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Old 11-26-2011, 03:18 PM   1681 links from elsewhere to this Post. Click to view. #1 (permalink)
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Question Inverted forks vs regular forks

Hi all,

Want to find out what are the pros and cons of inverted forks vs. regular forks; and why are inverted forks more popular on expensive bikes. My plan is to compile a list of my findings (from this forum and other places) and to put it out for guys like me who'd be looking for this.

Thanks,
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Old 11-26-2011, 03:42 PM   #2 (permalink)
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New rider here and also I'm curious about this term. So found some education reading material through Google.


From wikipedia:
Quote:
Conventionally, the fork stanchions are at the top, clamped to a triple tree, (aka "yoke"), and the sliders are at the bottom, attached to the front wheel spindle.

On some modern sport bikes, this system is inverted, with "sliders" (complete with the spring/damper unit) at the top, clamped to the yoke, while the stanchions are at the bottom . This is done (i) to reduce unsprung weight by having the lighter components suspended, and (ii) to improve the strength and rigidity of the assembly by having the strong large-diameter "sliders" clamped in the yokes.[2] The inverted system is referred to as an upside-down fork, or "USD" for short.

A disadvantage of this USD design is that the entire reservoir of damping oil is above the slider seal so that, if the slider seal were to leak, the oil could drain out, rendering any damping ineffective.

From Yamaha:
Quote:
Inverted forks are positioned on the motorcycle opposite or upside down when compared to conventional forks. The leverage forces that cause fork flex are greatest at the triple clamp area and weakest at the front axle. On inverted forks, the large outer tube of the fork is clamped in the bike’s triple clamps and the sliding inner tube holds the axle and front wheel. By locating the large diameter tubes in the triple clamp, the inverted or upside down fork have their largest and strongest parts combating the highest stress. This arrangement gives the forks high rigidity, which improves their response by reducing the side loading of the internal bushings (sliding surfaces). This kind of response is particularly important in high performance applications. Most inverted forks use cartridge-type damping systems.

Also, since the damping mechanisms are now held by the triple clamps, unsprung weight is minimized. Reducing unsprung weight is one of the biggest contributors to quality suspension performance, particularly for featherweight motorcycles like the YZ series or R1 and R6.
YAMAHA MOTOR CANADA | Technology


From a random Ducati forum post:
Quote:
There may be some unsprung weight difference (although you are replacing unsprung aluminum with unsprung steel), but the primary improvement is front-end rigidity. The smaller, more flexible, inner tubes are 3 - 4 times as long on "conventional" forks as "upside-down" forks. The triple clamps gripping much larger diameter tubes also makes a really big difference in rigidity there. Those two things combined result in upside-down fork and triple-clamp assemblies being WAY more rigid. That's why the first place they became popular was in Supercross, where they were far better at handling the stresses of the giant jumps.
What's so special about inverted forks? - Ducati.ms - The Ultimate Ducati Forum


So in conclusion, it looks like inverted forks provide better performance (more rigid, less sprung weight, etc.) but at cost of bit more maintenance (no easy fork oil drain it seems like on a standard fork)
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Old 11-26-2011, 04:31 PM   #3 (permalink)
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American-V Classics

Speaking of 1991, that year saw Buell became the first manufacturer to fit inverted (upside-down) forks to a production bike.
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Old 11-27-2011, 01:20 AM   #4 (permalink)
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Thanks Nist ! Great info....
I keep on hearing that for normal road riding, there is not much of a difference between inverted and conventional forks from a performance perspective but it does show up when track riding is involved..

Will also dig more and post whatever I find as well.
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Old 11-27-2011, 02:15 AM   #5 (permalink)
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Quote:
Originally Posted by nist7 View Post
So in conclusion, it looks like inverted forks provide better performance (more rigid, less sprung weight, etc.) but at cost of bit more maintenance (no easy fork oil drain it seems like on a standard fork)
That's true for the high end stuff...

On the real world there is little, if any, difference between the mass produced crap. I can't recall where, but I saw a comparison of USD and convetional forks, and there were no unsprung weight advantages and flex was the same. For example, my SV1000S has 46mm conventional forks, whereas most SS bikes with USD suspensions have just 41-43mm sliders.

