10 Tips To Get Better Mileage From Your Petrol, Diesel Or CNG Car
In this article, there are 10 points or tips you can follow to get the best mileage or fuel efficiency from your car or vehicle. This list is based on my personal experience after covering 1 lakh kilometres with my Chevrolet Beat diesel. I have managed to consistently achieve mileage figures, which are between very close-to-advertised and better-than-advertised. My car’s official mileage figure is 25.4kmpl, and my car has always given me between 23.5 and 27kmpl. Let’s get started with #1.
1. Tyre Pressure
I can’t stress this point enough. This is the single biggest culprit, but the good news here is that you can even break some rules in this area to get better fuel efficiency.
The trick is not just to keep the tyres inflated as per company specifications, but to over-inflate them just a bit. Don’t worry about your car’s tyres exploding while you’re driving. I’ve explained more about this at the end of this article. For better mileage, you need to know that the tyres are never supposed to stay round. They squish just a bit at the bottom and create a flat contact patch. If you fill more air, then this contact patch will decrease, and if you keep the tyres under-inflated, then it’ll increase. We all know how difficult it is to drag a 2-wheeler with a flat tyre. The car also needs to use more power/torque to drag itself if the tyres don’t have sufficient pressure. We need to find a suitable balance between these two aspects.
Carmakers usually recommend maintaining a consistent tyre pressure in all 4 tyres. But, you know that the weight of the engine in the front will naturally put more load on the front tyres and increase their contact patch even if all the tyres are equally inflated. We can balance this contact patch and make it consistent on all four corners. For this, you can add 2-5PSI of additional pressure in the front tyres to get a similar contact patch from the front as well as rear tyres. Don’t worry about uneven wear because we’re only matching the front contact patches with the rear.
Don’t worry about braking either. The front tyres provide the majority of the braking force. So, when we brake, the car’s weight transfers forward and temporarily adds extra weight there, which increases the contact patch when you need it. I’ve personally driven my car for 1 lakh km and experienced pretty much all of the surprises our roads have to offer. I maintain 35PSI in rear tyres and 40 in front tyres. I haven’t faced any situation where the tyre pressure became a cause of concern. My car’s tyres wear out pretty evenly and they also tend to last a bit longer than usual because of lower rolling resistance and other driving habits mentioned in this article.
This is easily the second biggest reason for getting poor fuel efficiency. When we drive through potholes or drive around on broken roads, it takes a toll on our tyres alignment. As a rule of thumb, you should get your car’s alignment corrected every 5,000km. Every 10,000km, you should get the alignment, tyre balancing and rotation done. The engine will have to use more fuel to keep the car in a straight line if one tyre is trying to go left and the other is trying to go right. Or, if the front tyres want to go in a different direction than the rear tyres. This is a bigger concern for uneven wear than driving around with slightly higher tyre pressure.
You don’t have to stick to the 5,000km interval. If you drive on smooth roads, then you can increase or decrease the tyre service interval as per your needs. However, if you hit one or more potholes hard since the last time you got the tyres aligned, then you don’t have to wait to cover 5,000km. You can get alignment and wheel balancing the service done sooner.
3. Big Alloys And Tyre Upsize
Have you noticed that ballet dancers and ice skaters open up their arms to slow down their spinning and bring them closer to speed it up? That’s because if a rotating object is heavier towards the outside, it’ll prevent it from rotating too fast. So, the engine will have an easier time spinning a 14-inch wheel wearing tyres with bigger sidewalls than rotating a set of big, 16-inch alloys. This is valid even if the overall diameter in both cases is the same. I won’t ask you to empty the trunk and keep some of the stuff home just to get a few extra miles out of a full tank. 1kg heavier wheels will affect the efficiency 5 - 10 times more than carrying that much static weight in the boot. There’s a reason F1 cars run on tiny 13 - 14-inch wheels. It’s just more efficient that way as it wastes less in twisting heavy metallic wheels.
Similarly, if you get wider tyres, it increases the overall rotating mass, and it will affect your mileage. If you want a better grip, then you should stick to the same tyre size and instead consider getting softer compound tyres. You should check the speed rating of a tyre and buy tyres with a higher speed rating to get a better grip without increasing the rotating mass.
