Figuring out the right tire pressure to use

[ptjones]

To start with you should use the door sticker and then pay attention to tire wear. If it shows more wear on the edges of the tire it is under inflated. All FFH/CMAX I have tested show signs of under inflation at 35/38 psi.

 

I asked My FORD Service Mgr to ask FORD about tire pressures and he got a no comment.   I did talk to Tire Rack tire testers and they said that it is common for FORD to under inflate their tires to get a little softer ride, tire pressures are a compromise between ride quality, gas mileage, handling and stopping among other things. The FFH/ CMAX have 35/38 psi recommended which is odd for two FORD  cars that weight the same and have similar suspension.  It would appear that ride quality/ smoothness is high on their priority list. 

 

 Talking to Michelin Rep they recommend starting with FORD's recommended pressure and then find the pressure that gives even tire wear.  I told him I was using 50 psi and getting even tire wear.  He Said "Then he wouldn't have problem with that and not to exceed 51 Cold tire pressure"  BTW the bursting pressure is around 200 psi , so you don't have to worry about that. An auto mechanic on CMAX forum used 55 psi with no problems, but I wouldn't recommend this.  I did look at a number of used FFH in Dealers lots and sure enough the tires were wearing more on the edges than the center which is a sign of under inflation. So it is obvious 35 psi is to low to get even tire wear.

 

Facts: FFH/CMAX can use 35/38 psi to 51 psi from OM and on the sidewall of Michelin ES safely according to the Michelin.

           With 220k miles of experience my tires last longer and perform better than they did at 38 psi and get better gas mileage +1.3 mpg at 50 psi.

           My last set of Michelin Energy Savers lasted 87k miles, only warrantied for 55k miles. 

            The nice thing about tire pressure is you can raise it up and try it out and then decide what to do next, you can always go back.  

Note: Tires aren't very sensitive to pressure, if you go up to 40 psi you will probably not notice a difference.  At 45 psi you will notice a little difference and 50 psi a little more.

 

Also Your tire pressure should change with Gross Vehicle Weight .  There is no info in OM about changing tire pressure unfortunately.    For me I have saved about $500 going to 50 psi tire pressure by improved mpg's and tires lasting 25% longer.  50 psi does make for a little stiffer ride and I think all the improvements in performance, gas mileage, tire longevity and 1/4" increase in ground clearance is definitely worth it .  

 You should have a tire pressure gauge and tread depth indicator  in your car so you can monitor the pressure when you put air in your tires and also measure tread often to see how the tires are wearing.

I use these to measure  FFH/CMAX tire wear also have digital tire pressure gauge too.   

  Paul

[ptjones]

Time to use Physics.

I tested stopping distances for 30 mph at 35 psi and 50 psi. There doesn't seem to be noticeable difference between the two, At 35 psi the front tires are under inflated wearing on the outside of the tread and leaving tire marks on the concrete.

The rears show no wear pattern.

At 50 psi the fronts are working great with no tire marks, but the rears are using the ABS to keep from locking up. If stopping distance was the only consideration you would put 50 psi in the fronts and 35 psi in the rears, but I doubt  you would gain more than a couple feet.  The Big Picture Here Is You Can Use 35 psi to 50 psi With No Significant Difference In Stopping Distance And Tire Pressure Isn't A Safety Issue!  And Again I'm Only Putting Out There The Experiences and Facts That I Have Found From My Testing and Members Can Decide What they Want To Try Out If Anything, I'm Not Telling Anyone To Do Anything!  BTW I have 233k miles on MADMAX, must be doing something right.  

 

I found a problem in that not all tire pressure gauges are created equal.   I have been using a Slime Pen gauge and it turns out it reads 2 psi high as compared to ACCUTIRE, TEKTON and Slime Digital gauge. Slime Sport digital gauge reads another 2 psi lower. It is important to have an accurate tire pressure gauge.  Digital pressure gauges sell for $10 to $20. The three center ones seem to be accurate.

 

 

Tire wear also shows you also how the tire is wearing front to back too, there is no difference with side to side.   

