An Unholy Union II: Wp Extreme 50mm Conventionals on a G/S

First a short stroll down ADVR memory lane....​

Three years ago the original "Unholy Union" came about and documented Elmoreman's adaption of Suzuki DR650 forks onto a R80G/S, following an example by Crankshaft who adapted Honda CR250 forks onto his R80G/S.

Elmoreman's G/S with Suzuki DR650 forks:

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Crankshaft's G/S with Honda CR250 USD forks:

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Elmoreman's thread showed the way and fellow members bgoodsoil and Hardwaregrrl (who now has the WP 50's as of Feb 2012) and Beater to name a few have tasted the yellow kool-aid and followed this path.

For me, the ideal front end needed to be conventional for the aesthetics, have adjustable compression and rebound damping and be European... nothing against the adapters of the alternative non-Euro sources... but defiling and R80G/S is one thing and putting Japanese parts onto it is a whole different and perhaps a bit edgy proposition than I wanted to take.

Early investigations showed that famous BMW tuners HPN use Marzocchi Magnum conventions in the 50mm size that do have adjustable comp and rebound.

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I picked up a set of Magnum 50mm's, my local suspension tuner told me these had two significant negatives one was that the comp and rebound worked in such as way it has no effect for the first 1/3 of the stroke, and two the sliders were too soft and tended to destroy themselves, this he said would be a significant issue on a large bike like a G/S.

While I didn't take any pictures, when I stripped the forks to clean and inspect them I found that the oil looked like melted aluminum. Clearly Magnum's weren't the forks for me.

This left one choice.... from 1997 (or 1998) until 2000 KTM used WP Extreme 50mm conventional forks. Some more digging on the internet showed that many riders consider these to be the best conventional forks ever built.

Having this information I again headed to the internet for Inspiration:

Here's my original inspiration who did this before the others below, CrazyIvan HPN conversion with 50mm Marzocchi Magnums:

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Another CrazyIvan creation, with WP 50mm's this time...

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And the finished product on the move!

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Our own roadsacallin' G/S with R-Dubb triple clamps and KTM 250SX WP Extreme forks

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Jay.T's GS with R-Dubb triple clamps and 1998 KTM 380 EXC WP Extreme 50mm's

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Redboot's G/S stolen from the UKGS'er forum... his uses triples from Boxersupplier and unknown KTM Wp's

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Another unknown, but hosted by Matt Beakers of Boxer Toko/ Boxersuppliers so I would guess these are his triples

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Stolen from another thread, can't remember who's bike... unknown model KTM WP 50mm's with a larger rotor and caliper adapter from HE in Germany

Another unknown, but hosted by Matt Beakers who runs Boxersupplier and Boxer Toko (assume these are his clamps)​

R-Dubb's G/S wearing some R-Dubb/HPNGuy triple clamps, circa 2008 (no idea on the current status)​

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used from this thread LINK​

I like em all, but that CrazyIvan's bike looks tough, dig that one!

What's involved in this conversion you ask?

Well to start with there are three ways to get alternate forks onto a G/S (or GS):
1. Use the stock triple clamps as-is and make a spacer to account for any difference in triple clamp height:

Here is an example of a DR650 conversion spacer in place:

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2. Have a custom stem made for the triples that works with the BMW steering tube height:

Here are apair of KTM clamps, stock on the left and with a custom stem for a G/S on the right:



3. Buy a set of triple clamps that are designed to work. There are three sources I know of that sell these now, http://www.gletter.de , http://www.cti-fahrzeugtechnik.de and BMW Boxer Supplies all three run around 500 Euros for a set.

Option 3A that was used by Roadsacallin and Jay.T was to use the plans from R-Dubb's thread to have custom triples made... I believe something like 10 sets were made R-Dubb using three and others going to ADVR's... there are some rumblings of someone else running a few sets and I have my name down for one! These do require a custom stem made and for those choosing this path I can suggest Banke Performance in California who used to make custom triples for $125 or so...

***2012 edit***... you'll see later in this thread that HPMGuy did a second run and pushed out ~12 more sets, as of Feb '12 is is ramping up to do a third run. Look for the HPMGuy triple thread in the vendors forum.

R-Dubb's plans and product (sadly no longer available)

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My Path:

Initially I was going to choose path number one, and run stock KTM triples with a spacer, but when I was recently in the Belgium I happened to run into CrazyIvan who passed on to me the KTM lower triple with the custom BMW stem, as well as the swing arm below... but that is for another thread...



