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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 05-25-12, 07:02 AM   #1
PMK
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The carbon fibre fork, good or bad

Without jinxing us, since we ride a carbon fork, I was wanted to share some information I learned this past week while attending SAMPE, pretty much an industry trade show for aerospace composites and other industries (sporting goods, racecar, medical, etc) that utilize high end composite materials, with lectures and so forth.

One of the sessions I attended, and expected an aerospace topic based on the session title, was a pleasant surprise. The presenter opened his topic and explained that this would be in regards to carbon fibre bicycle forks.

In typical engineering fashion, there was a planned set of goals and theoretical data to show possible expected results.

The primary focus area was in regards to the carbon crown area. This was on a single bike style fork with a a full carbon fork (blades, crown, steer tube).

After some slides on dimensions, loadpaths, CG, rider weight and speeds, some resultant data was presented.

The data was then applied into a graph of sorts to illustrate expected loads induced onto the fork crown at given speeds vs given road feature defects.

The theoretical end was one of the emergence of a defect (I believe it was a 3mm x 6mm defect) and how it would ultimately reduce the strength.

This was not lab tests where forks were actually tested, rather an information project that began to emphasize quality manufacturing, with no built in defects at manufacture. Also, mentioned was the importance of the manufacturer to test designs and sample forks to ensure good quality control.

Suffice to say, for all inspections done to OUR fork, these will be accomplished with a proper tap test, with the fork loaded with the disc brake applied. Thereby, putting a slight amount of deflection into the fork, to make any defect more apparent.

During the Q&A time after the presentation, it did become apparent that this is an area where one should consider a quality component from a reputable manufacturer.

As a side note, I have read here on BF that there was a similar study done where forks were lab tested. I have never seen those results and wonder if they are available.

In summary, inspect your fork, and composite wheels. The loads on these items get crazy high on singles...tandems I suspect are no doubt beyond doubly worse.

PK

Last edited by PMK; 05-25-12 at 07:05 AM.
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Old 05-25-12, 08:58 PM   #2
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34,000+ miles on our Alpha Q X-2 fork on our Zona tandem.
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Old 05-28-12, 07:02 AM   #3
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Sorry quality products from reputable manufacturers don't exist in the bicycle industry. First of all you don't make a spring out of carbon fiber, the fork is a spring. Second of all the public has not been warned of the dangers of matrix failure due to ultraviolet light. In the aircraft industry you either design a part to last forever in normal use. Or you design a part for a limited lifespan and replace the part when the law requires you to do so. When bicycle parts fail the nation transportation safety board will not show up to inspect the damage and recover the black box. I can give you the horror stories of failures of reputable manufacturers but I don't want to be sued never the less I will give you one. Teledyne built a frame out of titanium they made the tubes over sized except they had to swage the down tube so the Campagnolo shifters would fit. This is where the frame broke. As an aside the head of the EPA in Oregon a Mr. Petrovitch told me he didn't have enough inspectors to keep up with the violations Teledyne Wa Chang a place that catches on fire on a regular basis. If you had to work with carbon fibre on a regular basis you would be looking for an alternative. The human body ignores carbon other fibers it can deal with this is why you can eat glass but not diamond dust "bort" it will chew up your stomach and kill you. All of these "reputable" manufacturers will eventually decide that dealing with the EPA is too much trouble then they will transfer manufacturing to china which does not have any heath and safety laws.
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Old 05-28-12, 09:03 AM   #4
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Sorry quality products from reputable manufacturers don't exist in the bicycle industry. First of all you don't make a spring out of carbon fiber, the fork is a spring. Second of all the public has not been warned of the dangers of matrix failure due to ultraviolet light. In the aircraft industry you either design a part to last forever in normal use. Or you design a part for a limited lifespan and replace the part when the law requires you to do so. When bicycle parts fail the nation transportation safety board will not show up to inspect the damage and recover the black box. I can give you the horror stories of failures of reputable manufacturers but I don't want to be sued never the less I will give you one. Teledyne built a frame out of titanium they made the tubes over sized except they had to swage the down tube so the Campagnolo shifters would fit. This is where the frame broke. As an aside the head of the EPA in Oregon a Mr. Petrovitch told me he didn't have enough inspectors to keep up with the violations Teledyne Wa Chang a place that catches on fire on a regular basis. If you had to work with carbon fibre on a regular basis you would be looking for an alternative. The human body ignores carbon other fibers it can deal with this is why you can eat glass but not diamond dust "bort" it will chew up your stomach and kill you. All of these "reputable" manufacturers will eventually decide that dealing with the EPA is too much trouble then they will transfer manufacturing to china which does not have any heath and safety laws.
FWIW, I DO work with carbon fibre everyday. Actually, "hands on" at an aerospace level of quality.

