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Old 12-21-11, 12:57 PM   #1
reddog3
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Fork Builders- Steerer tube question

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?
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Old 12-21-11, 01:08 PM   #2
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A broken steerer tends to fall into the catastrophic failure category.
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Old 12-21-11, 01:33 PM   #3
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How good is your insurance?
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Old 12-21-11, 01:38 PM   #4
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been nice knowing you.

in all seriousness, it depends on what you are going to do with this. If you are actually going to ride it hard, you will break it. People used to put hardwood dowels in their steerer tubes because there is a history of breaking them. If you would only do things like ride the occasional time trial, and inspect regularly, it probably would be ok
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Old 12-21-11, 01:51 PM   #5
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The weight difference wouldn't be as much as you think. Steerers are butted 2.3-1.55. I seem to remember some reputable builder using 0.065" (1.65) Reynolds straight gauge steerers. Probably higher strength than 4130. Even then you won't same much weight.
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Old 12-21-11, 02:24 PM   #6
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By the way I doubt you will find anyone that has done that. If you really want to know, build one and sent it for fatigue testing.
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Old 12-21-11, 02:31 PM   #7
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Probably the worst area to trim weight.

Most riders use the front brake because it's the most effective, due to the forward shift of the CoM loading the front wheel's contact patch. Under hard front wheel braking, you potentially load the front wheel (and steerer) with >80% of the bike's gross. Throw-in a small pothole and 180 lb rider and the dynamic bending loads on the steerer can easily double.
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Old 12-21-11, 03:21 PM   #8
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Make a list of lightweight 1" steerers being produced today..........

See my point?

FWIW, 1.125" OXPLAT steerers are lighter, stiffer, AND stronger than the available 1" stuff.

BUT, since you seem above listening to reason, if you hurry with your build you might still be able to get nominated for a 2011 Darwin Award!
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Old 12-22-11, 12:15 AM   #9
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1" fork's steerers are substantially butted for a reason..

Keith Bontrager saved weight on the Cross forks he made in the 80's

by machining an aluminum triple clamp fork crown..
all 3 tubes potentially can be heat treated,

since only the fork tips need to be brazed in ,
the heat treatment isn't changed around the fork crown.

columbus mandrels imparted a ribbed interior on the tube butts,
including the fork.

Last edited by fietsbob; 12-22-11 at 12:30 AM.
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Old 12-22-11, 10:33 AM   #10
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Make a list of lightweight 1" steerers being produced today..........

See my point?

FWIW, 1.125" OXPLAT steerers are lighter, stiffer, AND stronger than the available 1" stuff.

BUT, since you seem above listening to reason, if you hurry with your build you might still be able to get nominated for a 2011 Darwin Award!
Actually I'm not above listening to reason, and have given this some thought, short of actual testing. I'm aware that immediate failure/breakge would be a problem, but would like to think that inspections would catch a problem before it gets to that point if it will.

One thing I'm curious about is the actual load o the steerer tube and how strong it actually needs to be. Obviously the major stress will be at the tube/crown joint area. I'd think there's more strain on the legs to crown connection than on the steerer tube, even though there's two legs. I don't think it needs to be overbuilt- we'll see.

I could just go 1 1/8, but it defeats my purpose.

As I don't weigh much, or run a front brake, and won't bang too many RR tracks or let anyone else ride it... to me it's worth testing. Why err on the cautious side? I'll let you know where to send flowers.
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Old 12-22-11, 04:14 PM   #11
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Lots of 'reasoning' in the following, but of course, you need to read it.... and understand it. But given your present attitude, I suspect you won't.

http://www.wpi.edu/Pubs/E-project/Av...cycle_Fork.pdf
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Old 12-22-11, 05:13 PM   #12
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if you never run a front brake then that will probably kill you first. I think braking forces are significant elements in fork fatigue failures.
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Old 12-23-11, 11:18 AM   #13
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Lots of 'reasoning' in the following, but of course, you need to read it.... and understand it. But given your present attitude, I suspect you won't.

http://www.wpi.edu/Pubs/E-project/Av...cycle_Fork.pdf
Hey- thanks for providing that link- interesting stuff. The failures exhibited were where I'd expect them to be in a fork of that style construction. There was no analysis
of failures in the steerer tube proper since the cracks appeared in the blades first. One could assume that if the blades had not failed, there may have been similar failures of the steerer in the same zone.

