I set all my P-Metric (passenger car) tires at 35 psi. I only check them about once every three months and during that time they typically lose a couple of pounds. They last a long time and wear perfectly flat. Any lower and I get edge wear.
“Any lower and I get edge wear.”
I’ve noticed that, too. My car tires always get edge wear at the prescribed 30 pounds. 33-34 makes them wear just right. I suspect that, while time-consuming, this may be a good way to find the tire pressure that works best.
29 to 35 is no big deal. I run all of mine at 32-34. I think 29 would give a slightly softer ride but that about it and not much of a margin if you get a nail in the tire like I have twice in the last few months.
A pencil gauge, like any gauge that is not periodically checked for accuracy can be accurate or not. To state that all pencil gauges are not accurate is not correct. I have several gauges including dial and pencil gauges. Some of each type match a dial gauge that I had calibrated some years ago against a large diameter gauge with fine gradations that was checked against a standard gauge in a laboratory setting whose accuracy was traceable to NIST.
Tire pressure per the mfr’s. spec should be used for best traction, wear, handling and ride. The vehicle mfr can best determine the optimum tire pressure for the tire size chosen for a particular vehicle.
Fortunately for all of us car owners, tire pressures are tolerant to somewhat low and high pressures. If somebody has good wear results with several psi over specified, I have to wonder if their gauge is correct.
Sidewall max pressure - what is it? How is it determined? Is it consistent from tire manufacturer to tire manufacturer? If it isn’t derived from a test (or a theoretical calculation) AND the methodology of determining what is written there isn’t consistent, how can anyone point to that pressure with any degree of confidence?
I will stop there - andf make a clear statement: If anyone points to the pressure on the sidewall, and suggests using that pressure (or some value derived from that pressure), you can be sure they do NOT understand tires and how they work!
When it comes to mountain bikes, who should know better!
Somehow, Steve, that reply ended up on the wrong thread. It was supposed to be on the thread about upsizing tires. I’ve moved it.
You must have thought I’d lost my mind. The post made no sense on this thread.
Yes, I’ve moved my post too. Stuff happens.
The tires I’m running at 44 PSI sidewall max are BF Goodrich 70K mile touring radials and are wearing evenly across the tire. Most radials if ran at door placard pressure will look like they are running low putting more stress on the sidewall (weakest part of the tire) and edge of the tires and often causing the front end to wonder. I’ve ran 90% of my tires at max sidewall pressure since I started driving in the '70’s and have never had a tire failure associated with it in about 900K miles of driving. On the first car I ever owned ('77 Buick Regal bought new) I ran the original tires (40K mile Goodyear) at door placard pressure and they needed replacing at about 30K miles due to the outside edges being worn out with the center sill being about 30% tread wear left… I’m sure sidewall pressure is like other ratings on tires such as temperature, traction, tread wear rating that undergo testing for reliability and safety. (US made tires) Sidewall pressures are also cold pressure so there’s no a factor in over inflation at highway temperatures. Many sidewall pressures vary depending on the type of tire. You can probably buy tires of almost any brand with different sidewall rating. I know my dad’s car (Mercury Grand Marquis) has Michelin 80K mile radials on it also rated at 44 PSI maximum, they have about 50K miles on them now and still have better than half the tread wear left on them and are worn evenly across the tire. I would expect them to last 100K+ if they don’t dry rot first, because the car is seldom driven anymore since he passed away last year. I’m the one who drives it 95%+ of the time so I keep the tires checked for proper inflation and signs of deterioration regularly. As far as excess center tread wear at higher pressure that was true back in the days of bias ply tires when tires ran flatter on the road at lower pressures. I ran a set of 40K mile Bridgestone radials that came new on a Mazda pickup I bought new in '84 for about 80K miles before they needed replacing. The max sidewall was 35 PSI and that’s where I ran them.
I’ve had the same experience with most pencil type pressure gauges not being calibrated correctly. I’d test them for calibration and adjust accordingly. I now have a digital gauge that is calibrated correctly and reads to the nearest 0.5 PSI.
Does anyone remember several years ago when Ford was having problems with tire failure on their SUV’s due to under inflation? I do!
“Most radials if ran at door placard pressure will look like they are running low putting more stress on the sidewall…”
What the tires look like shouldn’t matter. How they stop and handle in emergency maneuvers is what’s important.
“I’ve ran 90% of my tires at max sidewall pressure since I started driving in the '70’s and have never had a tire failure associated with it in about 900K miles of driving.”
Back in the 1970s, tires were made differently, and what the tire looked like (side wall bulge) mattered back then.
Lastly, there is more than one potential cause for uneven tire wear, and improper inflation is just one of them. Your solution might just be mitigating the symptoms, but not solving the real problem.
Lastly, there is more than one potential cause for uneven tire wear, and improper inflation is just one of them.