It appears from your reply that you have involvement with carbon fibres or graphite fibres, I'd guess possibly nano fibre enhanced matrix products also. So if as you state, carbon is a poor material for a fork, and from your reply it sounds like titanium is prone to failure from the swaging, which in theory could carry over to low quality titanium welds. Aluminum has neat modulous numbers but is crack prone or notch sensitive in some of the preferred high end bicycle alloys. Plus again requires many operations besides welding to have strength and longevity. Steel is proven and often simpler to work with, however once internal corrosion goes unnoticed it can be just as crazy in a failure mode as any other material.

I started this topic to bring awareness to those of us that run carbon fibre forks. Once the actual report data is in hand, if not copyrighted I'll see if it is possible to share it.

I'd really enjoy hearing your best fork material for a tandem bicycle that is ridden by an average team of say 300 pounds and will occasionally push the speeds close to 45 / 50 mph.

Awesome reply you posted, excited to hear more.

PK
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Old 05-29-12, 06:35 AM   #5
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Without jinxing us, since we ride a carbon fork, I was wanted to share some information I learned this past week while attending SAMPE, pretty much an industry trade show for aerospace composites and other industries (sporting goods, racecar, medical, etc) that utilize high end composite materials, with lectures and so forth.

One of the sessions I attended, and expected an aerospace topic based on the session title, was a pleasant surprise. The presenter opened his topic and explained that this would be in regards to carbon fibre bicycle forks.

In typical engineering fashion, there was a planned set of goals and theoretical data to show possible expected results.

The primary focus area was in regards to the carbon crown area. This was on a single bike style fork with a a full carbon fork (blades, crown, steer tube).

After some slides on dimensions, loadpaths, CG, rider weight and speeds, some resultant data was presented.

The data was then applied into a graph of sorts to illustrate expected loads induced onto the fork crown at given speeds vs given road feature defects.

The theoretical end was one of the emergence of a defect (I believe it was a 3mm x 6mm defect) and how it would ultimately reduce the strength.

This was not lab tests where forks were actually tested, rather an information project that began to emphasize quality manufacturing, with no built in defects at manufacture. Also, mentioned was the importance of the manufacturer to test designs and sample forks to ensure good quality control.

Suffice to say, for all inspections done to OUR fork, these will be accomplished with a proper tap test, with the fork loaded with the disc brake applied. Thereby, putting a slight amount of deflection into the fork, to make any defect more apparent.

During the Q&A time after the presentation, it did become apparent that this is an area where one should consider a quality component from a reputable manufacturer.

As a side note, I have read here on BF that there was a similar study done where forks were lab tested. I have never seen those results and wonder if they are available.

In summary, inspect your fork, and composite wheels. The loads on these items get crazy high on singles...tandems I suspect are no doubt beyond doubly worse.