One note on the WP Extreme forks, while these were used for all KTM's from 125cc up to the 640 Adventures, only the ADventures ran a 300mm diameter front rotor... I believe the fork lower that thread onto the slider has a unique caliper holder on the 640's. For the smaller cc bikes you can source larger discs elsewhere but most are 260mm or 280mm or smaller... there are also "supermoto" kits with rotors as large as 320mm, but there there may be issues with these and 21" wheels, I also hear that 4-piston caliper conversions conflict with the 21" wheels due to spoke/caliper spacing... again, more later on this.

Simply put, if you want to run a 300mm rotor, get the forks from a 640.

Here's my starting point, a new Braking USA 300mm rotor is on the way and I am searching for a stock 640 caliper now

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For those going this way, here is a link to a great downloadable color WP Extreme tech manual LINK



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Hey SOLO....link isn't working. I'm curious if you will be doing the frame bracing, if nothing else, at least the steering head? I apologize if you've already mentioned this. Looking forward to results!!!

Hi Jenna,

Which link?

Frame bracing will come perhaps next winter.. for now I plan on adapting the forks with the travel shortened a bit for this summer. This winter I will tackle the swing arm and frame... still waiting to hear if Brad ever got ahold of Paul Rooney....

Ive used these forks on an Lc4 620,best forks Ive tried for stock forks,plush and took high speed desert hits amazingly well. Ive thought of putting a set on my DR.

sorry, the manual for the extremes.

Oh my, this is like watching someone open your christmas present, one...













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You're a legend Solo for starting the thread with history, reasons & details

I take it most of this knowledge can be transferred to whichever forks/ front end you choose as the only difference would be fork diameter & height? Using the new triples, the offset would be the same no matter what type of fork used to achieve the original BMW turning circle?

Fixed! thanks for letting me know!

I am all for the engineering it takes to put those massive forks on it ... custom triples and all. But ... DRZ400 forks are a bolt on swap ... Just saying (and they're 49mm)

(I'm also quite sure that the WP forks are are a large upgrade in quality ... But I don't know ... )

Beater. good engineering, Must be 2x4=8 airhead ingenuity

Yes sir. That's actually a 2x6 ... GhettoTech, yo.

With the new rear shock, and the DRZ400 front forks ... that center stand when deployed is a full 2 inches off the ground. We'll be addressing that and other unforeseen issues.



Solo! Sorry for the hijack ... continue!

Beater,

Gotta say I love your airhead... but I would say that you and I started with different questions. Yours may have been something like "What can I put on the front of my RT that will make it a better airhead dirt bike, is easy to find and is a relative straight forward project?"

Where mine was something like, "OK, I already have an Airhead dirtbike (although it is a great big heavy pig) if I was going to replace the front end with another conventional fork, what would be the optimal match given my desire for easily tuneable comp and rebound damping, being already fit to a larger (read heavy) bike to avoid significant internal valving changes and springing and carrying a sufficient front brake to stop this big and heavy bike with easily obtainable and stock off-the shelf parts?"

I am sure your DRZ front end will be superior to the stock RT one, and better than the stock G/S front end... you will be able to change the springs, add an emulator and buy a super-moto brake if you want or ride it as is too. The WP front end has the lead in the other areas... also going into my consideration were the opinions from the WP users discussing this front end versus many others.

just my opinion...

Have you ever considered just gutting the internals of the stock R100 forks (beefy, good axle size) and then fitting a cartridge insert? I know that the BMW (HPN) one isn't available anymore, but MY suspension guy thinks that this is still the best route. He seems to think that he can also rig up a way to add pre-load adjustment. He call the inserts "suspension pumps' and supposedly all modern forks have these. 25mm is the size he recommends.
Seems like an easier change and then you get 2011 technology.

is this the same sort of set up?
http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItemnext&item=180648518681.html
I've been watching them on ebay. Glad I wasn't hoping to buy them because I never would have won:eek1

Well, no one makes internals for the stock R100GS forks now... and HPN's (as well as the Ohlins version not for BMW's) were really expensive. Going your route will require some custom machining to make the caps work as well as custom valving and springing.

A R100GS front end by itself can be >>$500 (complete) add to that the cost of these cartridge internals that allow adjustment at the top, not the Race Tech emulators) and it's more that I will spend.

I had an R100GS with stock forks and Race Techs for three years and they were OK, but nothing like what these WP's can be. Remember, I will also need longer travel on the front end when I put on the extended swingarm.

That's exactly what I have now, perhaps I should sell mine in Germany?????

Well actually those aren't from a 640 and are from something smaller.. the brake is only 260mm