4. AC Vs Windows
Now this one will depend on personal preferences and weather conditions. On a hot and humid day, you obviously can’t afford to turn off the AC and drive in city traffic with windows down. But at highway speeds, you definitely should roll up the windows and use the AC if it’s hot outside. Up to about 60kmph, you can use the windows to catch some fresh air if the weather allows. Above that, you’re not saving any fuel if you turn off the AC and roll down the windows. At high speeds, the aerodynamic drag from open windows does more damage to your car’s fuel efficiency than a running air conditioner.
5. Gear Changes
You probably already know that accelerating too fast is not good. That you should be easy on the acceleration pedal. I’m here to add one more bullet point here: it depends on the selected gear ratio. For example, if you’re flooring the pedal till you hit the red line in every gear, then it’s bad for fuel-efficiency. But, if you upshift at 2000rpm and push the pedal all the way, then it’s alright. If you feel like you're not getting the desired performance from the car by upshifting early, then you can change gear at higher RPMs like 2500 or 3000 or even 4000rpm. But, if upshifting at 2000rpm or 2500rpm is giving you adequate acceleration without any juddering, then this is the most fuel-efficient way to drive for getting good mileage.
6. Defensive Driving
While driving, do you play this game in your head, trying to predict what each vehicle around you is going to do next? I play this in my head all the time when I’m driving. I don’t wait for them to do something stupid before I react. I try to anticipate and predict their movements and plan my lane selection and speed accordingly. If a particular driver is applying brakes too late and abruptly, then I maintain more distance ahead of me or change lanes altogether.
If someone is suddenly changing lanes, then I slow down in advance or speed up to get away from them. If a car is following me too closely, then I either give it away or dab my brakes well before I need to. This way, my brake lights start glowing before I even start slowing down and limits the chances of getting rear-ended. If you anticipate the behaviour of other road users, then there are fewer surprises in your way. This means the fuel you burn to accelerate is not wasted with braking. So, defensive driving habits not only saves you fuel but also saves you from accidental repairs.
Here’s the deal with coasting. Some think you shouldn’t do it at all, while others think it’s okay to coast. Those who are in the second group are further split about whether you should coast in gear or in neutral. Some say it’s not safe to coast in neutral, even if it’s the more fuel-efficient way.
Consider this as the second level of defensive driving. Once you get good at anticipating the behaviour of other vehicles around you, then you can consider coasting to improve your fuel efficiency. Whether you should coast in gear or not depends on the traffic situation. If you see that there’s a red signal in 60m or so, and you have enough speed to get there without any more accelerator and clutch pedal input, then that’s coasting. You can do it in gear or in neutral.
If you feel that you’re too fast and will need to use the brakes, then you can consider coasting in gear and use engine braking. The higher the gear, the longer you can coast. Since all cars are fuel-injected, coasting in gear means there’s no fuel being consumed during that time. If you want to coast for longer distances, then you need to disengage the wheels and the engine, which you can do either by pushing the clutch pedal or by switching to neutral. During this kind of coasting, the engine runs at idle RPMs and consumes fuel. But, the fuel burnt is negligible even if you’re coasting between 20 and 30kmph. At higher speeds, it’s obviously even more efficient.
As a self-certified hypermiler, I can say that coasting in neutral is not only more fuel-efficient but also okay once you gain more experience in defensive driving. Coasting also saves your brakes and helps your brake pads and tyres last longer.
WARNING: DON’T become a nuisance on the road. Please keep up with the traffic and avoid coasting if there are other vehicles following closely behind you.
8. Big Engine Vs Small Engine
Let’s be clear with our objectives: we’re not just trying to get better fuel efficiency from the car we’re driving. Our goal is to save on fuel expenses and burn less fuel in general. So, if you have multiple vehicles at home, then for shorter trips, consider picking the car with the smallest displacement engine. It’s all the more important that you do so if you’re going to drive in slow or stop-and-go traffic. Smaller engines are more efficient at slower speeds. On the other hand, if you’re planning to cover long distances at high speeds on highways or expressways, then the bigger engine will burn less fuel. That’s because cruising at 100 - 120kmph in the top gear on the expressway is like a walk in the park for, say, a 1.5-litre Nexon diesel engine. Meanwhile, a Celerio with a 1.0-litre normal petrol engine will have to rev hard and burn a lot of fuel to maintain such speeds.
