Upside Down Forks - Why?

Discussion in 'Old's Cool' started by Wirespokes, Jul 31, 2009.

  1. Wirespokes

    Wirespokes Beemerholics Anonymous

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    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?
    #1
  2. RecycledRS

    RecycledRS Along for the ride

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    You got it. Unsprung weight and stiffness.
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  3. 2xdisco

    2xdisco Been here awhile

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    they tend to be torsionally stiffer due in part from the triple clamp.
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  4. Wirespokes

    Wirespokes Beemerholics Anonymous

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    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.
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  5. Airhead Wrangler

    Airhead Wrangler Long timer

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    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?
    #5
  6. Tarka

    Tarka Doesn't wave back.

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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.
    #6
  7. bgoodsoil

    bgoodsoil Dare to be Stupid

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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.
    #7
  8. Wirespokes

    Wirespokes Beemerholics Anonymous

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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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  9. squish

    squish Out of the office.

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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.
    #9
  10. enduro Dan

    enduro Dan Sticks and Stones™..

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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.
    #10
  11. espressodrinker

    espressodrinker Cape Town Wanderer

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    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.
    #11
  12. Caddy82rats

    Caddy82rats Long timer

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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
    #12
  13. reddirtjoe

    reddirtjoe motorcycle addict

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    Something "new and improved" so you have to buy a new bike?
    #13
  14. Wirespokes

    Wirespokes Beemerholics Anonymous

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    You guys are no help at all! :lol3

    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!
    #14
  15. Jasper ST4

    Jasper ST4 Guest

    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.
    #15
  16. anotherguy

    anotherguy unsympathetic

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    1.)Rigidity due to the fact that larger OD tubing is stronger.
    2.)Light weight due to the fact larger OD tubing is stronger with thinner wall thickness.
    3.)Less friction and slop due to increased bushing engagement.The bushings are further apart meaning it takes more power/force to flex the unit.Goes to the rigidity referred to in #1.
    4.)Easier to manufacture due to the larger castings.Larger casting molds pay for themselves faster and are easier to make with a longer life.Only the $10K+ forks are billet.
    5.)Easier to access cartridges and more room for them.
    6.)Less unsprung weight.The sliders on a conventional fork are indeed heavier than a USD slider.The USD slider is machined,hard chromed and stronger material per given weight so it can be thinner therefore lighter

    I valve my own suspension and have been to school for it.You're missing out on a lot of performance ( that you paid for) skipping the adjustments provided.Performance means more than speed.You'll be safer,less tired and in most cases surprised at what you can accomplish with some time,understanding and a screwdriver.Someone earlier referred to the adjustments being "bling".Every time I ride with some guys on my favorite roads they bitch about it being bumpy.I don't even notice and I set my bikes up (use the adjustments) firm.Learning how to ride your motorcycle includes suspension adjustment.It's easy to criticize what you don't understand.The OP was asking for an explanation not opinions.
    #16
  17. puncar thogoole

    puncar thogoole Been here awhile

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    Are they really upside down?

    Funny thing I remember in the 80's, talking to my farther I mentioned a bike my workmate had bought with upside down forks, the first I recall seeing, my Dad replied, they aren't upside down, thats how they used to be, all the newer ones (conventional) are upside down!

    :gerg

    (not the best picture, but as you can see, nothing's new.)

    Attached Files:

    #17
  18. Tarka

    Tarka Doesn't wave back.

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    Correctomundo !!!!

    Today`s 'upside downers' are yesterday`s 'conventionals'. :evil
    #18
  19. Wirespokes

    Wirespokes Beemerholics Anonymous

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    Very interesting! Now I understand the advantage of the upside downs, and the disadvantages too.

    Thanks guys! :clap
    #19
  20. dlrides

    dlrides 1:1.618

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    Good explanation, and spot on !

    :thumb
    #20