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2008 Impreza 2.5i auto tr
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Discussion Starter #1
I recently replaced my original Potenza tires with a pricey set of Michelin Primacy tires. After 1,000 miles here's what I've found, and I sure don't get it with all the good ratings on this tire:

1) Gas mileage has decreased at least 2 mpg (annoying since AWD gas mileage isn't great anyway)
2) Car now does not handle as crisply, and tends to wander (crosswinds on the interstate push the car around)
3) Harsh, choppy ride
4) Snow handling not a whole lot better than the old Potenzas.

Anyone else have this experience with the Primacy tires? My driving habits are just normal everyday to-and-from work, and interstate.
 

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2001 Forester S, auto
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471 Posts
Assuming they are balanced properly, you likely need to let them break in a bit more. You probably went from tires with very little tread to tires with thick tread. That alone will account for a huge difference in handling, and MPG.

Regarding snow handling, the Primacys tend to be one of the better all-season tires, but you're not going to notice a huge difference, the only way you'll notice a huge increase in snow performance is if you switch to a dedicated snow tire in the winter.
 

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I recently replaced my original Potenza tires with a pricey set of Michelin Primacy tires. After 1,000 miles here's what I've found, and I sure don't get it with all the good ratings on this tire:

1) Gas mileage has decreased at least 2 mpg (annoying since AWD gas mileage isn't great anyway)
2) Car now does not handle as crisply, and tends to wander (crosswinds on the interstate push the car around)
3) Harsh, choppy ride
4) Snow handling not a whole lot better than the old Potenzas.

Anyone else have this experience with the Primacy tires? My driving habits are just normal everyday to-and-from work, and interstate.
What tire pressure are you running, that can have a huge affect? The primacy are a pretty mediocre tire from a performance standpoint, but pretty decent for a daily driver/family car.

For an all season that handles snow well, I'd have gone for the continental extremecontact DWS, nokian wr series, or something like the goodyear tripletred.

I thought the primacies on my mom's car were pretty mediocre, but they were the hmxhxclkdjkhd (no idea, its a bunch of random letters) version and its a 3+ ton car.

I'm not really a fan of michelin, seems you can get better elsewhere for much less money.
 

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2008 Impreza 2.5i auto tr
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Discussion Starter #4
I'm running the tires at the recommended PSI front/rear on the inside of the driver door. When they were installed, the tire place aired them at a higher PSI, and I eventually had someone else adjust it. Re: break-in -- how long does that take, and will the problems I listed improve at all (particularly the bad MPG, and having to keep correcting steering so much because the car wanders)? I had Uniroyal Tiger Paw on my 96 Legacy wagon, two sets, and they seemed to perform perfectly well.

This seems like such a dice roll -- you buy a high-priced well-rated tire, and you really don't know what you're going to get!
 

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2005 Forester 2.5X LEV II
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There's your Problem, You are running them Under-Inflated. Under-Inflated tires are more dangerous then over-inflated. I run Hydroedges at 36psi, I hate it when the Dealership lowers it to the Door sticker. The ride is soft and gas Mileage drops. I always recheck and re-inflate them.
 

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2015 Highlander AWD XLE 6AT
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OLD,

I read your original post late yesterday afternoon. I’ve been trying to find the right way to phrase my hypothesis, so here goes.

A “harsh and choppy” ride and/or wandering is sometimes the result of over-inflated tires. Accordingly, the first thing to do is to check the cold pressure on your tires to verify that they are “properly” inflated per the vehicle placard on the bottom of the driver’s “B” pillar and/or the owner manual. (Page 12-5; 32 psi front and 32 psi rear, I believe).

I believe the OEM Bridgestone Potenza (RE92A’s?) tires on your 2008 Impreza were size 205/55R16 89V. I believe the new Michelin Primacy (MXV4?) tires you recently installed are 205/55R16 91H or 91V.

Although the new tires are the same size as the old ones, they are a different "service description" (load index and speed rating), and therein may be the issue. I suspect a different speed rating (V = up to 149 mph, H = up to 130 mph) alone would not be a major issue.

The old Bridgestone’s 89 load index (probably) means that its load rating was 1,279 lbs at 51 psi max pressure. Your car’s owner manual says to set these tires at 32 psi front and rear.

The new Michelin’s 91 load index means that its load rating is 1,356 lbs at 44 psi max pressure. All of these numbers can be verified in the documentation that came with your tires, on the Michelin website, and/or on the tires’ sidewalls.

Since the new tires have a higher load capacity at a lower maximum pressure, I would expect for the new tires to subjectively feel “harsh and choppy” (compared to the old tires) if set to the Subaru recommended pressure.

Accordingly, you may wish to consider trying slightly lower tire pressures. Specifically, you may want to try 30 psi all ‘round, and then maybe even 28 psi. If this experiment cures the “harsh and choppy” problem it may also cure the wandering problem.

