[EVRAC]

So the proflex/girvin/noleen/K2 fork was the most well-known example, and it basically sucked. The j-shaped axle path tucked under and shortened the wheelbase, they had a tonne of flex, had bearing issues, and had terrible shocks.

But why not design a proper DH fork?
With only a few fork options on the market, there must be room for some competition.

The advantages could include stiffness, sensitivity, reliability, ability to use standard rear shocks, plus it allows some customization of the axle path, trail, and anti-squat characteristics.

Here's some historical and modern linkage forks for mtb and moto.

 

[Calid0wnhiller]

Not to mention extreme weight savings!

 

[Bikerpunk241]

Two major arguments you forgot, weight and production...... Shock and spring without the linkages and rest of the fork are already more than half the weight of offered forks on the market, plus extra production costs for more specialized parts, etc. Just doesn't make sense from the production cost alone. Do you see off-road motorcycles with linkage forks?

 

[manwithgun]

I'd say that in the relm of mountain bikes it would be difficult for the performance gains to match or exceed the weight penalty at the outer most point from the fulcrum. A telescoping fork benefits from an increase in strength/overlap as force is converted to compression. They are structurally weakest at full extension and strongest at full compression. This inherent design is hard to compete with.

 

[3D.]

problems would be creating better performance and a more desirable axle path while still being as light. Our front wheels moving rearward at bottom out isn't a bad thing you know?

 

[Fly]

A friend has a pair of the original Yuri forks hanging in his garage. Pretty sure he has one of the frames as well, but that's a different story....


Linkage forks are an interesting concept, but the Proflex I rode, and the Yuri felt pretty ****ty. The Yuri's weren't too bad at absorbing square edged bumps, maybe even better than a telescopic. But something weird with the design meant that landing a jump, or even just bouncing the bike, it was impossible to get more than half travel. It felt like bottom out, only it was nowhere near. Very disconcerting.

 

[HaveFaith]

So the proflex/girvin/noleen/K2 fork was the most well-known example, and it basically sucked. The j-shaped axle path tucked under and shortened the wheelbase, they had a tonne of flex, had bearing issues, and had terrible shocks.

But why not design a proper DH fork?
With only a few fork options on the market, there must be room for some competition.

The advantages could include stiffness, sensitivity, reliability, ability to use standard rear shocks, plus it allows some customization of the axle path, trail, and anti-squat characteristics.

Here's some historical and modern linkage forks for mtb and moto.

I thought about this 2 years ago when thinking about brake dive and suspension performance entering into rough whooped-out corners. I passed the idea onto my colleague and he has designed up a system and is in the process of building the prototype out of steel. I truly think you can get a lighter system that performs better in every aspect, except for maybe aesthetics. The only real problem I foresee is the public preconception (misconception??) of how a fork performs.

 

[boogenman]

thank you for burning away a good 2 minutes of my life that I will NEVER get back.

 

[ChrisKring]

why would you want the contact patch to move rearward through the travel? It would make it extremely difficult to ride over sharp edged bumps on a steep pitch with a moving pivot point.

 

[bdamschen]

If anyone's going to be discussing a linkage type front fork, BMW's motorcycle suspension needs to be in the examples of good ideas. Scroll to the bottom of the article for front suspension: http://www.motorcycleinfo.co.uk/index.cfm?fa=contentGeneric.dnvjxqtaqfhxwmvv&pageId=205807

 

[Westy]

 

[bdamschen]

heh, they ALMOST got it right.

 

[Jeremy R]

There is a simple formula to remember regarding what forks need:


More linkages = NOOOO!

MOAR SHIMS = YEEESSSSS!

 

[bdamschen]

There is a simple formula to remember regarding what forks need:


More linkages = NOOOO!

MOAR SHIMS = YEEESSSSS!

I'm writing it down now for my next build. Can I PM you if I have any questions?

 

[Jeremy R]

I'm writing it down now for my next build. Can I PM you if I have any questions?

Yes, I have that posted up on my refrigerator, just in case I start forgeting the power of moar.

 

[tuumbaq]

There is a simple formula to remember regarding what forks need:


More linkages = NOOOO!

MOAR SHIMS = YEEESSSSS!

Love it ...

 

[Jm_]

There is a simple formula to remember regarding what forks need:

Forks need electrolytes.

 

[EVRAC]

I truly think you can get a lighter system that performs better in every aspect, except for maybe aesthetics. The only real problem I foresee is the public preconception (misconception??) of how a fork performs.

Cool, we are in agreement then. Any chance you could pm or email me any info that your friend has (if he's willing to share)?

 

[SkullCrack]

Do you see off-road motorcycles with linkage forks?

Rarely.

 

[EVRAC]

why would you want the contact patch to move rearward through the travel? It would make it extremely difficult to ride over sharp edged bumps on a steep pitch with a moving pivot point.

I would not design it with a rearward axle path. The girvin was a poor performer for that reason (among others).

 

[epic]

Coolest linkage fork I ever rode was a Nuke Proof. It had a shock inside a giant headtube. It actually rode really well. Of course this was compared to Mag-21s and the like.

 

[ChrisKring]

I think on paper you might be able to design something pretty good. However in practice, a big problem is going to be any bearing slop is going to be a big problem. All bearings have some clearance. The problem is that this will multiply by the time it gets to the wheel.

With a conventional fork, there is very little angular slop due to the large bearing surface overlap.

I rode an Amp Research fork along time ago and this, along with the wheel path, were big problems. Solve those and you might have something.

