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Old 06-27-2014, 08:38 AM   #1
rich tintera OP
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Upside down forks?

Educate me on upside down forks. I've never had a bike with them. If they're so advantageous, why don't all bike come with them stock? Why would they cost more to make than "regular" forks?
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Old 06-27-2014, 09:00 AM   #2
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Originally Posted by rich tintera View Post
Educate me on upside down forks. I've never had a bike with them. If they're so advantageous, why don't all bike come with them stock? Why would they cost more to make than "regular" forks?
They're generally more rigid than conventional forks of the same dimensions, which is the main advantage. I suspect they might originally have been more expensive because they had to go through an effort to design and tool-up for them in addition to the fact that most USD forks have more expensive (i.e., to provide adjustability) components compared to many regular forks which only provide preload adjustment and have relatively unsophisticated damping components. MC manufacturers, like all manufacturers, build most products to price points, which is why conventional forks are still available where cost may be an issue and performance of them is adequate to the real or perceived need.
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Old 06-27-2014, 09:25 AM   #3
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In performance applications, there is less unsprung weight at the wheel, which helps the wheel react a little quicker to bumps in the road and improves feedback/feel to the rider. modern day USD forks are more ridged than conventional forks (early versions of USD were little wobbly under hard braking).

All things being equal (materials and features) from a manufacturing standpoint, the cost differences would be very minimal between a USD and conventional fork. The cost differences come from the higher level materials and features typically built into USD forks since they are spec’ed on higher level bikes, compared to conventional forks.

If moto company X is going to invest more RD into front-end suspension design, most likely it will be in a USD fork, which also drives up the cost.
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Old 06-27-2014, 09:34 AM   #4
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I think its just style and hype.
They put the heavy STEEL parts on the wheel (unsprung weight) and the alloy parts on the frame (sprung weight) and call it better.
And if a fork seal leaks, all the oil comes out fast.

Its just a trendy thing I think.
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Old 06-27-2014, 10:26 AM   #5
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Just "trendy"? i don't quite know about that. Definitely more rigid on my SV with the GSXR front end on it.

Also gained loads of adjustability over the stock front end. but that's more due to the swap than forks themselves.
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Old 06-27-2014, 11:03 AM   #6
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Originally Posted by NJ-Brett View Post
I think its just style and hype.
They put the heavy STEEL parts on the wheel (unsprung weight) and the alloy parts on the frame (sprung weight) and call it better.
And if a fork seal leaks, all the oil comes out fast.

Its just a trendy thing I think.
Damn whipper snappers and their fancy USD forks
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Old 06-27-2014, 11:27 AM   #7
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One thing that USD forks seem to have over RSU forks is damping adjustments. Obviously there are other benefits as well, but looking at what truly different between the two, that seems to be a big one to me. It seems far less common to see damping adjustments on old style forks.
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Old 06-27-2014, 11:31 AM   #8
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The reasoning I once read/heard, is that USD forks put the larger diameter "outer tube" at the top making them less prone to flexing and twisting. I suppose that benefit would be most apparent to someone who's riding ability is capable of pushing a bike to the max. Me?......my riding skills are more in line with the technology you'd find on a 1960's Honda S-90 or something

Regarding unsprung weight, that's probably a consideration too, but maybe someone else has the weight figures?

Cost differences....I dunno.

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Old 06-27-2014, 11:39 AM   #9
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For me, the more important question is how the fork internals are designed. Quality components that have full adjustability always cost more than cheaper, less adjustable components.

Also, just because the fork is a USD design doesn't mean that it is a cartridge fork. Many cruisers have USD's that are damper-rod forks (primarily for looks, since most cruisers don't push the suspension performance envelope very hard).

USD's were originally developed for racing applications as indicated above, providing rigidity and lower unsprung mass, all other variables held equal. It is also true that if a fork seal is leaking, you will lose fork oil much more quickly on a USD than on a conventional fork.

Remember too that USD fork designs also require larger diameters in the triple clamps, which must be designed for the fork tube diameter. This can affect overall width of the triple clamp and indirectly affect turning limits and location of steering stops. It is a domino effect.

Personally, I want high quality, fully adjustable, cartridge forks. USD or conventional is moot since I'm not buying a race bike. But then we could talk some more about open vs. closed cartridge designs, etc. which is of current concern in higher-end enduro and moto-cross (racing dirt bike) suspension designs.
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Old 06-27-2014, 12:26 PM   #10
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Quote:
Originally Posted by NJ-Brett View Post
I think its just style and hype.
They put the heavy STEEL parts on the wheel (unsprung weight) and the alloy parts on the frame (sprung weight) and call it better.
And if a fork seal leaks, all the oil comes out fast.

Its just a trendy thing I think.
If it were just trendy (since the early 90s btw) then why would every race bike (dirt and street) have inverted forks? In fact I think the supercross bikes were some of the first to have that set up.

How many steel parts are on the wheel on a modern street bike? My stock wheels are pretty darn light. Much more so than any of the sprung weight.

As was mentioned earlier, it has more to do with the rigidity than anything else. Think about big jumps like in supercross or heavy braking in street racing. Think that a rigid fork would be more or less helpful?

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Old 06-27-2014, 12:30 PM   #11
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It ain't just trendy.

Go ahead, take your pick

But since this is AdvRider, I guess will commence
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Old 06-27-2014, 12:33 PM   #12
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I would love to see you call usd forks "trendy" to the face of a team of engineers, I am guessing it would either be facepalm or shock. You really think they just do what is trendy on serious bikes?
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Old 06-27-2014, 12:54 PM   #13
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This is a great question and I don't know the answer to it. Obviously, to most basic street riders, you'd think the internals and over all diameter matter more.

With hockey sticks, we design around something called a kickpoint - where the load flexes and then releases for maximum snap to the shot. Good for mph on a slap shot -- not good for controlling a motocycle. In that evironment you fight to keep it down by the blade rather than traveling up so that you still get the snap, but more control of aim/ placement.

I wonder if the stress and flex on the front wheel (fewer mm's at the wheel, but more mm's as it travels up the forks) doesn't mean that the wider radius at the top serves to create a more stable steering environment by flexing less at the far end of the whip so to speak. Flexing a few mm's at the bottom, but remaining stable at the top where flexing would be quite a few more mm's if allowed to do so. In other words, more stability under load.

So, that is a heaping pile of non engineer guessing.....
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Old 06-27-2014, 02:29 PM   #14
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Quote:
Originally Posted by NJ-Brett View Post
I think its just style and hype.
They put the heavy STEEL parts on the wheel (unsprung weight) and the alloy parts on the frame (sprung weight) and call it better.
And if a fork seal leaks, all the oil comes out fast.

Its just a trendy thing I think.
Absolutely not just trendy. They are tremendously more rigid than standard forks, and have a LOT less unsprung weight. You are right about the leaking fork seal issue though.
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Old 06-27-2014, 04:44 PM   #15
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How is steel lighter then alloy?

I think its all just a trend, if you made normal forks the same size, included damping adjustments, they would likely work just as well as USD forks, plus the part that gets hit with rocks and dirt would be the outside part, not the part the fork seal slides against.
Otherwise you have to put some cheap ass plastic guards over the forks.

If there really is any difference, its got to be very slight all other things being even.
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