Since the fork construction in the test is different (mine isn't unicrown) I didn't find the actual info I was hoping for. I'm thinking that the actual strain on the steerer tube above the crown race is way below the yield point in the steerer tube I'm contemplating.

I wish I could afford some destructive testing of a controlled and safe nature, but not in the cards just to satisfy my curiosity. So, I'll just have to put one together and bang it around a bit, then do some visual inspections, place it back in the jig for an alignment check, and maybe even some magnetic particle tests.

For all you well wishers I appreciate the thoughts, I am however a risk taker, but do so with at least one eye on safety. It's the risk that is the fun part!

Unterhausen- I do have bikes with front brakes and realize the value, but my fun bikes don't. When I was a pup (60's and 70's) racing flattrack and speedway, any brake at all was just a handy feature to have for maneuvering around the pits. In some classes and events brakes were prohibited. You turned the front wheel abruptly at the end of the straight, to shift the weight forward, so you could set up the slide that got you around the corner. If you had brakes you weren't goin' fast enuf. That's probably where my "attitude" comes from. LOL
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Old 12-23-11, 01:16 PM   #14
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if you read to the end, they "optimized" the fork and it broke at the steerer.
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Old 12-23-11, 01:37 PM   #15
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Why not braze-in a short section of smaller diameter tubing at the bottom of the steerer, where forces acting on the fork will be greatest...?
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Old 12-23-11, 02:02 PM   #16
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because it will break at where the reinforcement ends. The best thing to do probably involves machining, hopefully on the id
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Old 12-24-11, 04:29 AM   #17
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Every time I visit this thread, it instantly disturbs me. Why initiate a thread in the first place, when you were irreversibly fixated on altering such a vital component?... and throughout, rigidly defiant of the potential consequences.

To me, this thread isn't about modifying a bicycle part... it's about the loss of common sense, and the absents of respect for your own well being. Before you post again, take a gander and read through all the carbon fork failures posted on BF. It's glaring, undeniable evidence that no other, single bike component embraces the capacity for serious injuries & death.... than fork failures.

All I can say is... you're damn lucky I'm not a Mod.
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Old 12-24-11, 07:31 AM   #18
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It wasn't long after the mountain bike world decided that handlebars would be a good place to shave some grams when somebody coined the term "stupid light". I hadn't thought about that phrase for a long time... until I saw this thread.
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Old 12-24-11, 11:40 AM   #19
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All I can say is... you're damn lucky I'm not a Mod.
Add me to that list of being lucky you are not a mod.
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Old 12-24-11, 04:51 PM   #20
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Originally Posted by reddog3 View Post

One thing I'm curious about is the actual load o the steerer tube and how strong it actually needs to be. Obviously the major stress will be at the tube/crown joint area. I'd think there's more strain on the legs to crown connection than on the steerer tube, even though there's two legs.
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I'm thinking that the actual strain on the steerer tube above the crown race is way below the yield point in the steerer tube I'm contemplating.
Two things: Firstly, you are confusing load, stress and strain. A load on the part causes stress in the material, strain of this material is its response.

There may well be more stress in the blade / crown connection than the crown / steerer connection but I can only see that being true when there is more material there, which is exactly what you are taking away. The load doesn't magically disappear.

Last edited by Mark Kelly; 12-25-11 at 12:21 AM.
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Old 12-24-11, 06:11 PM   #21
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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.
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Old 12-24-11, 06:15 PM   #22
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Why not braze-in a short section of smaller diameter tubing at the bottom of the steerer, where forces acting on the fork will be greatest...?
As Peugeot did on the UO-8 perhaps 50 years ago, if not more.
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Old 12-24-11, 10:57 PM   #23
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Jesus Christ! The dude is just asking for some evidence or even feedback on People who have used custom 1" steerers on steel forks. The advice against what he proposes is one thing, but the obvious petty insults to the dude is just wrong.
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Old 12-24-11, 11:29 PM   #24
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Jesus Christ! The dude is just asking for some evidence or even feedback on People who have used custom 1" steerers on steel forks. The advice against what he proposes is one thing, but the obvious petty insults to the dude is just wrong.
There are sensible places to try to save weight, and then there are stupid places to try to save weight.

Steer tubes are heavy for a reason. Save your weight somewhere else.
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Old 12-26-11, 08:51 AM   #25
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There are sensible places to try to save weight, and then there are stupid places to try to save weight.

Steer tubes are heavy for a reason. Save your weight somewhere else.

Yeah, no sh__ Sherlock.
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