Auxilliary fuel tank installation on a motorcycle

I ride a 2005 BMW R1200 GS – it has a range of around 300km before the fuel-warning light flicks on – a lot less if I’m forced to use 91 octane. When the light comes on I might have another 75km before I’m running on empty.

In a small country like New Zealand, you could be excused for thinking that this wouldn’t be a problem. Afterall, towns aren’t that far apart, and there are petrol stations in virtually every town. The prevalence of 24hour petrol is increasing with the proliferation of self-serve pumps – Allied has unmanned petrol stations in many small towns all around the country, for example.

I ride long distances as part of the NZ Distance Riders group. I’ve also done a couple of TT2000 rides. Invariably I find myself riding through the night so a 300km range can be problematic – especially on the South Island. I solved this in part by creating a Google Map of 24-hour petrol stations but that doesn’t help if you’re in an area where there are no fuel stops. There had to be a better way.

As a premier member of the Iron Butt Association, there’s a heap of information on how to install an auxiliary fuel tank. Most riders in the USA who are lucky enough to compete in the Iron Butt Rally will have aux tanks.

There are a number of ways you can do this. It all depends on whether your motorcycle is fuel injected or not, and where you choose to position the fuel cell. If it’s positioned below the original tank then you’ll need a pump to transfer the fuel. If it’s above the original tank you’ll be able to rely on a gravity fed system.

The process

I’ve read so many articles on this subject it makes my eyes water. And it’s a little bit scary if, like me, your motorcycle is fuel injected and you are going to drill into your tank. I was helped along in the process by finding an installation of an auxiliary fuel cell on a motorcycle exactly like mine. I saved the link, the link died, I found it again on The Wayback Machine, I lost the link once more, and now I’m afraid it’s gone forever. Right before I was due to do the installation I found the link again.


On a BMW R1200GS auxiliary fuel cells are usually positioned behind the rider. It helps that there are separate seats for the pillion and the rider. By removing the pillion there’s a perfect space for positioning the aux fuel cell. Because the fuel cell is higher than the main tank you can refuel using gravity. Tubing is routed from the fuel cell to a flange on the right-hand side of the petrol tank. It’s this flange that I’ll need to drill in to when I do the final install.

It’s important to me that the tank is easily removable. If I can remove the tank then I can take a passenger, or stow extra gear for more sedate rides. I discovered a luggage rack made by AltRider that clips into the same mechanism that the seat does. In theory, if the tank is mounted to this plate then I can remove it in a matter of seconds. I found one on Amazon and bought it. It’s perfect.


The next problem to solve is what sort of tank. I looked at many different brands and styles. I would have loved to buy one from Summit Racing – they make a range of very good looking fuel cells but they appeared to lack mounting hardware.

I eventually settled on a Tour Tank. They are ugly brushed aluminium barrels, but they come with brackets and a complete installation kit. I felt that given I was setting this up to be removable that I could live with the ugliness.

Tour Tank and installation kit

I settled on the larger of the two that they have available – a 5 US gallon tank which effectively doubles my fuel capacity.

The Tour Tank comes with the following:

  • the tank
  • mounting hardware
  • 1 yard of fuel-safe hose, plus clamps
  • a tip-over valve
  • a petrol cap (non locking)
  • an inline filter
  • a fuel valve to start the flow
  • various fittings for the bottom of the tank depending on your method of mounting. I used the 90-degree outlet.
  • a stick of thread sealer

So, I have the AltRider luggage rack, and I have the tank. What else do I need?


Summit Racing in the USA are experts at aux fuel cells and the connectors you need to make that happen. I needed a 90-degree bulkhead fitting, some washers, a few nuts to hold it in place, and then a reducer so I could connect the 5/16 inch fuel line to it.

Bulkhead fittings from Summit Racing

Despite all the reading I did about this set up I couldn’t for the life of me work out how this was going to be leak proof. I directed a few questions to Summit, and they assured me that what I was intending to order would do the trick – in fact, I told them what I wanted to do and they made the recommendations. I pressed BUY NOW and waited for the delivery.

The white flange on the lower right-hand side of the petrol tank is removable with a ‘special’ tool which is available, at great expense, from BMW.  I had ordered one of these from MAX BMW nearly a year prior, and it was sitting in a filing cabinet in my study, ready for action – that’s how long I have been contemplating undertaking this project. It’s a piece of aluminium that slots into the locking ring that keeps the flange in place. You use a 1/2 inch drive on the tool.

BMW special tool 16 1 021

Behind the flange is a big black washer. The recommendation is that you replace the washer each time you remove the flange. You should also replace the O-ring on the quick-disconnect fuel line. To be safe, I ordered both of these parts before I started the installation, but in the end, didn’t use either.

Mounting hardware

As I described earlier the tank was going to sit where the passenger seat is located. Instead of getting a mounting plate fabricated (at considerable expense) I found that others had used the AltRider luggage rack as an easy alternative. It clips into place in the same way as the seat, secure and lockable. I found a black one on Amazon at a good price.

AltRider luggage rack to replace the pillion seat – mine is black.

I bought some right-angled aluminium extrusion and bolted them together to build a riser which was, in turn, bolted to this plate.

The tank mounting went perfectly. It was now a matter of waiting for the items from Summit Racing, and the washer and O-ring from BMW. They arrived a week later. It was now or never.

Drilling the hole

The post that described this installation suggested that I used a step drill bit. This is a bit that looks a bit like an ice-cream cone. Apparently, unlike a normal drill bit, it will make a genuinely round hole, whereas the normal bit will be slightly oval. The science escapes me, but I wasn’t taking any risks. I had ordered one of these with the paraphernalia from Summit.

Stepped drill bit for drilling a perfectly round hole

I used the special tool from BMW and loosened the white flange. I couldn’t remove the flange from the tank completely but I could pull it away from the tank enough to use the drill without getting plastic files and detritus into the tank. It was a nerve wracking process. If I made the hole too big then the bulkhead fitting would leak.

Once the hole was drilled I inserted the 90-degree fitting, placed a nylon washer on each side of the fitting, then a nut. I also used some of the thread sealer on the fitting to give me some more insurance against leakage. A word of warning for those of you contemplating this – don’t use sealing tap (like plumbers use). For a start, it needs to be rated for fuel, and secondly, the tape is more prone to flaking meaning blocked carbs or fuel lines because the tape isn’t soluble.

The flange

This is what the flange looks like on the left side of the petrol tank. The top feed is the high-pressure fuel line, and the two smaller fuel lines are an overflow from near the fuel cap.

The flange with locking ring, removable with special BMW tool

You don’t want to be messing around with this cacophony of tubes and connectors.

The tubes behind the flange

I marked the spot where I was going to drill the hole.

I drilled a small hole

The 90-degree bulkhead fitting was installed.

The 90-degree bulkhead fitting

Bulkhead fitting in place, and no leaks.

The bulkhead fitting, fitted.

And here’s the tank on the motorcycle. I rode 2,800 km around the South Island over a 5 day period a few weeks back. My journey took me off road twice. The tank performed flawlessly with no leaks. I would wait until the low fuel light came on, then reach behind me, flick the switch, and within 10-15 minutes my tank would be full again! Perfect. Job done!!

Final installation.


2 thoughts on “Auxilliary fuel tank installation on a motorcycle”

Comments are closed.