PK
Very interesting post. I am not an engineer and have a basic question. Is the stress on a fork a linear relationship to the weight of the bike and riders? In other words, if the weight of the bike and riders is doubled, would the stress on the fork when hitting a pothole for instance more than double?
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Old 05-30-12, 12:31 PM   #6
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As a side note, I have read here on BF that there was a similar study done where forks were lab tested. I have never seen those results and wonder if they are available.
Bert Hull was the product manager at True Temper Sports / Alpha Q before they exited the composite cycling business (a by product of True Temper's bankruptcy recovery plan) and now consults for several different high-end bicycle manufacturers. His test protocol for forks at True Temper and the changes they made to the Alpha Q forks after the brand and patents were acquired from AME was once describe to me by another manager whose name escapes me at the moment. However, they had an incredibly robust series of tests that they ran on forks pulled at random from every production run to ensure they met their stringent standards for strength and fatigue life... a fatigue life that few tandem owners would likely ever reach in a lifetime of riding. I'm pretty sure I mentioned this in at least one posting after we had one of our early True Temper Alpha Q's sent back for an inspection and replacement of the drop-outs, i.e., circa 2003. I believe Co-Motion used True Temper to test their candidate forks when they were looking to develop a house-branded composite fork, which I also mentioned here in the forums.

As far as UV, heat, etc... you can find all kinds of data and anecdotal reports on some of the things composite manufacturers have done over the years to subject their products to real world rigors. Bert Hull once described a test they did in San Diego where composite hockey sticks were attached to a composite roof rack and left exposed to the elements for 5 years before being subjected to their normal new product testing: zero degradation.

While I'll wait with anticipation to see the test report mentioned by PMK in the OP of this thread, I will note that at least for the forks and frames that we have purchased over the years, the folks doing the development and manufacturing have been adamant that things such heat (up to 300*F) and UV will not degrade the strength and durability of the composites they have used to make their products. I have no reason to doubt them, as some of them are long-time friends. Yes, UV will cause the expoxy resins to yellow -- which you can see on all three of our unpainted Calfee frames despite frequent application of RaggTopp & Aerospace 303 UV protectant -- but it's purely cosmetic. I've been told the very same thing by friends and friends of friends who produce composite components and major structural components for motorsports racing, e.g., the Panoz Motor Sports Group and others.

FWIW, I do not have any special concerns for the various composite forks or our unpainted Calfee frames. They get inspected with the same frequency as our steel, aluminum and titanium bikes and forks. Having seen a few of the older AME Alpha Q forks that did eventually show signs of fatigue failures, I have a good idea of what to look for and when to start looking in earnest. However, we've passed at least two of those benchmark milestones on two of our Alpha Q forks and are approaching another with no hint of any issues. Our Reyonlds Ouzo Pro forks will most certainly outlast us... those things are far more robust than even the True Temper version of the Alpha Q and don't get used nearly enough. In fact, our triplet uses a 1.25" Reynolds Ouzo Pro Tandem fork: very stable through very hard corners even with 450lbs of riders on board this past Sunday.

Last edited by TandemGeek; 05-30-12 at 12:45 PM.
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Old 05-30-12, 02:56 PM   #7
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As with any product proper use and inspection of the carbon component by someone who can spot any possible problems is the key. Steel, Ti or carbon if you ride it you should keep an eye on it.

For my part I am confident with the long term durability of carbon in normal use. On the other hand after a crash I feel more comfortable in my ability to recognize a problem in a steel fork than a carbon one. As a result I would be more likely to replace a crashed carbon tandem fork than a steel one.
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Old 05-30-12, 03:43 PM   #8
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Bike Rumor has a factory tour at Enve Composites, which I think is interesting, informative, and confidence inspiring as to the safety and reliability of carbon fiber in general, and Enve's products in particular.

ENVE COMPOSITES FACTORY TOUR INSIDE LOOK AT COMPANY & CARBON FIBER MANUFACTURING

An example is Enve's impact test on their carbon wheels. A 50 lb. weight is dropped from increasing heights until the rim fails.