The load index hypothesis above is just my opinion, but, as a fairly technical guy, it makes sense to me. Nonetheless, you may wish to seek out a second- or third opinion, as my hypothesis may be complete nonsense. Also, the new tires' higher load index may directly correlate to a stiffer sidewall, which in turn may deliver a subjectively harsher ride.

It’s not unusually for worn tires to handle a bit better than new tires under favorable conditions. It’s also possible that the worn tires’ slightly smaller rolling diameters were delivering false high odometer readings, and therefore delivering erroneous fuel economy results. Winter gas and/or driving conditions may have also taken their toll on fuel economy (three or four tanks on the new tires?).

We had a tire load index issue with tires on our 97 Plymouth minivan. The original pressure spec was based on tires with a max pressure spec of 35 psi. The last tires we bought had a similar load rating, but a max pressure spec of 44 psi. Driving on the the new tires at the old pressure spec was a bit too “soft and floaty” for us, so we added ~4 psi to each tire, and this seemed to cure the “problem”.

I just purchased a set of Michelin Primacy MXV4 tires (205/60R16 92H) for my wife’s Honda Accord. The OEM tires were 91V. Fortunately for our application, there's very little difference between the two indexes: max pressure for both is 44 psi, and there's only a small difference in the max load capacity (33 lbs.).

Accordingly, I have high hopes for these new tires!

I hope this helps, and I apologize for the rather long-winded response.
Jim / crewzer
 

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2008 Impreza 2.5i auto tr
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Discussion Starter #7
Crewzer -

Interesting hypothesis (and a fine technical explanation - even this ol' lady driver could understand it!) - and I'm willing to tinker with the tire pressure to see what happens. I checked my tires, and they conform to the specs you quote on the Primacy MXV4; they are 91V - (1356 lbs, 44 psi). The Subaru owners' manual says 33 psi front, 32 psi rear. Whatever I do with the tire pressure, I just want to make sure the inflation is within safe limits one way or another.

Thanks, all, for the comments and suggestions.
 

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I do not agree with crewzer's hypothesis, it sounds to me like you need to inflate your tires more, not lower the pressure. under-inflated tires display the symptoms you are describing (lower mileage, muddy-handling, wandering). Tires that are over-inflated shouldn't (?) exhibit wandering characteristics, but will feel slippery in turns and oversteer will be really easy to induce.

as for safe pressure, it is completely safe to run them at the max pressure listed on the sidewall. My family has always run our tires at their max pressure without any problems, least of all premature wear that some people will say will happen.
 

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2008 Impreza 2.5i auto tr
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Discussion Starter #9
Forgot to ask: if I underinflate or overinflate very much, won't I set off that tire pressure warning light?
 

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2015 Highlander AWD XLE 6AT
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OLD,

I found this interesting post while Googling "load index", "pressure", etc.

Returning to your car's apparent drop in fuel economy, it's possible that your new Michelin tires' 91V service rating may be some part of the problem.

The Primacy MXV4 tires do indeed have a reputation for exhibiting relatively low rolling resistance, which generally translates into good fuel economy. In fact, Consumer Reports' #1 ranking of the Primacy MXV4 in their "Performance All Season" test of 14 "H"-rated tires was due in part to the tire's "excellent" (low) rolling resistance results. Only the Goodyear Assurance Fuel Max matched the Primacy MXV4 in this category. However, the tested Primacy MXV4 carried an "H" speed rating.

The same test report separately ranked 15 "V" speed rated tires, although a "V"-rated Primacy MXV4 was not included in this group. The best (low) rolling resistance rating in this group was "good" (two increments below "excellent"), and the vast majority (12/15) scored just "fair" (down one notch from "good". The Bridgestone Potenza 019 Gris scored the worst in the group, with relatively "poor" (low) rolling resistance (down two notches from "good").

All tires tested were size 215/60R16. Although its results were rather scattered, the group of "H" rated tires scored better (low) rolling resistance marks than did the "V" rated tires. IMHO, if fuel economy is an important parameter, then a "V" rated "performance all season" tire (up to 149 mph) would typically not be one's first choice.

Curiously, CR's test of 15 "ultra high performance all season" tires ("W" or "Y" speed ratings) revealed generally good group results in the (low) rolling resistance category.

Finally, I apologize for misstating the Subaru recommended front tire pressure for your car. My pdf copy of the owner's manual (and/or my brain) is a bit fuzzy, and I quickly read "32" instead of the correct "33".

Ain't this fun? :huh:

Regards,
Jim / crewzer
 

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2015 Highlander AWD XLE 6AT
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Good point!

IIRC, the TPMS will illuminate if the monitored pressure drops to/below 26 psi. My current thinking is that you probably don't want to go below 31F/30R for every day driving, and you may want to go back to 33F/32R if you're carrying additional passengers and/or other loads.

"Flat spotting" may also be causing a bit of harshness. When the tires are warm, and the car is then parked in otherwise cold conditions, the cooling tires my develop temporary "flat" spots where they contact the cold road surface. This is not uncommom, and should dissipate when the car is driven and the tires warm up and begin to flex more freely.

HTH,
Jim / crewzer
 
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