I am in favor of a complete new front end. The question is, what triple clamp is the best to adapt to the bmw.

To fit the triple-clamp is the easy part. It’s “only”to adapt the stem and get bearings (and covers) that fits. If you don’t want to do this you can buy bolt-on clamps for the most common forks.

Example, bolt on 50mm from Gletter (original wheel fits):




In my opinion more important factors are.
* Brakes, is it room for the setup you want? (As Mr Ron says)
* Front wheel
* Geometry (esp if you increase the height)
* Can the frame handle it?
* Increased turn radius

I would not underestimate the stress on the frame when you use a longer fork. Personally I think that a straight and solid frame is very important:




I think the BMW cross spoked wheels are a good option. They also leave more room for the brakes.
The Brembo-hub used for the GS-models (don’t know for the G/S) is a very stable unit with huge bearings. My bearings were as new after 180kkm. The KTM (and many others) wear out much faster. Most KTM rims are not sturdy enough for a big powerful GS.

The geometry is harder to solve. Some people prefer to fit a longer fork and see what kind of modifications that has to be done to make it work. Other people calculate everything before they start. Both groups have failed and both groups have made nice bikes. Maybe it depends on the type of skills you have.
There are numerous started projects that never got finished.

After all the front is the easy part, it’s harder to make the rear end match

I have seen this picture around the internet. It looks like the rider hit something head on with this frame.

I don't think so. It looks more like the forces have tryed to rip of the front in forward direction. It could be after a bad wheelie or a jump - with a longer fork.

Edit: You notice that the frame is upside down?

Thanks for that explanation - so the opening of the cracks is initiated from the bottom edges of the frame members; I agree, it looks like the force applied has "rotated" the frame members upward & around the headstock - a big, overweight rider maybe?

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Dave

ha, no i did not notice that.

Wow! Excellent guys! Lots to learn on this thread.

Does anybody know what the advantage of a r100gs and r80gs swingarm over a regular swing arm, The regular swing arm mounts on the final drive.

I am still looking in to the forks. I think I am gonna go with the honda cr500 fork. Is there any other USD forks out there that I should consider?

Also, anybody know how to compress the spring in the driveshaft to take it apart?

If the bike was an original G/S you will not be able to fit the Paralever swing arm of the R100 80GS. You can do the other way round.
The main advantage of the Paralever is that it prevents the rising of the rear when accelerating and dipping as you brake.
The main advantage of the fixed arm is it's simplicity and durability.

To undo the spring I use a bearing puller and extent the bolts by replacing them with threaded rod cut to the right length.
An interesting fact about the HPN extended swing arm and shaft is that they use the older 70's shaft extended by 100mm with a piece added by friction welding. This shaft does not have a spring and the splined knuckle on the rear fit direct to the shaft( less parts to wear and possibly brake.) and the extended swing arm is machined on the inside to be large enough for the shaft to fit through the swing arm without having to disassemble the shaft.

Well my project is coming along, I sold most of the extra parts from my bike. I just picked up a new brand new r80 4 bolt monolever finaldrive, I will be machining a r100gs hub to use with it, i will be using a tubed rim. I also got the gasket kit to rebuild the engine. I got the enduralast alternator. Should be fun to install. I got a subframe, tank, seat, new oilfilter and k&n airfilter. Should have some pics soon. Oh yeah, just picked up a pair of KTM WP 4860 suspension from a 450sx, hopefully i wont have to tinker with the springs or valving to much. Pics to come soon. I am traveling in europe right now and I still cant get away from my little project I have going.

I want to use the ktm front end, are you mentioning the ktm rims from the smaller bikes or all of them? The 990 seems to be a big bike, i think that wheel should be fine on a bmw. what do you guys think?

r-dub over at adv rider recently had a number of custom triple clamps machined to adapt KTM USD (and conventional) forks to R80G/S's... you might ping him or search for his threads in the "old school" forum that tracks his developement. One thing that hasn't been mentioned (unless I missed it) was the huge difference in offset from BMW to KTM, I believe my R100GS has 36mm's and the largest you can find for a KTM is 20mm.

Great Project!

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\"I empty a bottle I feel a bit free\" Mick Jones

I think I am going to go with the 20mm offset. I have some pics, I need to upload em though. I am trying to figure out the spacing between the ktm bikes, like how interchangeable are all the wheels?

20mm offset sounds about right, I can check tomorrow...