Kimmo

Does anyone have any insight into why the only ally forks you'd see for years were bonded, and why now that you're starting to see TIGed ally forks, it's pretty much just big beefy things for hydroformed hybrids.

Is it just too hard to build a fork light and strong out of aluminium? I'm sure it's possible, but why haven't I seen one, isn't it feasible?

Maybe nobody can be bothered heat-treating a fork?

unterhausen

weight and liability.

Scooper

It's possible, but thay wouldn't be very durable.

Aluminum alloys do not have a fatigue limit. Even the slightest cyclic stresses in aluminum structures add up, so that eventually fatigue failure occurs. Designers compensate for this physical property of the material by beefing up the structure, but that makes it heavy. Lack of fatigue limit is the reason pressurized aluminum airframes are retired after a specified number of pressurization/depressurization cycles.

Ferrous alloys (steels) and titanium alloys do have fatigue limits; a virtually infinite number of cyclic stresses that are below the fatigue limit amplitude can be imposed on structures made of these materials and they won't fail from fatigue.

Since forks are continuously subjected to cyclic stresses when the bike is being ridden, aluminum as a material for fork blades is a poor choice where light weight is a requirement.

fietsbob

Aluminum frames are reliable because they are rigid.

AlAn And Vitus used to make aluminum forks .


then again ..

I Think there were some Unicrown style.. TIG to the steerer..

to be safe they may have been rather thickwall, so weight savings marginal at best.

Kimmo

Except that, as I mentioned, bonded aluminium forks were common as mud (I recall the Kinesis D was all the rage in the 90s), and I don't think the blades were generally very hefty on those... I have one here that weighs about 550g, and a lot of that weight seems to be in the crown and 1" x 175mm steerer.

It could be just a fluke, but come to think of it, I've never come across a failed fork of this type, so apparently more durable than cheap steel IME.

unterhausen

the limit stress aspect of aluminum fatigue life is a little overblown in my opinion. I say this because I've been bored out of my mind waiting for aluminum to crack when on a fatigue machine. However, if you have to weld a fork, and nobody wants a bonded fork, then you have to worry about the fatigue resistance of the welded zone. So you need to beef that up to the point where it's not worth doing. They can cut corners on steel forks all day and effectively never have a life-threatening failure. And carbon forks are so cheap now, there just isn't a place in the market for aluminum forks except for fatbikes.

There are 3 factors that seem to dominate what is offered to the cycling public: cost, what the lawyer says, and bull****. It may be as simple as the fact that the "death fork" got a lot of attention, people decided they weren't going to offer aluminum forks as a result, and nobody ever thought about doing it since then. I certainly see no reason for a company to do this. You either build steel or go carbon. There is no compelling reason to go aluminum.

Andrew R Stewart 

Bonded Alu forks usually (BITD) were found on uper end bikes. Which means that the rider was more "savy" of issues, or just moved onto the next trend sooner then others did... I also emember of many better bikes coming with Alu forks for a few years. But i also remember many complaints of pad rub. As carbon fiber forks took over the flex issues were sorted out (pretty much) and that next thing has stayed in the market for a couple of decades since.

Have you actually ridden an Alan or Vitus, down hill at an angry speed? Even at my (back then) 135 lbs and my like of thin wall steel i felt the then current bonded Alu bikes were not as stable as steel was. But my income was not dependent on the finishing line photos. Andy.

ftwelder

One of the things that made them less practical than other types is the short distance between the tire and the bottom of the head tube.

Kimmo

Thanks for your thoughts, guys.

Mark Kelly 

I think I agree with you, but then there are lots of carbon forks with aluminium crowns, which seems to argue for the opposition.

ftwelder

I thought we were talking about welded forks. DOH!

Mark Kelly 

There's no need to be insulting, this isn't the 41.

If an aluminium crown can be strong and rigid enough when bonded, why can't it be when welded and heat treated?

unterhausen

I speculate that the aluminum fork crowns bonded into carbon fiber forks are cold forged. You probably could make one that is weldable, but the costs would be high unless spread over a large number of forks. So the kind of fork that the inestimable FTW would make out of built-up tubing would be a different animal.

Which leads back to my assertion that the reason people don't build aluminum forks basically goes back to a lack of desire for people to make them combined with a lack of desire to buy them. My new fatbike actually does have an aluminum unicrown fork. plenty of room to put a giant fork blade in there.

ftwelder

I thought I was being self effacing but it's difficult to express sincerity with text, please accept my apologies. I hold all of my contemporaries in the highest regard, including Mr. Mark Kelly. What is a 41?

If you add all the processes required to make aluminum work, a low profile application seems to be the furthest stretch of the technology.

I made this segmented fork a couple of weeks ago with Canondale fatty R fork legs. It's around 2 lbs but you would need a lot of I don't know what to make that blend in. It reminds me of those things you slip on your car antennae to make it look like a waving Saguaro cactus. I hope to do some bends on these legs soon and see what can be done.


30 522 by frankthewelder, on Flickr


30 523 by frankthewelder, on Flickr


30 525 by frankthewelder, on Flickr

Mark Kelly 

Frank

Sorry for taking your post the wrong way and thanks for the explanation.

The 41 is the road cycling section of this forum, where several long term members are habitually rude to anyone they think doesn't measure up to their standards, reinforcing the stereotype that all roadies are up themselves.

All the sections have numbers, this one is 229. If you roll your mouse over the text "framebuilders" in the direction ribbon below the reply box, it should pop up a mouse-over text "www.bikeforums.net/forumdisplay.php/229-Framebuilders" (bottom of page in Firefox, don't know where for other browsers).

taras0000

Look at the work! I know where my next track bike is coming from!

ftwelder

I have seen "41" brought up a couple of times but wasn't aware of it's meaning. Ya, they seem to pile on people a bit..

Thanks Taras!

Kimmo

Wow, cool.

repechage

Frank's work always has a purposeful style to it.

Only welded aluminum forks I can recall of any qty were for a short period of Klein pre suspension mtbs.

They looked beefy, I think used a very oversized steerer, 1 1/4"? and of course had a tall crown region.

A few years ago Novarra (REI) marketed a decent looking cast or hydroformed aluminum fork as part of the Big Buzz, it looked pretty nice, accepted a disc but I have no idea how much it weighed and after two years or so dropped it in favor of some unicorn unit of material unknown to me, never saw one in person.

Scooper

Schwinn equipped the Peloton and Circuit models with aluminum forks in the late nineties. Both models had nice TIG welded 853 frames made in Asia. The Peloton and Circuit had the same geometry, and the major difference between the two was that the Peloton was equipped with Ultegra and the Circuit had 105.

This only lasted two or three years, and many owners who rode their bikes regularly replaced the aluminum forks with steel or carbon. What's odd to me is that the Super Sport, Passage, and Le Tour had 7005 aluminum frames and chromoly forks.

Kimmo

Hah, only 1/6 of the models listed there use the same material for frame and fork, weird.

MassiveD

What are the forks on all those cheapo aluminum comfort bikes made of? Are any Al, or is it all steel

Kimmo

I've seen hydroformed, TIGed ally forks on cheap (~$600) aluminium bikes lately. With smoothed welds, even!

It's a shame there's nothing fancy that's made like that, let alone in 1" for my hotrod... it should be possible under a pound, IMO. But to have a one-off properly made would cost as much as the rest of the bike...



That fork is a bloody boat anchor. Going to carbon.