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

[igormortis]

OK, what’s everyone using to work on their forks? Is there a reasonable source for the special tools or are people making their own?

[Airhead Wrangler]

Originally Posted by igormortis

OK, what’s everyone using to work on their forks? Is there a reasonable source for the special tools or are people making their own?

They can all be improvised with random stuff you have laying around, but this stuff would probably make life a lot easier:
http://slavensracing.com/products/su...pension-tools1

[igormortis]

FYI, here are the bits I used to make the GS wheel fit the KTM forks with HPM/R-dubb clamps.



From left to right:

- Monolever road bike axle. 30mm, 25mm (mine was from an ’85 R80)

- standard axle spacer. 11mm
- standard axle spacer, machined down to approx 17mm (spacers and axle came from the same road Mono bike)

- steel sleeve, 0.5mm thick to bring the BMW axle up to the KTM’s 26mm. Split to allow tightening. Approx 58mm in length, with about a 4mm “hat” to keep it located. This is against the inside of the axle clamp and acts as an additional spacer.

- steel shim. This is what the hat part of the sleeve tightens against when the axle is pulled into position by the end bolt.

Not pictured: Axle end shim and bolt. These are standard items from the above Monolever bike.

[aerone]

That looks much the same as what I did to use the BMW axle and wheel with the 950 sm front end. I have not measured the length, it does have to be split so that it will clamp.

As far as machining the top, I guess it depends on which application you are using, sm, adventure, sx or what. I believe there is enough metal in the tube not to worry about getting too thin, no matter how long a surface you cut the taper out of.

[SOLO LOBO]

HPMGuy is making a new run of his triples for this application:

http://www.advrider.com/forums/showthread.php?t=778520

Originally Posted by HPMGuy

Group Buy Number Two for the R-Dubb designed triple clamps that will mount KTM 50mm Extremes, 4860's, or 43mm forks to your Airhead BMW.

Many have expressed interest in another run of these triples, so I am starting a list to see if we can get enough to do a second run. A lot of info can be found about this setup here on the previous group buy thread.

Pricing will remain the same as the last run, $536 for the Upper and Lower Triples, New Stem pressed in place, Stem Top bolt/washer and hardware.

I will PM everyone on the list to confirm interest, and then chart it here so we can see where we stand.

Also, there has been some interest expressed in a lower triple with a greater depth to properly grip the 4860's that come on the 950/990 Adventure Bikes. If anyone else is interested in this, join in as well. If we can get a few takers the cost should be close to the same as the regular setups.


Thanks!
Guy

[Airhead Wrangler]

Another question. Has anyone actually installed their 4860 triples and forks? I know 6 people bought them, but I haven't seen any questions or photos posted here. What happened? I'd be all over this myself if I weren't frameless and my forks and triples weren't 3000 miles away.

[AntonLargiader]

I wonder, also. I'd really like to ride a bike with this installation to see how the geometry works. The impression I got was that the offset was selected to create the right trail on a Monolever when the front is higher but the rear isn't.

I don't want to raise the front much at all. Looking at the forks I have,it seems that I'll end up a bit higher just due to the position of the clamping areas, which is OK, but I want to limit that as much as possible.

Interestingly enough, the KTM triples (from the EXC at least) have very little offset, meaning more trail. In fact, the R100GS has less trail (100mm) than any comparable bike, which I suspect is why there is so much kickback when you hit rocks sideways. I'm not in love with the BMW geometry so I see no need to duplicate it for handling's sake. OTOH, of course, I do appreciate the greater steering lock that comes with more offset, but you have to compromise somewhere.

So, the new group buy is tempting, but I'd like some sort of indication that the offset is appropriate for my particular needs. I'll have to sift through the details more, but in the meantime I'd like to see some feedback from the existing user base.

[Airhead Wrangler]

Originally Posted by AntonLargiader

The impression I got was that the offset was selected to create the right trail on a Monolever when the front is higher but the rear isn't.

I don't think that's right. R-dubb designed these for his own bike which had an extended monolever swingarm - 100mm longer than stock, not sure on the shock length. Also, they were originally designed for the leg-to-axle offset of WP 4354 USD forks I believe. It's all in his design thread (which I'm too lazy to go back and check myself right now)

[AntonLargiader]

OK. Dunno if the 4354 has a different axle offset (I sort of doubt it's significant) but the last diagrams I see in his design thread show 35mm offset and the clamps are made to 38mm, so clearly there was some more work done.

Anyway, you sort of confirm my suspicion that this clamp may not be optimized for my wants. I'll just have to do a bunch of figuring and see where the trail ends up on an R100GS.

[Airhead Wrangler]

Try talking to Mex on here. His bike uses a stock monolever and 4860 forks. He used triples from a german company that have 39mm of offset and said the handling was much improved over the stock KTM triples that he tried. I'm not sure how much if any he shortened the forks.

[Stagehand]

I love when you guys talk dirty.

[OZbeemer]

Originally Posted by Airhead Wrangler

Another question. Has anyone actually installed their 4860 triples and forks? I know 6 people bought them, but I haven't seen any questions or photos posted here. What happened? I'd be all over this myself if I weren't frameless and my forks and triples weren't 3000 miles away.

I'm waiting on the next run of triples to be made . Then I will be attacking this. Picked up the 4860's off a 2003 450exc from an inmate. Need to be re-built and new springs etc. Now I'm trying to decide if I adapt the gs front wheel or buy a ktm front. Looking forward to this. This will be a great learning process for me!

[larryscustomcycles]

Can the travel of the 06 950SM 4860s be extended by a couple of inches? From 200mm to say 250mm?

[aerone]

I have ridden about two hundred miles dirt since I put 06 KTM SUMO front end on my 88GS. I'm running stock length dropped in the triple a few inches. No problems at all so far. I'm not jumping off cliffs or any thing, they're great for"normal" riding. Next comes the Heinrich.

[aerone]

From my experience, I would recommend using the wheel that fit's the front end that you have. I know mine was more difficult using the 950SM brake rotors and calipers than say a 450 EXC using a single brake rotor and KTM wheel. I wanted the keep the tubeless BMW front wheel and did. It took a lot of thought and trial to have a complicated, two piece adapter made for each side. Then another adapter for the BMW axel to the KTM fork legs.

I would go with the BMW head bearings, dust covers. I used all the BMW stuff and turned down and shortened/rethreaded the KTM stem to the right length. That also took a couple of tries to get the right length.