Shorten WP43 Fork for the R80 Project

Discussion in 'Airheads' started by R-dubb, Mar 3, 2013.

  1. ontic

    ontic

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    Sorry for the thread drift R-dubb, just stirring the pot a little until your next post:D
    A little bit of USD vs RSU ponderings.

    Around the net in various discussions I've read of this being challenged in many examples, and in both claims- ie some USD's have been shown to have just as much flex as the conventionals they replaced- probably less twist, but this can be remedied with a fork brace on a conventional. Where they most certainly are stiffer is up top where they are clamped... however when they flex here (as they still do) you get stiction because of the bushes, whereas conventionals when they flex, even if they do flex more, don't suffer this the same flex-stiction problem.
    Also, in a crash or big front impact, rather than the conventional fork routinely bending the tubes at the bottom of the triple clamp (tubes being the easiest to replace or even straiten), the USD often bends at the sliders in the triple clamp (destroying the fork) while also often bending at the tubes where they meet the sliders, and/or might be more likely to damage the frame/headstock because of all this stiffness... If you get lucky and just slightly bend the tubes where they met the sliders, then the USD fork is still buggered and gets stiction until the tubes/lowers are replaced, whereas a conventional fork bent up top there will often keep you riding and get you home or round the other side of the world... maybe without you even realising.:D

    The less unsprung weight claim is also often in dispute (and often less emphasised as the main advantage- stiffness is)- I've seen a few broken down weight by weight comparisons of conventional and USD forks (including clamps) of the same tube diameter, and in these cases the USD was often heavier in total, and heavier in unsprung mass- however, of the few cases that went into something approaching adequate detail, I didn't see any inclusion of oil weights within this break down (correct me if I am wrong, but USD oil is sprung weight and conventional are unsprung?- on a WP50 fork, not a small omission!).


    So, advantages IMO:
    'unsprung weight' depends on a case by case basis, but potentially not a huge advantage either way. (btw, it would be interesting to get some actual weights on these, I can pull apart and weight my spare WP50's when I return home in a month or so).
    Stiffness yes, definitely, however if flexing when it does occur causes stiction then this needs to be weighed up against the stiffness 'advantage'- and this and all the other positives and negatives (of both kinds) speaks to the 'just a better design' claim- it depends on the details and the application.

    I'd emphasise a third advantage as has often been stated here and elsewhere, and I think it is the main one (when talking RSU and USD apples and apples- ie both good forks), modern USD's are modern. They are pretty much all that is being made on the top end, will be newer and will be the home of ongoing tech improvements, have more parts for longer, etc, etc.
    Using the newest best forks are probably the best forks to use...


    Exactly.
    However, I question the performance advantage in principle and specifically for a heavyweight bike like an airhead- well set up I don't think there would be much in it to the point it doesn't matter at all.
    Even if I do expect a fine set of 4860's properly set up to (slightly?) outperform (at least in some types of use) my WP50's once they are dialed in, there are other considerations- if I blow a seal in the middle of nowhere in my country or somewhere else, I like it that I keep my oil in my fork for longer and have a much smaller chance to dump it over my caliper and rotor- and I'm prepared to accept positives and negatives and compromises along these lines because of how and where I intend to use it.

    Regardless of all this, I do think it comes down to Aesthetics and Parts.
    Good modern USD's win for parts and seem a more sensible option I rekon.
    Aesthetically either look good to my eye but conventional look a little better for me.

    At the moment I plan on keeping and using my G/S until the WP5060 and WP4354 and WP4860's forks are ALL considered too old to service, so just as long as I can stockpile enough parts for a decade or two of use it doesn't matter much to me- I'll probably have to change forks again someday (and by this time they might be making conventionals again:wink:)
    #21
  2. AliBaba

    AliBaba Been here awhile

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    For me this is the most important factor.

    I have two bikes (HPN & EXC400) with WP4860. Please remember that the name WP4860 is more like a family of forks. There are quite a few different WP4860 so take care if you are shopping at e-bay and remember that a lot of the forks have been used for MX/Enduro.

    On my bikes stiction has never been a problem as long as the fork are aligned (take care when you mount the wheel).
    The forks has approx 100mm sag so the bearings are not close to each other. You can also find that different WP4860 has different length innertubes.

    When it comes to seal-failures I have not had any more problems with the USD then the RSU, but I do take care of the forks (dry them off with a dry rag when they are dirty and use some special grease for the seals).
    IMHO the consequences of a seal failure on a USD is not worse then on a RSU. In fact I see the failure earlier on the USD because it doesn't have
    rubber boots.

    For me the negative sides is that I have to carry two more tools to be able to service the forks and I think they will be a bit stiff if I have to use ATF-oil in a third world country.

    If you have a look at offroad-racing you will se that everyone use USD, and I've never heard of a single rider that has given up the Dakar rally because of a seal failure.
    #22
  3. R-dubb

    R-dubb Dubbious Adventurer

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    Proper setup is king. I've had lot's of WP USD forks on various bikes, probably six or seven pair. I've seen them mushy and and like a jack hammer. Always a challenge to get dialed. One of the nicest sets was a pair of 43's that started out way under-dampened on rebound. Rather than re-valving, I tried 10w oil and cranked the top clickers down to like three notches from all the way in. Worked like a dream on my heavy-ish KLX650. The thing never packed down. Go figure.

    By contrast the 48's on my KTM690 are still way too harsh and stick like crazy even after being re-valved and sprung by one of the best guys in town. They are much better than before the work, but still harsh. Go figure again. The ones on my first 450exc were always excellent. Light bike = less challenge, I guess.

