An Unholy Union III: WP 4860 USD Forks on an Airhead

[AliBaba]

Originally Posted by Airhead Wrangler

YES!! Thanks. That's some really good info. I was surprised that the offset was as small as 25mm. Everyone so far has told me that HPN used roughly the same offset as BMW, but looking at your photos it's obviously not even close.

The offset on my KTM is even smaller.

Originally Posted by Airhead Wrangler

Any idea what your spring rate is??

Sorry, the springs are not marked, that's the (main) reason that I haven't ordered softer srings.

[SOLO LOBO]

Just read about another ADVR getting custom wound 0.65 springs from this place:

http://www.sonicsprings.com/catalog/

[Airhead Wrangler]

Originally Posted by SOLO LOBO

Just read about another ADVR getting custom wound 0.65 springs from this place:

http://www.sonicsprings.com/catalog/

I've seen off the shelf (non-custom) springs available from .36 all the way up to .70 for 4860s.

[Airhead Wrangler]

Originally Posted by AntonLargiader

I finally got around to measuring the ones I have.

66mm upper clamp area
137mm gap
91mm lower clamp area

These measurements seem to be consistent for the dirt bike models. However I was missing data on the 950/990 models, but as luck would have it someone on their way south on a 990 adventure is crashing at my house for the next couple days. I measured his forks and got a very different measurement between clamping areas:

65mm upper clamp area
175mm gap
92mm lower clamp area

I used a crappy tape measure and judging by anton's avatar, his numbers for the clamping area lengths are probably better than mine, but the gap between the two is obviously MUCH bigger on the 990 I measured - not sure what year - so much so that they probably wouldn't work on an airhead.

[Airhead Wrangler]

Does anyone have a KTM dirtbike to pull some measurements off of? Could you measure the center to center of the diameter of the hexagonal brake rotor bolt pattern? I'd like to compare them to the pattern from a 990 adventure which uses dual 300mm floating rotors as stock. The 990 rotors use no lateral offset, so if the rotor bolt pattern is the same, I might be able to use a 990 rotor with dirt model forks.

[AliBaba]

Originally Posted by Airhead Wrangler

Does anyone have a KTM dirtbike to pull some measurements off of? Could you measure the center to center of the diameter of the hexagonal brake rotor bolt pattern?

EXC400, 2006, +-2mm:
Straight accross (center to center) 125mm
One hole to the next (center to center): 65mm

[Airhead Wrangler]

Originally Posted by AliBaba

EXC400, 2006, +-2mm:
Straight accross (center to center) 125mm
One hole to the next (center to center): 65mm

Thanks for that, but DAMN. Not the same as the 990 which is about 143mm. Back to the drawing board. Maybe if I start with a 690 enduro hub. Hmmm...

EDIT: OK, after a bit more checking it looks like the 950/990 adventure, the 950 super enduro, and the 690 enduro all use the larger 143mm rotor bolt pattern. While the 950/990 adventure use the larger 30mm, the super enduro and 690 enduro use the same 26mm axle as the RFS model. I might have to start with a 690 enduro or 950 superenduro front hub. I'll also need a different caliper holder if not an entirely different caliper.

Measurements ripped off of metalgear's website:


Measurements (mm)
Outside Diameter: 300
Inside Diameter: 124
Bolt Hole CTC Diameter: 143
Bolt Hole Qty: 6
Bolt Hole Size: 6.5
Thickness: 5.0
Minimum Thickness: 4.5
Offset: 0.0

Metalgear makes some nice rotors at pretty reasonable prices too:



$189AU

[aerone]

I just finished my bike, rode it yesterday. (88GS} Short story, new cnc offset trees using stock SM forks and radial mount brakes. Shortened KTM stem turned down to fit BMW stock bearings. I used both KTM calipers and the stock KTM brake lines. The brakes are great, not too much as on the SM. I used a 16 mm BMW master cylinder and all my stock switchgear and throttle work fine on the KTM fatbars that are mounted in the stock rubber isolators. The stock springs in the 06 USD seem to be about right for me at 190 pounds.

I'm not too good a posting pictures. I will share if one of you send me an email address.

I was inspired by all of these unholy reunion threads and had to take action. Thanks !

[Airhead Wrangler]

Originally Posted by aerone

I'm not too good a posting pictures. I will share if one of you send me an email address.

Check your PMs.

[igormortis]

Originally Posted by aerone

I just finished my bike, rode it yesterday...I'm not too good a posting pictures. I will share if one of you send me an email address.

Originally Posted by Airhead Wrangler

Check your PMs.

[Airhead Wrangler]

Originally Posted by aerone

I'm not too good a posting pictures. I will share if one of you send me an email address.

Here you go. That's one hell of a big offset in the triples. I guess that's necessary in this application as the SM forks are non-leading axle. Have you shortened the travel at all? If not, it looks like you could bottom out your front wheel in the fender.

[aerone]

That is quite the offset. I left the clamps pretty thick, they are strong enough to set a house on. I have done some real hard braking while testing the rig, no issue yet on tire to fender clearance. I made sure the axle location is real close to stock, the geometry seems to be spot on.

[Airhead Wrangler]

Originally Posted by aerone

I have done some real hard braking while testing the rig, no issue yet on tire to fender clearance.

I bet. Those brakes look like they'd stop you like a brick wall.

[Airhead Wrangler]

Originally Posted by AliBaba

EXC400, 2006, +-2mm:
Straight accross (center to center) 125mm
One hole to the next (center to center): 65mm

Are you sure about this measurement? I had a manufacturer of aftermarket KTM hubs tell me that the front rotor bolt diameter on ALL KTMs 125+ is 143mm. He said that 125mm is the diameter of the rear rotor bolt pattern on a lot of the dirt models.

[AliBaba]

Originally Posted by Airhead Wrangler

Are you sure about this measurement? I had a manufacturer of aftermarket KTM hubs tell me that the front rotor bolt diameter on ALL KTMs 125+ is 143mm. He said that 125mm is the diameter of the rear rotor bolt pattern on a lot of the dirt models.

Aaarggh, you are right, it is 143 mm. I have a lot of trashed parts and picked a rear one. Sorry.