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

[Waldo]

Also Your tire pressure should change with Gross Vehicle Weight . There is no info in OM about changing tire pressure unfortunately. ;(

Paul

 

This is not true. The Ford recommended sticker pressure accounts for the max GVW that, not-coincidentally, is printed on the same sticker. You can run a vehicle perfectly safely at the GVW rating with the recommended pressure. Of course this does just prove the compromise that goes into the recommended sticker pressure. It also indirectly means that when you're running less than GVW you can probably run below the recommended pressures perfectly safely, although nobody including myself would ever recommend this.

 

Here are some of the factors that go into the OEMs recommended tire pressure in no particular order:

 

Fuel economy (must meet CAFE regulations)

Tire load capability at max GAWR & GVW

Ride

Steering feel

Braking distance

Top speed

Tire wear

Emergency handling both loaded and unloaded

Suspension loading

Pothole damage prevention

 

Just about every characteristic of a tire is non-linear, meaning that for each of these factors, there is an optimum pressure where going higher makes it worse and going lower makes it worse. It would be virtually impossible for the optimum pressure of each factor to be the same, therefore compromises have to be chosen. That optimum pressure will also depend on the tire itself, the vehicle, the suspension design, the conditions of the roads, the external temperature and such. Since we will never really know the priorities of the OEM, all we can do is experiment on our own to see what effect changing the pressure has on our own priorities.

 

We must be sure to remember though that changing the pressure to optimize one of the factors is going to mean a reduction in performance of several other of the factors. Without easily being able to quantify those reductions, we have to assume there is a level of risk in varying from the OEM recommended pressure.

[ethermion]

Cripes sakes. Not this again, again, again.

 

Fact: Ford says follow the sticker in the door.

 

Fact: Michelin (stock tires) says follow the sticker in the door.

 

Fact: Goodyear (my tires) says follow the sticker in the door.

 

Fact: Bridgestone/Firestone (largest tire manufacturer in the universe) says follow the sticker in the door.

 

Fact: PT does not own a FFH.

[Timewellspent]

[Waldo]

FACT: If you just do everything you are told, you will miss out on a lot in life.

[Cobra348]

Wow. A whole thread on this dead (or dying) horse? I refuse to severely over-inflate my tires as it decreases the contact patch that is instrumental in stopping the car. Do I over-inflate? Yes, to 40 PSI cold - because I'm too bloody lazy to check pressure more often than 3 months. But ...

 

Ford does state on the sticker the pressure to run

 

Ford does state in the OM what pressure you should run

 

My tire dealer (Goodyear) also states that it is recommended to run OEM pressures.

Edited August 21, 2019 by Cobra348

[md13ffhguy]

FACT: If you just do everything you are told, you will miss out on a lot in life.

While I totally get the "dead horse" sentiment... I really like this post. Good on pt for trying something different and being happy!

 

On the other hand, I just don't understand the complete and utter obsession with posting about it and suggesting that others do the same. There is little way the benefits outweigh the risks... But, to each his own.

[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

Edited September 1, 2019 by ptjones

[ptjones]

 

Edited September 1, 2019 by ptjones

[billford]

Checked tire wear on a friends 2017 fusion with 75k energy savers. Car does a mix of highway and city.
Pressures are always set to 35 psi according to the door sticker and verified with the pressure readouts on the dashboard so you cant argue the tire pressure gauge is out of calibration.

At 35 psi, there is slightly more wear in the middle than the edges. So, it seems like 35 is the ideal pressure for a Fusion.

Edited October 25, 2019 by billford

[ptjones]

I wonder what the other tires looked like on the car, all the FFH I checked were wearing more on the edges. I had 95k miles on my tires. :) Apparently having 50 psi makes tires last longer. BTW in Post #8 it shows under hard braking the sidewalls touch the pavement, this is not good for the tires, they aren't designed to do that, 45-50 psi will safely keep the tire from wearing on the sidewall.

