering, not enthusiasts' perspective), limited in production but providing a huge amount of positive PR for them. I wouldn't be surprised if they lost money on every one.

 

We can tell.. you're still literate. Welcome to car talk!

Curious on the same thing, and EG - thanks for the info on the Insight.

Im pretty excited about all this. Regardless of the performance potential, cars like the R8 or Murcielago weighing in at 3400/3600+ lbs is ridiculous IMO. Same applies to more pedestrian vehicles.

Im down with the "less weight, less power" concept as it'll create a better performer out of the box in every category (braking, handling, accel), yet allow much more room for improvement when it comes to aftermarket modifications, since the weight is already down and in theory, most companys would use a smaller, factory boosted motor, like Audi's 2.0T.

 

http://xnet3.uss.com/auto/steelvsal/basicfacts.htm - read the "Fatigue" section

Or, as they put it on Wikipedia:

In other words, with steel or titanium alloys, as long as the cyclic (repeating) stress range (the difference between the highest and lowest load) in the material is kept below a certain level, it will "never" fail.

In other words, aluminum does not have a set stress limit for fatigue failure. There is no set value of stress such that, if you keep the stress in aluminum below it, the aluminum will never fail. The idea thus is to keep your cyclic stresses so low in the aluminum that the rest of the car will fail before the aluminum ever does.

 

[QUOTE=JonBoy,Jan 27 2010, 12:58 PM]In other words, aluminum does not have a set stress limit for fatigue failure.

 

Engine acoustics are becoming more popular these days (see Lexus LF-A and Yamaha's collab).

Smaller brakes are adequate to stop the car at the same rate as the original brakes/weight since the car weighs less.

What's also impressive to me is that (although this is a concept), it's the first car with these power ratings (211 HP/~250 TQ) to run low 14s in a while.

 

You design for what amounts to "infinite" life. 100,000 cycles is nothing for a car. Try hundreds of millions, probably billions, of cycles. Every bump you hit in the road is a cycle. Every time the engine changes rpm (changing torque), it's a cycle. Every time you turn the steering wheel, it's a cycle. Every time you slow down or stop, it's a cycle. Basically, any thing that "changes" the current state of the car is a cycle. However, there's a big difference between hitting a speedbump at 60 mph (big jump in load) and slowly stopping the car (minor change in load).

Again, the killer is stress RANGE, not just the absolute level of stress. If you're only loading the car gently for most of its life, it's not too bad (no big spikes in load on a regular basis). However, if you're racing or running it hard, it's a bigger deal.

The other thing is, depending on where you put the aluminum, you can effectively isolate it from high-stress cyclic loading.

 

I'm all for lighter cars, but keep in mind that reducing weight while maintaining power-to-weight ratio will result in reduced acceleration at high speed as aerodynamic drag comes into play.

All else being equal I'd still rather have the lighter car, but just wanted to point out it's not a complete win.

Since the car weighs less than the A3, why not?

 

Damn, Jonboy. I'm sure all the kids in school asked you to do their homework.

 

because it's sacrilege! a couple pounds of weight savings can't be worth the downgrade in torque and heat capacity w/ the braking system, not for an enthusiast (which i assume to be the target demographic for a lightweight a5). i guess it would make more sense to me that they would ultimately do it to reallocate funding to other areas for weight reduction.