Aux Fuel Tank


Premier Member
IBR Finisher
I'm not in the technical team.

The 'rules' you mention, are they specific rules for the Iron Butt Rally (IBR)? If so and you intend to run any aux tank when you participate in a future IBR it is wise to seek the input of the IBR technical team.

However, I and many others have run poly/plastic aux tanks like JAZ and RCI on Iron Butt Association (IBA) certificate rides. The IBR rules do not apply to such IBA rides.

Kim Leeson

Selfie Stick King
Premier Member
IBA Member
Nice concept, similar to the Camel Tank options, why they didn't come up with a version for our bikes is a mystery.


IBA Member
I have the Camel ADV aux tank works the same. cars and motorcycles have had plastic fuel tanks for years so i am a bit puzzled why the rules state metal tanks only.


Premier Member
IBR Finisher
In past IBRs, that tank would be allowable. Camel style aux tanks don't generally work well for LD riding, but you're an adult and welcome to give it a go if you wish. I haven't looked at the current rules and I don't know if the '23 rules are available at this time. As long as it's securely mounted and the vent/overflow line is routed down and away from the tyre, I don't believe it to be an issue.

According to the 2021 IBR rules, that tank would be acceptable - LINK

The section is below. I've worked as Tech inspector for multiple IBRs. Plastic tanks have always been allowed if they meet specific requirements, usually a race cell or one specifically designed for motorcycle use as this one is.

Appendix A: Fuel system capacity and auxiliary tanks
I. Fuel System Capacity
Fuel system capacity for motorcycles using liquid fuel will be determined by the
method specified below. For motorcycles that do not use liquid fuel, the capacity shall be
determined on a case-by-case basis to ensure that the “gasoline-equivalent” fuel capacity
of the motorcycle does not exceed 11.5 gallons (on an energy basis).
1. Original Equipment Tanks
For original equipment (OE) tanks, the manufacturer's specified capacity shall be
used unless the IBR has published alternative specifications 90 days in advance of the
event. In the case of conflicting manufacturer's specifications, and in the absence of an
alternative specification published by the IBR, the highest capacity published by the
manufacturer shall be used. For example, in the case of the BMW R1100RT, the highest
capacity specified by the manufacturer is 7.26 U.S. gallons, which our measurements
confirm is the correct capacity.
2. Modified Tanks, After-Market Tanks, and Auxiliary Fuel Systems
The capacity of all non-OE elements of a fuelsystem shall be determined by the
amount of water or fuel required to fill and empty system (including lines, pumps, filters,
etc.). Water may be used to measure individual tanks or whole systems. However, we
will usually use premium grade gasoline unless the motorcycle is designed to run on an
alternative fuel (e.g., Diesel fuel). For systems equipped with a fill pipe that extends into
a vapor space, the capacity will be determined by filling the system to the bottom of the
fill pipe, unless the system has been modified in some manner to permit a fill rate in
excess of 1.0 gallons per minute above the bottom of the fill pipe.
The volume of liquid required to fill the system will be calculated based on the
weight of the liquid required to fill the tank and the density of that liquid. For example,
using gasoline with a density of 6.180 pounds per gallon, if the weight of gasoline
required to fill the system is 30.90 pounds, the capacity of the system is 5.00 gallons
(30.90/6.180). The weight of liquid required to fill the system shall be determined by one
or more measurements of containers before and after their contents have been poured into
the fuelsystem. The containers shall contain at least 3.0 gallons during the "before"
measurement. The contents shall be poured into the fuelsystem until the container is
empty or until the fuel system is full, whichever occurs first. The temperature of the
liquid poured into the system shall be kept as close as possible to the temperature used to
determine the density of the liquid, as described below. When gasoline is used, it must
be from the same batch of gasoline used to determine fuel density. The scale used to
measure the weight of liquid dispensed shall be repeatable to 0.01 pounds and calibrated
with an NIST-traceable dead weight.
Determining the Density of Water:
For water at 60o
F, the density shall be assumed to be 8.337 pounds per gallon. At
F, the density shall be assumed to be 8.328 lbs/gallon. For other temperatures, the
density of water shall be determined from standard engineering tables or using the
following formula:
lbs/gal = 8.3286 +(0.000985*T) - (0.000014*T
), where T isthe temperature in degrees Fahrenheit.
Determining Fuel Density:
The density of the fuel shall be determined by the weight of fuel required to fill a
rigid, narrow neck "calibration vessel" of known volume in excess of 1.5 gallons. The
volume of the "calibration vessel" shall be determined by measuring the weight and
temperature of water required to fill the vessel. The temperature of the water used to
calibrate the "calibration vessel" shall be measured with a thermometer accurate to two
degrees Fahrenheit (F) and shall be within the range of 39o
F to 100o
F. The density of the
water shall be determined as specified above.
As an example of using this approach, if the temperature of the water is 70o
F and
the weight of water needed to fill the calibration vessel is 14.58 pounds, then the volume
of the calibration vessel is 1.751 gallons (14.58/8.328). If the weight of gasoline required
to fill the calibration vessel is 10.82 pounds, then the density of the gasoline is 6.179
lbs/gallon (10.82/1.751).
Alternatively, the density of the fuel may be determined using a precision
hydrometer with a resolution of 0.001 specific gravity or less. As an example of using
this approach, if the specific gravity of the gasoline measured by the hydrometer is 0.742,
then the density of the gasoline is 6.186 lbs/gallon (0.742 * 8.337). (Note that the
hydrometer will determine the specific gravity of the gasoline relative to water at 60F.
The temperature of the gasoline does not have to be at 60F, but the temperature of the
gasoline used to fill the tank must be equal to the temperature at which the specific
gravity of the gasoline was measured.)
II. Auxiliary Fuel Tanks
1. Expansion of the stock (OEM) fuel tank is permitted, provided that such expansion is
of similar material, gauge, and construction as that of the stock fuel tank and, when
viewed from the side, no portion of the modified tank surface, from the point closest to
the front of the seat to its highest point, is at an angle of more than 45 degrees above
2. Non-OEM main fuel tanks and auxiliary tanks are permitted if they are NASCAR-,
IHRA-, or NHRA- approved or, at the discretion of the rallymaster or the president,
determined to be of acceptable quality.17
3. Any auxiliary tank(s) shall be mounted in a secure manner so as to minimize the
17 For a list of auxiliary systems that will meet rally specifications, see §III.F. Metal containers are allowed.
However, thin-walled containers such as those used in marine or snowmobile applications are prohibited.
chance of its becoming separated from the motorcycle.18 Approval of attachment systems
rests at the discretion of the rallymaster or the president.
4. All fuel lines must be routed so as not to interfere with the operation of the motorcycle.
5. An electric fuel pump, if used, must be properly wired and fused, and the refueling
inlet of the auxiliary tank must be grounded.19
6. The auxiliary tank(s) must be properly vented for pressure buildup and overflow.20
7. Anti-slosh foam or anti-slosh baffles will be required for cells mounted on the pillion
seat or the rear rack of the bike unless the maximum volume of the tank does not exceed
1.0 gallon. A minimum of 80% of the dry capacity of the auxiliary tank must be filled
with anti-slosh foam, or the tank must be equipped with one or more longitudinallyplaced baffles that are at least 80% of the height of the tank and that divide the tank into
two or more chambers of approximately equal volume. The rallymaster or the president
may approve alternative configurations that are determined to provide effective control of
sloshing. Taildragger cells, cells no higher than the top of the OEM tank, and enlarged
fuel tanks in the OEM tank location (i.e.: Touratech tanks) are exempt from this
8. Fuel may not be carried in excess of the quantities set forth in this section, or in
containers not complying with the above standards, unless expressly approved in advance
by the rallymaster or the president.
18 When pressure is applied to the fuel cell, limited visible movement (i.e., 1/2") relative to the frame of the
motorcycles will be permitted only if it is due to the compression of padding on which the tank is positioned.
However, all tanks must be secured to the motorcycle with straps or fasteners that are securely connected to a
bracket or structural member that does not flex when pressure is applied to the auxiliary tank. No bungee,
shock cord, or similar attaching device will be permitted.
19 Non-metallic auxiliary tanks should be grounded to the frame of the motorcycle with a conductive strap or
wire attached to the tank in the vicinity of the fuel inlet. Metal tanks do not require a grounding strap if they
are attached to the frame with conductive brackets.
20 A vented gas cap is not sufficient unless it is determined that sufficient vapor space exists in the auxiliary
tank, after it has been filled to capacity, to prevent the expulsion of liquid fuel when the motorcycle sits in the
sun on either the centerstand (if so equipped) or the side stand. Unless there is sufficient vapor space to
prevent the expulsion of liquid fuel from the vent, there must be a hose attached to a vent located at the highest
point on the tank when the motorcycle is sitting on its sidestand. The entrance to the vent line must be flush
with the top of the tank so that it is not submerged when the tank is full. Vent hoses must be routed in such a
manner as to prevent any expelled fuel from coming into contact with any part of the motorcycle or from
being expelled into the path of a tire or onto a tire.


