If you’ve ever been on a trip that takes a few fill-ups to complete, you know that stopping for gas provides a nice break but burns through precious time. Depending on your car’s gas mileage and fuel tank size, it can stockpile fuel the way a camel conserves water or be the grumpy old man who needs a bathroom break at every rest stop. The more you pull off the interstate to accommodate your car’s small bladder, the longer it will take you to get where you’re going.

Say you’re driving from Peoria, Ill. to Myrtle Beach, S.C. for a week-long vacation. Your journey will be about 1,000 miles, give or take a few extra miles for stops at fun tourist traps like the World’s Biggest Baseball Bat at the Louisville Slugger Museum in Louisville, Ky. Let’s assume that each stop for gas will tack on 20 minutes, including the time it takes to get off the highway, find the gas station, fill up and get back to the interstate. In a 2009 Ford Flex with all-wheel drive and an 18.6-gallon tank, you’ll have to fill up three times over the course of the trip, or about every 409 miles. That adds an hour to your voyage, for a total of 17.5 hours.

On the other hand, say you drive a 2011 Honda Odyssey with the optional 3.5-liter V6 and five-speed automatic transmission. On this same 1,000-mile journey from Peoria to Myrtle Beach, you’ll only have to stop twice, chopping 20 minutes off your trip. Plus, you’ll pay less for the trip, since the Odyssey gets an EPA-rated 27 mpg on the highway, compared with the Flex’s 22 mpg rating. Twenty minutes isn’t much, but even a few minutes may mean the difference between getting ahead of rush hour and being stuck in an hours-long traffic jam.

Even though it’s nice not to have to stop and fill up your car all the time, driving for too long without a break can be unsafe. If you travel at a constant 65 mph, you can drive for about 6.3 hours without stopping in the Flex, and a whopping 8.7 hours in the Odyssey. That’s not often enough to stay alert while you’re driving. Since you should be stopping every few hours to stretch anyway, you’ll already be adding time to your trip. You don’t want your car’s small gas tank to add even more stops to your journey.