[MeImCounting]

For most non-architectural design goals striking the right balance of toughness strength and hardness is generally what you want correct? I would imagine for building a bridge you care much more about elasticity and creep strength.

[petertodd]

Also fatigue resistance.

Bicycle design is a good example of where this matters: steel has a significant fatigue limit, and can endure cyclic stresses below that limit indefinitely. Aluminum has no fatigue limit, so any flexing is inevitably eating away at fatigue life. Thus aluminum bike frames have to be made much stronger and stiffer than otherwise necessary, to avoid bikes breaking unexpectedly due to fatigue. And that in turn means that aluminum bike frames don't have as much of a weight advantage over steel as you'd expect.

[johnwalkr]

For a rigid road bike aluminum can definitely be made stronger and lighter, even though what you wrote about fatigue limit is technically true. People like steel because they feel it’s more comfortable to ride. For mountain bikes, you will find almost zero steel bikes. Here the stiffness and lightness of aluminum (and carbon fiber at the high end) is almost universally preferred.

One advantage that adds to the potential lightness of aluminum and carbon fiber bike frames is manufacturing method. Aluminum is cheap to machine and hydroform into efficient shapes, and carbon fiber can also be layed up into efficient shapes.

[justinator]

> For mountain bikes, you will find almost zero steel bikes

Surly makes (only) steel mountain bikes, and I think there are approx. a... there's a lot of them out there. One reason is that they are inexpensive (relatively) and take a lot of abuse.

https://surlybikes.com/bikes/trail

[petertodd]

> For a rigid road bike aluminum can definitely be made stronger and lighter,

Absolutely. What I meant was that while an aluminum bike frame can be lighter than steel, it's not as much lighter than steel than you'd expect. Steel bike frames tend to be only ~15% heavier than aluminum, not 50%.

Personally I bought a steel road because the difference in weight vs the aluminum alternative was small enough that I decided to go with the bike that looked nicer, and would last longer. Besides, I could use to lose a lot more weight than any bike ever could...

[ClumsyPilot]

> I could use to lose a lot more weight than any bike ever could...

Get a child trailer and load it up with groceries or cement! i tried it, the results are.. Surprising

[janc_]

Right now, top quality steel bike frames at the minimum bike weight allowed by the UCI are stronger than top quality carbon fibre bike frames of the same weight. Aluminum frames of the same weight would not be considered usable probably... (Pro cyclists would still use carbon fibre bikes because they can be made more aerodynamic).

[johnwalkr]

That’s with a minimum weight imposed. Doesn’t change the fact that aluminum and titanium alloys generally have better strength-to-weight ratios than steel.

[Gare]

And fork is made out of steel (or carbon) even on aluminium bikes