This Michelin ES has 95k miles with even  tire wear at 50 psi. , inside edge 2/32nd, center 3/32 nd and outside edge 3/32 nd 

 

    Here is a visual demonstration from the Tire Rack on tire pressure vs tire contact area. This same thing happens when you try to stop fast, 70+% of the weight of the car transfers to the front wheels making them go under inflated. https://www.tirerack...ge.jsp?techid=3  You can have a large contact area and less traction do to the center of the tire losing contact pressure.  You need to have more pressure to compensate for the added weight for the best stopping traction.

TIRE TECH: AIR PRESSURE VS. WET PERFORMANCE

(Lea en español)

Most drivers realize that tire load capacity is determined by tire size and inflation pressure. Larger tires and higher inflation pressures provide more load capacity, while smaller tires and lower tire pressures provide less.

An under-inflated tire will tend to wear the shoulder areas of the tread faster than the center. This is because there is insufficient air pressure to allow the center of the tread to carry its fair share of the weight. A correctly inflated tire receives appropriate support from the contained air pressure to provide an even distribution of load across the footprint. And while most drivers recognize that this has a significant impact on tire wear, rolling resistance and durability, only a few realize it also has a noticeable influence on how effectively the tires can resist hydroplaning to maintain wet traction.

As they taught us in physics class, you can compress and move a gas quite easily, but you cannot compress liquids and it requires significant energy to move them. Our tires easily push air around and through their tread designs as they roll. However, when water pools in highway ruts and builds up on the road surface during rainstorms, the vehicle's speed and weight, as well as the tires' tread designs, tread depths and evenness of their footprint pressures determines if and when the tires will be forced to hydroplane.

One of the ways tire manufacturers evaluate their products' hydroplaning and wet traction effectiveness is by driving them over a glass plate covered with a specific depth of water. The water is dyed for better visibility and to allow high-speed cameras in underground rooms to photograph the tires from below. Michelin has provided several photographs of its HydroEdge premium All-Season tire to help illustrate this tech feature.

Photo #1

Photo #2

Photo #3

Photo #4

The first photograph shows a tire properly inflated to 35 psi sitting still in the water on the glass plate. This provides an accurate idea of the tire's footprint size and shape.

The black area is where the tire's rubber compound is pressed on the glass, and the green areas identify water in the tire's circumferential and high-angle lateral grooves, and on the remainder of the glass plate.

A properly inflated tire will have enough pressure in the center of its tread to resist collapsing.

The second picture is of a tire properly inflated to 35 psi, driving across the glass at 60 miles per hour. If the glass plate were dry, the footprint size would be virtually identical to the first picture because air does not prevent the tread from contacting the plate. However, with standing water on the plate, the tire's tread depth and tread design must evacuate the water as the tire rolls across the plate at 88 feet per second. You will notice that the footprint still shows good contact with the plate, but is slightly smaller than the static tire's footprint.

A tire that is slightly under-inflated will apply less pressure to the center of the tread and it will become slightly concave.

The third picture is of a tire inflated to only 30 psi, again driving across the glass at 60 miles per hour. With the same amount of standing water on the plate, the center of the tire's tread is lifted as the tread design unsuccessfully attempts to evacuate water as the tire rolls across the plate. You will notice that the actual footprint shows poor contact with the plate and is significantly smaller than the footprint in the photograph of the properly inflated tire.

A tire that is significantly under-inflated will allow the center of the tread to collapse and become very concave, trapping water rather than flowing it through the tread design.

The final picture is of a tire inflated to only 25 psi, driving across the glass plate at 60 miles per hour. With the same amount of standing water, the water lifts the center of the tire's tread as its footprint rolls across the plate. You will notice that the actual footprint shows little contact with the plate and has been virtually reduced to the shoulder areas.

Members of the Tire Rack team had the chance to experience the effects of air pressure on wet performance at Michelin's Laurens Proving Grounds. Drivers were given the opportunity to compare identical cars on a wet-handling course with the exception of one car having four properly inflated tires (35 psi) and the other car having significantly under-inflated tires on the rear axle (25 psi).

While driving at the edge of a tire's ability in wet conditions is challenging, the car with the properly inflated tires provide handling that was predictable. Driving the car with the under-inflated rear tires proved to be much more difficult to drive and forced the driver to slow down to retain control, producing lap times that were several seconds slower than the properly inflated car.

While tire manufacturers can develop tires with great hydroplaning resistance and wet traction, poor maintenance of tire inflation pressures can make a great tire awful.