Then there is another little known fact of USD forks. As the fixed part of the fork flexes, the slider's bushings create more resistance, stiction. The upper bushing of the slider goes right past the lower triple tree. I'm tired, and really can't come up with a detailed explanation, but you can find it online.

Either way, USD forks look WAY cooler than conventional forks, and if you're planning on swapping a GSX-R front end into your SV650... DO IT!
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Old 11-27-2011, 06:08 PM   #6 (permalink)
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Quote:
Originally Posted by F4sSprintST View Post
American-V Classics

Speaking of 1991, that year saw Buell became the first manufacturer to fit inverted (upside-down) forks to a production bike.
The GSXR750 got them in 1990, Actually. There might be bikes that had them before that, even. I'm not sure.


Anyways, less unsprung weight (but actually more overall weight), higher possible rigidity, less stick-slip.

But this also comes with a MUCH higher chance of getting a knick in the slider from road debris, and a significantly harder rebuild process.

I like them, mainly for looks. Standard forks just look REALLY outdated compared to them.
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Old 11-27-2011, 07:13 PM   #7 (permalink)
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Quote:
Originally Posted by kevinwilly View Post
I like them, mainly for looks. Standard forks just look REALLY outdated compared to them.




Quote:
But this also comes with a MUCH higher chance of getting a knick in the slider from road debris, and a significantly harder rebuild process.
IDK, USD forks tend to be well shielded, the old style upright ones didn't usually have shields
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Old 11-28-2011, 12:11 AM   #8 (permalink)
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Thanks guys!
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Old 11-28-2011, 12:13 AM   #9 (permalink)
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Quote:
Originally Posted by F4sSprintST View Post



IDK, USD forks tend to be well shielded, the old style upright ones didn't usually have shields
Old style ones are high enough off the road that they are fine. USD ones get knicked all the time. I've had to replace at least 3 of them because of it.
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Old 11-28-2011, 03:40 AM   #10 (permalink)
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It should be noted that a number of hardcore SV junkies recommend against using GSXR forks for track use because they are rigid enough to tear the headstock off the frame in the event of a good roll.

(just a PSA, I'd use the GSRX forks too)
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Old 11-28-2011, 12:46 PM   #11 (permalink)
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nice post. learned something new
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Old 11-28-2011, 01:06 PM   #12 (permalink)
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Quote:
Originally Posted by Tripped1 View Post
It should be noted that a number of hardcore SV junkies recommend against using GSXR forks for track use because they are rigid enough to tear the headstock off the frame in the event of a good roll.

(just a PSA, I'd use the GSRX forks too)
They are also known tocause chatter on the 2nd generation SV650s.
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Old 11-28-2011, 02:52 PM   #13 (permalink)
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I dunno. I had GSXR forks on my first gen SV650 and they were tits.

You can't really compare shitty damping rod, undersized, standard forks with shitty twin piston calipers to inverted, cartridge damper, larger diameter forks with radial four piston calipers.

If you care about the ride of your SV at ALL, you WILL do the mod. It cost me like 300 bucks in parts (80 for the forks/brakes, 90 for a wheel, 20 for an axle, 100 for rotors, and like 30 for the top bearing), and then I sold my old parts for around 180. I had clip ons and a fender already from another project.

So 120 bucks net cost for a GIGANTIC improvement. Plus the bike looked awesome with that setup. If you're thinking about it, stop thinking and just DO it.
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Old 11-28-2011, 04:47 PM   #14 (permalink)
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Quote:
Originally Posted by kevinwilly View Post
I dunno. I had GSXR forks on my first gen SV650 and they were tits.

You can't really compare shitty damping rod, undersized, standard forks with shitty twin piston calipers to inverted, cartridge damper, larger diameter forks with radial four piston calipers.
Curvys had flexier frame than the 2nd gen bikes, that's why no one had chatter on the 1st gen bike with the USD forks. That being said, you should keep in mind that it's racers, fast racers, that have found chatter to be an issue. For most people, it won't be an issue...

And no matter what, the stock SV650 suspension is so bad that anything is an improvement.
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Old 11-30-2011, 06:35 PM   #15 (permalink)
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Quote:
Originally Posted by kevinwilly View Post
The GSXR750 got them in 1990, Actually. There might be bikes that had them before that, even. I'm not sure.

The've been around a while



NB photo randomly found by Google, the bike is a 1947 GTV 500 Moto Guzzi.
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