Well...

the reason for longer forks is to alow a softer spring (which can be softer because it has a longer stroke to absorb the energy from a bump). This means the fork can be soft enought to respond to small bumps, but still have the travel to take a big hit. If you reduce the length of the shock by lifting it in the triple clamps (which would be possible it you repositioned the handlebar - yes spacers are available) then you would need to reduce the travel of the fork by limiting the stroke with shorter/ stiffer springs. Dirt bikes that are converted to dirt track/ super motorrade (sp?) often go this route.

I think the main issue remains matching the front with the rear. Yes the R100GS forks are a bit longer, but not enough to upset the handling of the bike.

The way to do this conversion is to get a full front end, with brake, wheel, and forks. This way the only issues becomes matching a master cylinder to the new caliper. BMW sells lots of different sizes that bolt onto the stock lever. You might also run into problems getting the headlight, indicator lights, and guages to fit on, but this is all do-able. The advantage of the R100GS fork is that everything more or less bolts on in the right spot.

For a buget option you can fit any forks and front wheel as long as the travel is not longer than 220mm this including Marzochi forks from a R80/100GS. There is also WP USD forks availible with 220mm travel, might have to modify axel and brake disc to fit, or Touratech sell them to fit standard to the wheel of the R80/100GS front wheel and brake.
A lot of guys are right when they mention the lengthening of the swing arm by HPN when fitting long travel suspention, (more than 265mm) But on the main frame the steering haed area is reinforced as well as the fork rake angle is changed. This is a very specaliced job, and without this your bike will be very UNSTABLE at speed.
Check out HPN's site at www.hpn.de in english and feel free to e-mail Klause, it might take a while for him to respond but he is always willing to share information whether it means bringing in work or not.
If you have money to spend, HPN is the way to upgrade your bike, this will start with the reinforcing of the frame to adapt it to fit you suspension of chioce, 43 liter feul tank, fairing, as wel as reinforcing the subframe, lengtening the swingarm and centre stand.
Once you have done this and mounted the suspention you can rebuild the rest of the bike as is onto the new frame and modify and upgrade the rest of the bike with time.
I do not agree with the ST rider, a lower bike will have less travel and will bottom out mutch easier. One thing to consider as well is that more modern off-road forks employ a progresive method of regulating the oil flow. In short this means that the forks will adapt automatically to your riding style, speed and the road conditions. Older tipe shocks like those used on the ST or G/S have a small orifice that regulate this oil flow. It is obviose that this orifice will only allow oil flow at a specific rate, when the manufacturer decided what size the orifice must be they looked at the average use for the bike riden in European conditions and hence the forks will have hardly any performance for off-road use.
When building my HPN one of my greatest concerns was the ride high of the finished product, being very average hight I found that altough I am on tip toes when stopped this is no problem when you pay attention to the spot you want to stop, it needs to be firm and level and it is possible to stop with your right foot on the foot peg allowing your left leg more reach. This allow you imediate use of the rear brake if you have to let go of the handelbar. Afterward it is easy to shift your weight to the right side of the bike to get your left foot to the shifter. If you get the hang of this you can get the bike into neutral even before you come to a standstill.
Last but not least, if you dicide to add longer forks to your bike, do not do the frame modifications by yourself or anyone but HPN. These guys have been racing these bikes for over two decades, they use a large piece of equipment to striaghten and destress the frame after and before welding and they do this almost every day. By lengthening the suspention you place even more strain on the frame and it is very important that these areas are strengthened, I say this because I now of a no. of people that have done this themselfs and have seen photographs of some BIG DOG riders with so called HPN's of which the frame have never been to Germany.
Hope this is of some use
Altus / Cape Town

[This message has been edited by gsworkshop (edited 29 June 2005).]

I'm happy to tell everyone here that shortening the stroke on USD forks is very easy. I recently shortened a set of WP 4056USD forks from 36" to the required 32" for my PD, using a 4" spacer inside thr fork tube in the dampening rod and shortening the spring. This is still a work in progress, more later...

Hi everyone,
I would like to throw in my opinion.
I think you have to define what is a better fork. I have a BMW R80ST, same as the G/S but with the 650 front end which has a shorter fork tube and a shorter rear shock. When it comes to riding a fully loaded bike like the G/S-ST that short suspension is nice because at 5'10" inches I can get my feet flat on the ground. No tiptoes for me. The new 1200 BMW, no way, a big brute. The trade off is ground clearance but how often do I need that with a good skidplate. The axle on the ST is directly under the fork, on the G/S it is in front of the fork. This affects the trail of the fork. GP road racers use my style, offroad bikes use the forward mounted axle as on the G/S. This is what defines stability in terms of turning and speeds up/slows down the steering(more or less trail). My ST will turn easily and in a very small circle but offroad it is very unstable on loose surfaces. It has broken my collar bone twice off road. You can only do so much to improve stability without sacrificing turning radius and I have pointed out the two main design possibilities. One thing you could do is stiffen the fork with a brace or stronger tubes or a stronger triple clamp. That the more modern forks can do.
The ST is a great bike on the pavement and the GS is great off road if only turning is considered. The rest of the fork absorbs the bumps and here springs really help to get the preload/sag right so the suspension can work within its travel correctly. On my ST I used stock fork oil. I believe the dampening works as well as the antique design will let it with 4 wt oil and it does not bottom or top in use. I use Works Performance 2 piece springs and a Works Performance big body rear shock with a resevoir. I can drag the cylinder heads on a bumpy paved road and hold a perfect line fully loaded with all my travel gear and 8 gallons of gas in my G/SPD tank mounted on the ST. As I said, off road is where the hell is for me. I just did 40K with this setup from the Yukon to Tierra del Fuego and back to the USA. No problems on road. Crashed off road due to my own error, caused by little O2 and sleep in Bolivia. No failures with the suspension, front or rear.
For much of my travels I rode with others, an African twin, a BMW PD single and a KLR. No problem running with these bikes on the road, off road they were more stable so a little faster but honestly they were all on pigs and unless youwant to be the fool we all better slow down and concentrate on riding safely. You dont need a better front end than the stock G/S has. It is good for what it is and well thought out. It works with the bike and frame. A stiffer fork just puts the problems elsewhwhere so maybe a bigger problem in the end. For a single rider and gear the G/S is fine with a good fork brace. Compare the G/S fork to the KLR side by side, which is stronger? Save your money and travel longer and sooner. Pack the bike well. I am looking for a stock G/S front end for my ST if anyone takes one off. I would love to have one. My bike has 180K miles.
Ride well.
BMWST Bill.