Given this example I think would have to go to 40 psi to get similar results with Energy Savers.

 

Paul

[markd]

I opted for the middle and run at 45psi.

[ptjones]

Sounds like a good plan, I'm pushing for MPG's so I went for 50-48 psi.  :)

 

Paul

[SnowStorm]

Just a reminder that Michelin also makes an Energy Saver A/S 94V that is only rated to 44 psi.  Make sure you have the Energy Saver A/S 93V if going above 44 psi.

Edited September 2, 2019 by SnowStorm

[ptjones]

Don't buy the 94V ES, they cost more and don't get as good MPG's, I don't think any manufactures use them.

 

Paul

[pianewman]

ptjones: I've just scanned again your very interesting post. Maybe I'm missing something.

 

I totally agree that the doorjamb recommended PSI is low. How low is always open to debate, and how HIGH go is always worthy of discussion. I'm amused by your claim: "Note: Tires aren't very sensitive to pressure, if you go up to 40 psi you will probably not notice a difference.  At 45 psi you will notice a little difference and 50 psi a little more". I notice significant differences when raising PSI, even in small amounts. Maybe it's the rock-hard rough aggregate concrete roads around here!

 

I'm curious about the trend here toward PSI at or near the sidewall limit. After 45 years of driving a wide variety of cars, trucks, bicycles, I avoid getting anywhere close to the sidewall max PSI, because of my fear of loss of traction at higher speeds due to limited tread contact. (fyi, my 2012 and 2014 Passat TDIs, with both OEM Contis and replacement Contis would NOT tolerate PSI above 40, as the vehicle would "tramline")

 

ptjones: I'm curious why your Michelin photos only show 35 psi and less, and don't show the footprint with elevated PSI.

 

I can't find the specific post/thread over at TDIClub, but more than one member (IIRC) claimed, after years of autocross experience, that PSI close to the sidewall max created adverse traction when pushing higher speeds. I also recall one member commenting that the clubs he races with closely monitor PSI, and prohibit PSI levels close to the sidewall max.

 

For those of you driving at or near max PSI, I assume you've not actually experienced emergency maneuvers that felt compromised by the higher PSI. I consider myself a very assertive (I drive quickly), but attentive driver, avoiding dozens of potential accidents by simply scanning way ahead, and in my 48 years of experience, I've actually locked up the brakes fewer than 10 times, so I don't honestly know how I can compare. 

 

Thanks for a very informative thread. FYI, I will continue to keep my tires about 5-8psi lower than the sidewall limit.

[ptjones]

ptjones: I've just scanned again your very interesting post. Maybe I'm missing something.

 

I totally agree that the doorjamb recommended PSI is low. How low is always open to debate, and how HIGH go is always worthy of discussion. I'm amused by your claim: "Note: Tires aren't very sensitive to pressure, if you go up to 40 psi you will probably not notice a difference.  At 45 psi you will notice a little difference and 50 psi a little more". I notice significant differences when raising PSI, even in small amounts. Maybe it's the rock-hard rough aggregate concrete roads around here!

 

I'm curious about the trend here toward PSI at or near the sidewall limit. After 45 years of driving a wide variety of cars, trucks, bicycles, I avoid getting anywhere close to the sidewall max PSI, because of my fear of loss of traction at higher speeds due to limited tread contact. (fyi, my 2012 and 2014 Passat TDIs, with both OEM Contis and replacement Contis would NOT tolerate PSI above 40, as the vehicle would "tramline") I have been driving for 51 yrs. which included SCCA Racing a 86 SVO Comp Delete Mustang in the late 80's. There is a miss conception that larger tread contact area gives more traction which isn't true.  As you can see in Post #1 in the Hydroplaning pics larger contact patch doesn't improve traction. The ideal situation for a given tire is the pressure that gives even pressure per square inch over the contact area. This pressure will give you even tire wear. For the Michelin Energy Saver I think 45-50 psi seems to be the best with our wheels.

 

ptjones: I'm curious why your Michelin photos only show 35 psi and less, and don't show the footprint with elevated PSI. I actually made thread prints on paper that showed the contact area get a little smaller at 50 psi and like I said contact area is only part of the story.