 

Paul

Edited October 25, 2019 by ptjones

[billford]

All are wearing the same, as they are rotated regularly. The middle of tire has almost 1/32 more wear at 35, so If he was using 50, I would guess the middle of the tire would be worn out right now. 35 looks like it ideal.

[ptjones]

All are wearing the same, as they are rotated regularly. The middle of tire has almost 1/32 more wear at 35, so If he was using 50, I would guess the middle of the tire would be worn out right now. 35 looks like it ideal. Interesting that I'm using 50 psi and center isn't wearing faster than the edge and the tires are lasting 20k longer.

OM also says 35 psi is the minimum pressure to use, a logical person would give themselves some leeway as other members have commented using 40-45 psi. I have shown at 35 psi under hard braking tests in Post #8 you are running on the sidewalls of the front tires which is much thinner than the tread and easier to puncture making it much more dangerous in those situations. If you have a blowout under hard braking you turn a bad situation into a life threatening situation with loss of control of the car. 45-50psi is much safer in emergency stops as I have shown in my testing, 35 psi is not .

 

"billford" you aren't recommending members use their sidewalls of their tires for stopping are you? It sure sounds like it when recommending the minimum tire pressure of 35 psi.

 

Paul

Edited October 25, 2019 by ptjones

[billford]

I'm not recommending anything

I just posted pictures of tread measurements on a 2017 Fusion Hybrid with original 75k tires that have always been set to the door sticker at 35 psi, rotated regularly, and has resulted in slightly more wear (less than 1/32) in the center part of the tread.

Edited October 25, 2019 by billford

[ptjones]

I'm not recommending anything

 

I just posted pictures of tread measurements on a 2017 Fusion Hybrid with original 75k tires that have always been set to the door sticker at 35 psi, rotated regularly, and has resulted in slightly more wear (less than 1/32) in the center part of the tread.

Actually you said" So, it seems like 35 is the ideal pressure for a Fusion." So that sounds like you are recommending 35 psi is the ideal pressure to use. Even though OM said it is the minimum pressure and My testing shows you will be running on sidewalls of the tire under hard braking, not good, safe or ideal. My tires at 50 psi lasted 20k miles longer and improve mpg's by 1.5 mpg paying for half a set of new Michelin ES tires at replacement time. Win,Win, :)

 

Paul

[billford]

I'm not telling others what pressures to use.

 

Based on the pictures I posted, 35 seems like its the ideal pressure for this 2017 Fusion Hybrid.

You wrote earlier:

 

 

 

Talking to Michelin Rep they recommend starting with FORD's recommended pressure and then find the pressure that gives even tire wear.

 

 

By the pictures I posted, it has even wear within less than 1/32 at 35 psi as verified by the depth gauge, by the dash readout and pressure gauge. So, based on that, your Michelin rep and the door sticker, the pressure to use on this 2017 Fusion is 35.

All I did was to post my experience on the topic. People can make their own decisions.

Edited October 26, 2019 by billford

[ptjones]

I'm not telling other what pressures to use.

 

Based on the pictures I posted, 35 seems like its the ideal pressure for this 2017 Fusion Hybrid.

 

You wrote earlier:

"Talking to Michelin Rep they recommend starting with FORD's recommended pressure and then find the pressure that gives even tire wear"

 

By the pictures I posted, it has even wear within 1/32 at 35 psi as verified by the depth gauge, by the dash readout and pressure gauge.

You haven't commented on running on the sidewalls at that pressure, you actually think that is a safe thing too do? Or that I have shown better tire wear using 50 psi.

I started at 38 psi and got more wear on the edge so I ended up at 50 psi and Michelin Tire Rep said was the best given I was getting even tire wear. I will stick with Michelin Rep's advice. :)

 

Paul

Edited October 26, 2019 by ptjones

[billford]

You haven't commented on running on the sidewalls at that pressure, you actually think that is a safe thing too do? Or that I have shown better tire wear using 50 psi.

