waynesulak

Interesting test. I wonder what the tire was inflation was. Also it is interesting to see the failure mode. I would love to see a side by side test with a popular light weight aluminum rim with the same tire inflated at the same pressure. It would be nice to have a frame of reference and compare failure modes.

Anybody out their want to compute the speed of the 50lb weight when it hits the tire after falling 16 inches?

Ritterview

Another way to look at the reliability of materials is what cycling teams are using in a race with a lot of impact, like the infamous Paris-Roubaix. The teams have the expertise, the equipment, and the motivation to choose what is optimal. Carbon forks have long been used, and it doesn't appear anyone switches out anymore to aluminum forks. Lately it has been carbon rims as well.

The most famous fork failure in professional racing was George Hincapie, at Roubaix 2006. The aluminum steerer failed.

waynesulak

That is the way a lot of people look at it. Ride what the pros ride. That is why manufacturers spend so much money on the teams. I agree with you when the team uses a non-sponsor product. When it is a sponsor's product I'm not so sure.

PMK

The link to the paper is located here.

https://www.thetandemlink.com/MfgDefects_Forks.pdf

PK

Charles Ramsey

Actually I'm all for a titanium fork I have worked for a company that made seemed tubing from 6Al 4V it comes out of the welder looking like a banana the weld shrinks then is straightened so I know it can be bent into a fork without failure. Most of the titanium failures in bicycles have been caused by oxygen in the welds. You should also know the viscount first came out with a solid aluminum fork those failed. Schwinn decided to chrome plate some paramounts those failed from hydrogen embrittlement this information was common knowledge from from platers at the time and could have been prevented by heat treating the frames. It is now illegal to braze 4130 aircraft frames they must be TIG welded. All this information is available what is not available is fiber construction these are all closely guarded trade secrets.

reburns

Suspension forks have a very stiff column to which the caliper of a disc brake can be attached, so the bending due to the caliper load is negligible. Compliance to bumps and other road variation is handled by a separate mechanism housed inside the stiff column. In contrast, "rigid" forks need to bend to provide some small amount of suspension, and they need to do this in the same general rea but in opposition to the force a caliper exerts when braking. Kind of like being kicked in the left shin while running on a trail. Perhaps the compromises required have been worked out adequately to make this effect a non-issue in real world experience. Nonetheless, compromises are certainly required.

PMK

Whatever cowboy, run whatever makes you feel safe and comfy. FWIW, EVERYTHING can be made to fail at some point. You must be a bundle of joy to sit beside on an airliner.

PK

Homeyba

You should ride what you are comfortable with first and foremost. Beyond that, this is a bit of a chicken little thing. You are correct that these are proprietary engineered materials but that doesn't mean that there is no quality control or reliability engineering happening. Most companies are responsible enough to not want to put out a product that they know is going to fail and the track record for reliable manufacturers is pretty strong.

diabloridr

Here's a failure for everyone to chew on:

Yesterday while putzing along ~ 16 MPH on a residential street the captain's seatpost on the Speedster failed, leaving beloved stoker holding a useless stoker handlebar while I'll had to pull myself forward to get my hands on the brakes (good thing I had both hands on the bar). Stoker was super-smooth at keeping her balance, we got the bike stopped safely.

Specifics: Post is a Zoom aluminum post (no longer in biz, AFAIK). Failure was at the point where the post enters the frame (a natural stress concentrator). Approximately a 3/4" long fatigue crack at the front of the post, the remainder of the post cross-section failed in brittle fracture (textbook failure for aluminum). Post is 13 years old, has about 25,000 miles on it. It would have received a cursory visual check sometime in the last year.

I got Mel @ Tandems East on the phone to run through options for replacement posts. I need a setback post to get my position right, so a Thomson is off the table.

Mel had a couple of Ritchey's on the shelf which I pulled the trigger on.

WheelsNT

Thomson makes setback posts -- see here: https://bikethomson.com/seatposts/elite/ hit the Sizes tab and scroll to the bottom.

diabloridr

Not in 29.8mm.

Other potential issues since Thomson achieves the setback by placing a bend in the shaft, not by incorporating the setback into the head:

1) Our stoker bar has to clamp to the captain's seatpost right where that bend is.

2) Stoker's seatpost in our case doesn't have sufficient post length exposed to allow use of the bent shaft.

Thomson's is an interesting approach, but it has some real limitations, especially for tandems.

sine

Titanium as a material for a bicycle fork is questionable at best for singles........for a tandem............the tubing would have to be over sized (to increase stiffness) well beyond what has been done to date. There is no point.

Many titanium frames also failed due to improper finishing of machined parts. Titanium peels (breaks) faster than anything I experienced with steel or aluminum. Merlin had problems with cage bosses and Litespeed had problems with machined bullet stay ends.

Back to our carbon wound up duo.

I too wanted to switch to front disc so we could bomb down (relative) switchbacks without fear of a front tire blowout. The Avid disc was ok but the switch to Shimano ICE disc has worked very well. On a recent trip to France we (I) enjoyed one finger braking during a 15 mile descent. Well, one corner did require all fingers to action as I screwed up and entered a turn too fast. Of note, one could feel the heat coming of the disc but the al spider was not nearly as warm.

PS, we had Wound Up anodize our al fork drop outs and caliper mount black.

TandemGeek

Wow, that one lasted a long time. Most Zoom failures I've seen or heard about happened with far fewer miles.

One of our friends had one fail on their Cappucino about 20 miles from the end of a century: all of a sudden she was holding the bars and her captain's saddle. They raised her stem to free up some of the remaining seatpost mast (he was really tall, so it had a lot of exposed mast) and finished the ride with his saddle about 5" too low... still pulling a line of wheel suckers.

Anyone with those Zoom seatposts would do well to keep an eye on them or, at this point... to replace them if the tandem they were installed on was ridden very much. It seems like it's more about when, not if.

diabloridr

I take it their failure did not occur at the frame insertion point since it sounds like they were able to easily remove the portion of the post inside the frame?

Since our post sheered even with the top of the seat tube I couldn't get a good grip on the post to remove it with any of my tools.

My solution was to drill a 5/32" hole in the post where the seat tube is slotted to clamp the post. Then I inserted a some coat hanger wire, and made a loop to give me something to pull with. The post then slide out easily.

One of the not so good properties about aluminum is that it does not possess a "fatigue limit".

For steel, Ti, and CF - if you reduce the fatigue loading low enough (how much depends on the material) eventually you hit a limit where fatigue failure will NEVER occur (CF in particular seems resistant to fatigue failure unless damaged initially by impact loading. Maybe one of the resident CF experts can expound/correct me on this).

Aluminum does not process this limit, as stresses go lower the life gets longer, but it is still finite. I suppose even a Thomson post could fail due to fatigue, though it might take longer than the riders' lifetime.

What this means to me is that I'm also shopping for several handlebars to replace aluminum bars which may be past their "freshness date".