 

I can't find the specific post/thread over at TDIClub, but more than one member (IIRC) claimed, after years of autocross experience, that PSI close to the sidewall max created adverse traction when pushing higher speeds. I also recall one member commenting that the clubs he races with closely monitor PSI, and prohibit PSI levels close to the sidewall max.

 

For those of you driving at or near max PSI, I assume you've not actually experienced emergency maneuvers that felt compromised by the higher PSI. I consider myself a very assertive (I drive quickly), but attentive driver, avoiding dozens of potential accidents by simply scanning way ahead, and in my 48 years of experience, I've actually locked up the brakes fewer than 10 times, so I don't honestly know how I can compare. I would consider my Stopping Distance Testing Emergency Stopping although I have had some Emergency maneuvering situations and MADMAX Handled Great!

 

Thanks for a very informative thread. FYI, I will continue to keep my tires about 5-8psi lower than the sidewall limit.  So it sounds like you are using 43-46 psi.

Remember I talked to a Michelin Rep and he said if you are getting even tire wear at 50 psi. they said that was fine with them.

 

Paul

[fbov]

... After 45 years of driving a wide variety of cars, trucks, bicycles, I avoid getting anywhere close to the sidewall max PSI, because of my fear of loss of traction at higher speeds due to limited tread contact. (... "tramline")

... more than one member (IIRC) claimed, after years of autocross experience, that PSI close to the sidewall max created adverse traction when pushing higher speeds. I also recall one member commenting that the clubs he races with closely monitor PSI, and prohibit PSI levels close to the sidewall max. ...

I'm curious what "tramline" might be? Only thought is driving on trolly tracks, lumps of polished steel that rubber slides off when wet. 

 

40 years ago I went to my first autocross. A few years later, it was drivers' school at Watkins Glen (became an instructor). We set tire pressure based on what each tire told us it needed, anywhere between 25 and 45 psi, depending on tire design. We were competing, so we knew all about too-much pressure... this wasn't too much. All rookies had to up their front pressures to insure the tire would stay on the wheel long enough for them to learn from their mistakes. This was in an era of 44 psi sidewall limits, so folks didn't keep them that high... except those of use still within the sidewall limit. 

 

So, I've been running my tires at sidewall rating since then. Nothing adverse that I can blame on the tire. Same with the snow tires. 

 

And be aware that a tire's load limit is only available at rated pressure. If you run 10-20 psi lower than rated, you have a much lower load limit and will tend to heat up more. Look up "Ford Explorer Firestone tires." From Wikipedia...

"The Explorer weighs more than the Ford Ranger and has a higher Gross Vehicle Weight Rating (GVWR) while also having a lower recommended tire pressure.^[2] This difference in weight and tire pressure explains why Ford Explorers had far more tire failures than Ford Rangers even though they used the same tire models."

 

The only possible reason a club would limit pressure is because they are a track club where sessions last for long periods of time (not a 60 sec. autocross run). Tires get very hot and air pressure inside rises tremendously. It's why racers use dry air or N2, so moisture isn't a factor.

 

 

I just want folks to make informed choices. 

 

HAve fun,

Frank

[C-MaxA2]

I used to run cross country and track in college and we had a coach who would have us (as a warm up and strengh exercise) push his VW Bug. My family had a Bug and I tried raising the tire pressure to see how much difference it made on pushing.  A LOT.  I was shocked and the coach didn't notice at first and praised us for a 'super' effort. Eventually he noticed. And he left the tire pressure there and said he got better gas mileage (he had a long commute). 

 

I've always kept my tire pressure high. In my garage I occasionally put my car in neutral (5 speed) and if it doesn't roll slightly I check the tire pressure,  If it doesn't roll then it's almost inevitably too low for my liking. 

 

Just driving out of our neighborhood I can notice higher pressure - the car clearly rolls better. 

 

I run my C-Max (with Michelins) at 50 pounds.  Michelin's fine with it (I called and asked) and neither my wife or I feel the ride is at all uncomfortable.  We hover around 49-50 mph spring/summer/fall. 

[grege]

I used to run door-placard-manufacturer-recommended tire pressures until a couple years ago.  I now use the max. tire pressure (as indicated on the sidewall).  What amuses me is being told to use "cold" tire pressure settings.