I started at 38 psi and got more wear on the edge so I ended up at 50 psi and Michelin Tire Rep said was the best given I was getting even tire wear. I will stick with Michelin Rep's advice. :)

 

Paul

All I did was contribute to the thread and posted pictures of a 2017 Fusion Hybrid with even tire wear that has been set to 35 psi all its life.

 

People can make their own decisions on their Fusions as you made your decision of what psi to use for your Cmax.

 

If the pictures are off topic or causing a problem with you, I can delete them if you wish.

Edited October 27, 2019 by billford

[Waldo]

You haven't commented on running on the sidewalls at that pressure, you actually think that is a safe thing too do? Or that I have shown better tire wear using 50 psi.

I started at 38 psi and got more wear on the edge so I ended up at 50 psi and Michelin Tire Rep said was the best given I was getting even tire wear. I will stick with Michelin Rep's advice. :)

 

Paul

 

Paul, ever since the Firestone debacle Ford has been VERY VERY careful about how they test and recommend tire pressures. There is absolutely zero chance that the recommended pressure is ever going to have any kind of SAFETY issue. 35psi is not the "minimum" pressure, it is the "recommended" pressure. Ford already builds in several different safety factors into that recommendation. You are not going to blow out a sidewall under heavy braking with 35psi. That is the most ridiculous statement of all the ridiculous statements you've made on this subject.

[ptjones]

 

Paul, ever since the Firestone debacle Ford has been VERY VERY careful about how they test and recommend tire pressures. There is absolutely zero chance that the recommended pressure is ever going to have any kind of SAFETY issue. 35psi is not the "minimum" pressure, it is the "recommended" pressure. Ford already builds in several different safety factors into that recommendation. You are not going to blow out a sidewall under heavy braking with 35psi. That is the most ridiculous statement of all the ridiculous statements you've made on this subject. It isn't a ridiculous statement when the facts show it to be true. FORD has made other statements that aren't true like the gas mileage for one. :)

Why are you ignoring MY tire test? You complained about me not testing and then when I do you ignore it. What's up with that? My testing plainly shows the tire compressing down about an inch on the side of the tread,( scuff marks on the side of the tread in Post#8). That isn't a good thing and exposes the sidewall to potential blowout from running over debris. Only time you would use emergency braking is in a emergency like accident, debris on the road ect. Why are you ignoring the OM, it also says minimum pressure is on the door sticker. Firestone failure was caused by heat from running tire pressure too low, you know that, I'm talking about the tire compressing more than it should at 35 psi and exposing the sidewall of the tire. This doesn't happen at 50 psi. BTW. The sidewall is thinner then the tread. I can't believe you are telling me it's OK to run on the side of the tire under emergency braking, that doesn't make any sense.

 

Paul

[Waldo]

Why are you ignoring MY tire test? You complained about me not testing and then when I do you ignore it. What's up with that? My testing plainly shows the tire compressing down about an inch on the side of the tread,( scuff marks on the side of the tread in Post#8). That isn't a good thing and exposes the sidewall to potential blowout from running over debris. Only time you would use emergency braking is in a emergency like accident, debris on the road ect. Why are you ignoring the OM, it also says minimum pressure is on the door sticker. Firestone failure was caused by heat from running tire pressure too low, you know that, I'm talking about the tire compressing more than it should at 35 psi and exposing the sidewall of the tire. This doesn't happen at 50 psi. BTW. The sidewall is thinner then the tread. I can't believe you are telling me it's OK to run on the side of the tire under emergency braking, that doesn't make any sense.

 

Paul

 

I didn't ignore your test, I just came to a different conclusion. I don't see any wear on the sidewall, only the outer blocks of the tread. "More than it should" is your interpretation, it would have compressed the same amount when tested multiple times by actual Ford and Michelin engineers and they have all determined there is no safety issue. You're stretching and trying to nit-pick small details to support your opinion while ignoring the bigger picture.