 

[rosenamedpoop]

Forks need electrolytes.

 

[EVRAC]

I think on paper you might be able to design something pretty good. However in practice, a big problem is going to be any bearing slop is going to a big problem. All bearings have some clearance. The problem is that this will multiply by the time it gets to the wheel.

With a conventional fork, there is very little angular slop due to the large bearing surface overlap.

I rode an Amp Research fork along time ago and this, along with the wheel path, were big problems. Solve those and you might have something.

I think the key there is to space the bearings as widely as possible. It's really not that different from rear suspension.

 

[Sandwich]

With a little effort, I'm sure you could design up something light strong and effective. I'd love to lose the brake dive on the steeps.

DW probably already has it patented though.

 

[ohio]

It can definitely be done and should yield a system that is stronger, stiffer, and has better dynamics. Easier to make it fit at 5" than 8" of travel though.

Main reasons you don't see it in dirt bikes are, first, it gets really hard to make the system fit on the bike with 12"-14" of travel. Second and more importantly the conventional chassis are SO refined at this point and the dynamics so ingrained in riding styles, that it's a huge step backward for any pro-level rider to try to adapt something so different, even if it's technically an improvement. Imagine what hitting a 70 ft triple is like when you don't know how the front end is going to react to the ramp and lip, or balance in the air. The market follows racing.

 

[Huck Banzai]

3rd, its an inferior approach, no matter how much some random tiny group of enthusiasts insists otherwise.

Dismissing the 'improvement' as unfamiliar is the best counter-argument?

No.

 

[RMboy]

You should check out the company "German Answer". They have been standing by those types of forks for years.

They were opposite the Nicolai stand at Euro bike, and i got to know them quite well. Had ago on their linkage fork and we very impressed of how smooth and sensitive it was, with hardly any flex.

 

[Kanye West]

There is no way in hell that system could possibly steer or corner better on a DH bike. There are other improvements that are due for DH forks. Linkages are NOT one of them.

 

[MrPlow]

I know the Yuri fork boasted anti dive, a trait of linkage forks. However this turned out to be a bad thing by those who rode it. Back in the day Jared Graves rode the Yuri fork and hated it for that reason (among others I think). Makes sense really, Descent damping should take care of unwanted dive. Having a more rearward axle path would be bad too I reckon. Conventional DH bikes reduce wheelbase too much through their travel already .

 

[fluider]

It seems that diving of front-end under braking became our perception of the right behavior. Also Norman Hossack mentions on his website about road-bike racers who very quickly denied to use his front-suspension because they had no feedback about how hard they were braking.

What's the decent amount of damping that should take care of dive? It's a trade-off between dive-damping and fork sensitivity that can never be solved. That's why I'm for linkage forks. And rearward path in the front can be compensated by rearward path in the rear.

 

[Sandwich]

It seems that diving of front-end under braking became our perception of the right behavior. Also Norman Hossack mentions on his website about road-bike racers who very quickly denied to use his front-suspension because they had no feedback about how hard they were braking.

What's the decent amount of damping that should take care of dive? It's a trade-off between dive-damping and fork sensitivity that can never be solved. That's why I'm for linkage forks. And rearward path in the front can be compensated by rearward path in the rear.

true and true...and who's to say a 1/4 lb "floating linkage" couldn't be added to a traditional fork, so that all you "stiction rulez" folks can still have yer tubes in yer boxxer, but still not suffer brake dive?

There are a bunch of options, you don't necessarily need a huge telelever fork.

 

[Sandwich]

 

[Kanye West]

It's a trade-off between dive-damping and fork sensitivity that can never be solved.

Oh yes it can. A very properly set up fork damper and springrate will achieve exactly that. MTB cartridges can afford to be improved upon a LOT in that regard. A fully functional mid-valve is a start.

 

[3D.]

Not having some kind of rearward path for the front wheel would make certain square edged hits very uncomfortable for the rider. Having the initial movement travel up and back takes a lot of the potential hang up involved with diving your front end into a large hole, or taking on a set of deep, harsh braking bumps. Without some rearward movement to the path, I would imagine an endless thread on “how I got thrown over my bars today”.

Maybe a path that starts its way up/rearward and than goes more straight vertical for the last half of the travel could be an answer. I really think that at least the first 1/3 of the travel should move rearward to some degree.

Compensating with a rearward path for the back wheel too aggressively without the use of a floating bottom bracket (like GT) would result in undesirable chain growth as always.

 

[ChrisKring]

How does compensating with a rearward axle path fix the problem of rider/bike CG lacation verses pivot point (tire contact with the ground). The rider mass is far more than the vehicle. In addition, the rear wheel doesn't contact the same input bump until after the front wheel.

Draw a free body diagram of each system.

 

[rockofullr]

Draw a free body diagram of each system.

happy?

 

[iRider]

With a little effort, I'm sure you could design up something light strong and effective. I'd love to lose the brake dive on the steeps.

DW probably already has it patented though.

Didn't Outland (of VPP fame) show a linkage fork to go with their frame at Interbike back in the day? So DW might be too late....

 

[LMC]

the guys behind zerode had one built, using a fox air shock. ill try and find the pic.

 

[Sandwich]

Didn't Outland (of VPP fame) show a linkage fork to go with their frame at Interbike back in the day? So DW might be too late....

indeed they did, sir. I remember MBA describing it as looking like a steering damper attached to an erector set with 7" of travel, but it was actually a very elegant design, all CNCed, and single crown. It looked much like the e-fohrk I posted above.