 

Should that technically mean using the coldest temperature of the day???  For example, in winter, naturally, the coldest part of the day is early in the morning, so should cold tire pressure be set relative to that or relative to some benchmark air temp??? (32F, 50F, 71F, ... ???  

 

Somewhat minor and a bit anal I know, but an interesting question for me, espeicially given that every 10F-degreee swing in air temperature changes tire pressure by  ~1psi. 

 

And then sun exposure is a whole-nother animal!  Just yesterday (mild temps), my morning pressure on a different vehicle was 34psi; an hour later (as the sun came up), pressure was already reading 38psi.  Crazy, but cool. 

 

Greg  

[pianewman]

Great points, all! I am losing my fear of approaching sidewall max PSI. I'll have my lawyer contact you when I lose traction and wrap my car around a tree! HAHA!

 

"Tramline" is what the FE tech called it, when the front end wants to wander with or climb any trough on the (usually) asphalt surface, usually near a traffic light. Also at cruising speed, the car would wander, even when the alignment was dialed in correctly. 

[ptjones]

Great points, all! I am losing my fear of approaching sidewall max PSI. I'll have my lawyer contact you when I lose traction and wrap my car around a tree! HAHA!

 

"Tramline" is what the FE tech called it, when the front end wants to wander with or climb any trough on the (usually) asphalt surface, usually near a traffic light. Also at cruising speed, the car would wander, even when the alignment was dialed in correctly. 

I know of one mechanic that was using 55 psi with his CMAX and the bursting pressure is around 200 psi. :)

 

Paul

[pianewman]

Not worrying about bursting pressure, worried about traction loss "at the limit".

 

Another thought: Track experience, with newer (?) smoother (?) pavement isn't the same as real world pavement. On a less-than-smooth road surface, are higher PSI tires more prone to wheel hop, at the limit, than a more moderately inflated tire?

 

...of course...YMMV...

[ptjones]

Not worrying about bursting pressure, worried about traction loss "at the limit".

 

Another thought: Track experience, with newer (?) smoother (?) pavement isn't the same as real world pavement. On a less-than-smooth road surface, are higher PSI tires more prone to wheel hop, at the limit, than a more moderately inflated tire?

 

...of course...YMMV...

I have more traction at 50 psi than 38 psi and I have never seen wheel hop with this car. We have ABS brakes and Traction control.

 

Paul

[fbov]

Not worrying about bursting pressure, worried about traction loss "at the limit". ...

Then consider these points about static and dynamic behavior. 

 

Static 

There are a couple relationships involved here.

 

Pascal's Law tells us the force caused when pressure is applied to a surface. F = P x A for area A. 

- Force is the sprung weight on the tire's axle, plus the wheel and tire

- Pressure is the "normal" force in the friction calculation, a measure of how hard the tire bites the road

- Area is variable as pressure varies. 

 

The dry friction equation ( F = u x N) relates this "normal" force (N) to traction (F), through a "coefficient of friction (u)."We'll assume the friction coefficient is constant (this is where road surface matters). We'll also assume a level surface, no hills. 

 

The trick is that pressure changes affect the normal force, how much force is applied to the road by the tire. As pressure rises, contact area falls, but normal force increases by exactly the amount needed to maintain the same maximum friction. In a straight line, there's a small effect; braking and acceleration aren't very sensitive. Lateral acceleration is another story. 

 

Dynamic

All consumer vehicles have more traction laterally than in a straight line, and all tires create traction by slipping. Let's look at what happens when you turn the wheel. 

 

Tire are never pointed where you're going, they're pointed past it, so they can slip a little and still get you the turn you expect. The chart shows how the amount of slip varies as you ask for more traction. 

- the slope of this line changes with tire design and rubber compound.

Race rubber gets very steep while consumer tires are shallow. 

- the roll-over before max. traction is due to geometry changes in the tire.

Race tire sidewalls are very stiff and fall off a cliff at the limit, while consumer tires deform and only drop slightly.

 

Tire pressure will change a tire's behavior as you approach max. traction. 

 

Maximizing traction is all about keeping the tread on the road. At low pressure, the tire will deform significantly and the tread will lift off the road and traction will fall. At high pressure, deformation is much lower, but contact area diminishes eventually. In both cases, the tire tells the tale. At too-pressure, you'll see treadwear on the sidewall of the tire. That's bad. At too-high pressure, you'll wear-out tires in the center. That's bad. too.  

