Running tires at max sidewall pressure?
 

I came out of the dentist this morning to find a flat tire on the mustang. (I think all fords need to be recalled and the company investigated because of the missing air in my tire. My tire air has been cleverly camouflaged and hidden within the surrounding air by Ford. Anyway, I installed the mini spare and went to a Les Schwab's tire center, because they fix flats for free. They refused to fix it because the tire was worn past legal limits. I knew they were getting thin and have been tire wheel shopping for a few weeks now. I just ordered Bullitt wheels with 255 45 18"'s. Back to the reason for the post. I get home and plug the flat, pressurize it up to 30 psi, car sticker says 36. The rear tires are wearing in the middle, the fronts look even. Car says 36 front and rear. Install repaired tire, go to other rear tire to reduce pressure to match and find it at 44psi. Last week I aired them all to 36, check the fronts and they are also at 43, 44psi. I have 2 digital gages, both read same. About a year ago I had a flat on the X5, same story took it to Schwab's and it came back with 45 psi n each tire. I call them and ask what is up with pumping my tires up to max rating. I get a story about how I will get better gas mileage and longer tire life. I tell him the car manufacturer recommends 36. He says its probably ok to lower them back to 36, but doesn't recommend it. The guy I talked to was not a kid, he is the asst manager and has been there for years. I told him the max press on the sidewall is just the max the tire is rated for and the car manufactures tell you the press you should run based on the weight on each tire and vehicle handling. He still told me I would be better off running at max psi. Am I messed up? is there some new info about running max air?

The manufacturers spend a lot of engineering hours calibrating tire pressures. The pressures listed from the factory are what you should follow unless you deviated substantially from the factory tire.

Based on the wear pattern you describe..... Max pressure is TOO MUCH....

u always go by the door jam. 30-35 is somewhat norm. i've seen upper 30's too. but 40+ is overpressure.

effects of boosting tire pressure is it can support more if you have a alot of payload. like if yer going fully loaded in your minivan on a road trip. it also decreases the contact patch and thus your rolling resistance since there's less contact patch to friction. this goes wonders for your straight line gas mileage, but messes with your braking distance. side effect is that your center tread wears but your sidewalls don't wear as much

You ARE checking them cold, right?

Follow the specs listed on the door.

When I bought my Trailblazer with 15k miles, the dealer put 45psi in the new Michelins (35 or so recommended). Said it would be OK with cross rotation at 5k. Slightly hard ride, but it IS a truck. I have since avoided several hydroplaning adventures while towing, when others around me did not. Now, dead even wear on all four, still 3/32; turned 100k miles today. YMMV.

How could the 'door jamb' psi be taken as the ultimate recommendation ?
Safe guideline, I'd say.

You could set any tire in any application to 35 psi and be OK.
No optimal, but definitely safe.

Tires pressures vary by manufacturer.



KT

I'm wondering the same.
Just put new tires on the gf's ride, and changed from max35psi to max44psi. The installer filled them to 35psi.

The new ones have good grip, but I feel like there is too much effort needed at 35psi while making slow speed turns. Wonder if that affects the power steering system and/or mileage.

I go by the tire rating, instead of the door sticker, as it is supposed to determine the area of the contact patch.
-Summer is usually 38-42 for a smaller contact patch(and less heat), and winter is 34-38.
-The result from a blowout is greater, and greater wear on the suspension, but mileage is #1 for me.

Also contrary to industry standards, I prefer the bald tires in the back because oversteer and a rear blowout is safer. Rebel:D

Les Schwab guy is an idiot.

Worn in the middle = TOO Much pressure..

Simple - Reset the pressures and ask LS to set them per the Manufactures suggestion in the future.

My thoughts exactly.

I always go with the manf. suggested press + or - after watching the tread wear. I only raise the pressure when adding extra heavy loads to trunk. I add air all the time on my truck when hauling stuff or pulling trailers. The max press on the tire sidewall is just that, a max press, usually when at max load. The tire manufacturer can't possibly know what type and weight of vehicle their tire is going to be installed on. The rear tires on the mustang were worn in the middle, but still had tread when we bought it 1 year ago. I rotated them to the front and back again. I stuck with 36 psi on the front and 32 rear. I ordered wheels back in April from speed concepts in Cal. I waited a week without any emails saying they were processing or shipping my order, so I called them to see what the status of my order was, called a dozen times and emailed over a 2 day period without an answer so I canceled the order. I get an email 3 days later from some idiot telling me I was having a heart attack because I could not contact them on good Friday and they were allowed to take a holiday off. He also said he emailed me stating the wheels were on back order, never got the email. Don't buy from Speed concepts, bad BBB rating (checked after I ordered):eek:

I pump the Prius tires to 44 psi for better gas mileage. They are wearing evenly and grip okay. If they were wearing in the center, I'd lower pressure.

