Tire pressure (of winter tires)
 

Why is it that the usual maximum pressure indicated on the sidewall of a winter tire is 35 psi while an all season tire is 44 psi? If it is safe to up the pressure of an all season tire to 50 psi, is there any major structural difference in a winter tire that would forbid upping the pressure as high as an all season tire? Is it simply that above 35 psi the tire might not perform as good as it should on snow/ice?

I would really like to up the pressure even higher on the TDI which I use solely for low speed city driving. Especially since every 0.3 bar increase in tire pressure leads to a 7% reduction in tire rolling resistance.

This is just a guess, but the temperature differential is going to be greater in the winter after the tires warm up. My current tires don't specify whether the max psi is hot or cold, but I've seen tires that specify it as the cold pressure. I have observed on our Jeep with the fancy tire pressure monitor during cold winter trips (0 F ambiant) running 80mph that our 44psi rated tires will increase 7-8 psi before it plateaus. I've observed in the summer (100 F ambiant) during the same trip the pressure only increases 3-5psi. (Kind of off topic: One time after parking in the sun I actually managed to get the psi to go DOWN by driving 35-40mph for a few minutes; I'm guessing it was because of the wind.)

All that might go straigh out the window when you consider that all season tires are run in the winter too, so take what you will.

I have been running 100 psi in my E-rated tires (sidewall pressure = 80 psi) in warm weather and cold. No "crowning" is visible and the wear seems even across the tread.

OK, I'm at a lose as to what is a "safe" pressure to run tires at. My tires are rated for 32 or 35 PSI, and are the tires that I bought the car with. That is the "maximum" rating on the sidewall. What has been done to determine the "maximum" you can run safely at. I see a lot of guys running 50 PSI or even Big Dave at 100 PSI without a problem. What can I do to figure out what the "maximum" PSI is for my tires?

I do plan on getting new tires on my car, but I cannot push myself to throw out good tires that have at least another year of tread left on them. I'm easing into the Eccomodder car as it makes monitary sense to.

My NON LEGAL ADVICE is try 37; and if that's good go 40 . . .

My experience is that when you become overinflated that car acts very bouncy, like super bounce jet ball bouncy, or is difficult to keep going straight.

Bear in mind that big Dave has E-load rated tires with a rated max of 80, he's only around 20% over .

I ran my winter tires (35 psi max sidewall) at 45 all winter. I run my summer tires on my Matrix at 50 (51 max sidewall), and my Paseo is currently at 55 psi (44 max sidewall) and I'll be going to 60 once it is back on the road. I know that doesn't really answer your question, but if I have a tire blow out, you'll know. However, there are a handful of guys running at these pressures, and some running more that I know of without problems...

My sidewall max pressure says 44psi, I am running 50 psi, with no problems yet ... I am also running Nitrogen in my tires to help curve the temperature variations since average mid day temp here is now closer to 90 degrees. The ride does rely more on your suspension now because the tire is much stiffer. But other than a slightly harder ride, which I already got use to I see no adverse effect.

In fact and as an aside, I also run 50 psi in my 4 runner now and recently had a blow out, as a result of debris, I saw no additional hazard to the extra PSI other than a bit more time to get over to the side before the tire went completely flat.

I run 55 in 44 max sidewall tires and the only downside I've noticed other than some ride/noise changes is that traction on wet roads isn't as good. Fortunately the breakaway is progressive. Winter traction seemed fine.

I'm not willing to exceed the maximum sidewall pressure. I just bought tires with a max psi of 44. Some low profile tires go even higher if you want, but with overinflating, the law of diminishing returns applies. If you're inflating a tire that explodes at 60 psi, they'll find puddles of you in three zip codes. I'm only half exaggerating.

In the sticky in general efficiency subforum, there is a link to a pdf titled zero inertia powertrain. Look in the rolling resistance section.

Actually, it's even more than that: 20/80-iths is 1/4 = 25% over.

Just an update. For the last 3 months I have been running my 35 psi rated tires at 50 psi on the TDI. There is nothing to report so far apart from lower RR.

i run 5psi over speck on the tire .. warm pressure.. my crx is at 50 psi and my truck is at 40 psi.. thats what i do..

both sets of snow tires that I have are labeled as 51psi, and are silica rubber (beter grip with lower rolling resistance) and they work great, nice even wear over the last two winters, great traction at 50psi and if they were on ally rims instead of steel I might not even notice a change in how they handle.

