Significant reduction in MPG

[Nickp001]

I recently had new tires put on my car (Goodyear ComfortTread's) and had an oil change. At the tire place I asked them to put 42psi in the front and 40 in the rear. This is when I really began noticing a significant drop in MPG, about 3-5 MPG to be exact. I was averaging between 44 and 45 before the new tires and now I was not even hitting 40.

Then I went to Jiffy Lube for a MobileOne oil change. I asked them to make sure the oil level was at the line and not a hair over. I also asked them to check the tire pressure, again 42 in the front and 40 in the rear. They said the tire pressure was off, and they said they made the necessary adjustments.

I was still getting poor mileage, so I decided to check the tire pressure and oil level myself. Tire pressure was set at 35 all the way around, so I adjusted it to 42/40. Oil level appeared to be ok, but it was really hard to read. I'd get different results every time I pulled the dip stick out.

After adjusting the tire pressure, I was still getting poor mileage, so I tried 44/42. No Change. Went to 40/38 and noticed a slight improvement, but sill only averaging about 40 mpg. Is it possible that this decrease in mileage is due to the new tires?

Should I expect the manufacturer installed tires to outperform the ComfortTreads in mileage? Very disappointing if that's the case.

[ncc1701mda]

I wonder if the tire diameter is different than the original tires? That could affect what the system thinks it is getting for mpg.

[Nickp001]

<div class='quotetop'>QUOTE(ncc1701mda @ May 31 2006, 07:49 AM) [snapback]263373[/snapback]</div>

I wonder if the tire diameter is different than the original tires? That could affect what the system thinks it is getting for mpg.
[/b]

When I ordered the tires I ordered P185/65R15's, but I should probably check and make sure they installed what I asked for. Another thing I should do is calculate actual mileage and not just rely on the cars calculations.

[marcdare]

<div class='quotetop'>QUOTE(Nickp001 @ May 31 2006, 09:14 AM) [snapback]263356[/snapback]</div>

I recently had new tires put on my car (Goodyear ComfortTread's) and had an oil change. At the tire place I asked them to put 42psi in the front and 40 in the rear. This is when I really began noticing a significant drop in MPG, about 3-5 MPG to be exact. I was averaging between 44 and 45 before the new tires and now I was not even hitting 40...


[/b]

There is a whole thing in the manual about changing tires. Anything besides the manufactuerd tires for the car need to be entered into the system. I'm pretty sure you have to account for the dimensions of the tire, because even tiny insignificant changes over hundreds of miles greatly affects the output on the screen. I wish I could be less vague, but look in your manual and you will find it.

[galaxee]

new tire breakin is a big MPG killer. i wonder if they're also not LRR (low rolling resistance) tires- that would have an effect too. there are plenty of others here who have changed to the comfortreads- if you do a quick search i'm sure you'll find plenty of opinions.

[Nickp001]

<div class='quotetop'>QUOTE(galaxee @ May 31 2006, 08:07 AM) [snapback]263381[/snapback]</div>

new tire breakin is a big MPG killer. i wonder if they're also not LRR (low rolling resistance) tires- that would have an effect too. there are plenty of others here who have changed to the comfortreads- if you do a quick search i'm sure you'll find plenty of opinions.[/b]

Yeah, I wonder if that has something to do with it. Incidentally, over the past couple of weeks I had done several searches here hoping to find something. I did find a brief mention of a similar problem with the ComfortTreads, but not much else. Thanks!

<div class='quotetop'>QUOTE(Greenfoot @ May 31 2006, 08:05 AM) [snapback]263380[/snapback]</div>

There is a whole thing in the manual about changing tires. Anything besides the manufactuerd tires for the car need to be entered into the system. I'm pretty sure you have to account for the dimensions of the tire, because even tiny insignificant changes over hundreds of miles greatly affects the output on the screen. I wish I could be less vague, but look in your manual and you will find it.[/b]

I'll have a look and see what I can find. Thanks for the suggestion.

[hdrygas]

There have been a number of posts on the subject of tire break in. I think you need to be prepared to take a hit. We all feel for you. We will each have a turn at this and it will be difficult. I am going to do mine in winter if possible so I can blame the weather. The spring is a bad time, I look forward to the rising MPG and get depressed every time the weather takes a turn for the worse.

[Nickp001]

<div class='quotetop'>QUOTE(hdrygas @ May 31 2006, 07:45 PM) [snapback]263798[/snapback]</div>

There have been a number of posts on the subject of tire break in. I think you need to be prepared to take a hit. We all feel for you. We will each have a turn at this and it will be difficult. I am going to do mine in winter if possible so I can blame the weather. The spring is a bad time, I look forward to the rising MPG and get depressed every time the weather takes a turn for the worse.
[/b]

Thanks for your input. I took your advice and read several posts regarding the tire break in period and that could very well be where I'm at right now. I'll keep my eye on it and see if it improves over time.