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Old 06-19-2011, 12:19 AM   #27
ontic OP
Joined: Jul 2008
Location: Melbourne
Oddometer: 1,048
Originally Posted by Sibbo View Post
Jeez Ontic , brilliant mate ! I'm going to have to quiz you about the intricacies of airhead dirt bike construction though .This is all about suspension travel ? How much extra ? What are the ubeaut clamps for ?

On the subject of headers , have a look at this ....
Hi mate, thanks,
I'm far from an expert regarding these intricacies and am purely stumbling my way through things bit by bit.
It has taken me a long time to develop a plan, and I still haven't finished that plan yet- it is enough to get started though.

regarding the front end- first some background-
I was not very happy with mine as it came to me. It was way too soft for my liking, diving hard under braking, and kinda floppy feeling all over, and this was just riding with a small tank and no other loading on the bike. As I looked into things I found that many consider these front forks to be a little underbuilt- especially for loaded down touring.
Anyway, I looked into improving things. I could have tried for stiffer springs, for race-tech gold valve cartridge emulator thingies, for a stiffer billet upper triple clamp (unlike your 80ST which I believe came with a proper upper triple clamp the G/S one is just flimsy stamped steel), for a fork brace, etc, etc. Some people seem happy with this sort of outcome. This didn't seem optimum for me as I was rapidly loosing my drive to 'keep the bike as stock as possible' and wanted to go for a better end result. Also, things like my G/S front wheel wanting a respoke and general rebuild steered me away from sticking with this front end. Getting it working like I wanted would likely have been very expensive.

Next I started heading towards doing a GS Marzocchi front end swap. These have a much better reputation and are considered by many to be a good bang-for-buck plug-and-play upgrade. Of course, unless I wanted to work out custom axles and whatnot to fit my G/S wheel (which still needed work), the whole front end from a GS is required, wheel and all- and this too was looking to be very expensive to source. Also, it was looking like to get the most out of these forks a re-spring and gold valve might also be a good idea. More $$$. I did start going down this route though and came a hairs breadth from buying forks from German Ebay which fell through at the last minute.

After a lot more reading and gradually overcoming my trepidation to attempt anything greater than a simple 'plug-and-play' option I decided to go for a WP Extreme 50mm conventional fork swap.
The timing of this decision concided nicely with Solo Lobo having started his Unholy Union thread
and he has been a great help through many PM's in talking me through this

While I have largely overcome any inclination to keep this G/S stock, or even 'bmw' in all its parts, one thing I haven't managed to get over is my aversion to USD forks on an old airhead like this. It is silly, but they just look wrong to me, and conventionals just look right...
So, the 50mm WP's seemed like a good workable option. Of course the net is full of opinion going in just about any direction you could want- but there seems to be a fair few people who think these forks are some of the best conventional forks ever made... I don't know about that, but at the very least they should represent a significant enough upgrade to start to justify the money that was going to be spent on any option. They will need some tuning and re-working, probably new springs and re-shimming the valves.
But, they are reasonably modern big stiff forks with adjustable compression and rebound.

At first I plan to limit the full extension of the forks to keep them at the stock bmw height in order to maintain the 'right' geometry. This is a relatively simple operation of changing spacers inside the fork and is completely reversable. Solo Lobo goes over this in his thread.
Later, if I wish to extend the swing arm, then I will re-extend the front forks. I have no rush on that and plan to get it well set up at stock height first. If I extend the rear it will mean re-springing my Ohlins rear shock and also changing things like centre and side stands, so I want to be sure I want to go that route. That may be round two of the build.

Now, those ubeaut clamps (the R-Dubb ones right?) are for fitting these forks to the bmw. With a bit of work (again gone over in Solo's thread) it is possible to use the KTM triples, but these have much smaller offset than the huge 38mm bmw offset. Using the R-Dubb triples allows one to basically preserve the same bmw steering geometry.

Anyway, there is the background and the justification. All up this front end is going to be expensive (a bit more than the other two options), but so was the rear shock, and the rear shock upgrade deserves a good front end upgrade!
This will be the first time I have tried anything like this, so aside from hoping to gain some significant performance improvements, I am also just in this for enjoyment and experience to see a project like this through from beginning to end.
1974 R90/6
1981 R80G/S
1994 XLR250R
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