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Old 05-30-12, 06:46 PM   #9
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On the other hand after a crash I feel more comfortable in my ability to recognize a problem in a steel fork than a carbon one. As a result I would be more likely to replace a crashed carbon tandem fork than a steel one.
How did you learn to recognize what to look for in a steel fork? How about when those aluminum forks hit the market for a while? What makes it any different for a composite fork, i.e., just learning how to do the same.

Yes, I hear folks talk about the subtleties of composite failures all the time but having seen crash damaged composites they have their own way of letting you know there's something amiss, i.e., visible damage, or excess deflection under static loading, new sounds or changes in handling, etc. Close attention is simply called for after every ride or when some type of change is noticed. Obviously, when in doubt, it's time to consult the experts who made your fork, or Calfee when all else fails.

Just something to consider.
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Old 05-30-12, 10:00 PM   #10
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Speaking of carbon forks, is anyone using disc brakes up front? What fork are you using? How do you like it?
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Old 05-31-12, 06:26 AM   #11
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How did you learn to recognize what to look for in a steel fork? How about when those aluminum forks hit the market for a while? What makes it any different for a composite fork, i.e., just learning how to do the same. ....
My comfort with steel vs carbon is partially logical and I admit like all gut feelings partially emotional. I have lived 54 years using and working with steel products. I am more comfortable with it and how it feels, looks and sounds prior to failing.

I am sure one can detect damaged carbon however I have not had the experience of seeing and hearing damaged carbon for myself. At this point I am examining and tapping on carbon trying to compare it what I imagine a failed carbon member should look or sound like. It is possible that I would easily notice any damage but the lack of personal experience is not confidence inspiring.

This is not an indictment of carbon as a material. I have used carbon forks and will most likely use them again. Each material has its strengths and weaknesses and we should not view them all the same. For instance I would avoid a aluminum fork simply because I know it should be designed stiff enough not to flex and fatigue. This can be done and aluminum forks are found on some low cost bikes and I am sure they are safe. On the other hand I don't see any advantage other than cost of a very stiff aluminum fork and do not want a flexy one because it might fail from repeated flexing (unlike carbon or steel).

By the way if anyone can find be a carbon tandem fork that has about 60mm rake and canti studs set for 650B wheels then let me know I will buy it and save some weight. I may buy two just in case we crash one.

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Old 05-31-12, 01:03 PM   #12
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By the way if anyone can find be a carbon tandem fork that has about 60mm rake and canti studs set for 650B wheels then let me know I will buy it and save some weight. I may buy two just in case we crash one.
On Wound Up Composites pricing page, they have the following note: "7) Some Custom Fork Geometries Can Be Accommodated. (Please Inquire for Pricing)" But, unless you are an OEM, they want you to purchase through your LBS or online through Aspire Velotech, whose Wound Up Ordering webpage states:
[TABLE="width: 436"]
[TR]
[TD="align: left"]Wound Up Fork options...
[/TD]
[/TR]
[TR]
[TD]
  • Fender Eyelets Added to a Wound Up Fork
  • Dual Option Brakes (Disc & Linear Pull)
  • Satin/Matte Finish Coating (Fork Legs)
  • Set Up Road Fork for Cantilever Brakes
  • Add Disc Tab to Road Fork (40mm, 45mm Rake)
  • Black Anodized Set (Crown, Dropouts, Disc Tab, etc.)
  • Custom Geometries are Reviewed.
[/TD]
[/TR]
[TR]
[TD]Please Contact Us for details.[/TD]
[/TR]
[/TABLE]

