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Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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Old 10-27-09, 06:15 PM   #1
mikefranktroymi
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Wound-up Fork Problem

We have a two year old Davinci with front and rear disc brakes. While on a ride about a month ago, another rider questioned if my fork was cracked. I looked at it and thought it was just a reflection. Playing it safe, I took it to the shop that I purchased the bike from for an inspection and they too thought it was cracked. They sent the fork back to Davinci who subsequently sent it to Wound-up

I found out that it is cracked and I am awaiting for wound-up to decide if it is under warranty. I sure hope it is under Warranty, we only have about 1500 miles it and we have never hit anything, never ride hard nor crashed. Couple of questions for this esteemed group:

a. How long should it take for wound-up to tell the shop if it is covered or not under warranty
b. Have any of you also experienced fork failure after 1500 miles?
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Old 10-27-09, 06:33 PM   #2
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If it were me, I'd expect an answer within a week of receipt. If I didn't hear by then, i would follow up with a polite phone call.

Prior to getting a new Calfee we put 35,000 miles on our wound-up equiped Robusta and haven't seen any evidence of failure. I am certainly going to take a very close look at it before we ride it again however. Also, ours wasn't spec'd with a front disk.
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Old 10-27-09, 06:57 PM   #3
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I real interested in this thread since our daVinci has front and rear brakes and a Wound Up! :-O
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Old 10-27-09, 09:08 PM   #4
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Hopefully it is resolved quickly.

Maybe I overlooked it, but did you mention the location of the crack.

PK
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Old 10-27-09, 09:21 PM   #5
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I have a wound up fork on my Ti single bike with over 26000 miles on it ....

good luck
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Old 10-28-09, 11:33 AM   #6
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woundup fork

We have a daVinci with a Wound Up fork, V brakes rather than a disc.
At about 500 miles and less than a year old I discovered a small crack in the shoulder of the crown. The dealer thought it might really be a crack so sent it to Wound Up. They provided a new fork under warranty. It took a month or so to get resolved. I am not sure where the delay occurred, at the dealer or WoundUp.
Eric
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Old 10-28-09, 12:21 PM   #7
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I personally would not have a carbon fork on a tandem, least of all one with disk brakes. Rim brakes try to stop your bike from the top of the fork and therefor cause less stress on the fork than a disk brake that tries to stop the bike from close to the axel causing more stress on the top of the fork from leverage. I would put a disk on the rear as well as a drag brake, but not on the front. Also it is harder to get that 'good' bond between two dissimilar materials such as carbon and steel or alum.

I have friends that had there carbon fork on there tandem break while on a flat road doing about 15 mph. The break was at the shoulder of the crown. The result was a broken collar bone for each of them and about 6 months of rehab and recover time.
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Old 10-28-09, 01:16 PM   #8
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Originally Posted by gbenth View Post
I personally would not have a carbon fork on a tandem, least of all one with disk brakes.
Have you not heard of steel or aluminum forks breaking? What would you have them made from?

Forks need to be properly designed to be safe. Carbon disc forks are considerably stronger and heavier than non-disc forks to handle the additional stresses.
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Old 10-28-09, 01:29 PM   #9
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Have you not heard of steel or aluminum forks breaking? What would you have them made from?

Forks need to be properly designed to be safe. Carbon disc forks are considerably stronger and heavier than non-disc forks to handle the additional stresses.
+1

Here is broken steel from our Santana:



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Old 10-28-09, 05:15 PM   #10
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I have friends that had there carbon fork on there tandem break while on a flat road doing about 15 mph. The break was at the shoulder of the crown. The result was a broken collar bone for each of them and about 6 months of rehab and recover time.
Was this a brand new tandem with a brand new fork ridden by a lightweight team that simply failed "just while riding along"? Or, is there some other background that might shed light on this failure? In other words, please share the brand and model of the fork as well as any other details regarding how many years or miles of use the fork and tandem had, the weight (aprox) of the team. Also, what type of brakes were installed on the fork? Caliper, cantilever or disc? Was the tandem ever crashed, dropped or banged into a garage door?


Quote:
Originally Posted by gbenth View Post
I personally would not have a carbon fork on a tandem, least of all one with disk brakes.
Just how many years have you been riding upright tandems? Did you have a bad experience with a failed fork at some point? Again, please elaborate. As best as I can tell from your profile, you appear to be pretty much a recumbent enthusiast at this point in your life. When was the last time you rode an upright, modern tandem with or without a carbon fork?

From the rest of your post:

Rim brakes try to stop your bike from the top of the fork and therefor cause less stress on the fork than a disk brake that tries to stop the bike from close to the axel causing more stress on the top of the fork from leverage. Not even close to accurate. There are differences in how brake energy from a rim brake act on the fork's leg and crown vs. a disc brake, but at the end of the day the greatest force that act on the fork's crown are generated by the tire and wheel via the fork's drop-outs.

