Here's how I measure my true fuel tank capacity and reserve capacity.

[ben2go]

I noticed I had crap settling into my clear fuel lines,so I decided to head it off and clean everything out.I must have got the crap at the last fuel stop, where I put 5.34 gallons in.I was on fumes and the bike was sputtering a lot.While I was doing the clean up,I decided to see how much fuel my tank would empty with the petcock on and reserve.I grabbed a commercial food container that is marked in gallons,quarts,and ounces.It's one of those 2 gallon units made from that really hard clear plastic.It had a white lid that I cut a 1 inch hole in for my drain hose.First thing I did was grab a cheapo angle finder at Harbor Freight.I parked my bike on my level walkway.I sat the angle finder on the fuel cap pointing forward. I used the built in marker to set the angle with all my weight on the bike.I then propped my bike up with pieces of wood.I added roughly 125 lbs of weight to the rear of the seat, to get the angle to match, as if I were setting on the bike.I used 60lb bags of corn feed for weight.With the bike at the same angle as it was with me on it,I commenced to draining the fuel tank into the commercial food container.

I need to stop and point out a few things on my bike,everyone else's bike will be different.I have an 89 GS with an 04 large capacity tank,89 tank petcock,with a 2004-07 Honda CRF250X frame petcock.I also have a modified Katana 750 front end and a Katana 750 rear shock,so my forward rake is a little different than a stock bike.

Back to the capacity check.I set the frame petcock to ON position and drained exactly 2 gallons into the container.I wrote it down on a cheat sheet, and then funneled the fuel into a clean fuel can.I repeated the process again.This time I got 1 gallon,3 quarts,and 6 ounces, give or take a half ounce.So I get roughly 3 gallons,3 quarts,and 6 ounces out of the tank before hitting reserve.I funneled that round of fuel over into the clean fuel container.I stuck it back under the fuel hose and set out to see what kind of reserve capacity I have.This will aide me in knowing how far I can go to find a fuel source.I set the petcock to reserve and let it drain till it stopped.When the fuel gets to a point, that it's below the tank petcock's lowest point,it will have little bubbles, then big bubbles, as it finishes emptying.I got 1 gallon and 1 quart for my reserve capacity.Maybe a little more when the bike is moving,because the fuel can wash over and into the petcock.I am going to stick with 1 gallon and leave the rest as a little extra cushion against running out of fuel.So,in total I got 5gallons and 6 ounce of fuel out of my tank.I know you're thinking,"Wait!You put in 5.34 gallons of fuel!"Yes I did and rode exactly 2.5 miles home,which consumed a little less than a quart of fuel.The large GS tank will hold right at 5.5 gallons when filled from bone dry.The tank will also retain almost half a gallon(2 quarts) of fuel after the bike runs dry.

OK.Now that I have this info,I can estimate my reserve capacity fuel mileage.This is to easy.I get 45 to 48 mpg when I'm just riding around,So my reserve capacity is 45 to 48 miles, if I limit it to 1 gallon reserve.If I go with the 1 gallon and 1 quart,I could probably make it 55 to 60 miles.If I am in an unfamiliar place,I let up and just ride until I find gas. 

I have to apologize for the lack of pics.I know, I always try to include detailed pics.The GF had our camera with her at work.She forgot to take it out of her purse this weekend.

Here is a food container kind of like the one I used.I had one left from when I managed a local pizza chain in high school.
http://www.paradeplastics.com/shop.cfm?action=details&categories_id=56&product_id=8589

Here's the angle finder I used.This pic doesn't show the plastic marker that slides around the outside.
http://www.harborfreight.com/dial-gauge-angle-finder-34214.html

[scooky]

Thanks for the details. This is exactly what I was hoping to find this morning. I've considered doing the exact same thing with my stock 09.

When you filled it with 5.3 gallons, how high did you fill it? To the bottom of the inlet marker? higher?
Also when you filled it was it sidestand, centerstand, or you sitting on it?

Thanks

[cbrfxr67]

This forum rocks!  Where else can you get this kind of info?!  Now if only someone would just take a picture of their bike with a suit.   

[ben2go]

Thanks for the details. This is exactly what I was hoping to find this morning. I've considered doing the exact same thing with my stock 09.

When you filled it with 5.3 gallons, how high did you fill it? To the bottom of the inlet marker? higher?
Also when you filled it was it sidestand, centerstand, or you sitting on it?

Thanks

All of my local fuel stations have there pumps on flat level concrete and for cars to park onto.I set the bike on the center stand,stood beside it, and kept pumping fuel until no more air bubbles came out and the fuel level settled half way between the top of the hole and the lower edge of the hole.It helps to kinda bump the side of the tank with your hand to break up the trapped air.If your bike has all the California emissions stuff on it,you won't get as much fuel in there.I think it's 4.9 on Cali bikes,but can't be 100% on that.

[ben2go]

This forum rocks!  Where else can you get this kind of info?!  Now if only someone would just take a picture of their bike with a suit.   

I don't have a suit but I'd like to see someone from around the UK in top hat and tails riding through town.Maybe Sledge will do it.