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Old 10-25-2011, 08:57 AM   #16
One Less Harley
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You'll still have forks that weigh a metric ton. Plus I doubt changing internals can be easily done. There might be some machining involved. The WP forks are so much better and lighter than the stock ones. Not sure that chaning over to WP would have cost that much more than the change over to GS forks, well at least for me. I found GS forks and wheel in Germany, a complete front end, $700-800. Wheel was unu$able so I changed the tubliss rim out to an Excel tube rim, More money. Then switched the brake MC for a better brake response w/ a Brembo 4 pot, plus a gold valve and heavier springs. The suspension is adequate for fire roads, gravel and such, but has limitations on the rough stuff.

Of course the GS forks are BMW if that matters to you and it's an easy swap.
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Old 10-25-2011, 11:12 AM   #17
Airhead Wrangler OP
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Quote:
Originally Posted by One Less Harley View Post
You'll still have forks that weigh a metric ton.
The forks themselves aren't much heavier than 4860s at all. It's the front wheel, brake rotor and caliper that are much heavier than the KTM ones.


Quote:
Originally Posted by Airhead Wrangler
R100GS front end:

Fork legs with oil 24 lbs
triples 4.0
Front wheel 13.4 lbs
Axle .9
caliper 2.75 lbs ($822.25 on maxbmw!?!?!)
rotor 4.59 lbs
rotor bolts (4) .6 lbs

total excluding small fasteners: 52.04 lbs (yikes)

WP 4860 front end w/ ktm wheel:
substituted a few numbers from G450X front end because it's probably pretty close and I still don't have all the 4860 parts to weigh
wheel 7.2
rotor 2.0
axle .75 (actual 4860 axle)
fork legs 20.5 (4860 legs with oil)
caliper 1.3
bottom triple 2.5
top triple 1.6
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Old 10-25-2011, 12:42 PM   #18
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Alright. So with a mix of real measurements and derived measurements (scaled photos) I sketched up the mounting situation with the R-Dub triples. It looks like the clamping sections fall right where they need to, but I STILL NEED TO CONFIRM THIS WITH REAL MEASUREMENTS.



If anyone has a set o 4860s and/or a bare airhead frame to measure I need the lengths of and distance between the clamping sections of the fork legs as well as the length of the BMW steering head between the two bearing races.
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Old 10-25-2011, 02:31 PM   #19
igormortis
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Here are some approximate measurements. Tape is illustrative - not what I measured from.

- top of fork, to bottom of upper clamping area: 63mm
- lower scribed line on fork, to bottom of upper clamping area: 56mm
- bottom of upper clamping area, to top of lower clamping area: 139mm
- length of lowerclamping area: 93mm

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Old 10-25-2011, 02:34 PM   #20
Airhead Wrangler OP
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Quote:
Originally Posted by igormortis View Post

Here are some approximate measurements. Tape is illustrative - not what I measured from.

- top of fork, to bottom of upper clamping area: 63mm
- lower scribed lineon fork, to bottom of upper clamping area: 56mm
- bottom of upper clamping area, to top of lower clamping area: 139mm
- length of lowerclamping area: 93mm
Excellent. For the record, what year and model of bike did these come from??

Also, you don't have a bare airhead frame to measure the distance between races, do you?
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R80ST Gets The HPN Treatment
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Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.
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Old 10-25-2011, 02:49 PM   #21
One Less Harley
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6-9/16"" from the bottom inner race to the bottom of the knurled adjuster nut just below the top clamp. which If I can tell wraps down past the top of the inner race. My best guess would be 6.75" allowing 1/16" for the metal thickness of the silver knurled nut.

R100GS front end on a G/S frame.

Does this give you what you need??



Not sure how far the race goes into the silver ring, guessing the top of the ring is <1/16" thick...something like that.
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Old 10-25-2011, 02:53 PM   #22
igormortis
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Forks were stated to be off a 2003 KTM 250SX. Fork lower clamps are stamped ’02.

I have an Airhead frame I may be able to measure from. *edit: should I just confirm OLH’s measurement above?
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Old 10-25-2011, 03:24 PM   #23
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Quote:
Originally Posted by igormortis View Post
*edit: should I just confirm OLH’s measurement above?
No, I need the measurement between the bottoms of the bearing seats inside the steering head. Those are the stepped shoulders that the bearing races rest on. Here's a drawing:



139mm is just an estimate. I need the actual. Thanks.
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Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.

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Old 10-25-2011, 04:09 PM   #24
One Less Harley
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Don't think I'll pull my bike apart to get you those measurements, hope someone comes through for ya!

BMWblake had a busted up GS frame, wonder if he still has it laying around???
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Old 10-25-2011, 04:14 PM   #25
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Quote:
Originally Posted by One Less Harley View Post
Don't think I'll pull my bike apart to get you those measurements, hope someone come through for ya!

BMWblake had a busted up GS frame, wonder if he still has it laying around???
Oh come on. You mean you have something more important to do?

Doesn't need to be a GS frame. I'm pretty sure they're all the same.
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Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.
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Old 10-25-2011, 04:58 PM   #26
One Less Harley
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I'll guess about 142-145mm, by looking at the outer bands of the headset. See where it is straight then angles inwards at 6'1/4" mark on the tape. The race cannot go lower than that, but you don't want a guess huh. It'll be very close to that.

I May have some old bearing races to help get me even closer if no one comes through for you.

How much tolerance do you need??
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Old 10-25-2011, 05:10 PM   #27
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Well, I just looked it over and it looks like we have a huge cushion with the measurements you gave me. The steering head would have to be a huge amount longer or shorter before we'd run into trouble. Here's what it looks like in the middle of your range with a race to race dimension of 143.5mm. We'd get a full 27mm of height adjustment sliding the legs through the triples. Everything looks healthy to me:

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Old 10-25-2011, 05:15 PM   #28
One Less Harley
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I know 139 mm is way to short do to the angle of the bearing recesses at the head tube, 142- and no way over 150, closest to 143-145 trying to allow for the unknown .

What year/model of KTM's have the 4860's or has this been discussed elsewhere? What about spring rates, would stockers be useable??
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Old 10-25-2011, 05:23 PM   #29
AntonLargiader
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I finally got around to measuring the ones I have.

66mm upper clamp area
137mm gap
91mm lower clamp area
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Old 10-25-2011, 05:25 PM   #30
One Less Harley
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137mm really!!!! didn't think they could go down that far at least looking at it from the outside.
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