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Old 07-31-2009, 07:19 PM   #1
Wirespokes OP
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Upside Down Forks - Why?

A friend has some bikes with them and we got to talking about them, but he didn't know why they might be better than the conventional right-side-up variety.

What are the advantages to having them?

It seems there's more unsprung weight in that configuration. Is that just an apparency?

It appears they could be much stiffer, and that's about the only logical reason I can come up with.

What's the story?
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Old 07-31-2009, 07:21 PM   #2
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You got it. Unsprung weight and stiffness.
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Old 07-31-2009, 07:45 PM   #3
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they tend to be torsionally stiffer due in part from the triple clamp.
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Old 08-01-2009, 12:46 AM   #4
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Quote:
Originally Posted by RecycledRS
You got it. Unsprung weight and stiffness.
Seems to me that steel tubes attached to the axle, along with the valving, would be heavier than aluminum sliders. Are you sure there's less unsprung weight?

Quote:
Originally Posted by 2xdisco
they tend to be torsionally stiffer due in part from the triple clamp.
That makes sense to me.
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Old 08-01-2009, 01:33 AM   #5
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Quote:
Originally Posted by Wirespokes
Seems to me that steel tubes attached to the axle, along with the valving, would be heavier than aluminum sliders. Are you sure there's less unsprung weight?


That makes sense to me.
Those heavy walled CAST (usually) sliders also contain around half a liter of oil each too though. Don't USDs carry it in a cartridge up top?
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Old 08-01-2009, 02:00 AM   #6
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In real world street riding I seriously doubt that there`s any great advantage or disadvantage to having either 'upside down' or 'conventional' forks.

Brochure bonus points and car park chest pounding seem the major reason why many street bikes have them.

I do remember that 'upside down' forks were long proclaimed to be more rigid and suffer less from 'stiction' on motocross bikes.
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Old 08-01-2009, 06:43 AM   #7
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bling. I put a conventional suzuki front end on my G/S and I wish I had gone to the trouble to get a set of USDs mainly because I think they look cool. I don't ride anywhere near good enough to notice the difference in suspension. the looks aren't a big enough deal to make me do a fork swap again though.
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Old 08-01-2009, 07:38 AM   #8
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I was reading a thread, and believe it was one here about swapping G/S forks, and someone recommended using a KTM conventional saying it worked as well as the upside down, bolted right up, and also had adjustable damping which the upside down didn't.
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Old 08-01-2009, 09:30 AM   #9
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It's all about the bling.
There can be some reduction in unsprung weight, and more stiffness

But there is also a higher amount of damaged fork tubes and leaking seals.

For the vast majority of riders they would feel no difference between a well valved USD or traditional fork.

It's like how sportbikes need to have lots of dials to adjust.
Most riders don't adjust them, most riders would even know it if the forks had been adjusted and they didn't know

but in the end USD's look bitch'n and that's part of what makes motorcycles cool.
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Old 08-01-2009, 09:40 AM   #10
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Another advantage off-road is less underhang= less chance of digging in the ground below the axle.

don't think that would be a problem on-road.
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Old 08-01-2009, 01:32 PM   #11
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Negatives about upside-down forks

A big minus with upside downs is that you can't use a fork brace. Unless you have a really big diameter axle, there isn't anything stopping the forks from twisting.. Some of the early KTM upside down forks were like this, and I was told that the new BMW X-challange is like this.
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Old 08-01-2009, 03:45 PM   #12
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The other big minus for UPSD is that up tubes are large and reduce steering movment possiblity
Conventional cartridge fork are great choice for me. UPSD seems for me like puting disk brakes on a Vincent
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Old 08-01-2009, 08:48 PM   #13
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Something "new and improved" so you have to buy a new bike?
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Old 08-01-2009, 09:38 PM   #14
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You guys are no help at all!

Here I am trying to understand this momentous stride forward in fork technology and look at what I get!

I have no bikes with upside down forks and really have no desire to go that route. I'd just like to know what the advantage is.

If I believe you, it's because Joe Racer won several races on a bike with upside down forks, so now everyone's gotta have em. It sure doesn't sound like they're a better way to go! With my bikes when a fork seal goes, the fork tubes get slimey. With upside downs, you'd lose all your fork oil and possibly the brakes as well. I don't think I want to go there; no thank you!
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Old 08-02-2009, 07:11 AM   #15
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My Ducati has the upside down forks. The disadvantage is changing the fluids, can't drain them like conventional units. The plus side is that they work very well. I assume It's because the diameter of the "sliders" is much larger and thereby stiffer so less flex. Fork braces aren't necessary so there's less weight.
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