Agreed...wear in the center means you're running too much pressure. FWIW, I run my Bullitt Mustang's stock BFG G Force TA's at 34 all around. That's cold, checked with a blue point gauge sold by snap-on. Cheap tire pressure gauges are for entertainment purposes only...

I can't imagine running at 40+psi unless you were specifically doing it for mileage reasons. Tire manuf are putting their MAX on the tire, that's max, not recommended. I think the guys at Les Schwab are idiots.

My opinion, I think you'll get the best compromise of performance, mileage, wear, etc... out of something in the 30-35 range or Ford's recommended specs.

The Ford Explorer debacle makes me suspicious of car manufacturer's recommendations. Ford lowered the recommended pressure to 26 PSI to cover up chassis design deficiencies that made the car unstable. Firestone reluctantly OKed the change, even though the low pressure caused excessive heat and tire tread separation. You know the rest. Blowouts, crashes, deaths, recalls, lawsuits etc etc. I put 5 to 10% more than the car maker recommends and monitor tread wear and handling.

I run the RX-8 tires at 38F / 36R Tire wear evenly

F250 get 80F and 75R unless loaded then it 80 Rear. Tires wear evenly and the vehicles are way more stable.

Wow, really? Is that the recommended on the tire or the vehicle, or is that something that you came up with via trial and error. I've never had a truck so I don't know if that's the norm or not.

You should use the pressure on the door jamb, MOST OF THE TIME.
There are exceptions.
My 2007 Tundra was one of those exceptions. With the pressure at OEM recomendations, the front tires wore terribly on the outer edge.
The alignment was right on but the wear was still there. A guy at the alignment shop said to kick the pressure up to 42 even though toyota said 33. I tried it and the truck handled better, rode better, got better gas mileage, and the tires lasted longer. No downside.

I'd say it's a case by case decision taking into account the type of vehicle, the design, the tire wear, handling, safety, etc.
But if in doubt, use the car manufacturer's rating.

Passenger car tires usually max out at around 35 psig, light truck tires usually max out at around 44, heavy truck tires (like the ones used on an F-250 or 1 ton truck or superduty) take gobs of pressure like described above. They are also way more expensive and heavier.

So no, not all trucks take that kind of pressure, only the big heavy ones. ;)

Normal. Used to run 90 psi in my F550.

Yep, my truck tires max is 85. I run 80 in the front because the front axle has 5000 lbs on it. I laugh when people say trucks don't do good in snow because the back end is so light. My rear axle has 3100 lbs on it. I keep around 45 psi in the rear duals and they don't have full contact. When it's wet out you can see that the outside part of the tread doesn't make contact.

Hmmmm....

On my Silverado, the factory recommends 35 psi all around, but I've been keeping them at 37 psi cold, as I notice a much better ride and handling. At 35 they feel too soft and the steering is mushy. At 37 the steering is crisp.

Anyway, my truck has an onboard tire pressure monitoring system, so I can see what pressures the tires are at all the time.

With the OEM American General tires, I kept them at 35 psi (that's where they felt the best cold). When they heated up, they would get to 39 psi. At that pressure, the handling was squirrelly at best. There was a noticeable loss of grip. Winding mountain roads were taken at 10- 20 mph below the posted speed limit.

After hydroplaning just south of Nashville coming back from Florida last year, I bought new Firestone tires. Like I said above, these seem to like 37 psi cold. When up to temperature, they will hit 40 or even 41 psi. (Max pressure on the sidewalls is 44 psi.) But the handling and grip IMPROVE dramatically at that pressure. I feel like I have racing slicks on, the grip is so good. They even do a better job in the wet or snow than my old tires.

LOL, you get what you pay for, right?

I have a bunch of tire pressure guages I've accumulated over the years.
Back when I was doing AX and TT I bought a couple of the more expensive gauges in an attempt to make sure I was making accurate pressure adjustments for optimum performance.

One is an top end dial gauge that I calibrated at work one time just for fun (we do that in our instrument shop all the time as we have tens of thousands of gauges here).
One of my gauges is a nice digital one, and the others are varying design and cost down to two small cheeeep stick types. the type you throw in the glove compartment for emergencies.

They all read within about 1 pound of each other.

The two 98 cent stick gauges are surprizingly accurate. They are more accurate than my $$$ digital gauge.