So, you might be able to get Wound Up to build you a custom fork (or two) for 650b wheels. If you do contact them, let us know what you find out, as I can see a small market for this type of fork.
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Old 05-31-12, 01:23 PM   #13
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On Wound Up Composites pricing page, they have the following note: "7) Some Custom Fork Geometries Can Be Accommodated. (Please Inquire for Pricing)" But, unless you are an OEM, they want you to purchase through your LBS or online through Aspire Velotech, whose Wound Up Ordering webpage states:
[TABLE="width: 436"]
[TR]
[TD="align: left"]Wound Up Fork options...
[/TD]
[/TR]
[TR]
[TD]
  • Fender Eyelets Added to a Wound Up Fork
  • Dual Option Brakes (Disc & Linear Pull)
  • Satin/Matte Finish Coating (Fork Legs)
  • Set Up Road Fork for Cantilever Brakes
  • Add Disc Tab to Road Fork (40mm, 45mm Rake)
  • Black Anodized Set (Crown, Dropouts, Disc Tab, etc.)
  • Custom Geometries are Reviewed.
[/TD]
[/TR]
[TR]
[TD]Please Contact Us for details.[/TD]
[/TR]
[/TABLE]

So, you might be able to get Wound Up to build you a custom fork (or two) for 650b wheels. If you do contact them, let us know what you find out, as I can see a small market for this type of fork.
Thanks for the info.
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Old 05-31-12, 01:54 PM   #14
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... you might be able to get Wound Up to build you a custom fork (or two) for 650b wheels.
Agreed; Wound Up would be the logical source for any custom fork work. Their fork design -- in addition to being the one that provides true steel fork stability & tracking -- is also the most modular and easiest to "tweak", e.g., steerer, crown, fork legs, I.S., disc mount, drop-outs are all individual components that end up being bonded together.
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Old 05-31-12, 02:44 PM   #15
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Speaking of carbon forks, is anyone using disc brakes up front? What fork are you using? How do you like it?
Wound Up Duo on our travel tandem. We like it and the carbon crown improves the look.
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Old 05-31-12, 03:34 PM   #16
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Wound Up Duo on our travel tandem. We like it and the carbon crown improves the look.
I just located a Wound Up Duo, that will be built up for travel purposes, I am interested to see the if there is an improved stopping distance. My reason for going disc up front was to eliminate the possibility of heat induced front tire failure.
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Old 05-31-12, 04:59 PM   #17
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Speaking of carbon forks, is anyone using disc brakes up front? What fork are you using? How do you like it?
Carbon fork yes, Wound Up carbon Duo, all carbon with aluminum drop outs and disc caliper mount. Yes we run a 203 front disc on it.

PK
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Old 05-31-12, 05:02 PM   #18
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FWIW, Wound Up, was at the SAMPE composites show. I spoke with them briefly, sounds like they have a lot happening at their facility.

PK
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Old 05-31-12, 08:15 PM   #19
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Just asking, but doesn't it cause problems to put a disc brake on a non-suspension fork? Seems like the forces associated with braking would be at odds with the other jobs the fork needs to perform...
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Old 05-31-12, 08:31 PM   #20
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...but doesn't it cause problems to put a disc brake on a non-suspension fork?
No.
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Old 05-31-12, 09:44 PM   #21
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No.
Thanks for the clarification. I'll withdraw the question. And forget what I learned in all those classes on statics and dynamics! 8^)
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Old 06-01-12, 12:46 AM   #22
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Thanks for the clarification. I'll withdraw the question. And forget what I learned in all those classes on statics and dynamics! 8^)
What did you learn in those classes that made you ask the question? All I can see you getting from a disc brake fork is an uneven (one leg only) bending and torsional load from the caliper. I would of thought a rigid fork could handle such things better than a suspension fork.
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Old 06-01-12, 03:27 AM   #23
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Thanks for the clarification. I'll withdraw the question. And forget what I learned in all those classes on statics and dynamics! 8^)
Obviously the loads induced are not symmetrical. However like anything with a quality design, at that phase the proper design will offer additional strength to handle the loads.

A rigid fork, regardless of material with identical legs, will flex the same for each side during almost all cycles except with a disc brake. The disc mount will induce additional bending into the fork leg, which could alter where the axle is positioned under braking.

The axle itself can play a huge role also. Not only inregards to steering precision but also handlebar feedback. Depending upon the design, this could be a blessing or a curse.

In the real world, none of the forks we run on the tandems, (Wound Up Carbon Duo, Fox 40 Kashima, or the Modified ATC) exhibit any noticeable tracking, steering or deflection under braking concerns.

