I ride a large thumper with a factory rear fuel tank.

Off road I really enjoy its low weight – 140-ish kg.
Easy to pick and ride aggressively on trails if desired.

On road I really do NOT enjoy its low relatively low weight.
Especially in windy conditions at freeway speeds its fatiguing to maintain position.
Heavier twins pass me all day – good for them.

To compromise I installed an additional front fuel tank.
My range is now double (600ish km), I have a built in backup fuel pump/tank, a 300 km reserve and best of all I can plan for added ballast as desired depending on the terrain I plan to ride.

For on road travel I fill the front tank to the brim and the bike riding manners are significantly improved at speed.
For off road I leave the front tank empty for improved agility.

IMHO the extra fuel tank makes my particular bike much more versatile in aspects beyond extended fuel range.

YMMV

One aspect to consider, I think, is the ratio of fuel range to butt range.

My current bike (Yamaha FZ-1S Fazer) is relatively thirsty, and has a smaller-than-average tank. On a long transit, I can get maybe 250 km out of it. Well, that's about as much time as I want to spend in a saddle anyway without an opportunity to get off the bike, stretch my legs, go to the bathroom, maybe have a drink of water.

On my last year's big trip, I rented a V-Strom 650 in New Zealand... it got me from central Auckland out to the Coromandel peninsula, did the full Coromandel loop, and back to just north of Auckland on a single tank - about 420 kilometers - of spirited riding, without anything extra! And that was a mix of spirited curve-carving, long highway transits, and fighting through traffic. On an upright bike with full panniers and topbox. I can't legitimately see a situation where I would ride more than that without needing to stop anyway.

On my Fazer on the other hand... well, my record I think is central Riga to central Tallinn - ~300+ kms, three urban traffic areas and a border (okay you don't actually have to stop at that border), in 3 hours 20 minutes, including two fuel stops! Don't do what I did.

So, I would say that on the rare occasion where you would need extra fuel capacity, you can always find a container - and throw it away once you get back to civilization.

A plastic 10L fuel container is, what, five euros in my local supermarket - and can be ratchet-strapped to a hardpoint on the bike. No need to carry jerry cans with you permanently.

The point is if you have a great fuel range you can stop anywhere you want. But if you have a short fuel range you have to stop and fill up some places even though you had a coffee and toilet break 20-30 minutes ago.

When riding through remote parts of Kazakhstan in a group of bikes - we once had approx 200 kms between gas stations. But upon arriving at that gas station it turned out it was out of fuel. Then we rode another 120 kms to the next gasstation and even that one was out of fuel. Then the riders of the bikes with a range of 350-375 kms started to become uneasy, and had to get overprised low quality fuel from a truck.

A 10 liter fuel container does not easily straps securely on to an already loaded bike when riding on gnarly gravel roads in remote parts of the world. It will be very prone to fall off and cause havoc.

I had a range of 450-500 km on my bike and to be honest I never needed to use fuel from the extra jerry can I had attached to the panniers. I actually used one of those cans for water, which came in very handy many times.

__________________
In the end everything will be fine. If its not fine its not the end....

In some places in the world you know you will need the extra range. Although you may only need it a handful of times, you just might not know when and where that will be. You may carry extra fuel for thousands of kilometers before suddenly needing it in a place where intel has told you that availability won't be a problem.

In Senegal I suddenly found myself in a nation wide truckers strike - with no fuel being distributed to gas stations. The lines at the gas stations were very long, and growing every hour as more and more gas stations ran out, and more and more people were panic hoarding. I literally got the last drop filling up my 7 liter tank and my two 10 liter jerry cans, right at the boarder to guinea Bissau. Those in line behind me were out of luck as the country was now pretty much bone dry - I got the last drop in the country. If I was going in the other direction, I would have needed to resort to black markets at insane prices.

In Senegal my bike sputtered and coughed the last stretch to a gas station that had fuel, having expended my two jerry cans - this the last few gas stations were out of fuel.

I believe that had my main tank have been bigger, I would not have topped up as frequently, and likely have run out of fuel that one time in Zambia. With cans you too up your main tank more often rather than having to deal with the hassles of 6singvabd refilling cans.

I resorted to both jerry's frequently, but only once have & been close to run out.

If it was an option for the bike I had, I would gladly have spent the money for a larger tank - and teach myself to top up frequently. Cans are a hassle in more ways than one.

__________________
Blog: www.bamakobyvespa.no
My Youtube Channel

I had a 450 mile tank on an F650 in the noughties. Nice to have, but mostly just makes you slack at filling up. Price then was fine when you consider how much you can sell them for.

Today with FI increasing range on bikes that have normal sized tanks and the hassle of fitting pumps into big tanks I wouldn't bother.

Andy

That's more a centre of gravity thing in my experience - bikes that carry their weight up top are blown around much more than those that carry it low. A few years back I was riding through the Texas Panhandle with a friend on a late 90's Triumph - a bike with a high centre of gravity - in a strong crosswind. His bike was all over the place - 20 degree list and at times two carriageways widths to keep it straight, whereas mine - a Honda GoldWing - with all the weight low down didn't notice the wind at all.

Re big tanks - they're like part of an overlander's uniform. Nothing says 'the real deal' like a tank you can hardly see over. That plus soft panniers caked in an inch of mud and a laptop on the handlebars so you can blog as you ride. After all keeping the sponsors happy is your top priority

I've had a couple of 600 singles with large tanks (still have one in fact) and while they're unwieldy (the 40L one on my XR600 in particular) they can give you peace of mind. It's all very well saying that you rarely have to do more than 200 miles between fuel stops but I'm uneasy heading off knowing there's no fuel for 200 miles with a fuel range of 220 miles. That doesn't have to be across a desert somewhere, it could be a cross country trip at night. I think I only ever filled the 40L tank completely to the top three times but they were times where range anxiety was an issue. Fuel stations can be shut or shut down or out of fuel. The capacity to get to the next one is a bit of a comfort blanket. At the other end of the scale the 9L tank on my 125 means a stop every 70-80 miles - just in case you can't find anywhere open later on. You're not heading out anywhere remote with a range like that.