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Old 02-23-2020, 07:09 AM   #1
RidingOnRailz
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Cool Why Do Original Equipt Tires Rate So Low?

Why Do Original Equipt Tires Rate So Low on Sites like Tire Rack?


If vehicle mfgs work with tiremakers to design and build tires specifically for certain car/truck models, why do such tires often earn such low consumer ratings, particularly for wet, snow, and icy operations?
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Old 02-23-2020, 08:16 AM   #2
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Re: Why Do Original Equipt Tires Rate So Low?

It isn't so much that the vehicle manufacturers work WITH the tire manufacturers as much as it is the vehicle manufacturers DICTATE the specs. And because fuel economy is so important to a vehicle manufacturer (and tire wear isn't!), vehicle manufacturers specify low rolling resistance values.

To get low RR values, the treadwear and/or traction (especially wet traction) gets sacrificed. And since the vehicle manufacturers don't provide a warranty on tires, unlike almost every other part of the car, the vehicle manufacturers can specify low RR values with impunity.
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Old 02-23-2020, 03:10 PM   #3
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Cool Re: Why Do Original Equipt Tires Rate So Low?

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Originally Posted by CapriRacer View Post
It isn't so much that the vehicle manufacturers
work WITH the tire manufacturers as much as it is
the vehicle manufacturers DICTATE the specs. And
because fuel economy is so important to a vehicle
manufacturer (and tire wear isn't!), vehicle manufacturers
specify low rolling resistance values.

To get low RR values, the treadwear and/or traction
(especially wet traction) gets sacrificed. And since the
vehicle manufacturers don't provide a warranty on tires,
unlike almost every other part of the car, the vehicle
manufacturers can specify low RR values with impunity.

Thanks!

So it should be good enough just to make sure the replacement tires match the OEM size and are equal to or greater with regards to load and speed rating.

Going from a regular(passenger) All Season - such as might be specified by the car maker - to a Touring or Grand Touring is probably a better idea than seeking out the exact make and model of tire that came on the car new.

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Old 02-24-2020, 08:51 AM   #4
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Re: Why Do Original Equipt Tires Rate So Low?

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Originally Posted by RidingOnRailz View Post
Thanks!

So it should be good enough just to make sure the replacement tires match the OEM size and are equal to or greater with regards to load and speed rating.....
Good enough - Yes! But you should consider what you want the tire to do. If grip is a high priority, then you're going to sacrifice wear - and vice versa.

Quote:
Originally Posted by RidingOnRailz View Post
……. Going from a regular(passenger) All Season - such as might be specified by the car maker - to a Touring or Grand Touring is probably a better idea than seeking out the exact make and model of tire that came on the car new.
If one is satisfied with the OEM tire, by all means, do that.

But if one isn't, chose a tire that is more in tune with what your goals are.

But I get the sense that you think that there is some sort of quality improvement going from - say - an All Season to a Touring, then on to a Grand Touring. That is not the case.

These categories are to help you select a tire more appropriate to your needs - the scale being mostly about speed rating. The problem is that there are other things going on as well.

For example: The higher the speed rating, generally the lower the aspect ratio - and also, generally, the better grip and the harsher the ride. But there are enough exceptions to make this rule hardly a rule.

Last edited by CapriRacer; 02-25-2020 at 09:09 AM.
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Old 02-24-2020, 07:25 PM   #5
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Cool Re: Why Do Original Equipt Tires Rate So Low?

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Originally Posted by CapriRacer View Post
Good enough - Yes! But you should consider what you want the tire to do.
If grip is a high priority, then you're going to sacrifice wear - and vice versa.



If one is satisfied with the OEM tire, by all means, do that.

But if one isn't, chose a tire that is more in tune with what your goals are.

But I get the sense that you think that there is some sort of quality improvement
going from - say - and All Season to a Touring, then on to a Grand Touring. That
is not the case.

These categories are to help you select a tire more appropriate to your needs - the
scale being mostly about speed rating. The problem is that there are other things
going on as well.

For example: The higher the speed rating, generally the lower the aspect ratio - and
also, generally, the better grip and the harsher the ride. But there are enough
exceptions to make this rule hardly a rule.

The user ratings tend to be higher for tires that are the same size, load, and speed category, but have terms like "grand touring" or "performance all season" attached to their name or model number.

I've seen higher profile tires(60-70 series) as well as lower profile,(50-40 series) in the higher tier all season categories(touring, performance), so I don't sense that correlation - between touring and performance attached mainly to higher profile models.
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Old 02-25-2020, 07:17 AM   #6
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Re: Why Do Original Equipt Tires Rate So Low?

