Fuel Mileage Questions

Since most of your questions are fuel mileage related. Check your tires and if they are not Low Rolling Resistance tires, that should be the problem. I know, its hard to believe tires can make that much of a difference. Believe it! Check air pressure, depending on the tire manufacturer some of us run close to max. My tire presure is 40 front and 38-39 rear (Mich. Energy Saver A/S). Also, depending on how many miles you have on the 2010, a transaxle fluid change would be a good idea in the 30-40k mile range (first time). Last calculated mpg was 56 mpg on flat roads and some hills. Sorry, have to run!

 

That is too low. According to the door label, the fronts should be 35, rears 33 when cold. Many of us take that label as the minimum, and more is better for mpg, though the harsher ride may limit how high you wish to go.

When you checked, were the tires still at morning cold conditions, or had you driven within the past few hours? If the later, the cold pressure could be even lower than 32.

If the the tires are not Low Rolling Resistance models, you will lose few mpg.

Were the tires new when you acquired the car? If so, the newness will also cost a few mpg until they get broken in.

Any one of these tire issues can't explain your mpg shortfall, but all three together could possibly account for it all.

B will cost a bit of mpg, compared to a judicious use of the regenerative braking. D mode with light to moderate braking (without pegging the CHG bar on the HSI screen) is best, but many people will brake harder than that, wasting some regeneration potential.

 

Just checked out the Master craft tyres they are not low rolling resistance (LRR), in fact they are very poor in that department.
They could be loosing 5 mpg or more against good LRR tyres, something that the Prius requires to get the sort of mpg you are looking for. The pressures you are running at will also not help, try 38f/36r or even higher if you do not mind the harder ride.

John (Britprius)

 

44 MPG does sound low. I have a similar drive and get an average of 50 MPG. When I bought my used 2010 it had brand new Pep Boys Futura tires that are not LLR. I have just left them on because I don't know if it make financial sense to buy new LLR tires.

After reading other posts here I increased my tire pressure to 42/40 and noticed a increase in MPG. You should also check your engine and cabin filters. They might need to be replaced.

How fast are you driving on the highway?

 

Check side wall of your tires for max psi number do not excede that psi number, If you can increase to 40 psi front and 38 PSI rear. (will make a big difference).
Do not use B mode unless needed. Use when coming down mountains. Using B mode on a daily basis will cost you mileage.
Just start car and drive off. No need to warm up.
Set air cond. as high as you can live with 77-80 is good, fan speed as low as you can live with.
Light on gas and gliding is good. Don't try to stay in electric, us the battery as little as possible as it has to charge the battery later causing loss of mileage.
These things will get you up to 50 mpg or better!
Enjoy your car!

 

Obviously it depends on the price of fuel, but in the UK with our high prices the difference in 2mpg will pay for 4 tyres in there own lifetime making it worthwhile to change tyres to the best LRR tyres.

John (Britprius)

 

If you have money to throw away then buy new tires, otherwise, I would just wear them out because it's already paid for. Check the max pressure your tires can handle and then fill them up to 90%. My tires can handle 44psi so I fill mine up to 40psi. But I must warn you, high pressure = less safe. Therefore, I don't drive as fast with high pressure tires. If it's raining, I definitely slow down more than usual.

LRR aren't for everyone. IMO, there's a trade off. To me, my ride is less comfortable with LRR tires. So it's up to you. I have LRR tires, my overall average is 55 mpg. Driving on local roads under 45 mph, I could easily get 65 mpg.

 

If he is driving in the mountains, (Ozarks?) then he may wish to use B from the top of long downhills.

B under the D in the Drive gears? | PriusChat

 

The "high pressure = less safe" view is disputed, not a consensus. You will find several conflicting views here.

I'm on the side that higher pressure lowers the risk of hydroplaning, a significant issue here in the Pacific Northwet. This is backed up by NASA and other aviation sources linked in previous threads.

The opposition points to changes in wet traction in the absence of hydroplaning. I haven't seen enough documentation to convince me.

But when the road is wet, drivers should slow down or allow greater spacing regardless of tire pressure.

 

Slow down on hwy to 62-65 mph and you will gain about 3-5 mpg instead of going 67-70 mph, but only if it safe to do that!

 

When I was at the dealer, I asked them to make sure that my tires are at 40 psi, the refuse to do it. They set them at 35 psi. I had to bring them back up to 40 psi when I got home. They said over inflated tires have less surface touching the road. Therefore, the stopping distance will be longer. They didn't say anything about hydroplaning.

 

Toyota puts about 40 psi in the tires at the factory, to reduce tire flat spots during their long Pacific cruise. The dealers are intended to reduce that to the door label values during PDI, but neither of my Prii were so reduced. Numerous other PC readers found similar over-label pressure upon delivery.

When getting service on a very long road trip, while the tires were highway hot at high elevation, a dealer technician claimed my tires were dangerously overinflated, and refused to leave them over 40 psi.

Unfortunately, he didn't understand pressure vs temperature and pressure vs. altitude changes. The next cold morning at sea level, a mere two hours away, my tires were actually UNDER-inflated.

On a subject were we want to know the advanced details about tire traction, your dealer doesn't even know the basics of classical friction physics.

I learned about this the hard way, in a previous car, long before seeing the papers linked here in PriusChat.

 

Fuzzy1 - it's either they don't understand it or they are just covering their butts. I don't mind filling up the air myself but it's just a pain to get those hubcaps off and putting them back is even harder. To tell you the truth, I could not see the tire shape change by just adding 5 psi

 

By the way, I didn't say high pressured tires are not safe. I said they are less safe. The link provide some good information about this. Of course, the info is general and not specific to any particular brand or model of tires. For me, I think high pressured tires are fine since I drive slower than most people.

Over-inflated tires are a bad idea - Wheels.ca

 

We have been through this many times, possibly before any of your identities here were established ...

I used to religiously follow the car company recommendation. Then my new Accord suffered seriously premature hydroplaning, which was eventually cured by increased pressure. Then the Ford Explorer - Firestone Fiasco struck, with many fatalities, and a too-low pressure recommendation was one of several contributing culprits.

Tire wear patterns on several of my past cars, and on many Prii as reported in this forum, also point to door label recommendations being too low.

Pressure is a compromise between many conflicting goals, with comfort being very high on the list. Many of us are willing to put less weight on that.

Safety? While multiple articles such as the one you linked say one thing, a similar number of others keep pointing the other way, and numerous driving professionals go for increased pressure. Then we find more evidence that the research on the high pressure side is actually very skimpy and sparse compared to research of underinflation. The issue remains unsettled.

 

I never follow any tire pressure recommendation religiously. But I do believe there's a trade off. under inflating a tire is also unsafe. I guess as long as we are working within a certain range, we will do fine. I'm just saying for myself, if I'm going to inflate my tires to the upper limit, I should at least slow down a bit to compensate.

 

Over inflation is not when you inflate your tires to the max setting on side wall of tire. It's when you excede that max psi!
So for my tires 44 front and 42 rear are just fine, just don't excede that!.
So I set mine at 42 front 40 rear.

 

You are correct! Under in flation is the worst thing you can do! Just ask Ford and Firestone!