9. Warm Engine
Engines consume less fuel when they are hot enough to warm up the cabin. Till the time they attain this temperature, they have to burn more fuel as they splash in thick and cold engine oil and have loose piston rings. It also causes more damage to the engine over time if it has to heat up over and over. Once the engine achieves its preferred temperature, the piston rings expand to form a perfect seal, the oil becomes thin enough to lubricate the parts, and it becomes easier to move it around.
Petrol engines typically take about 5 - 10 minutes to attain their operating temperatures and diesel engines take 15 - 20 minutes to get there from a cold start. To make sure you do most of the driving with a warm engine, try to club your tasks and plan them in such a way that you only have to warm up the engine only once. Or at least as few times as possible. Else, you’ll have to put the engine through 10 heating and cooling cycles for 10 tasks on your to-do list.
10. Common Sense Maintenance
The last point on my list is just to have common sense and do preventive maintenance. If the owner’s manual says that you should change the oil and filters every 10,000km, then don’t shy away from changing them every 8,000 or 9,000km. These simple habits will go a long way in keeping the engine healthy in the long run, which will also benefit you as the car will return better mileage. Sure, it’ll cost you 10 - 20% more in routine maintenance costs, but it’ll more than make up for that loss by avoiding bigger failures and repair bills as the engine stays healthy. Cleaner filters will keep the fluids passing through more freely, which will also have a marginal improvement in your mileage figures.
To conclude, I’ll say that you should also maintain a log of the mileage your car typically gives. The easiest way to do that is to always fill up the car with a full tank of fuel till auto cut-off at the pump nozzle and then reset the trip meter. Now, drive normally and see how far you get before the low-fuel warning light pops up.
This becomes your benchmark to beat. When you top up fuel the next time, note the reading in the trip meter before resetting it. Then, divide this trip meter reading, which is the distance you covered since the last tank up, with the number of litres of fuel you just filled up to get a real-world figure of your car’s mileage. If you notice a big drop in either of these numbers, you can immediately diagnose the problem and fix it.
11. Bonus Tip: Tyre Upsize
While I don’t recommend you go for wider tyres, you can choose a set of tyres with slightly bigger sidewalls for the same rim size. This will increase the car’s final drive ratio and make the overall gearing slightly taller. So, you end up covering more distance at higher speeds while maintaining lower RPMs even though the odometer and speedometer might disagree.
The thing with this tip is to never overdo it. Adding 5 points to the stock tyre size is okay but NEVER EVER add more than 10 points to your sidewall rating. Compare on a tyre size calculator to make sure that you’re within 5% of the standard circumference. If you overdo it, then it could limit the car’s ability to put the torque down on the road effectively and could get you stuck on a steep incline. It’ll also affect the odometer and speedometer reading and will show a lower figure than the actual.
On the flip side, a small 5 point up on the sidewall will also improve your car’s ground clearance. Going with 165/70 R14 instead of 165/65 R14 alone has added about 8mm to my car’s already impressive 175mm ground clearance rating. Thus, my car’s final unladen ground clearance reading stands at an SUV-like 183mm.
Now, you can become a hypermiler yourself and save fuel and save the planet.
Off-Topic: Why do car tyres burst when driving?
It mostly happens when you keep the car parked with under-inflated tyres for several days, then drive the car around in hot weather before pumping them up. Keeping the car parked with under-inflated tyres makes the tyres crack around the point where they were getting squished. When you get the car out and drive it around on a hot day, the tyre flexes a lot because of a wider flat contact patch. This creates a lot of heat and weakens the tyres mostly in the area where the tyres are already building up cracks. As soon as you fill the back in the tyres, these weaker areas become vulnerable to explosions, especially if you’re driving on a hot day and on concrete roads. Tar roads manage to dissipate the heat better.
To avoid tyre blowouts, you should keep the tyres inflated even if you’re not driving the car around. You can use a portable 12V pump to fill up the tyres if you’re not driving the car regularly. If you’re driving the car out after a long time, then try to get the tyres filled back up as soon as possible. This will limit the contact patch of the tyres on the road and contain the flexing, which will keep the tyres from overheating.