New Tires- Big Mileage Drop

percentages can be misleading, what were your former mpg's and what are they now?

what tyres pressure are you running?

who installed them, could any of the brakes be dragging?

 

FWIW, short answer tire pressure - increase by 4 pounds and report back.

The long answer is the rolling resistance rating difference of the OEM (or former) tire vs. the Conts.
Even if both say 400, the rating is as compared to same-brand tires, not between competitor brands.
Ditto, the tire pressure door sticker is for OEM tires and may be different settings for aftermarket/ other brands.
A pyrometer is a great tool to own (as is an accurate tire pressure gauge).

Lastly, brake drag is a valid comment as mentioned above.
Lubing the brake pad pins is good maintenance plus a failing/ old 12volt battery is also known to reduce mileage.
Both items have been discussed on our forum before.

Good luck.

 

New tire tread is typically less stable (squirrly) than worn tires due to the tread depth. It does take some time for them to "scrubb-in"

When I changed my tires I saw a 2-3 mpg drop even after 2-3 PSI increase from normal (33 to 36 psi).

After 5,000 miles I did get 1-2 mpg back.

I also noticed you changed out in December. Did it get colder temps after the tire change?

Cold weather really eats mpgs. Typically I get 35 in winter and 45 in the summer heat. (40 mpg avg.).

 

It's probably too late, but were there any signs of unusual wear on the old tires?

Jack up the front end and try to wiggle the wheels side to side to check the tie rod wear and bearings. Wiggle up and down to check the ball joints and bearings.

Maybe try the same on the rears to see if there are any bearing problems there too.

Maybe check the alignment?

 

Replacing the the stock Michelin Pilot HX MXM4 (in 215/45R17, on our 2010), with Michelin Primacy MXM4, our mpg dropped, near 10% IIRC. That was a few years back, and it’s only partially recovered to date. Is what it is.

 

See rear brake drag link in my signature (on a phone turn it landscape to see signatures). It’s Gen 3 but Gen 4 rear brakes may be similar. The rear brakes can be reassembled with misaligned brake caliper piston, and this imposes drag on wheel rotation. May or may not be a factor, but good to check.

 

How many miles did the OEM tires have on them when you replaced them? If these were the factory installed tires in 2017 and you are driving 7000 miles in five months, I would assume the old tires had a lot of miles on them. I would think really worn tires would get phenomenal fuel economy. when I switched from the OEM Dunlop East save tires with 43,000 miles on them to new Michelin X tour tires, I noticed a 10% drop in EV efficiency. It took over 20,000 miles on the x tour tires to notice any improvement. It took almost 40,000 miles to gain half of the loss back. I don’t know what the loss would have been if I had something like 70,000 miles on the OEM tires.

Also, because the MPG includes the EV range, small changes in efficiency can wildly swing the number. For example, take a 90 mile commute with 30 miles EV range and 60 miles per gallon when driving in HV mode. If the drop in efficiency of new tires changes your EV range to 25 miles and your mpg in HV mode to 50 miles per gallon, your total MPG drops from 90 MPG down to 69 MPG. In this example a 16.7% drop in efficiency lead to 23.3% drop in the mpg displayed on the dash. I think the miles per kWh gives a less distorted picture. There is a display where it shows you the monthly miles/kwh. I recommend looking at that. I included a picture on my dash as a reference.

 

I recently got new tires for one of my fleet of Prii. That was my exact same thought too.

I change over to winter tires, and it was the summer tires I was buying. I looked for tires with "low rolling resistance" and kept coming up with all season tires, where they kept reviewing the winter weather handling. I'm not concerned with that because I switch to studs for the Wyoming winters.

I finally gave up as there's no specific rolling resistance number. In the end, I figured that the mileage rating might somewhat serve as a rolling resistance proxy. A harder compound tire would probably last for more miles as well as have a lower rolling resistance. At least that's how my thinking went. I ended up with a set of Pirelli "high mileage" (80,000) tires from Sam's Club (no Costco here, and I went around to see what just about everybody in town had for tires).

I can't tell you if the new tires are any better or worse for gas mileage. The car I put them on was my 2019 "new to me" Prime. I bought it in late December, and immediately swapped over to a set of Winter studs. Those definitely take a bite out of the gas mileage, but I don't want to worry about the winter icy roads. The whole fleet (Gen 2, Gen 3, and the Gen 4 Prime) use 195/65R15, so the tires don't have to go back on the car they came off of. At the end of the winter we decided to put the tires that came with the new car on the Gen 3 and get new summer tires for the car that drives the furthest distance.

I read one review after I bought the Pirellis that said they were really noisy. My experience was not that at all. Maybe just a little more noise than the ones that came with the car. I figured were cheap and soft, something that a car dealer would put on a car to sell and not what I'd put on a car to drive. The Gen 3 Prime is still quieter and smoother than either of the previous Prii - especially when running in EV.