HPN front-end??

Discussion in 'Old's Cool' started by Ron Seida, Aug 14, 2005.

  1. Ron Seida

    Ron Seida Adventman

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    Does anyone out there have an R100GS with the HPN front end? If so, i could use some specs. I'm copying the design myself with WP4860 forks shortened to the correct length, but i would like to know how much steering off-set the HPN triple-clamp has, and the resulting trail would be handy too. I plan on using a KTM 20mm off-set clamp, but only if the resulting trail is acceptable. Any comments??
    Thanx in advance.
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  2. jtwind

    jtwind Wisconsin Airhead

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  3. Ron Seida

    Ron Seida Adventman

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    I tried, no responce. Actually, i tried e-mailing them twice before, never got an answer.
    Thanx for the info, i'll send this guy a letter. Maybe he can help me out.
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  4. Frank Warner

    Frank Warner Traveller

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    Err I think the HPN stuff uses the full travel ... so there offset may not be aplicable.

    If your going to use the same travel length of the original then why not use the same 'effective' offset. (Note 'effective' - look at the trail [distance between tyre contact to steering head axis extended to road]). I take it you were happy with the bikes handleing before? If noit thne you need to talk to someone who does frame modifications .. some one local.
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  5. Ron Seida

    Ron Seida Adventman

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    Hi Frank, i had a feeling i would here from you. I just took some rough measurements and have determined the stock trail to be aprox.60-65mm. This is with a stock 36mm off-set triple-clamp. Currently the only triple-clamp i can find to fit the WP4860 forks has a max. off-set of 20mm. I can also buy a 22mm from Emig Racing for $500, this is not an option. The reduced off-set will increase the trail to maybe 75-80mm. My understanding is trail effects the bikes ability to go in a strait line, similar to the caster on a shopping cart. The more trail, the better strait-line stability. The other side of this is you loose the fast-turning capability desired for off-road riding. I've discovered many bush-riders and hare-scramblers prefer this increased off-set, providing faster, tighter handling in the woods.
    The big beemer has always felt kinda twitchy, with the ability to change your line in the middle of a corner with min. effort. A few times i've mis-juged corners too fast, only throwing it down nice and deep, dragging the pegs on the way out. The existing trail seems to be on the minimalist side if the scale for a large street-bike. Granted, the GS does handle surprisingly well in slow twisty off-road situations. Say, ever try to let go of the handle-bars while doing 60 down the highway? Pretty scarry, huh!
    I supose i could build a new triple-clamp from scratch out of billet, but i would rather not. Owning something one-of-a-kind is cool when your close to home, but sucks when your in the middle of Bolivia. KTM parts are easy to find on E-Bay and are actually quite cheap and of high quality. I only turn a custom spindle on the lathe to suit the BMW bearing size and length of steering head.
    I would like to know what HPN may have changed from stock geometry, and if someone out there could comment or give me some specs, it would help me immensley in making my final decision and finally finishing this project once and for all. I'll send HPN one last letter begging for their specs, but like i said before they don't return any of my e-mails.
    Thanx again...
    #5
  6. crankshaft

    crankshaft Guns are for pussies

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    Hi Ron,

    Would you consider posting the information when you find out? I've been thinking of a similiar project on an R80 g/s. I've got a KTM 640 ADV and I love the front forks. The WP stuff is great.

    Thank you

    Aaron
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  7. Ron Seida

    Ron Seida Adventman

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    Hello Aaron. The numbers are as follows:
    Steering offset-37mm
    Fork rake-27 degrees
    Fork length-32"
    Floor to axel-13.625"
    Resulting trail-3.5"

    Sorry for mixing up metric and imperial.I currently have a couple of blocks of billet aluminum in the mill and i'm machining them to this geometry. More on this later.
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  8. crankshaft

    crankshaft Guns are for pussies

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    Thanks Ron! Keep us posted.

    Aaron
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  9. Ron Seida

    Ron Seida Adventman

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    ...Okay, here's a current up-date. The triple-clamp in almost done, just need to do some final machining and fitting the handlebars. Now i;m dealing with clearence issues with the stock front wheel and working out some brakes for the beast. I may just go with bolt-on KTM Hardparts. More on this later...[​IMG][​IMG][​IMG][​IMG]
    #9
  10. Frank Warner

    Frank Warner Traveller

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    Some comments

    Handle bar mountings- Use 4 mounting blots - not two - two will twist if given a little force.

    You will also need front mud guard mounting holes. I'm using a after market one for a Honda XR650 - the guard has slots on the sides to let air flow - not on the back of the guard - so y u don't clog the cooler with mud.

    I use some bicycle bidons on the back side of the forks - this gives you a bit more water and I can just reach from a sitting position when stoped and get the water bottles off if I need too.
    #10
  11. ozadvntr

    ozadvntr Planning that trip, again

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    I fitted a WP front end, set up for the G/S. 275mm travel. I had the swing arm lengthened 100mm and rear travel set up to match the front. Pretty happy with how it turned out. I have it stripped again strengthening the frame.

    [​IMG]
    #11
  12. Ron Seida

    Ron Seida Adventman

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    ...nice!:ricky
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