Steel is preferred over aluminum because it wins in two key categories: elongation (how much the material will flex before it plasticises or fails) and endurance limit, or fatigue life. What this means is when steel and especially titanium are flexed, they retain their strength. They can be flexed again and again and never weaken until the material hits its endurance limit...for steel that's a pretty long time, Ti it's virtually forever. Aluminum loses strength any time it's flexed, and since its elongation numbers are low already, the chance of catastrophic failure looms. One of the myths about aluminum is that it's a very stiff material. It's not...the elastic modulus is actually much lower than steel or titanium. But since aluminum is about 1/3 as dense as steel, the tubing can be made very large to compensate. And since flex is aluminum's Achilles heel, most framebuilders will overcompensate, shooting for a finished product roughly 3 times as strong as steel (sometimes more, sometimes less depending on application).

Now (just like carbon, IMO), it's *possible* to design a strong, light and most importantly, *reliable* aluminum frame with the proper application of fistfuls and fistfuls of cash...cutting-edge alloys, expensive and time-consuming manufacturing processes and design tricks like hydroforming and internal or external butting. Would the market support such experimentation? Probably not, since there's no demand for anything to replace steel. ;)

hypersnazz

Dude, you rock. I didn't know all that. Thanks. That's why I ask, because I don't know.

Now what about a rubber frame? :)

Kevlar reinforced chewing gum matrix supporting multiaxial carbon nanotube weave? :D

No I didn't sorry EX

The FMF frame was mentioned in post 23. Long time ago. It helps to read through before posting.

Back to the cromoly vs carbon discussion; another difference between the two is that carbon absorbs vibration better than steel. I didn't see that in the thread and doubt it is particularly relevant to BMX, but thought I would add it nevertheless.

Hate to ask, but what's your gender?

BMX races last seconds, not hours like road or even XC races. Vibration damping is hardly an issue. ;)

How many guys do you know that are named "Maureen"?

Hey i used to be a sponsored paintball player and we used carbon fiber air tanks that could hold up to 4500psi, which is much more pressure then a BMX er would put on a bike, however every 4 years or so you have to get your tank hydro tested(they over fill it to the point of explosin ,almost)if it failed(exploded) then ur in buying a new $200 CF air tank, Well my point is that Carbon material wise blows steel/chromo steel out of the water for performance ex: if you have ever played paintball and used a steel tank instead of a CF one you will notice the weight difference is like night and day. And when it matters, that extra weight savings could mean the difference between grabbing the flag, or getting bunkered by the noob still using Co2...Thats my 2 cents...Gracias

You realize that our tires are rubber, not steel, right? And rims are aluminum.

"Performance" is a factor of many material properties, not all of which are analogous between BMX and paintballing. Just because CF shines as a material in creating high pressure gas cartridges doesn't mean it'll make a good BMX frame. It might, but the 'stresses' involved literally have very little to do with each other.

Still none. But since there are several countries represented here, I wasn't sure. You never know. Someone from some where could possibly be a guy named Maureen. It could happen.
:)

Ok, why isn't Stainless Steel used in BMX? I know there are spokes, perhaps nuts and bolts, but why not frames?

Because stainless steel isn't as strong as 4130 or other heat-treated steels.

That was true until this year (supposedly), when Reynolds introduced 953. It's trickling into the road market, I guess we'll see what comes of it.

They wouldn't be looking for a BMX shop in NorCal.

Man you guys are tough.

and those tanks were carbon wrapped.

http://photo.pinkbike.com/photo/689/pbpic689630.jpg

Check out the fork.

Oh sorry, haven't read the whole thread. My bad

Judging from the writing on the side of the bike, THAT BIKE IS INTENSE!

Someone needs a chain tensioner. Those crank arms look like pretty stout alum cranks.

XT on a BMX? So wrong. So very wrong.

that's the ugliest stem i've ever seen besides the profile stems