 

Ford engineers are not a bunch of dummies, they didn't go through the Firestone thing and just say "oh, let's make sure we don't have a situation where a low pressure causes a heat build up" and not improve the process for everything else concerning tires. Ford instituted some very conservative processes related to all things concerning tires so you can be 100% sure that the recommended tire pressure will be safe under EVERY circumstance.

[ptjones]

Here is a very obvious pic of emergency brake test on flat cement pad at 35 psi., you can easily see scuff marks on the side of the tread blocks. They weren't there before the test. I have recreated the test by lowering the pressure in the tire to when the side of the tread blocks just touch the cement , I used a post card about .01" thick to tell when the side of the tread block touched the card. At 5 psi. it didn't, but at 4 psi it did. This test was done at 75*F and here are the scary results by measuring the rim height above the cement.

at 4 psi. 1.25"

19 psi. 2.5"

35 psi. 2.9"

50 psi. 3.1"

 

I put my Swiss Army Knife next to tire to give some perspective, it's 5/8" thick which is half the distance of the 4 psi test and running over anything an inch or more in diameter could cause the rim to pinch the sidewall of the tire causing a blowout and loss of control of your car.

 

Here is what it looks like at 4 psi.

Here is what it looks like at 19 psi(15 psi more than 4 psi which = 19 psi) 50 psi is 15 psi more that 35 psi which makes a big difference looking at the pics.

 

At 50 psi you end up with twice the ground clearance of 35 psi. in an emergency braking event which is a lot. I didn't think it would be this bad, but then again this is why I did the testing to get the facts. To me it seems Ford compromised to much for ride smoothness. CMAX is listed at 38 psi minimum pressure, which is an improvement, but given the results of my test I think 45 psi should be the minimum pressure. Michelin determines Max pressure at 51 psi.

 

Paul

Edited November 5, 2019 by ptjones

[Waldo]

OK, I see what you're trying to do. You're trying to establish what the sidewall looks like when under maximum braking. But you're trying to simulate statically what is happening dynamically. You can't do that with a tire, they don't behave linearly. They stretch and contract differently when spinning and with 35psi vs 4 psi. Try to picture that as the center of the tread is reacting to the braking load on the road, it's actually pulling the edges of the tread inwards. If you really wanted to find that sidewall height while braking, a better method would be to find a way to put about 700-800 extra pounds on the front of the car and see how much sidewall deflection there is.

 

You're suggesting that there is some sort of epidemic out in the real world today where people are blowing tires left and right while braking. It's just not happening because it's not a real issue.

[ptjones]

My point is that the tire is going to be pretty close to my test in that you will get maximum G Force when almost stopped. I think you would agree that at 50 psi is safer under those conditions, having 2.5' vs 1.25" rim clearance. The only time this would be a real problem would be running over debris from accident or junk on the road. Actually I don't think people use Max Braking very often, but when you do 45 psi is going to be much safer. In reality we don't have anyway of knowing how many blowouts there have been from using 35 psi. At 50 psi and 238k miles I haven't had one.

 

Paul

[Waldo]

My point is that the tire is going to be pretty close to my test in that you will get maximum G Force when almost stopped. I think you would agree that at 50 psi is safer under those conditions, having 2.5' vs 1.25" rim clearance. The only time this would be a real problem would be running over debris from accident or junk on the road. Actually I don't think people use Max Braking very often, but when you do 45 psi is going to be much safer. In reality we don't have anyway of knowing how many blowouts there have been from using 35 psi. At 50 psi and 238k miles I haven't had one.

 

Paul

 

Please stop making stuff up, 45psi is not going to be "much safer". My point is that when under max braking you're not at 1.25in rim clearance. Measuring statically at 4psi IS NOT THE SAME THING. What your testing has proven is that at the higher pressures, you have less rubber in contact with the road, which means your braking is not as effective and is therefore LESS safe.