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Diiference between USD and telescopic forks???

Discussion in 'Bling and Appearance' started by lil, Sep 3, 2006.

  1. This is going to seem really dumb coming from someone who's been riding as long as I have, but I would like someone to explain the difference/reason for each.

    I was sitting in the garage the other day looking at our ever increasing bike population :LOL: and noticed that both the Hondas have telescopic forks and the Duke has USD (upside down) ones.

    Is it just that Jap bikes are too cheap and nasty to get better parts :p :LOL: :p , or is there no real difference, or is one better suited to performance and one to touring?

    [best Pauline Hanson voice] PLEASE EXPLAIN [/best Pauline Hanson voice]
  2. for one, usd have much lower unsprung weight.
  3. They are both a cheap solution for a complex problem, one I'm working on.

    USD forks have less inertia to allow the suspension easier movement, less weight is always better.

    Two main parts to forks, big heavy chrome bit and a little hollow tube. The little hollow tube is lighter and is easier to move due to less weight needs to be moved around. (inertia).

    As I read back, it all looks believable.
  4. they operate the same way hydromechanicaly (valves, springs, ect) USD forks are better due to less unsprung weight which = less mass and inertia for the shocks to deal with.

    for basic shock info have a look at link, nothing specificaly on USD's but basicaly a shocks convert kinetic energy in to thermal energy, the less mass a shock has to deal with the less thermal energy created, so the shock oil dosent heat up as quick which makes the oil thin which in turn changes the shock rate. so USD's give a more even damping rate as the oil heats up less.

  5. Many of the 750cc and litre class I4 sports bikes that have come out of Japan in the last 10 years have USD forks. Recently they've started shipping 600cc sports bikes with USD forks too.

    You didn't specify what bike it was in your garage that didn't have them.
  6. This is a non technical link....


  7. It was only meant as a shitstir, Stew....us Ducati riders rarely get to give it back :wink:
  8. Oh. :oops:

    Still, if it's any consolation, I reckon most Jap bike owners all secretly wish that they could afford a Ducati equivalent, and so settle for sour grapes instead. :wink:
  9. As people have said USD forks have an unsprung weight advantage. Unsprung weight is more important than sprung weight as the intertia of the unsprung weight effects the ability of the suspension to respond quickly and accurately to inputs from the road surface.

    However that isn't the end of the story, many off road bikes have conventional forks because USD forks are much more prone to damage from mud and grit and stones, partly because the fork sliders are lower and partly because the fork seals are facing towards the direction that rocks and stones come from rather than away from as in conventional forks.

    Also as bikes get heavier the small amount of unsprung weight saved becomes less important (because it is the sprung to unsprung weight ratio that most matters), so you'll also see many heavier touring and sports touring bikes fitted with conventional forks.

    Lastly conventional forks tend to be a bit cheaper to make, so you see them on lower end and midrange machines more than on top end machines.

    *edit* Yes some high end motorcross machines also have upside down forks and they tend to come with plastic protectors which attempt to protect the sliders, this is ok for a competition machine but isn't very suitable for trail bikes or all roaders :)
  10. Thankyou people! It wasn't such a stupid question after all!