New tires hope I didn't make a mistake

The tire place was wrong about the pressures. 40/38 is fine or even higher, just don't exceed the maximum pressure on the sidewall, 44 psi for your tires I think. They will be fine.

 

I'm not familiar with those tires, but all tires have a break in period. You'll see slight increases in fuel economy for the first few thousand miles.

 

I wouldn't jump to any conclusions based on the ride home. There could be several factors at play. I don't know anything about the tire you bought, but as long as it was the same size as the previous tires, I would think you'll get similar fuel mileage. I think you should give them some time and then see what you have.

 

New tires sometimes take up to 800 miles to break in. There are curing agents and other additives in the tire that need to come out. Sometimes they might be noisy for awhile.

I considered a swap of new Integritys at the Goodyear dealer. But I really wanted a wider tire, and they wouldn't change sizes because of the Toyota spec. At the same size, the Goodyear manager said it would not be worth it unless I drove a lot of miles. He said the Integritys were a good OE tire on a lot of new cars, but not a high mileage tire.

 

It will be 1 to 2 MPG less. I lost 2 mpg but I also went up one size to 195s.

 

A new tire also has fewer revs per mile. That means that when you travel a mile it makes fewer revolutions. As the tire wears, the revs per mile increase. It turns more times per mile. So when our tires are almost worn out, they are spinning faster at any given speed. This makes the electronics "think" that the car has traveled farther than it did when the tires were new. If you use the same amount of gas to travel a given distance in both cases, the indicated and calculated mpgs will be higher on worn tires.

Food for thought.

I replaced my Integrities at 50K with Primacies. I also realized a cut in mpg. Now with 10K on them, I'm getting better mileage than ever. Oh, by the way, I'm running 50/50. A hard ride but the car does roll on and on and on. I'm averaging 63mpg though I'm a conservative driver on and off the highways.

Tires are but one factor of a multi-complex equation for high mpg.

Kaos1

 

How do you like the Primacies Kaos? Those are the Michelins... right?

 

What is the max pressure rating molded into the side of each tire?

 

mrblaise,

The Primacy is made by Michelin, you are right. I really like them but I was uncertain when I first had them mounted because I was going into cold weather and new tires to boot. This had a dramatic impact on the MPG over the worn Integrities. I was running both the Integrities and the Primacies at 42/40.

There are hills that I measure on my daily route by coasting down and monitoring the entrance and exiting speeds. A crude, but indicative, measure of rolling resistance if you compensate for temperature, air density, wind, wet/dry pavement, and so on.

The new Primacies did not perform as well as the worn Integrities but the new tread thickness creates a squishy layer between the wheel and the road. I bumped up the pressures. This helped.

As far as traction, the Primacies are light years ahead of the Integrities.

Now with summer here, the increased pressures that I've been running, and improved driving techniques, I'm consistently banging out 63+mpg tanks. The "calibration hills" are returning results as good, if not slightly better, than the Integrities.

In no way am I endorsing that people run their tires over the max pressures printed on the sidewalls. It can be very dangerous for vehicle handling afterall there is less rubber on the road.

Over all, I like the Primacy as a tire for the Prius. Mine are the OEM size. I did not go with the wider tire because there would be increased friction and the OEM size is sufficient. Not worried about looks, if there were bicycle width tires to mount, I'd consider it. The harder the tire, the lower rolling resistance. (Also lower friction to the road)

Remember that just putting on a set of tires is not going to yield magical mpg results. Excellent MPG is the result of many variables working together. I am still learning how to get more mpg everyday and I've had the Prius for over two years now. A tenth here, a tenth there. What a game!

Kaos1

 

Agreed. Here in Albuquerque, about half the town is built on a gently-sloping hill which averages just about the grade at which my manual-shift Audi A4 will coast in neutral at 40 to 50 mph. As someone who cares about fuel economy (our other car is a Prius), I coast a lot and pay attention.

So when I replaced the original equipment Pirelli P6 P205/65 R15s at about 45,000 miles with what I believed was the identical model replacement tire, it was immediately obvious to me that my rolling resistance was up. Stretches where I had maintained speed before slowed me down, even ones where I'd slightly accelerated did. Now, with about 10,000 miles on the second set of tires, I'm back to a condition not obvious different. By the way, my impression is that the two most important environmental factors to match in making same-hill comparisons are wind and air temperature.

People talk a lot about the false loss of mpg on new tires because the greater tread depth causes offsets in all mileage and speed readings. Simple arithmetic agrees that effect exists, but for my 15 inch tires would seem limited to about 4% from beginning to end-of-life, so more like 1% in the first quarter of life. But I've seen much bigger than 1% initial mpg loss in like-for-like circumstance, plus the above more subjective rolling resistance indications.

So my tentative, overly personalized conclusion is that there can be a pretty significant new-tire mpg penalty, much of which disappears in the first 10 to 25% of tread life.

I'd assume this depends to some degree on specific tire materials and construction, so might vary a good deal from model to model.