PK
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Old 06-01-12, 10:44 AM   #24
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First off, you asked a closed-ended question as to whether a disc 'caused problems on a non-suspension fork'. Secondarily -- and given you and yours are a seasoned tandem team & experienced cyclists -- your curiosity regarding how a disc brake installation might present problems for a rigid fork that aren't present on suspension forks suggested you knew something about, or at least had experience with discs on suspension forks. Therefore, a simple and clear answer seemed appropriate.

Had you not been so specific in your comparitive reference to suspension forks vs. rigid forks or had you used an open-ended question I would have likely eleaborated... but that didn't seem necessary to answer the question as it was framed.

Clearly there are design considerations for rigid forks, but they're the same ones a suspension fork designer needs to consider, i.e., how to design or spec materials for the asymmetric loads, the load path of the brake energy relative to drop-out alignment and/or the need for passive axle retention, how best to incorporate the I.S. caliper mount, cable routing, etc.

Now, to be fair, there was some 'junk science' floated around regarding front-mounted discs on tandems a few years back by one of the OEMs who was also quite vocal about the suitability of certain disc brakes for tandems. Some of those writings may still be floating around and a casual reader could certainly be led to believe that there are "problems & risks" associated with using discs on road tandems and with rigid forks if they had never been exposed to the subsequent and extensive discussions -- never mind vast amounts of real-world experience -- that rebutted the purported problems and risks.

However, at least as far as current state of the art, production forks designed to support front disc installations on tandems present no special "problems" in terms of how they perform for all levels of users. In fact, Cannondale has been spec'ing OEM dual discs on their road tandems since 2003 at a time when only boutique tandem builders were just beginning to sort out how to modify chromoly forks for use with discs that addressed the design considerations. Since then, the OEM tandem builders have sourced both chromoly and composite production forks that accommodate discs for their tandems such that there are several different options for folks who believe that having a front disc brake is preferrable to a rim brake. Boutique tandem builders have simply adopted the production fork offerings, as would be expected
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Old 06-01-12, 02:22 PM   #25
waynesulak
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Location: Ft Worth, TX
Bikes: 650B tandem converted from Santana Arriva, Santana Noventa, Boulder Bicycle 700C, Gunnar Sport, Trek TX700,
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Quote:
Originally Posted by rhino919 View Post
On Wound Up Composites pricing page, they have the following note: "7) Some Custom Fork Geometries Can Be Accommodated. (Please Inquire for Pricing)" But, unless you are an OEM, they want you to purchase through your LBS or online through Aspire Velotech, whose Wound Up Ordering webpage states:
[TABLE="width: 436"]
[TR]
[TD="align: left"]Wound Up Fork options...[/TD]
[/TR]
[TR]
[TD]
  • Fender Eyelets Added to a Wound Up Fork
  • Dual Option Brakes (Disc & Linear Pull)
  • Satin/Matte Finish Coating (Fork Legs)
  • Set Up Road Fork for Cantilever Brakes
  • Add Disc Tab to Road Fork (40mm, 45mm Rake)
  • Black Anodized Set (Crown, Dropouts, Disc Tab, etc.)
  • Custom Geometries are Reviewed.
[/TD]
[/TR]
[TR]
[TD]Please Contact Us for details.[/TD]
[/TR]
[/TABLE]

So, you might be able to get Wound Up to build you a custom fork (or two) for 650b wheels. If you do contact them, let us know what you find out, as I can see a small market for this type of fork.

I received a response from Wound Up Composites on my request for a 650B tandem fork with 60mm rake. The "custom" fork geometry is limited to a rake of 50mm. They could place the canti studs at the proper 650B height however. This is basically one of the standard rakes available on their web site specs below of 49mm.

http://www.woundupcomposites.com/specs.html

Oh well it was worth a try. I will stick with the heavier steel that can be made in the geometry I like.
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