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Originally Posted by RidingOnRailz View Post
The user ratings tend to be higher for tires that are the same size, load, and speed category, but have terms like "grand touring" or "performance all season" attached to their name or model number.

I've seen higher profile tires(60-70 series) as well as lower profile,(50-40 series) in the higher tier all season categories(touring, performance), so I don't sense that correlation - between touring and performance attached mainly to LOWER-profile models.
I meant lower-profile! darn!
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Old 02-25-2020, 09:23 AM   #7
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Re: Why Do Original Equipt Tires Rate So Low?

When it comes to these performance categories, it's a trend, but there are enough exceptions to make it difficult to sort out.

In the old days, All Season tires were pretty much S and T rated and Touring tires were H rated, but high performance tires were V rated. Further, it used to be that high performance tires were stiff riding, All Season tires soft riding, and Touring tires in between.

Lots of changes since then. In particular, the Ford/Firestone thing back in 2000 pointed out the need for higher speed capability - that is, problem tires were all S rated, but H rated tires hardly had any failures. To insure that the tires coming from the vehicle assembly plant were of higher quality, the vehicle manufacturers started specifying higher speed ratings. However, the ride quality was specified at the same level as the S rated tires.

The good news is that ride quality isn't tied to the same tire components that speed rating is, so it was possible to get the same ride quality in a V and higher rated tire (albeit by sacrificing steering crispness.)

Nowadays we have a mixed bag, and while the tendencies are still there, it is a lot harder to see them.
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Old 02-25-2020, 07:27 PM   #8
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Re: Why Do Original Equipt Tires Rate So Low?

Quote:
Originally Posted by CapriRacer View Post
When it comes to these performance categories, it's a trend,
but there are enough exceptions to make it difficult to sort out.

In the old days, All Season tires were pretty much S and T rated and Touring
tires were H rated, but high performance tires were V rated. Further, it used
to be that high performance tires were stiff riding, All Season tires soft riding,
and Touring tires in between.

Lots of changes since then. In particular, the Ford/Firestone thing back in 2000
pointed out the need for higher speed capability - that is, problem tires were all
S rated, but H rated tires hardly had any failures. To insure that the tires
coming from the vehicle assembly plant were of higher quality, the vehicle
manufacturers started specifying higher speed ratings. However, the ride quality
was specified at the same level as the S rated tires.

The good news is that ride quality isn't tied to the same tire components that
speed rating is, so it was possible to get the same ride quality in a V and higher
rated tire (albeit by sacrificing steering crispness.)

Nowadays we have a mixed bag, and while the tendencies are still there, it is a
lot harder to see them.

The "Ford/Firestone thing" had more to do with Ford specifying '60s-era pressures - 26PSI if I recall - for their then new Explorer utility, to counter vertical stability issues in that new platform. By 1990, a contemporary competitor, S10 Blazer, recommended 35psi cold at all four corners.

Running 26psi in any recent RAV4, Explorer, New Blazer, or Grand Cherokee, is almost begging for a blowout, even on just a long drive home from the dealer you picked it up from.

Last edited by RidingOnRailz; 02-26-2020 at 06:05 AM.
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Old 02-26-2020, 10:11 AM   #9
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Re: Why Do Original Equipt Tires Rate So Low?

Quote:
Originally Posted by RidingOnRailz View Post
The "Ford/Firestone thing" had more to do with Ford specifying '60s-era pressures - 26PSI if I recall - for their then new Explorer utility, to counter vertical stability issues in that new platform. By 1990, a contemporary competitor, S10 Blazer, recommended 35psi cold at all four corners.

Running 26psi in any recent RAV4, Explorer, New Blazer, or Grand Cherokee, is almost begging for a blowout, even on just a long drive home from the dealer you picked it up from.
I go into great detail about this here: http://www.barrystiretech.com/fordfirestone.html

Bottomline: There was an identifiable cause for the tire failures - unique to the tires in question - AND - while the inflation pressure wasn't helping things, it was within the bounds of what was being done in the timeframe (where other vehicles and other tires did NOT have this problem)

So, No! The pressure specified by Ford was NOT the thing that caused the problem.

(Please note: The key to sorting this out is to look at the GAWR's and tire load carrying capacity at the pressure specified.)
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Old 02-27-2020, 06:12 AM   #10
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Re: Why Do Original Equipt Tires Rate So Low?

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Originally Posted by CapriRacer View Post
I go into great detail about this here: http://www.barrystiretech.com/fordfirestone.html

Bottomline: There was an identifiable cause for the tire failures - unique to the tires in question - AND - while the inflation pressure wasn't helping things, it was within the bounds of what was being done in the timeframe (where other vehicles and other tires did NOT have this problem)

So, No! The pressure specified by Ford was NOT the thing that caused the problem.

