Help -10% Mileage Drop with New Tires!

(1) We normally expect a temporary MPG reduction with new tires, until they are 'broken in'. Though 10% is too steep for that alone.
(2) What is your tire pressure now? What was it before replacement?

 

Ditto the above remarks.

It typically takes several thousand miles for the tire friction surfaces and siping to 'bed in'.

Be sure the tire pressures are what you previously ran, if not the high recommended pressures we typically see quoted -- 38-42 psi front, 36-40 psi rear. (We run 42/40.)

 

From the marketing pitch:
"offering long wear, wet traction and low rolling resistance"

The sad truth is that there's no such thing as one tire that does it all. You get tread life or LRR, but not both. You get traction or LRR but not both. Goodyear is claiming all three in one tire - not likely. It may be a tire that offers tread life and traction with better MPG than most. Pump them up and see how they work out. Honestly, the difference in cost for a really LRR tire doesn't justify paying more for it unless gas is at $4/gal and the tire gives you 3-4 MPG more.

 

need break in as mentioned, but also, new tyres have larger radius, affecting your screen average and miles driven. nothing you can do about that.
put a few tanks on her and report back with hand calculated total average

 

With modern steel belted radial tires, inflated and loaded to their normal working range, radius change has very little impact. The contact patch on the ground is flat, not round, so the normal circle equations don't work out as expected.

What matters is the rolling circumference, controlled by the steel belts beneath the wear portion of the tread. This controls the "Revolutions Per Mile" specification on the tire's datasheet. A little bit of arithmetic will reveal that this doesn't match up with the turns you'd expect from the radius if the tire acted as a perfect circle.

 

I put a set of Michelin Defenders on our 2012 Prius v (wagon). Sure enough, I took around an 8% MPG hit. However, after a 5,000 mile road trip I'm happy to say that things are back to normal. So hang in there!

 

Add more air to your tires until they “break in”

 

Everyone's piling on, saying new tires take time to deliver their best LRR. Maybe yes, maybe no, but several times I went to new EP20 and they REALLY hit the ground running, great mpg from the moment they were put on. So, I'm a little sceptical, and suspect the break-in adage is at least in part created by tire dealers, to blow-off customers.

 

There's some good answers above.
Especially new circumference vs. old.

Perhaps best for the OP:
1) Report back in 5000 miles
2) Bump air pressure a few pounds.
3) Check wheel alignment, not mentioned, could be a good thing too.

 

Yep, we are all tire dealers here.

Seriously though...of course EP20's will give you great mileage. They are one of the premiere LRR tires on the market. We are not talking about that here. Rather, we are talking about going from the 'original' tires ( which I'm assuming were a 'good' LRR tire )...to new 'not so good LLR tire' that is certainly not one anywhere new one of the 'good ones'.

• Edit: Question...I'm assuming Toyota does use a 'good LRR' tire as original equipment on the Prius v (wagon)? If not, that would certainly affect my reasoning.

I have never had brand new 'non LRR' tires get better mileage than what I previously had on. However, I'm basing this on Michelin tires ( usually Defenders ) that have an extremely high treadwear rating and a pretty deep tread. Perhaps that could have something to do with it? At any rate, I have had Michelin Defenders on three vehicles so far and have noticed that all three vehicles needed a 'break in' period.

Of course, talking about tires is like talking about oil...or religion ...so there is that!

 

Yeah I like the Defenders, got them for our son's Civic one time. They're a good balance. I drove his car across town to the airport, pretty much right after installing them, and found them very easy rolling. If they were available in 215/4R17 they'd be on my short list, too bad they aren't.

 

How does "break-in" actually effect rolling resistance?

Do they get harder as they break-in? What exactly causes the better mileage some people report after a tire breaks in?

 

The tire contact patch becomes smoother and more 'LRR' as the mold flashing and sipes are -- for lack of a better analogy -- 'sanded down' by thousands of miles of road contact and a million or so revolutions (at 832 to the mile). Prior to 'smooth', deformation and hysteresis of the tire flashing and sipes as they come out of the mold generate heat, which lowers 'LRR' and MPG.

 

Are you sure you don't have a hub problem? I fixed a very similar problem by replaceing a wheel hub with bad bearings. If you are hearing any slight "scraping" sounds, this could be the culprit, not the tires.

 

Glad to hear it's working out.

 

Yep..I have noticed a similar 'break in' period with two sets of Michelin Defenders. However, it took more than one tank of gas for me.

 

On my 2008 Prius every time I put new tires on it my MPG went down. The last set were a no name non LRR but the second set were Michelin A/S LRR tires, I forgot what model. I never hit 50 mpg in the summer again. With mpg on the decline I kind of lost interest in hypermiling.
When I got my Gen 4 it all came back.