Radrick you answered your own opinion:
"The only reason Yamaha felt the need to switch was to keep up with Honda, Suzuki and Kawasaki. It has more to do with marketing than performance.
If you can't beat them, join them. Marketing sells and makes money and yamaha has made squat off there 450 for the past couple of years. Sometimes change is good and this case if yamaha didn't release an aluminum frame they would of been written off for another year while there competiors reaped the benefits.
I agree. You hit the nail on the head. The aluminum frame is only a necessity from a marketing standpoint. I've personally never felt the aluminum frame has any real advantage over steel. There is no doubt the whole YZF (not just the frame) needed to be updated, but it could have easily and probably more cheaply been done with a steel frame.
Sure there are some minor advantages to aluminum like the paint doesn't wear off or it doesn't rust, but in this application (motocross bikes) aluminum doesn't offer any real performance benefit. People think it's lighter, but in reality, aluminum frames weigh just about the same as steel frames. Want proof? Check it out, the aluminum Honda's have never had any big weight advantage over any of their steel framed competion. Look at the weight of the '06 YZF compared to the '05. There's no difference. It's true look it up.
Why do you think it took 8 years for any other major manufacturer to developer an aluminum frame? Does anyone actually think it took all the other manufacturers 8 years to catch up to Honda? Any of the major manufacturers certainly had the capability to developer one any time they wanted. It's not rocket science. Last August or so, Dirt Rider had a big article detailing the development of Yamaha's 2 stroke aluminum frame. According to this article, Yamaha engineers fought to keep steel frames because they could see no real benefits to aluminum. As a mechanical engineer myself, I can see why they would think that. Compared to steel, aluminum is expensive and much harder to design for and manufacture. You have to have a good reason to pick aluminum over steel as a material. Don't get me wrong, there are times when aluminum is the best choice. I just don't think motocross bike frames are it.
The market is the real driving force behind Yamaha switching to aluminum. The perception is that aluminum is better so Yamaha didn't really have a choice. The fickle consumer sees aluminum as "sexier" and more "cutting edge" and those are very real attributes when you're building bikes to sell. After all, the only competion that really matters is in the showroom.
Do I like the look of the '06 models? Hell yea! I think they look awsome. The aluminum frame looks sweet. It's a work of art and as an engineer I think I have an extra appreciation of how cool it really is. But do I think it is any real advantage? No. It's a sales tool.
Sorry. I just read through my post and realized I got a bit carried away. I just get tired of seeing people say "oh the aluminum frame is so much better". For the most part, as you can see, I think that's a bunch of bull. [/RANT]