Want to get silly with steel?

http://reynoldstechnology.biz/our_materials_953.php

Quote from: stopintime on August 27, 2011, 03:39:20 PM
That's not exotic 

Reason I ask is I was offered a custom frame while entertaining the idea of an oversized Monster (matching me)

Monsterize an ST for a larger bike.

  Some of the bicycle builder told me about some new lighter weight steels they were going to start experimenting with.

  I don't think I would want a CF frame. Hell, even Rossi can't ride one of those

how about magnesium for a frame?

Quote from: RMartin on August 27, 2011, 05:06:23 PM
  Some of the bicycle builder told me about some new lighter weight steels they were going to start experimenting with.

  I don't think I would want a CF frame. Hell, even Rossi can't ride one of those

Yeh but Stoner can

Quote from: Punx Clever on August 27, 2011, 03:16:28 PM
As for the aluminum frames... looking at my swingarm, the aluminum is quite thick.  To make a similar trellis style frame out of aluminum that would last, the tube walls would have to be pretty thick too.  The question is, would it be cost or weight effective to build an aluminum tube copy of the trellis frame we all know and love?

Yes, the walls would have to be quite thick, and the tubes should probably have significantly larger OD as well so that the stiffness is high enough to prevent flexing which will induce fatigue.  We already know what a successful Al trellis frame looks like:

its just beautiful... 

Quote from: Punx Clever on August 27, 2011, 03:42:49 PM
chromoly steel has a much higher strength to weight ratio than plain steel, while still being able to machine, weld, and bend easily.

http://en.wikipedia.org/wiki/41xx_steel

Yes, but strength isn't a very significant issue on frames, I.E. we see *very* few frames break or fail in normal service.

A more appropriate spec to look at is Specific Modulus; the stiffness to weight ratio.
A heap of info here:
http://en.wikipedia.org/wiki/Specific_modulus

Examining it for even remotely suitable frame materials, you find....

Steel, magnesium, aluminum, and titanium all have essentially the same specific stiffness, 25x10⁶ m²s^âˆ'2.

So if you want to reduce frame weight, with the same physical layout/design, you sacrifice stiffness.

Quote from: Speeddog on August 28, 2011, 12:45:59 PM
Yes, but strength isn't a very significant issue on frames, I.E. we see *very* few frames break or fail in normal service.

A more appropriate spec to look at is Specific Modulus; the stiffness to weight ratio.
A heap of info here:
http://en.wikipedia.org/wiki/Specific_modulus

Examining it for even remotely suitable frame materials, you find....

Steel, magnesium, aluminum, and titanium all have essentially the same specific stiffness, 25x10⁶ m²s^âˆ'2.

So if you want to reduce frame weight, with the same physical layout/design, you sacrifice stiffness.

so what you are saying... a way to reduce weight isn't trough material, but design.

Quote from: Speeddog on August 28, 2011, 12:45:59 PM
...
Steel, magnesium, aluminum, and titanium all have essentially the same specific stiffness, 25x10⁶ m²s^âˆ'2.

So if you want to reduce frame weight, with the same physical layout/design, you sacrifice stiffness.

Only carbon fiber seems to have a better stat in this regard...

Except glass(!) seems comparable to the various metals, so consider me confused.  

I'm guessing that the elasticity/ brittleness / fatigue would have to factor in somehow. Otherwise some fool would be building glass frames (Quick! Tell the 'hideous custom' guys about this. It's our chance to thin the herd!   )

[edit] NM. I read a bit further:

Stiffness versus strength in bending

Note that the ultimate strength of a beam in bending depends on the ultimate strength of its material and its section modulus, not its stiffness and second moment of area. Its deflection, however, and thus its resistance to Euler buckling, will depend on these two latter values.

Quote from: Speeddog on August 28, 2011, 12:45:59 PM
Yes, but strength isn't a very significant issue on frames, I.E. we see *very* few frames break or fail in normal service.

A more appropriate spec to look at is Specific Modulus; the stiffness to weight ratio.
A heap of info here:
http://en.wikipedia.org/wiki/Specific_modulus

Examining it for even remotely suitable frame materials, you find....

Steel, magnesium, aluminum, and titanium all have essentially the same specific stiffness, 25x10⁶ m²s^âˆ'2.

So if you want to reduce frame weight, with the same physical layout/design, you sacrifice stiffness.

This all makes plenty of sense.  But you still run into issues of fatigue loading.  20 years down the road, steel will hold up, Al, Mg, and Ti will have failed.

My Seven mountain bike frame was Ti and I thought THAT was a work of art.  And that cost $4,000+ just for the frame....a BICYCLE frame.  And this was a few years back.  I can't imagine what a titanium motorcycle frame would cost. 



She was a beauty!  Selling her off paid for my motorcycle gear and a few mods....

Your frame is stunning.  Hope it's half as amazing as it looks. 

Joel

Awesome work!  imo the Ti will hold up fine -- it makes a perfectly good spring material (rear shock springs on all the factory MX bikes are Ti and they get hammered), it holds up exceedingly well in MTB use and there its really pushed to the limit of just how thin/light it can be without breaking.  Yours with the extra thickness will probably last 'till the next ice age -- I'd ride it      

Quote from: Punx Clever on August 28, 2011, 08:59:04 PM
This all makes plenty of sense.  But you still run into issues of fatigue loading.  20 years down the road, steel will hold up, Al, Mg, and Ti will have failed.

You just pulled '20 years' out of thin air.....
I'm ten feet away from a 20 year old Honda, that has 20k miles on it, and it has an aluminum frame.
It's not broken.
As long as the operating stresses are below the limit for the number of stress cycles, failure is unlikely.

I'd be really surprised if the average lifespan of a bike was more than 30k miles.
Most die due to neglect or a crash before that.

Does anyone here have FHE with an aluminum frame cracking in normal service?
Or does anybody here know someone who did?

I do re aluminum (have physically seen friend's cracked frames), but it was due to faulty casting on one model year, not faulty engineering.  My frame, which is of the year that could be so afflicted, has 60k rather hard miles and no cracks.  The potential crack point is a rear shock mount.  It'll be irrelevant when I fit my fancy bitubo rear shock as its not even utilized by the bitubo.  Virtually all japanese bikes of the past two decades have aluminum frames.  Very few have cracking issues -- even ones used for stunting. 

For that matter my XR650R and CR250R have aluminum frames.  Both see impacts and forces way beyond what a street bike will see.  Try 120' jumps on a MX track or head-deep whoops at 70mph.  Both rock solid and crack-free (and both a decade old now).