How much fuel does pumping your tyres to optimum pressure in your car save?

I’ve heard up to about 5% better fuel consumption. However, if your tyres are too low, this can be dangerous because low pressure reduces the load that the tyre can safely handle and also results in the tyre building up heat more and faster.

3%

According to our current Commander-In-Chief, a lot.

It depends on the tires and how low they are on pressure. If they are within 10 lbs of max inflation,the difference will be minimal,less than 1mpg
however if they are significantly low,there will be a big difference
if you want a good demonstration of the difference in rolling resistance, take a bicycle,let 15psi out of the tires,ride it a mile,then re inflate and ride another mile.

I wish I could know some formula for you, but I bet it’s a bit different with different cars. I know I actually calculated that years ago when I was driving a diesel VW Rabbit 5-speed, but, that’s been around 10 years ago, so, “I’ve slept since then”, but, I can tell you that I bought an air pump and keep it in my garage to keep my tires inflated properly since I can’t regularly find a gas station with a reliable pump, and I LOVE the gas mileage I get out of my 2002 VW Jetta TDI (turbo diesel). God Bless you.

Can’t give you exact figures, but keeping your tires at the manufacturer’s recommended pressure does help. In fact, overinflating your tires will give you even more fuel savings, because by pumping up the tire more you are decreasing the amount of rubber that drags against the road. However, overdoing it may increase the car’s braking distance as well as cause “cupping” of the tire (increased wear in it’s center), so it’s not recommended to pump them more than 5 PSI higher than the manufacturer’s specs.

5% but if you really want to save on gas you should buy a spark plug,
it can save up to 30% more gas

I read about 3.3% but it also depends on how under inflated the were to begin with.

If you are driving long distances on a highway, think about gassing up on the highest octane gas available. In my Sunfire I might normally get around 30 miles to the gallon with mid-grade gas, and worse if I get the cheapest stuff. However, when I get 91 or 93 octane gas, I can get as much as 40 miles to the gallon! Again, that for long distance driving on an open road without stop signs or stop lights.

Also try to coast more in rush hour. What I mean is, don’t speed up to 55, 65, or 75 and slam on your brakes; coasting at 25 or 35 is better than going 55, 10, 55, 10, 55, 10! Leave a good space between you and the car ahead of you. Don’t ride their bumper! Besides being safer, it also saves you some gas, cause you aren’t flushing the engine with fuel every time you try to pick up speed!

But, to answer your original question it is in the ballpark of 3.3%. For other fuel saving tips take a look at the links below.