New Tires Lowered MPG UNTIL...

I agree - she didn't answer my question - which can make a huge difference - might give us a better idea of what the problem is:
"Do you keep accurate records of your fuel use - or just the dashboard display which is only a calculation from a number of sensors, and sometimes errs considerably?"

 

BTW, fuel injector cleaner helped this issue on a 2009 Prius.

 

If somebody believes they already have the answer-sometimes you can't give them any other answer.

I think a lot of sound advice and opinion has been stated throughout this thread. But the OP already has an answer and a premise:

Now, personally?
I don't buy this premise. Given the shocking, huge scandal VW suffered when it was discovered they had built vehicles by design to defraud, I think the idea that Toyota would design their vehicle to somehow need a "secret" adjustment, that ONLY Toyota dealers know, in an effort to lure owners to the dealership is, well I'll just say....very, very, very, very, very unlikely.

I would say, don't ignore the far less dramatic, simpler possible explanations.
Which COULD be as simple as the common thread...Brand New Tires. You often take a mileage hit, right after new tires are installed.
Basically, it's tires, inflation, and possibly alignment.

I mean, if you really believe the OP's premise? Then what other answer would you expect or accept?

But I personally just don't accept the premise that the Prius is somehow designed to create a MPG loss after tire replacement, with a publicly undisclosed adjustment needed, that ONLY Toyota dealers are aware of.....

For one thing? If this was true....you'd have a MUCH LARGER contingent of people complaining. The number of Prius that have tire replacements, and/or rotations at non-Toyota facilities is huge. If this was happening, Prius Chat would be filled with never ending posts about mysterious MPG loss after tire changes.
IMO...that isn't happening.

Also? With as many engineers, mechanics, etc...that work with Prius and their own Prius's...there is no way something like this could be kept hidden.

Nah... Sorry, I'm not buyin it.

 

No - having read every Gen 4 post in 3 3/4 years - if this was a "thing", there would be 1000s of posts saying the same thing. There have been some mentioning that they got worse MPG after new tyres, but only by a relatively small margin.

My concern is that she didn't answer my first question "Do you keep accurate records of your fuel use - or just the dashboard display which is only a calculation from a number of sensors, and sometimes errs considerably?"

Flo - can you provide this answer?

Unless full fuel records are kept, with odometer readings and calculated MPG, it can be very erroneous and inaccurate. Yes, maybe she did - but she hasn't mentioned how the calculations were made.

Actually, 46 MPG is extremely low for a Gen 4 - and 37 MPG seems near impossible, particularly in summer.

Also, Flo - did you ask your the question about your car on the Gen 2 FORUM - this is Gen 4 and many of us don't know much about Gen 2 cars. You would get better answers there.

 

Not to mention many people report improved economy (me included) when they change their tyres. Again, many of those factors could work both ways... Higher inflation pressure, more economical tyre design, slightly different size, and of course all the random variables, such as the weather, being in your favour.

 

What I've read, not only in Prius Chat but in other automotive forums, is a slight or temporary loss of MPG is often to be expected. My understanding (which might be flawed) is that it's the opposite of the LRR tire affect. With a brand new set of tires, you have new rubber on the road, and more traction/resistance. So a dip in MPG can happen. But usually this affect reduces, as the tires break in.

I should be clear, I'm not saying tires don't affect MPG. Tires have different weights, tread designs, etc. I just don't feel the premise the OP is presenting, which goes beyond just it being "tire related"- is valid.

I find the automotive tire industry to be a bit of a carnival of claims and statements.
With tire manufacturers being the traveling side show salesman, promising their new tire will make your vehicle, quieter, safer, sportier, and more economical. I kind of take it all with a grain of salt.

BUT...there are design realities with tires. Some are designed to promote better fuel economy--Low Rolling Resistance primarily.

Even if you replace with the exact same type of tires...the new tires..are new.

I've been lucky enough to have 2 new cars in the past 10 years, I traded in my Prius before I had to replace the OEM. So I haven't bought a set of new tires in a while.
The Fit is getting close to needing a new set.

For the most part, unless I've bought a tire primarily designed for fuel efficiency, I expect a mileage hit when changing tires.
I think you have to monitor the mileage for a longer period after a tire change to get a true idea of what the mileage with those new tires is going to be.

I have NO conspiracy theory about a manufacturers plot to lure me to the dealership.

 

Put on new tires earlier this year, red X marks the spot:

 

I mean it looks like your MPG dropped by around 10MPG, from 50MPG down to 40MPG, immediately after you added new tyres, right?

But what happened in January/February? The MPG was down at around 42MPG. New tyres again? Or are swings of that size quite normal?

And really that's the point... it's easy to read into things and see cause and effect, but even the small amount of data presented shows big swings in fuel economy of similar sizes, even when the tyres haven't been changed. This suggests a 10MPG swing from one month to the next might be normal.

There are many factors at play, and without a LOT of data from a LOT of tyre changes, or controlled studies where the only changing variable are the tyres, then I don't think it's safe to point to finger at the tyres.

 

I hear you. But, it was tough, tank-after-tank, after that tire change. My "butt meter" was saying I couldn't catch a break, no matter how hard I tried. The in-dash trip meter display of mpg stayed stubbornly low*. This was coming out of winter, into summer, time when mpg is normally improving significantly.

* Actually liters per 100 km staying high, same difference.

 

Old true story on my 2004 Honda Hybrid Civic.

This car ate rear tires for lunch due to bad suspension issues. So I tried el cheapo Goodrich tires from SamsClub on the rear and my MPG went up. I thought well if they are that good I will put two on the front.

MPG went down 12 per gallon and stayed low until I got rid of the car.

The rear suspension and rolling characteristics are unique for front wheel drive cars. Engineers ! Jump in!