Mr. Ron,

I have a set of 4054's arriving next week and hope to do the same thing you have done in fitting them to my 1993 R100GS. Can you supply me with any information on your process to shorten the springs and use the spacer?

I am just south of you down in Seattle.

I would send you a PM, but am not allowed to do so until I have 15 posts. If anyone can send this along to Mr. Ron I would appreciate it.

My contact email is listed in my profile.

Thanks!

SL

Hello Solo! I recognise you from Advent...welcome. I forgot about this thread and therefor haven't updated my endevours. Too bad, you may not like what i have to say:
I found the 4054's to be unsuitable for the GS100. They are too small and light, mainly fecause the trippleclamp on the GS has a much shorter pin. Also, the 4054 has a very small 12mm axel. Basically, the fork would not be much better than the stock in the end. I ended up buying a set set of 4860's from E-Bay for $400.
This is where things get tricky. You will need a trippleclamp to go with it. You can use a KTM trippleclamp which will alter the geometry of the bike, but only slightly. This affords you the option of using a KTM front wheel (Accel) and KTM brakes. I actually built my own trippleclamp, milled from billet aluminum, and had a 210-21 wheel built by Woody's Wheelworks with the heavy spokes and a Rad Eagle billet hub, and then machined up the required spacers. The major problem i had with a stock KTM trippleclamp was the off-set. The stock BMW offset is 26mm, the KTM offset is 18-20mm, depending on the clamp. This tightens up the front end considerably, and i had clearence issues with the PD tank, the clamp hits the tank and reduces your turning radius. I don't know if this is a problem with the stock GS tank. If you decide to go the rout of building a custom trippleclamp, bake sure you copy the KTM fork spacing EXACTLY! I was off by 2mm and this created a huge clearence problem with the brake disk. I had to machine the fork itself, and my wheel is offset by 2mm :(. Only change the offset to 26mm.
Yoiu need to machine a new pin which holds the bearings for the steering head, there is no stock match to the BMW bearing size. Also, the pin is a specific length and much dhorter than most dirtbikes by about 25mm.
The KTM950 forks are a standard 4860 fork found on ALL their later bikes, only with shorter springs and a 3.5" spacer on the dampening rod. Basicly, the spacer doesnot allow the fork to fully extend back to 11.5". The springs are cut short the same amount. The springs i used are .48kg/mm Raceteck, and are very stiff, good for a heavily loaded travelbike and very agressive. The forks were modified by Holeshot Racing in Langly, ant the mods cost about $400.
Ditch the 4054's and get the 4860's! If your going to go through with this mod, may as well do it right. The current KTM Hardparts are awesome! I use the 310mm Wave rotor and a Berringer 4-pot caliper. I reduced the master cylinder to a 12mm (stock BMW)...the brakes are HUGE!!
You can check out some photo's in the Copper Canyon file at http://homepage.mac.com/adventman/

Thanks for the reply, and from what I hear custom triple-clamps seem to be mandatory. I was wondering about the 4054's, but know of one GS in New Zealand that has them. The HPN R100GS front end kit does come with 40mm WP's, R-dubb (over on ADVR) has the HPN set-up on his R100GSPD. Seems like I need to do more research on my end.

Any change you would be interested in making another set of the tripple clamps you are running? I do know of a german company making a tripple clamp set for 45mm Marzocchi's that runs around $550, suposedly a "plug-and-play" solution for R100GS's. Honestly I don't know if the $550 is a representative cost, but that plus the cost of the forks, and fork mods make make this change too spendy for me to try and attempt anytime soon.

Cheers!

Here is the one that I know of (with 4054's). I have asked the owner a few questions about how well these forks work, hope he will answer.

I can promise you that any fork you try to mod to the GS will end up being expensive in the end. After the price of forks, re-working them, wheel, brakes and rotor, and lets not forget the tripleclamp...mucho $$$! Then you got handlebars, SS brake line, ...my setup was aprox. $2000 in the end. The tripleclamp took me two full weekends to build after R&D. Its a great winter project!
I've considered producing the tripleclamp in mass by a buddy who owns a CNC mill to my design, but thats not in the books right now, sorry.:( Maybe you should look into the Marazzocci clamp. If they are the forks i think they are, they should serve the purpose well.

Thanks Ron,

I appreciate your wise words... once I get the 4054's I will do some serious looking and thinking about this project.

WP 4860 fork conversion
 

Mr Ron et al Ive just bought some WP4860s with triple clamp of a KTM for my r80g/s upgrade. Can anyone please advise if only the springs require stiffening to say 0.48s? Valves etc? Cheers!

Probably the best place to find an answer to that is in the airhead section of ADVrider, this thread might have the answer and there are a couple more on the subject, other forks on G/S are also dealt with not just DRZ.

An Unholy Union V: DRZ forks on an Airhead | Adventure Rider