 

Optimum tire pressure maintains tread contact with the road under high slip conditions (hard cornering). From many users here, we know 50 psi isn't too-high or folks would report tire wear issues. You can find the low-pressure limit by marking the edge of your tread with white shoe polish, and doing donuts in the parking lot. You want it removed from tread area, but just to the edge. 

 

Make sense? Similar arguments apply to snow tires. Only a few odd cases where it doesn't (eg. dragster wrinkle-walls). 

 

Have fun,

Frank

[grege]

I know of one mechanic that was using 55 psi with his CMAX and the bursting pressure is around 200 psi. :)

 

Paul

 

A friend of mine used to drag-race cars during his misspent-youthful years.  Racers would often safely pump and run tires at 3 times the max-rated pressure.  Not sure about ideal conditions (temperature, sun, track surface) for that because I'd expect slightly lower pressure would grip better, especially for shorter runs.    

 

Greg

[pianewman]

fbov: Excellent post. It's nice to see a real analysis of tire/traction dynamics. 

 

There have been so many developments in tire design, QC, suspension design, traction control, ABS, etc, that the principles taught in the 60s and 70s, when I learned to drive, require similar updating. I get that. I also appreciate and respect the experiences of several here that have posted about positive results while driving on maximum sidewall PSI.

 

To further flog this horse, though, I'd like to highlight and add to 3 of your statements: 

 

"We'll assume the friction coefficient is constant (this is where road surface matters). We'll also assume a level surface, no hills There are 2 assumptions in this that are exactly the variables that I'm addressing: road surface, slope, hills. We all have to take into consideration these variables. Someone driving on the ribbon-smooth Autobahn has very different traction dynamics than on poorly designed and maintained US road surfaces (as always, "YMMV" applies here!)

 

In a straight line, there's a small effect; braking and acceleration aren't very sensitive. Lateral acceleration is another story. Again, taking into account the infinite variables of road surface, etc, I'd offer that the risk of loss of traction is greater at higher inflation.

 

... the slope of this line changes with tire design and rubber compound. Yet another variable. We all know from experience the broad range of traction differences of different tires.

 

Again, I respect the experiences of others here, and that they've not experienced traction loss attributable to PSI, because of traction control, ABS, etc. I'm not confident, though, that max sidewall PSI is advisable across all brands of tires. 

 

FYI, with my 2015 Nissan Leaf, I have experienced substantial wheel hop/loss of traction AND BRAKING (ABS gets confused) when braking aggressively on an irregular road surface. The first time this occurred was terrifying, and I have since learned to be aware of this tendency. It is because of this that I've become more interested in optimum PSI, to minimize the wheel hop while braking. I'm confident that, with this vehicle, and with these tires (Bridgestone Ecopia Plus) that PSI LESS than max works best, although I know I could maximize MPG and treadwear life by raising the PSI.

 

...and yes, I know...this thread is about Ford Hybrids, and I shouldn't assume the experiences posted here are universal across all vehicles and tire brands.

 

Thanks again for an enlightening thread. I've learned a lot.

[plus 3 golfer]

...

 

Again, I respect the experiences of others here, and that they've not experienced traction loss attributable to PSI, because of traction control, ABS, etc. I'm not confident, though, that max sidewall PSI is advisable across all brands of tires. 

 

...

and maybe even the E/S. :) ;)

 

I posted a link to a very lengthy NHTSA report on the Pneumatic Tire - It's somewhat dated but the principles and laws of physics don't change.  Lateral forces, sidewall stiffness, and psi are linked.  We don't know what psi is best for cornering (handling lateral forces).

 

Based on my experience with the E/S, Ecopia Plus, and General AltiMax on my C-Max, I believe that the PSI for best cornering is not the same for each tire and not the maximum pressure.  As the link states at some PSI the cornering stiffness peaks and starts to decline as PSI is increased.  So there is likely a point at some PSI after peak stiffness that increasing lateral forces and declining cornering stiffness will cause the tire to slide.

