Suspension Fork Design Question

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Suspension Fork Design Question

Postby Diamond Jim » Wed Jan 09, 2008 5:15 pm

Here's a discussion topic for you:

One of my first suspension forks was a Halson Inversion Fork, which, through a set of slotted uppers for the brake bosses, was a design where the bottom sliders slid INTO the larger uppers. I figured this style of fork would take off once disk brakes became the norm, since, as any motorcycle rider can tell you, it's much stronger than the current style of mountain bike fork. But it hasn't happened. Why not?

Here's what it looked like:
http://images.google.com/imgres?imgurl= ... n%26sa%3DG
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Postby spurk » Wed Jan 09, 2008 8:23 pm

jim,
mavericks are inverted.

marz. shivers were as well.

lefty's too but that is a bit of a different animal.

a pretty knowledgable source once told me that the key to an inverted fork was a solid thru axle. for some reason the stiffness of the axle has a pretty big influence on the success of the inverted fork. i think it helps keep the sliders from twisting. I am only paraphrasing from a talk we had about them though. i could be wrong.
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Postby Indy » Wed Jan 09, 2008 11:34 pm

I had the chance to ride a stumpy FSR with a Maverick fork on it. I gotta say it's a pretty darn good fork, and is far stiffer than any QR fork. I don't have enough experience with other through-axle forks to be able to make a little bit more direct comparison.

Like spurk said, though, it seems the real limiting factor is that the thru-axle design is catching on slowly and may not ever catch on for the xc racer set. Adding to the mess is that everybody's got a different thru-axle standard. It used to be that there was only 20mm, but I think Maverick came up with their own standard (24mm, I think) when they introduced their forks, and I read that Fox is introducing yet another thru-axle standard soon (10mm, I think). How are fork mfrs and wheel mfrs supposed to make money on something that's not standardized?
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Re: Suspension Fork Design Question

Postby Justin » Thu Jan 10, 2008 12:14 am

Diamond Jim wrote:One of my first suspension forks was a Halson Inversion Fork, which, through a set of slotted uppers for the brake bosses, was a design where the bottom sliders slid INTO the larger uppers. I figured this style of fork would take off once disk brakes became the norm, since, as any motorcycle rider can tell you, it's much stronger than the current style of mountain bike fork. But it hasn't happened. Why not?


I'm still a little confused on that Halson fork, does it work the same as a normal inverted fork or is there more to it? Why does it have boots where it does?

For mountain bike applications, inverted forks are not necessarily "stronger" than their normal counterparts. There are a few other issues with them as well that prevent their wide acceptance. A few minor things are oil leakage can be a problem since the seals always have oil resting against them, the stanchions are more exposed to damage from rocks, etc, and large diameter tubes are required to make it stiff enough. In order to make it lightweight with big tubes they must be thin, which also increases chances of damage.

The big difference is what spurk hit the nail on the head with by the thru axle comment. Inverted forks have no arch above the tire like a normal fork, so in order to remain torsionally stiff enough a thru axle is a necessity. Hence why they have mostly only been used in DH applications. Bigger is better here too, which is why Maverick made their trail forks use a 24 instead of 20 mm axle to keep it stiff enough while still being lightweight.

I kind of disagree with Indy's comment about thru axles though. The accepted thru axle standard is a 20mm x 110 axle. Maverick had to go and make their own 24mm axle, and now Specialized jumped on board with a 25mm axle for their new Enduro forks. I did just read something about a new Fox/Shimano 15mm standard, but I'll wait for more definite proof on that. If anything this shows that thru axles are becoming accepted and the manufactures are just making their own axle sizes to set themselves apart in the market. I can only hope that eventually thru axles will eliminate the normal weak and flexy quick release axles that are still used on so many bikes.
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Postby Diamond Jim » Thu Jan 10, 2008 8:39 am

The design of the Halson fork was acutally quite clever. The rubber boots cover slots in the uppers. The slots are where the brake bosses and the arch, both connected to the lower sliders, poke out through the uppers. Of course, the Halson was a rubber-bumper fork, not hydraulic.
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Re: Suspension Fork Design Question

Postby Indy » Thu Jan 10, 2008 11:03 am

Justin wrote:
Diamond Jim wrote:One of my first suspension forks was a Halson Inversion Fork, which, through a set of slotted uppers for the brake bosses, was a design where the bottom sliders slid INTO the larger uppers. I figured this style of fork would take off once disk brakes became the norm, since, as any motorcycle rider can tell you, it's much stronger than the current style of mountain bike fork. But it hasn't happened. Why not?

I kind of disagree with Indy's comment about thru axles though. The accepted thru axle standard is a 20mm x 110 axle. Maverick had to go and make their own 24mm axle, and now Specialized jumped on board with a 25mm axle for their new Enduro forks. I did just read something about a new Fox/Shimano 15mm standard, but I'll wait for more definite proof on that. If anything this shows that thru axles are becoming accepted and the manufactures are just making their own axle sizes to set themselves apart in the market. I can only hope that eventually thru axles will eliminate the normal weak and flexy quick release axles that are still used on so many bikes.


I see thru-axles gaining ground for trail bikers (the all mountain crowd, if you will), but not so much elsewhere. There are still a lot of 5" travel bikes running QR front ends. I don't think it's a good thing that companies keep coming out with new thru axle standards. Unless someone comes up with a front hub that's at least compatible with most of them, it's going to be a pain and I would hope that many of the additional standards just die out. I'd also like to see quick releases go away permanently because not only are they the weak link structurally, but they're a security liability for people who use their bikes to commute. Maybe road racing bikes need the ability to swap a wheel in seconds, but it's no big deal for the average rider and especially for mountain bikers.
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Postby Diamond Jim » Thu Jan 10, 2008 11:13 am

Dude, I don't know about you, but quick releases make it a whole hell of a lot easier and quicker to put bikes into most roof racks.
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Postby pratt » Thu Jan 10, 2008 11:54 am

the newer thru axles are easier to get off than quick releases....

true though that most roof racks need adapters to accept the fork.

what you should have is a roof rack that doesn't require you to take off your wheel...heck of a lot easier and faster than the fork mounts.
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Postby Indy » Thu Jan 10, 2008 12:23 pm

pratt wrote:what you should have is a roof rack that doesn't require you to take off your wheel...heck of a lot easier and faster than the fork mounts.


The Thule sidearm is where it's at. I've got a pair of them and it's so nice that I don't have to pull my wheel off to load bikes. I do have fork blocks inside the car, but pratt is right...a lot of the newer 20mm thru axles are still really simple to remove. Just an adapter or two and I can load a thru-axle bike inside the car, as well.
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