Lakerat

Talked to a California tandem builder about the safety of forks on their older tandems. He said their "recommendation" is for a 15 year lifespan before replacement of investment cast crown forks. He also said that threaded forks were doomed to failure since the threading leads to stress risers.

Can't say I've seen or heard of threaded forks failing at or near the threads.

79pmooney

Threaded steerers can fail if the stem does not extend below the threading (either because of not enough stem insertion or extra-long depth of threading). If the stem is deep enough for the end to be below the threads, you should have no issues. I cannot say much re: investment cast crowns other than I haven't hear of them breaking (and as one who nearly lost his life to a crown breaking, that news would get my attention).

Now, I do not have tandem experience. But if everything was properly sized up for the additional loads and executed right, I wouldn't worry. But if the builder has concerns? Does he know something?

Ben

Chombi1 

Isn't that why they stuck wood dowels into steering tubes in the olden days.....??

79pmooney

That won't help either the crown failing or breaking at the bottom of the stem and above the wood. No, that was for non -butted (or poorly executed) steerers failing at the top of the crown.

Ben

Salamandrine 

Yep, if a steer tube fails at the threads, it's because the stem has been raised to an unsafe level. It used to be pretty common for people to raise stems above the safe limit, back in the quill stem days. I have seen a handful of failed steer tubes in my wrenching days, but I've never seen one fail at the threads when the stem is properly inserted.

Now that it's modern times, I'd prefer a threadless steer tube if I was buying a tandem.

unworthy1

this would explain why all the steel bikes over 15 years old with threaded steerers and IC fork crowns have broken!
Shocking that there are so many reports about CF failures yet this gigantic outrage goes almost completely unreported!
Call 60 Minutes!

obrentharris 

Could it be that aforementioned California tandem company wants to sell you a new carbon-fiber, threadless fork... or better still a complete new bike?

Could this be the same California tandem company that has been telling us for over 20 years now that on tandems we must use their 160mm axle spacing or subject ourselves to excessive wheel failure?
Brent

noglider 

I don't believe it.

non-fixie 

Ah! Death tandems!

79pmooney

Tom, how long have investment crowns been used? (I never paid attention to the manufacturing process; just selected the crowns I liked from the framebuilder's selection, trusting him to only show me good ones.)

So, is my 1984 semi-sloping scalloped crown for my Mooney investment cast? Should I have replaced it twice? My 1983 Trek? My 1973 sloped Competition? Am I three times lucky to be alive?

Ben

KonAaron Snake 

I agree with your builder. Because I also care deeply for this community, I am volunteering to dispose of everyone's unsafe custom bicycles. Send me your Mooneys, Ritcheys, Weigles and Kvales. Do it for safety.

Do it for the children.

CliffordK

The failures I've seen are:

• Bulged Threads (probably due to improper stem insertion as above).
• Split at lockring groove. Probably a bad design, only reason to have a keyed system is for centerpull or canti brakes.
• Stripped threads at keyway due to a stuck lockring.

I've had poorly tightened bars before, and was able to safely deal with them. Most steertube failures won't be catastrophic as long as one pays attention and deals with them if they crop up.

OldsCOOL

Geraldo is getting after it!!

CrankyFranky

Ok, I can see a keyed threaded steering tube could be damaged if the stem is raised beyond the safe point and overtightened by some idiot er uninformed bloke. But - do they want us to retire our all our forks with investment cast crowns? To my thinking, IC frame components are at least as strong as more traditional lugs/crowns.
Are they saying that the forks that they built for their tandems were poorly designed?
Am I misunderstanding this?

3alarmer 

.
...yeah. I don't get the logic behind predicting the failure of a casting. I spent a few years pounding on an anvil, and it was pretty old when I started using it. 20 years later I sold it to someone else.

Lakerat

And I was quite relieved to find the fork on my vintage tandem of theirs wasn't made by them since they seem to have little faith in the forks they made. It is a Tange 90A unicrown fork which they don't seem worried about and doesn't require a $450 upgrade including the headset.

Wulf

I think they want to sell you a steel unicrown (welded steel pipes) fork. I have more faith in my low-millage 'Tana' fork than they do.

dweenk

"Whoopee were all going to die!"

Is this a reference to a song by Country Joe and the Fish?

obrentharris 

"One, two, three, four, what are we fighting for...?"

Brent

dweenk

Exactly.

3speedslow

@Lakerat for a moment I thought you were channeling Country Joe and the Fish!

Someone beat me to it!

noglider 

Salamandrine 

So, is the company in question Santana, or someone else? Why beat around the bush about this?

FWIW I've never seen a failed investment cast crown on a fork during the many years I used to wrench. I've heard stories that there was a type of fully sloping crown in the 80s that would fail sometimes. Never saw one. There were those stamped tang-less forks that came on some Treks and other bikes that would fail, or at least cause the blades to fail.

Overall steel forks have exceedingly low failure rates. Very rare to have problems, and catastrophic failure is almost never. I'd be much more wary of a carbon fork on a tandem.

FBinNY 

Welcome to the CYA world. Ask anyone "sueable" whether it's "safe" to do anything, and the answer will be no, or there will be caveats.

There's absolutely no benefit for any manufacturer to say their product is to use beyond some reasonable time frame. However, in out litigious world, it makes sense to answer with a warning that it may jot be safe.

When my nieces were pregnant their OB/Gyn was a family friend who had daughters their age. They learned quickly enough never to ask the doc whether something was OK. Instead they asked his daughters what he told them in answer to the same question, and got much more tempered replies.

Lakerat

I can understand how when you first commence manufacturing, you follow conventional techniques. Then you improvise and improve, and after several generations of improvement and adding safety margins down the road, your first effort looks spindly and weak compared to the improved version. The proper recourse and customer relations method, balancing safety, service, profit, liability, and product confidence is difficult. The route they've chosen doesn't put them in the best light.

This tandem builder has no printed statement of fork reliability that I know of. They deal in hazy innuendo, making it difficult for a bike owner to make an educated evaluation. They've deliberately chosen this course of anxiety creation, real or not (don't know if they are failure prone since they don't say) for some reason, maybe just because they know their new forks are much stronger than their old ones. If they know they are actually defective, they shouldn't be doing what they are doing in my opinion. It could be that fessing up results in going out of business.

If they'd had a statement of weak or defective forks on their early bikes posted clearly on their website, I wouldn't have bought one of their bikes. If I found out later I had, the money spent would have been wasted, because it isn't worth forking out (!) $450 for a replacement fork and headset.