Originally Posted by The Jester
I currently have a small firm of fabricators (2 blokes with loads of experience who are just setting up their own business) working on a rear mounted auxiliary tank for the g650x bikes. Because they are a new firm they don't have much work yet and are getting this moving very quickly. If there is a demand, I should be able to get hold of an f800gs on demo from my local bmw dealer so they can attempt to measure it up for a tank as well. After they have finished the GX tank of course.
Keep an eye on the GX thread to see how the tank turns out and let me know if you're interested.
I picked up my GX aux tank last night and put 9.7 L in it, but I reckon I could squeeze 10L in there. I did the daily commute with the tank on today and it is working well. Fuel is being used from the rear tank and handling of the bike is virtually unaffected. I am aware that the suspension is compressing a fraction more than normal so I will put some extra air in the shock tomorrow.
The tank is mounted firmly on the bike with no movement. I am going to get a friend to follow me soon to look for signs of flexing but I don't expect there to be any. I did have the lower bolt on the subframe diagonal come out somewhere on the journey, but as I didn't tighten them up fully last night that will be my fault. Even so there is still no movement on the tank. We replaced the bolts when we fitted the tank as the originals got a bit chewed up. They had practically seized in there and I am going to copper-slip the new ones, but I didn't want to tighten them fully In case they got stuck again.
The pics show the tank clearly. The welding is really neat and the tank fitted perfectly. Clive said he used magnesium wire to weld rather than silicon. Apparently silicon wire is much easier to weld with but goes white if you try to anodise it. The middle bit of the tank is 3mm alloy, 16 guage I think Clive said, and the sides are 14 guage which is slightly thinner. There are 2 brackets on the top and one long one down the front edge.
I haven't let the shock down yet but will do that over the weekend. However if you look from the rear there is lateral clearance between the chain and the tank. On the wooden blank the chainguard touched the tank with no air in the shock but the chain would not. I believe the final tank is the same but will confirm that.
On the final versions I think Clive wants to radius the backets to make it a bit neater. The fuel outlet will be moved up and in so it is behind the plastics and the optional scottoiler attachment boss may also be repositioned further in.
Clive will sell this tank for the GX bikes, black anodised, for £325. I have also spoken to a dealer who is so impressed with the GX tank that he is prepared to let Clive have access to an F800GS. My First thought is something that looks like a dummy silencer on the right hand side and mounting to the pannier attachment points. I expect that Clive may want a deposit or some kind of assurance that he will definitely sell some of these as there is a fair bit of money and time in making the first tank. If you guys are interested let me know.