I recently took part in BMW’s ADV-X, a five-day adventure ride along logging roads, dirt roads and trails in beautiful British Columbia. I split my time aboard the new BMW R1300GS and the F900GS. On the fourth day, we were told during the morning briefing that fuel stops would be scarce. I filled the F900GS I was riding to the brim, as did fellow Mojo misfit Emily Roberts, who was also at the event, and who also on that day was riding a 900GS.

At 14.5 litres, the 900’s tank isn’t huge (compared to 19 litres for the R1300GS), and the bike was averaging about 5.8 L/100 km during the event, which translated to a range of about 250 km. Our guides, who’d pre-run the route, told us that the first gas station we’d see was about 230 km into the ride. While theoretically the 900GS could make the distance, that didn’t leave a lot of reserve, especially considering we were off road. 

Aside from making sure your bike is in good mechanical condition, there are other ways to make sure it uses the least amount of fuel possible. One of those is the way you ride. “High-vacuum” riding is a technique I use that helps reduce fuel consumption by keeping the engine in its ideal operating range in any given gear, while using the least amount of throttle to maintain speed. You also need to avoid excessively high and excessively low speeds, and ideally you want to be in the tallest gear as much as possible. 

The reason I call it high-vacuum riding is because for any given rpm, the less the throttle is open, the higher the vacuum will be in the intake manifold. This means the engine is in a low-load situation, and it needs less fuel to operate. An exaggerated example of this is if you’re going downhill with the throttle completely closed: vacuum is at its highest, fuel consumption is at its lowest. On the contrary, going uphill in a tall gear requires a lot of throttle to maintain speed; this creates low vacuum in the manifold because the throttle is open wide, which results in high fuel consumption.

This is where the way you ride will make a difference in the amount of fuel you use. In my previous column on the CVT (2024 July/August issue), I explained that this variable transmission is the most fuel-efficient because it automatically keeps the engine in its optimum operating range. To maximize fuel efficiency, you have to act like a CVT by using the gearbox accordingly. If you’re on level ground, you want to reach the lowest possible speed at which your bike can sustain top gear without forcing; lower revs also mean lower fuel consumption, and the bike will rev its lowest over a certain distance when it’s in top gear. 

As you’re riding along at the optimum engine speed in top gear (on the F900GS it was between 3,000 and 4,000 rpm) and you approach a hill, unless you open the throttle further, the engine speed will drop. While maintaining a steady throttle on the GS, I’d drop a gear as soon as the revs dropped below 3,000. I’d add a bit of throttle to maintain my speed in the lower gear, but it actually took less throttle to do so than if I’d left the bike in top gear, thus creating a high-vacuum condition. As soon as the ground levelled, I’d pop the bike into top gear again. I applied the same technique in the tighter, slower sections of the ride, with maybe third or fourth becoming my top gear.

I didn’t reduce my speed, and I took off from a start normally, not slowly; I easily kept pace with the group I was in, riding this way without anyone noticing. The proof that this technique worked was during our lunch stop. I rode behind Emily the entire time, keeping pace with her. While I rode my bike utilizing this technique, she rode hers like she stole it: roosting the rear wheel, sliding through turns, and blipping the throttle to hop over jumps. While she probably weighs about 80 lb. less than me, the range left in her fuel tank read 133 km at the lunch stop. My tank had 181 km of fuel left.

The trick is to not load the engine too much in any gear, keep the revs in the optimum range by using the gearbox, and to baby the throttle on downhills. You certainly don’t need to ride this way every day, but the added range you can achieve can mean the difference between making the next fuel stop and having to call someone to bail you out with a jerry can.