I know that. Suspension parts (ball joints, tie rods, bushings, struts, wheel bearings, alignment, tire rotation, wheel balancing). I do 99% of my own work and keep all these in tip top condition often changing all of them when something as simple as replacing only 1 tie rod or ball joint would take care of the problem. I’d much rather do it all at once and have it realigned than to replace them one by one and have to continually have it in for alignments. When I buy tires I get free lifetime balancing and tire rotation.
“If somebody has good wear results with several psi over specified, I have to wonder if their gauge is correct.”
This is the gauge I use, it’s about a year old. It reads down to 0.1 psi increments. I check early in the morning before the sunlight hits the tires. I feel that it just as important to have both tires on each axle at the identical pressure.
70* is the optimal temperature for adjusting tire pressure if I recall correctly.
"Does anyone remember several years ago when Ford was having problems with tire failure on their SUV’s due to under inflation? I do! "
Yes, I remember. It was more than several years ago. 1990, to be exact. Ford used Firestone tires on the Explorer that could be punctured by gravel. I had three flats with these tires on gravel before I ditched them. One flat was on a remote road on the north rim of the Grand Canyon. I changed brands and never had another flat.
Ford wanted you to run the tires at 25 PSI for a softer ride. I ran them at 30.
If you put the maximum pressure in a tire cold, you will be running that tire OVER the maximum pressure. I don’t care how lucky you have been, or how well the tire wears, you are taking a chance.
From Keith: This is the gauge I use, it’s about a year old. It reads down to 0.1 psi increments. I check early in the morning before the sunlight hits the tires. I feel that it just as important to have both tires on each axle at the identical pressure.
Yes and I also have an Accutire pressure gauge; mine is the ABS coated version with no features other than pressure. It agrees at 35 PSI with my Milton and Hafner tire pressure gauges and also my Madden bourdon tube gauge that was checked against a laboratory gauge with calibration traceable to NIST. Can you verify your gauge’s accuracy after some use and at a year old?
FordMan59,
There’ a lot about your posts that are factually wrong - but let’s just take this one:
“… I’m sure sidewall pressure is like other ratings on tires such as temperature, traction, tread wear rating that undergo testing for reliability and safety. (US made tires)…”
So what type of testing goes on with regard to how the pressure listed on the sidewall of the tire is determined? Do you know the source of this tesing? Is it a government regulation? An industry standard test?
Here’s another: “…70* is the optimal temperature for adjusting tire pressure if I recall correctly…”
No, the pressure is supposed to be adjusted at the ambient conditions - whatever they are. If it’s 100ºF outside, then measure at 100ºF. If it’s 45ºF, then measure at 45ºF. The only stipulation is that the tire has to be “cold” - that is unoperated for at least an hour and a half so that the tire is AT the ambient condition.
The testing is required by the government, therefore I would assume it has to meet government standards, but I don’t know how it’s regulated. The following link tells what information is required to be on each tire sold in the US.
http://www.nhtsa.gov/cars/rules/regrev/evaluate/807805.html
As far as the statement I made about 70* being the optimal temperature, I’m pretty sure I read that somewhere on a tire company web site one time, but can’t find it now. It may be because for each 10* variation in ambient temperature tire pressure will change by about 1-2 psi. If you air your tires at 100* during the daytime and the night temperature drops to 70* the tire pressure will likely be 3-6 PSI lower.
Does anyone remember several years ago when Ford was having problems with tire failure on their SUV’s due to under inflation? I do!
I do. The Ford/Firestone problem.
It indicates that tyre pressure is important.
A friend who has been in the tire business for 40 years says that normal load range C automobile tires as a general rule seem to give the best performance at 35 psi.
“Does anyone remember several years ago when Ford was having problems with tire failure on their SUV’s due to under inflation? I do!”
I’m still driving one of those Explorers. I have the 2000 model. I run Goodyear tires on it. The entire problem was due to under-inflated tires and Firestone tires with a design flaw. The design flaw let those tires get punctures very easily, and then the under-inflated tire made the truck very unstable. The real fix was better tires and checking the pressure. The Explorer problem were a text-book example of not letting your tires get under-inflated. Especially on a top-heavy SUV. Even with the Goodyears, you need to check the pressures. Under-inflated tires on the rear can still look normal to the eye. A pressure check is the only way to know.
The tire pressure on the sidewall is the maximum for the TIRE. That tire is made to fit many different vehicles, and proper pressure for the tire is based on the vehicle weight on that corner of the vehicle. I run 2 psi over the placard, but not the 16 psi that running the tire max pressure would be. That’s a recipe for disaster. Also, the tire pressure is based on the ambient temperature. The pressure will drop in winter and rise in summer. The pressure needs to be adjusted to maintain the placard pressure no matter the seasonal temps.