I would put a disk on the rear as well as a drag brake, but not on the front. This may just be poor writing, but if not... please note that you can't put a disc brake and a drag (drum) brake on a bike at the same time: it's one or the other based on what's presently available UNLESS you found a tandem hub with an internal rear drum brake that could also be fitted with a disc. I'm not aware of any such hardware in use for upright, multispeed tandems.

Also it is harder to get that 'good' bond between two dissimilar materials such as carbon and steel or alum. Is this making reference to a carbon fork that uses an alloy steerer and crown in conjunction with carbon fork legs, such as what you'd find on the non-disc Wound-Up forks? I only ask because the disc-compatible Wound-Up Duo-Sport is an all-carbon fork. However, that said, I've probably seen more problems with all-carbon forks failing than carbon forks that used carbon legs bonded to alloy crowns and steerers, never mind that most of the tandem forks on the market use alloy drop-outs bonded to the ends of the fork legs.

Last edited by TandemGeek; 10-28-09 at 05:22 PM.
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Old 10-28-09, 06:23 PM   #11
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I was under the impression the Woundup Carbon Fork is CF OVER aluminum tubes - like their seatpost. At least that is what I was told when I bought our CoMo with their post for the Captain and their fork.
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Old 10-28-09, 06:33 PM   #12
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The carbon fork failing resulting in injury to the riders is sad though attention grabbing.

Several months back, when the TandemGeek was discussing his comparison of forks, I became intrigued and researched more in regards to not only geometry specs, but also which forks were, as they say tandem rated. It became very apparent that many of the carbon forks were not rated for this type of use. Not saying this was the cause, but I'd be curious to know if it was a factor.

Granted Carbon and Aluminum don't play well together, especially when moisture is involved. It can be bonded effectively, but like anything can fail.

Maybe the time is right to post a method inspecting composites, with simple tools, to keep teams safe. If there is an interest, let's hear what you want inspected. Maybe I can post a video on using various methods to detect flaws in composite structures.

Although I try and be faithful to inspect our Wound Up Carbon Disc fork, many times I get lazy. This topic will get my but away from the computer and start giving it a good look over. We are big, and I can't say we baby our stuff, it gets ridden and deals with all sorts of road conditions.

PK
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Old 10-28-09, 06:34 PM   #13
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The crack is just below the crown. the fork is all carbon
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Old 10-28-09, 06:36 PM   #14
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That is exactly where mine cracked. Well it is good to see they stand by their product
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Old 10-28-09, 06:43 PM   #15
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Quote:
Originally Posted by joe@vwvortex View Post
I was under the impression the Woundup Carbon Fork is CF OVER aluminum tubes - like their seatpost. At least that is what I was told when I bought our CoMo with their post for the Captain and their fork.
The Wound-Up carbon fork steerers use an aluminum insert to reinforce the stem clamping area and to support the use of a standard star-nut, which is similar to the True Temper Alpha Q. However, the fork legs are filament wound, compression molded carbon as is the steerer.

On the standard rim brake Wound-Up forks a CNC aluminum crown and drop-outs are CNC'd 7075 bonded to the carbon fork legs and steerer. On the Duo, a filament wound, all-carbon crown replaces the CNC'd 7075 piece and a CNC'd 7075 disc caliper mount is added to the lower left fork leg.
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Old 10-28-09, 07:02 PM   #16
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On our Duo, I did not notice any aluminum in the steer tube. The setup uses an expanding type fastener that wedges to the steer tube ID via an internal wrenching bolt. The stem cap is special having internal female threads that engage male threads on the wedge fastener.

If our fork does have aluminum in the steer tube, I must have overlooked it or it's bladder molded internally and compression molded externally. It does if I recall correctly have a lower crown race aluminum seat securely mounted to the lower portion of the steer tube.

Regardless, I need to give it an inspection, in good light.

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Old 10-28-09, 07:14 PM   #17
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Maybe the time is right to post a method inspecting composites, with simple tools, to keep teams safe.
The most basic and simple tools: your eyes and other senses, such as the ability to detect a loss of rigidity in a carbon component.

With few exceptions the carbon parts I've seen that began to fail developed visible hairline cracks that propagated slowly. Again, with few exceptions, on carbon tandem forks the cracks developed around the crown, usually running parallel to the fork legs. In one case, the owner was pretty oblivious to those tell-tale cracks and after several years and thousands of miles of wear the failure migrated to the base of the steerer tube. The failing fork was only 'noticed' by the captain when he lifted the tandem to put it away and realized is fork was flopping back and forth at the base of the steerer after a spirited 40 mile ride: imagine a carbon fork acting like a springer motorcycle fork. Of course, this same fork was nearly impossible to get off the frame because the spacers had become fused to the carbon steerer (can you say galvanic corrosion) after years of neglected head set maintenance. Yeah, the Chris King headset was also severely corroded and had to be replaced on this same tandem.