 

Again based on my experience, the AltiMax is the best performing tire of the three in cornering and in wet conditions, the E/S next and the Ecopia far behind the other two.  There is a very short on-ramp merge lane with a curve just prior to getting on the freeway. One has to have quite a bit of speed around the curve to merge seamlessly with the fast moving traffic. The Ecopias appeared to slide a lot at 50 PSI (as I increased psi thinking that would solve the sliding) but I settled on around 44 psi, the E/S slid somewhat at 50 PSI (at very high speed), and the AltiMax virtually no sliding at 50 PSI.  Of course add wet pavement, and the sliding gets worse for the E/S.  I did not trust the Ecopia in dry or wet conditions in emergency handling situations at any PSI.  The E/S dry emergency handling seemed OK but not the wet handling for me.

 

Tire Racks tests of these three tires seems to support what I experienced.  Consumer's rate the AltiMax significantly better than the other two in handling.

 

Of course, I understand some value ride quality, cost, or maximizing FE above handling and choose brand and model based on such.

 

[fbov]

fbov: Excellent post. ...

 

...I'm not confident, though, that max sidewall PSI is advisable across all brands of tires. 

 

FYI, with my 2015 Nissan Leaf...

Thanks for the compliment. While I agree that max sidewall pressure will not give you peak traction, it is still advisable across all brands of tires, if you're looking for minimum rolling resistance. Most drivers of unconventional drivetrains understand the huge effect of parasitic loses, and the primary ones are aero drag and rolling resistance. 

 

The reason suboptimal traction is OK, is that traction varies tremendously on a continuous basis, as road surface changes. You adapt to that very quickly if you're a good driver. And unless you test and adjust your tire pressure every day to verify you're at today's optimum pressure, you're always suboptimal. That makes the failure modes important. At too-low pressure, the tire rolls and the tread lifts, and traction disappears, or the tire gets hot and disintegrates (Ford's Explorer problem). At too-high pressure, the tire slides, but remains in contact so the driver retains far more control, with no risk of overloading. Easy choice.  

 

Lower tire pressure will give smoother ride over your poorly maintained roads. Given the braking problems you describe, you may need very low pressures to see improvement. Changing tires might help, but the fix is in upgraded shocks, to change the suspension hop resonance. 

 

... I believe that the PSI for best cornering is not the same for each tire and not the maximum pressure.  ...

Very true.

 

When I was autocrossing, pressure varied from 25-45 psi depending on the tire design. Normal street tires ran close to 45/35 front/rear. Then BFG introduced asymmetric-sidewall tires that wouldn't roll at 25 psi. The trick was that every event, you would want to check tire pressures every run so you could tweak it for the next run. It wasn't unusual to move 2-4 psi due to weather and course conditions. 

 

The argument for sidewall rated pressures still stands. 

 

Have fun,

Frank

[plus 3 golfer]

FWIW, below is a table of Rolling Resistance force of selected tires measured on a dynamometer in pounds by Consumer Reports.  Of course, ones RR force will be higher numbers because actual road surfaces are not steel and smooth. There are tables that show the approximate % difference from a smooth concrete surface (should be close to steel).  But the % difference in force between tires should be the same as the % difference in RR when comparing tires.  The NHTSA document linked below shows that for a 10% decrease in RR, FE increases by about 1% - which is based on the EPA FE cycles. So, if my FE with my AltiMax tires dropped about 2% from the E/S tires, the E/S pounds should be 20% lower than the 9.4 pound or around 7.5 pounds which would be the lowest number if on the table.

 

Here's the NHTSA link to download a report on testing of tires related to rolling resistance and its effect on FE, dry traction, wet traction and so forth.  Very good read. Now, I -know why the E/S wet traction is worse than my AltiMax tires. :)

 

[fbov]

I notice the top tire in the CR table, and three others, are part of a Tire Rack test. They're listed in the same order... partly by chance; the middle two are tied. 

https://www.tirerack.com/tires/tests/testDisplay.jsp?ttid=231

 

Continuing the thought, I looked for other popular tires that might have a TR test, and sure enough, there's one with four from the table, including a repeat from above. 

https://www.tirerack.com/tires/tests/testDisplay.jsp?ttid=237

 

Now thing are muddled; TR reports 1% differences between tires that are effectively equal RR on the CR chart, 10.0, 10.1 and 10.2. Still a ~1% effect, though. 

 

HAve fun,

Frank

Edited October 4, 2019 by fbov