Originally Posted by
reddog3
I'm somewhat of a weight wienie. Go ahead... lecture me all you want but don't expect me to take heed.
The story- I build my own forks and am always looking for solutions to reduce weight whenever possible. The last steel fork I did come in at 604g (650c). 700c forks are about 640-650g depending. The carbon forks I have (1" alloy steerer) are in the 450g neighborhood. I much prefer the appearance of steel forks, and inexpensive carbon forks with 1" alloy steerers are getting harder to come by.
The solution- Rather than use the 2mm wall thickness cromo steerer, utilize a 4130- 1" x .049" (1.2mm) tube. In a 250mm length the weight savings would be about 150g. That puts the completed weight right close to the carbon forks I have, and that is acceptable. Pretty inexpensive way to shed 150 grams.
The question- I'm not looking for warnings cuz I'm gonna do it anyway. What I want to know is, if you've done this did it work, or fail?
This is strictly for my own bikes so if there is a risk I don't care. It won't be catastrophic anyway, so what? C'mon let's hear it- how else are you gonna get a 450g steel fork?
Yeah, I think everyone does want a sound, risk-free fork that saves some grams, but ... are you thinking this through right? You say you're going to eliminate a 2 mm wall thickness CrMo tube in favor of a 1.2 mm 4130 tube. First, CrMo and 4130 are essentially the same alloy. You're really just going to reduce the wall thickness by 40%, which is a really big reduction in strength. When frame tube thicknesses are reduced, there's a change in alloy to one with higher yield strength, and hence can withstand the added stress and strain levels. You're not doing that, you're just greatly reduceing the strength of the fork. I'd recommend at least testing a prototype statically against a conventional design to see how big performance difference is for an actual finished fork. Get some reality behind the idea. If there's a standard for how to test forks for structural integrity and a set of minimum acceptable limits, use those. They're usually not just plucked out of the air.
I'm not sure it just being your frame makes a difference. This does not sound like a good idea.
How to same more weight? Find out where in the fork there is steel that does not contribute effectively to strength and stiffness, or which increases stress risers. Engineers use validated models on computers to do such studies. If you can't do that, question is, why would you believe fork blade and steer tube makers like Reynolds and Columbus, who do employ engineers, might not have done it well enough for your needs?
Be careful.