Premier Member
IBR Finisher
Keep in mind, if you're going to quote the rules, post the actual rule you are concerned about and a link to where you found it.

Also, there are NO Aux tank RULES for Iron Butt Association certificate rides, only for the Iron Butt Rally itself. You can put as much fuel as you want on the bike in any way you see fit for the standard IBA certificate rides.

Shawn K

Professional Cat Confuser
Premier Member
Also, there are NO Aux tank RULES for Iron Butt Association certificate rides, only for the Iron Butt Rally itself. You can put as much fuel as you want on the bike in any way you see fit for the standard IBA certificate rides.
The only thing I would add to that is the requirement to have a DBR at no more than 350 miles.

There's a certain "diminishing returns" point where a huge amount of auxiliary fuel is just dead weight - there's no point in carrying 500 miles worth of fuel on a cert run when you need to stop every 350 miles anyway.

(Not arguing in any way, just amplifying Eric's excellent points)


Premier Member
IBR Finisher
Ron should have talked to Morris Kruemcke, (and probably did). Morris had a way of dealing with bladder stops.

Russ Black makes an excellent point. Many, if not most organized motorcycle endurance rallies have some kind of rule for fuel limits. Some take it more seriously than others, in terms of inspection of aux tanks and bikes. If you're planning on doing the IBR some day and going to be riding endurance rallies, it's a good idea to just start out with the IBR rules guiding your set up.

The other common reasons for aux tanks are touring riders that are riding in areas with long distances between gas and places like Eastern Oregon where stations aren't always open at night and self serve is limited, (there is a county by county exception to the no self serve laws at the moment).

For normal touring, it's still nice to get gas when you want to, instead of when you have to, but it's an off the clock thing.