Heavy-sweat generators take note; perspiration left to collect in headsets, stem parts, shifters and bottom brackets will ruin those parts UNLESS they are flushed with fresh water after those hot rides AND serviced on a regular basis.

Thankfully, that particular fork design (AME Alpha Q) was acquired by True Temper who implemented changes and a more robust QA process that eliminated the weakness in the AME-produced Alpha Q X2s.

Same thing with stems and seatposts: check the highest stressed areas on a periodic basis during routine bike cleaning and maintenance.

Bottom Line: Visually inspect your carbon frames and components when you do normal maintenance or after any type of hard impact, e.g., crash, driving into a garage door with the bike on the roof, or after being shipped and showing up in a damaged shipping container. If you see what looks like a hairline crack in the clear coat or paint, it probably is. Send the part back to the manufacturer and let them do the biopsy.
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Old 10-28-09, 07:25 PM   #18
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On our Duo, I did not notice any aluminum in the steer tube. The setup uses an expanding type fastener that wedges to the steer tube ID via an internal wrenching bolt. The stem cap is special having internal female threads that engage male threads on the wedge fastener.
It's quite possible that Wound Up finally dumped the aluminum insert and adopted a new wedge-type insert similar to the one that Reynolds has been using in its Ouzo Pro tandem forks. (Photo below) I'll defer to anyone who's recently bought a Wound Up fork as to what the standard hardware might be.



However, at least for earlier Wound-Up forks, the low-tech aluminum insert was used and that's the only thing that came to mind with regard to there being any aluminum sleeves in his pre-Duo / non-disc Wound Up fork.


Last edited by TandemGeek; 10-28-09 at 07:47 PM.
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Old 10-28-09, 07:41 PM   #19
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My experience with CF is limited to our CF helmet mounted displays and the Wound-up forks on our daVinci. I would think almost any defect propagating to the surface with raise some tiny carbon fibers. If these can't be felt by finger tip, then certainly a cotton ball rubbed over the fork periodically would snag on a defect.
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Old 10-28-09, 08:07 PM   #20
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Quote:
Originally Posted by TandemGeek View Post
It's quite possible that Wound Up finally dumped the aluminum insert and adopted a new wedge-type insert similar to the one that Reynolds has been using in its Ouzo Pro tandem forks. (Photo below) I'll defer to anyone who's recently bought a Wound Up fork as to what the standard hardware might be.



However, at least for earlier Wound-Up forks, the low-tech aluminum insert was used and that's the only thing that came to mind with regard to there being any aluminum sleeves in his pre-Duo / non-disc Wound Up fork.

Without doubt the wedge fastener and not the aluminum tube.

PK
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Old 10-28-09, 08:11 PM   #21
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My experience with CF is limited to our CF helmet mounted displays and the Wound-up forks on our daVinci. I would think almost any defect propagating to the surface with raise some tiny carbon fibers. If these can't be felt by finger tip, then certainly a cotton ball rubbed over the fork periodically would snag on a defect.

If fibres can be noticed, either visually or by a "rag" test, there is extensive damage.

It is very common to have cracks in the surface resins or even into the carbon structure with no appreciable defect that can be felt. Sometimes at most, you may catch a finger nail when crossing the defect.

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Old 10-29-09, 09:16 AM   #22
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Originally Posted by TandemGeek View Post
The Wound-Up carbon fork steerers use an aluminum insert to reinforce the stem clamping area and to support the use of a standard star-nut, which is similar to the True Temper Alpha Q. However, the fork legs are filament wound, compression molded carbon as is the steerer.

On the standard rim brake Wound-Up forks a CNC aluminum crown and drop-outs are CNC'd 7075 bonded to the carbon fork legs and steerer. On the Duo, a filament wound, all-carbon crown replaces the CNC'd 7075 piece and a CNC'd 7075 disc caliper mount is added to the lower left fork leg.
Thanks. I haven't check the steerer tube and our Wound up is circa 2004.
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Old 10-29-09, 09:34 AM   #23
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Without doubt the wedge fastener and not the aluminum tube. PK
+1. Our Duo, (although it was for cantis, not disk), had no aluminum insert.
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Old 10-30-09, 05:15 PM   #24
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FWIW, I can attest to PMK's professional knowledge of CF materials, manufacturing, damage evaluation and repair, based on his experience in applications much higher tech than bicycles. I know that I will "funnel" any of my own questions about CF through him in the future.
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Old 11-04-09, 12:32 AM   #25
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A couple of years ago, at a Seattle Bike Expo, there was an engineer familiar with cf for bikes giving a talk. He said that the simplest test for checking on carbon fiber health was the "nickel" or "quarter" test. You just take a coin and tap it repeatedly across the cf surface. If the sharp tap turns into a soft thud, you've probably got a problem. At least, it bears further scrutiny.

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