OOps, sorry for discussing technical stuff on the OT forum. Moderators, can you move this thread? ;) j/k

Why would anyone think that a number on the door jamb is always proper??

While it's true that tire and car manufacturers spend a lot of time and money determining the correct tire pressure, there are a few things to consider:

A) That determination is made using a specific tire. A tire from a different manufacturer, or in a different size, or even in the same size and manufacturer but in a different model, can require different pressures.

B) That determination is made using a specific configuration. The car is loaded with a specific amount of weight, in a specific load arrangement. Changing loads can require changing pressure.

3) The determination is made to achieve a specific goal. In most cases, this goal is a compromise of ride comfort and handling. If you have a different goal, you may need different pressures.

Most people who drive on a track know that they have to frequently change their air pressures for optimum grip and handling; these changes can depend on track temps, track condition, and fuel loading, etc.

Door jamb tire pressure stickers are a guide - not some intergalactic law of physics.

Even if they aren't always *accurate*, they are quite *precise*, as long as it's a dial type gauge. You can tell exactly what the reading is, and it doesn't change based on usage. I'm more concerned that my two drive wheels are within 1 pound of each other, than I am that they're exactly 32psi.

The "stick"style gauges are junk. neither accurate nor precise.

I bought a dial type at Shuck's auto parts here...$4.95. It read 25 pounds when the blue point read 34, so I tossed the cheapy...My Blue point was "made in usa"...buy one off a snap-on truck today? "Made in China"... So, took my blue point along when shopping for my next gauge...did some comparison of readings.

All true, but 99% of the time for 99% of the conditions encountered, the factory recommendations are best. Moving from 36 to 44 psi in a MUSTANG is a huge leap of logic. The tire Service Description (i.e. 91W) can't be very different for same-size tire fitments. It's not like going from a P tire to a LT tire, or a C load range to an E, where sidewall construction dictates tire pressure.

As you mentioned, a psi here and a psi there can really change the way a car handles on the track. Going from 36 to 44psi can make the break away lightning fast vs progressive, and make the front tires lose a lot of bite on turn-in.

Messing that much with tire pressures is a variable that can have big unintended consequences

Yep, the free, 'over the counter' stick gauges they offer at the tires shops, read right there with the nice dial race gauges with the bleed-off relief valve.


KT

Anyone know where I can get a dial tire gauge that reads in tenths of a psi?

I would try a race shop or Summit.


KT

Longacre digital gauges read to tenths and are accurate to the tenth.
Their analogue is accurate to +/- 10%
Longacre Racing - Online Catalog: Electronic Wheel Scales, Gauges, Pyrometers, Chassis Setup and More!

They also have a temperature compensated gauge.
Longacre Racing - Online Catalog: Electronic Wheel Scales, Gauges, Pyrometers, Chassis Setup and More!

Wow, that's a little more spendy than I want to get for a tire gauge!

Ahhh So you DO get what you pay for. :rolleyes:

The two stick type gauges I have are as accurate and precise as my expensive gauges. That was the point of my post.

I checked them many times for not only accuracy but repeatability. The results showed that they were more accurate and had better repeatability than my expensive digital gauge which varied as much as a pound and a half over three or four consecutive readings.
One of mt stick gauges is round and the scale wraps around the gauge for very good seperation. the other has a straight rectangular shaped scale.
The round one could be read down to the 10th of a pound with interpretation, the other is basically good only down to the pound graduation.

Maybe it's just YOUR stick gauges that are junk. ;)

Sorry... I thought you were looking for a gauge to equip your amateur Formula team with. :)

Accutire also has gauges that read in tenths, for much less money, but I am not sure how their quality is. (It may be great - I have never used one.)
ACCUTIRE GAUGE


I use one of these:
http://ecx.images-amazon.com/images/...500_AA300_.jpg

Thumbs up on the Longacre stuff.

Bought a good stick gauge for the truck goes to 140 PSI.

Most gauges are most accurate when used in the middle of the range.

Yea when your truck is 6800 pounds dry and empty. ya needs good tires. Load rating for each tire is 3454 pounds. Load range E Must be why they weight 52 pounds without the rim.

Here's the current snap on version of what I use...Now made in China, but looks the same as my old made in the USA gauge. Still under $20... When RoninLB was here, we compared with his digital gauge. Readings were identical...
YA243A, Gauge, Pressure, Dial Type, 0 to 100 PSI

My main objection to digitals? A pressure gauge that needs a battery just doesn't seem logical to me...

digitals need the battery for the display.