Do you rally need a 35 ltr tank on a motorbike ?
1 yes if your going around the world.
2 or you could just buy 2 plastic cans and use them when needed
3 but for most of us a normal tank is just fine aprox 15/ 20 ltr depending on your miles per gallon !.............

Need - no, Nice to have - yes, Expensive - yes, Worth the price - probably not, as they're usually ridiculously expensive. You can always get something to carry fuel in temporarily. In fact at a couple of places where it's a long ways to the next fuel, locals sit at the side of the road with Coke bottles full of fuel.
My own experience with a 40 litre tank was that it was a nice to have, a real luxury not to have to think about fuel - but you could also get lazy.... We only NEEDED it once, in Nicaragua, when it was a three day wait to get a permit to get in the 3 day line to get the fuel. We ended up riding right through to Costa Rica, and literally coasted into the first gas station and stopped nicely at the pumps, bone dry.

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Grant Johnson
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Inspiring, Informing and Connecting travellers since 1997!
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I would say it is more about range and a minimum of 200 miles/320kms is enough in most parts of the world now with another 50miles/80km needed in a few other places.
Bikes are more economical now and those large tanks were needed on airhead BMWs which only did 50 mpg on a good day but some modern medium sized bikes can do 80 mpg.

As mentioned above - its about range, not about how many liters you get into the tank. On a Honda CT 125 Hunter Cub for example with a 1,4 US gallon tank/5,3 liter you will get a range of approx 350 kms. So no need for a 35 liter tank on that bike....

There are several things to consider when it comes to fuel capacity and range:

1. Where are you going to ride? What range do you need? In remote areas where gas stations are scarce, and sometimes even out of fuel? Try to do some research ahead.....

2. What range do you have? Remember that in some countries in the poorer parts of the world fuel sometimes is of lower quality than in the developed parts of the world. For example in Bolivia the fuel is (said to be) 85 octane RON. Which is approx 80 octane AKI as is the north american standards. In Indonesia the standard fuel is 88 octane RON, approx 82 octane AKI. And less octane number - the higher fuel consumption on modern EFI bikes at least. Carburated bikes might be different.

3. I wouldnt had gone anywhere without a fuel range of at least 300 kms!
A fuel range of 400 kms would actually be a minimum fuel range imo for a decent overland bike.
500 km fuel range - now were talkin.
600 km range and above - luxury!

4. As Grant mentioned above - the oversized tanks that are offered are often very highly priced. So that must also be taken into consideration.

5. I rode around the world with two 3,5 liter jerrycans attached to the rear of the side panniers. What a PITA! I have lost count over how many times I needed to reinforce the attachments of those jerrycans, and I lost a couple of those jerrycans too along the road! And that was with designated cans, designated mounts, designated straps etc etc. I wonder how it would work if one used something more amateurish stuff to carry outside gas in?
Imo fuel should be carried in the main gas tank. Carrying fuel outside the tank takes up space for other items such as water, spare parts, clothes, tools etc etc.
And as in my case - outside carried fuel cans tends to fall off. Maybe those rotopax cans work, but they still take up space for other potential stuff you would like to carry.

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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.

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.

That was really lucky as Susan would have been so hacked off having to push you sat on the bike to the next fuel station.

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You will have to do without pocket handkerchiefs, and a great many other things, before we reach our journey's end, Bilbo Baggins. You were born to the rolling hills and little rivers of the Shire, but home is now behind you. The world is ahead.

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.

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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.

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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

I agree with this 100% but would like to add that when you go to places where those extra 80km just maybe might be required, that you get in the habit of topping up your main tank often (30-50%). The fuel availability of the last 1000 km may be a poor predictor of fuel availability for the next 100km.

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But imagine what a great story you would have to tell if you'd been stuck in Nicaragua with no fuel!

I bought my 790 with the specific intention of riding through Siberia and the Stans, and my desktop research said there were stretches of over 400 kms with no fuel. The 790 is pretty economical and with a 20L tank will easily beat 400 kms (I think I did about 450 kms on one tankful in Italy in 2019). I don't really want to fall about with auxiliary tanks or huge top heavy monsters so the stock range should be adequate. That said with belt and braces in mind I will also be taking a 6.7 L Rotopax

As someone who is currently planning a RTW trip, the size of the gas tank is an important consideration for me. My goal is to have a min 500 KM range - not because there's not enough gas stations, but because of numerous mentioned accounts above. Anybody who's ridden distance has experienced that nagging insecurity of being in parts unknown and not knowing if you'll make it to the next gas station - and if there will be gas there. Then mentally doing the calculations to see how much further you've got before running out - and looking at the sky and seeing the weather locking in. Or waking up in a camp site far off the beaten track hoping that you make it to the next station....

Having to stop vs deciding to stop are two different things, and I want that flexibility. And we've all also experienced that gas station where we wished we coulda kept going....