    The HPN/WP 38mm variation on my old PD were downright horrible. Not sticky but flexed like mad and were way too soft. Never really set-up correctly because I bought the bike with them installed, parts were weird, and I didn't want to mess about and break stuff.

    The other huge variable is weight balance and rear shock. If the bike isn't centered, no amount a fiddling will result in a stable situation. Front too high, forget about it. Sometimes that's tough to figure out, specially if the rear shock is too soft, or under dampened. The rear squats or pogos, and it feels like the fork is out of whack. Many times, not so. The forces are translating. I'm no expert but even good hardware sucks if it's not well dialed.

    I just don't think you can properly judge a fork until every effort has been made to get it right! Certainly don't assume that because a buddy can't get his sorted that it is the fork's fault. It's hard to know, what the potential is. That's my 2 cents. The 43's going on this new bike will be made right even if I have to redo them five times.
    #23
  4. Prutser

    Prutser Long timer

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    Does this mean you are going to use progressive front prings too ?
    (to get it balanced)
    #24
  5. Ras Thurlo

    Ras Thurlo Desert Lion

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    Pls explain comment

    is it because the softer initial springing allows a bike to find its own balance more readily?

    btw- I had assumed that progressive springs are not good for off road use, because you quickly get to the firmer end of the compression, leaving you with stiff suspension with little travel. Is this right?
    #25
  6. Prutser

    Prutser Long timer

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    I just asked because I noticed the progressive spring that is mounted on his YSS shock.
    #26
  7. R-dubb

    R-dubb Dubbious Adventurer

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    That's a work in progress :D

    Yee ole airhead is full of compromise... as in, normal dirt bike logic need not apply.
    #27
  8. Prutser

    Prutser Long timer

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    What spring number did they use R-dubb ?
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  9. Beemerboff

    Beemerboff Long timer

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    Good post Ontic - covers up pretty much what I know of the relative merits of USD against RWU forks.

    And R-dubb, nice to see some recognition being given to front to rear balance, at last.
    Most suspension set up guides dont even mention it, but when you get anywhere close to the sweet spot that is mainly what you are setting.

    Any rear shock that is not perpendicular to the radius of the swinging arm will have a progressive action, and the more laid down the more progressive - simple high school mechanics.
    KTM recently returned to laid down shocks in lieu of linkages, and given that they were one of the innovators with USD forks maybe we will see them going back to RWUs as well!

    I think the uneven windings on springs has more to do with the harmonics of the spring, that is, the inherent resonances. Does next to nothing for progressiveness on evry set I have measured.
    Even some valve springs come that way now, but this is a complex subject I have no experience with.

    I have found that using the best synthetic fork oil I can find reduces stiction on my G/S forks, and my local KTM specialist sells nothing else.
    But I dont want to turn this into a "199 things you can put in your forks other than fork oil which dont work" thread.
    #29
  10. R-dubb

    R-dubb Dubbious Adventurer

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    As you may know EPM is the US dealer for Hyperpro. Klaus originally sent me a single rate spring with the YSS. It was too soft, resulting in excess sag, and preload was exhausted. Rather than going to a stiffer spring he offered the Hyperpro in a size which matches my needs.

    I've always used single rate springs and was reluctant at first. I once had a progressive spring on my Ohlins (1150 GS) and swapped it out because the going in rate was too soft, but the bike jacked too high when enough preload was applied to eliminate the wallow.

    Here I am giving it another go. Fingers crossed. Since this bike is a work in progress with the height adjustment and WP fork (I still can't test anything cause it ain't done), I decided to give the progressive another look. For the record, this bike will not be entertaining any rock gardens. I wan't a super smooth namby-pamby dual sport that I better not fucking crash. Too much work and way too pretty. A cush, but hearty traveler.

    The spring is: Hyperpro 1381 designed for a KTM 690 SMC. (SP-KT06-SSB002). If you have a way to decepher an equivilent single rate spring, I'd love to know how it plays.
    #30
  11. Phreaky Phil

    Phreaky Phil Long timer

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    I was speraking with Gary Emig of Emig Racing about clamps and offsets for my DR as I would like more stability on sand tracks and his opinion is USD's are the go. He reckons there is to much flex at the wheel with any RSU forks and the front wheel goes where it wants in the sand. He reckons they change all the XR650R's to USD. They have a USD clamp kit for DR650s. I quized him on the conventionals being smoother, he says they have no problems with the Showa's they use.
    Hmmmm :jjen
    #31
  12. Prutser

    Prutser Long timer

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    He is right about the showa's. They are smooth when setup correct.
    But they still try to bend in a place where the two tubes suppose to slide over each other...
    Not all the RSU forks are better than all the usd's :D

    Last week I spoke to some people with two ktm's one with a WP50 the other with a new ish WP48usd.
    The one with the usd had trouble with the handling. It always wanted to run to the outside of a corner, felt firm and still bottomed when braking hard or jumping.
    The bike with the RSU WP50 had no problems with stiction or handling. It was smooth and if you pushed on the seat the whole bike would go down like it should.
    The bike with the USD would NOT go down on the front when the owner got on the seat exept for when you would give it a good push. But than the fork would stay low :rofl thats what you see with most of those wp usd's even after some tuning they stick.
    They told me they were planning to do a fork transplant to go from RSU WP50 to USD because everybody told them that would be better.......:hmmmmm

    My girlfriend's G650xcountry just had a forktransplant from the stock 45mm to 45mm shiver. Which is waaaay smoother and a huge improvement compared to the sticky stock forks. Both the forks are the same brand.
    That fork is good enough now and almost without stiction. So it is posible to get some usd's set up right. With some brands or types its just harder or you wil never reach a satisfying result. Still they can be better than the stock forks in some ways.
    #32