(Please note: The key to sorting this out is to look at the GAWR's and tire load carrying capacity at the pressure specified.)

So are you suggesting that 26psi cold was an acceptable pressure, but that anticipated loads per axle weren't taken into consideration?

Confused..
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Old 02-27-2020, 10:00 AM   #11
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Re: Why Do Original Equipt Tires Rate So Low?

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So are you suggesting that 26psi cold was an acceptable pressure, but that anticipated loads per axle weren't taken into consideration?

Confused..
Let me put it like this:

Tires on the 1997-1999 Ford Explorer: *

P235/75R15 @ 26 psi = 1594# = size in question!!
P225/70R15 @ 30/35 psi = 1475#/1594#
P255/70R16 @ 30 psi =1913#

Tires on the 1997-1999 Chevy Blazer:

P205/75R15 @ 35 psi = 1452#
P235/70R15 @ 32 psi = 1643#

* - Tire load carrying capacities at the pressure specified INCLUDING adjustment for use on an SUV.

Please note that the load carrying capacity of the tire in question is NOT the lowest value.

I didn't show other vehicles, nor do I have the GAWR's, but at the time (Fall of 2000) I did ALL of the vehicles and had access to the GAWR's (which I don't now) and I gave that information to our VP of quality for the tire manufacturer I worked for. I was asked to do this to be sure we knew what was going on - particularly since Firestone was pointing out the pressure issue. Looks like they did a good job of obscuring the facts as the argument continues to sway people even 20 years later.

What did come out of this analysis was that - using our own data - certain tire combinations showed NO returns for the same time period - and those returns had one thing in common = H and higher speed ratings.

Our conclusion at the time was that it wasn't the pressure on the Ford Explorer that was the issue. I wasn't in a position (at the time) to know what the issue was (somebody in our organization did!), but I later found bits and pieces on the internet to get enough to make a coherent story - which lead me to write up the webpage I cited above.

So for 20 years I have been saying that the pressure was not the issue and the combination of the design of the tread pattern and the way the plant processed the rubber WERE the issue. This is also what the government (NHTSA) found.
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Old 02-29-2020, 01:23 PM   #12
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Cool Re: Why Do Original Equipt Tires Rate So Low?

Quote:
Originally Posted by CapriRacer View Post
Let me put it like this:

Tires on the 1997-1999 Ford Explorer: *

P235/75R15 @ 26 psi = 1594# = size in question!!
P225/70R15 @ 30/35 psi = 1475#/1594#
P255/70R16 @ 30 psi =1913#

Tires on the 1997-1999 Chevy Blazer:

P205/75R15 @ 35 psi = 1452#
P235/70R15 @ 32 psi = 1643#

* - Tire load carrying capacities at the pressure specified INCLUDING adjustment for use on an SUV.

Please note that the load carrying capacity of the tire in question is NOT the lowest value.

I didn't show other vehicles, nor do I have the GAWR's, but at the time (Fall of 2000) I did ALL of the vehicles and had access to the GAWR's (which I don't now) and I gave that information to our VP of quality for the tire manufacturer I worked for. I was asked to do this to be sure we knew what was going on - particularly since Firestone was pointing out the pressure issue. Looks like they did a good job of obscuring the facts as the argument continues to sway people even 20 years later.

What did come out of this analysis was that - using our own data - certain tire combinations showed NO returns for the same time period - and those returns had one thing in common = H and higher speed ratings.

Our conclusion at the time was that it wasn't the pressure on the Ford Explorer that was the issue. I wasn't in a position (at the time) to know what the issue was (somebody in our organization did!), but I later found bits and pieces on the internet to get enough to make a coherent story - which lead me to write up the webpage I cited above.

So for 20 years I have been saying that the pressure was not the issue and the combination of the design of the tread pattern and the way the plant processed the rubber WERE the issue. This is also what the government (NHTSA) found.

I ran the calculations using the formula posted elsewhere in this forum, assuming original size tire on a 2WD 1997 Explorer(using GAWRs from the placard image in the Barry's article you linked to).


Specifying the 2WD 1997 Explorer on TireRack, the recommended tire is 235/75R15, 105T, Max load 2,039lbs at Max cold pressure 44psi:

FRONT = 2,510/2 = 1,250/2,039 * 44psi = 26.97 cold (27)

REAR = 2,900/2 = 1,450/2,039 * 44psi = 31.28 cold. (31)

So the formula suggests significantly higher rear cold pressures, and only a slight bump up in the front pressures, presumably to maintain steering feel.


Most large legacy rear-drive vans(think: Econoline, Express, B2500), run at least that front-rear difference, if not at least 20psi higher rears than fronts.

I still implicate the low pressures on those Explorers as at least 60% of the culprit in those tread-sep/blow-out cases. Those cross-section photos(Figure 9) in the Barry's article could have been of any tire, from any vehicle or tire mfg. We'll never know definitively.
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Old 02-29-2020, 02:18 PM   #13
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Re: Why Do Original Equipt Tires Rate So Low?

Low pressure was indeed a major culprit in this mess. Ford, themselves, are the ones who recommended the lower PSI because their models showed that the Explorer would be more likely to rollover at 35 PSI. The recommended 26 PSI was already very low, and with a propensity to lose 2 PSI a month, the possibility of getting to dangerously low PSI causing tread separation, and therefor the possibility of a rollover.
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Old 02-29-2020, 07:15 PM   #14
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Re: Why Do Original Equipt Tires Rate So Low?

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Low pressure was indeed a major culprit in this mess. Ford, themselves, are the ones who recommended the lower PSI because their models showed that the Explorer would be more likely to rollover at 35 PSI. The recommended 26 PSI was already very low, and with a propensity to lose 2 PSI a month, the possibility of getting to dangerously low PSI causing tread separation, and therefor the possibility of a rollover.

They recommended those lower pressures because a fresh-from-the-ground up suspension redesign would have been far more expensive than re-using the Bronco II-based platfrom under the 1st and 2nd-gen Explorers in conjunction with those low tire pressures. I would have drawn the line at 30psi.

It seems that making money was more important at Ford than a safe suspension with reasonable cold tire pressures.

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Old 03-01-2020, 10:02 AM   #15
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Re: Why Do Original Equipt Tires Rate So Low?

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Originally Posted by RidingOnRailz View Post
I ran the calculations using the formula posted elsewhere in this forum, assuming original size tire on a 2WD 1997 Explorer(using GAWRs from the placard image in the Barry's article you linked to). ……
So first off, that formula is faulty. The formula used by the tire manufacturers is quite complex, which is why they publish charts - which is where I got my values.

Here's a version of that chart:

https://www.toyotires.com/media/2125...s_20170203.pdf

Yes, it is from Toyo tires, but the chart is the same regardless of who manufactures the tire. (and for completeness sake, there is some complication that makes it harder to understand. I go into more detail here):

http://www.barrystiretech.com/tirest...izingorgs.html

Quote:
Originally Posted by RidingOnRailz View Post
…….. Specifying the 2WD 1997 Explorer on TireRack, the recommended tire is 235/75R15, 105T, Max load 2,039lbs at Max cold pressure 44psi: ……..
No, do not use the max pressure for anything other than the max pressure.

Quote:
Originally Posted by RidingOnRailz View Post
…...

FRONT = 2,510/2 = 1,250/2,039 * 44psi = 26.97 cold (27)

REAR = 2,900/2 = 1,450/2,039 * 44psi = 31.28 cold. (31)

…….
No, the 44 psi value is not tied to the 2039# value. The 2039 value is tied to 35 psi.

So if you use the correct 35 psi value, you get 21.46 psi front and 24.88 psi rear.

Quote:
Originally Posted by RidingOnRailz View Post
…… So the formula suggests significantly higher rear cold pressures, and only a slight bump up in the front pressures, presumably to maintain steering feel. …….
But if you use the correct values, it says the pressures were OK. Don't forget that the government (NHTSA) looked at all this and had the tires recalled, not the vehicle.

Quote:
Originally Posted by RidingOnRailz View Post
……. Most large legacy rear-drive vans(think: Econoline, Express, B2500), run at least that front-rear difference, if not at least 20psi higher rears than fronts. …..
2 thoughts:

First, those are vans, not SUV's

You are pointing out vehicles that use LT metric tires, Look up the base vans that used P type tires (E-150, B1500, etc.) and you'll find a different story.

Quote:
Originally Posted by RidingOnRailz View Post
….. I still implicate the low pressures on those Explorers as at least 60% of the culprit in those tread-sep/blow-out cases. Those cross-section photos(Figure 9) in the Barry's article could have been of any tire, from any vehicle or tire mfg. We'll never know definitively.
Those photos were in Dr. Govindjee's report and were published in the NHTSA EA00-023 report used to justify the tire recall. Are you implicating that NHTSA (and Dr. Govindjee's) didn't use photos of the tire in question when they had abundant samples available?

Oh, and I don't think you've yet realized that I am Barry.
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