Hey Dave,

I'm also driving an F350, except that mine's a crew cab, long bed, automatic transmission, 4x4 with 4.10 gears. Totally stock, I was getting <12 mpg city, and ~13.8 hwy. Changing my driving style has now got me >17 mpg city, and >23 hwy, still stock, but with higher tire pressures.

I was running my tires at 80psi for a while, then tried some testing using the Scan Gauge. I ran a few miles of a section of a road with the cruise control set, noted the mpg, then ran it again with the tire pressure at 70psi, then again at 60psi, etc. Strangely, the fuel mileage got better and better as the tire pressure was reduced. Then I realized that the lower pressures were allowing the tires to "squish" more, reducing the rolling radius of the tire (the truck weighs just over 8,000 lbs full of a fuel and me). With lower tire pressures, the odometer was indicating that I had driven farther than when the pressure was at 80psi. =) Not a good test. I'm now searching for an appropriate hill to do a "coast-down" rolling resistance test instead and will determine rolling resistances by the distance the truck rolls at different tire pressures.

My question for you is if you've done similar testing, and found measurable/repeatable benefit going above 80psi, or if you just assumed that higher pressure = lower rolling resistance?

Also, thanks for all your posts. Your successes were instrumental in encouraging me to try to get better mileage with this beast.

Having installed tires for years, amongst other things, I observed a general set of rules that I incorperated into my own thinking. Tire pressures: 32 psi in a 35psi max - 35 in a 38 - 38 in a 41 - 40 in a 44 - 46 in a 50 - 75 in a 80 - 90 in a 100 - now for trucks with the higher psi rated tires, some are very picky on pressures, for example, a Ford F350 dually we would normally set the fronts to 70 and rears to 85 (80 psi max rated sidewall) and definately recommend the regular rotations. Doing that we would often see tires that were rated for only 50k miles regularly get over 100k before needing to be changed out. Now having said all this... lol... this is Ecomodder, and a working allowable increase beyond what I have observed is more the norm. My own Impala with 44psi max rated sidewalls are run at 44 psi so far. When I find a close reliable source of nitrogen filling, I plan on bumping things up to 50 to observe the changes. Old school thinking (and incorrect gas station air gauges) suggested that over inflating a tire would lead to more wear at the center or crown of the tire. This is still true in extreme cases (incorrect gas station gauges a prime culprit) as is wheelspin during slippery conditions. Personal note, wheelspin while fun, does induce increased tire wear ;)

Additional info - please note that vehicle manufacturers place a small plaque or datacard most often on the driver's side doorjam, which includes info on VIN and certain specs, including tire size and pressure recommendations. Many Toyota/Honda/Subaru specs are way below the tire max sidewall settings. Several domestic makers have done similar in the hopes of making the ride more supple, and less stiff. Ford Explorers used to have a dismal 26 psi rating for the tires, and subsequently had many rollovers and tire failures that they tried to pin upon Firestone. Well the truth came out when other tires were treated to the same low pressure and although Firestones used had a weaker sidewall (increasing the failure rate some) it was shown that the low pressure was to blame. Further testing showed that the Explorers were better off running tire pressures at the recommended 32psi (in a 35 psi max sidewall rated tire) and in some cases, even going up to a 41 psi max rated tire and using the 38 psi setting (although that was often set back down to 35 psi) Your vehicle datacard will tell you what the manufacturer thinks is the best tire pressure, time and experience will give you the tire pressure best suited for your mindset, driving style, and vehicle.
Good luck.

Consider a grasshopper, and dummies
 

Hello, Trik,

I had to answer your "signature" question-- what would a chair be like if your knees bent backwards-- Well, that's the way a grasshopper is constructed. The chair would be the same, but you would sit on it backwards.

Now about max pressure in winter tires. I have a possible explanation. Some dummies will leave their winter tires on all summer. What happens if the tire pressure is set when the temperature is 20 degrees, and then the tires are left that way into summer and 110 degrees? I'm sure somebody will check the summer pressure for us.

My personal experience. I run Michelin Energy tires very close to sidewall pressure and I have had two or three ply separations in them. It is undoubtedly a manufacturing problem, but might be an issue with other brands or more common in winter tires?

Ernie Rogers

Since this thread was resurrected and I missed it the first time, I'll throw in my 2 cents also:

The ForkenSwift runs on 35 PSI sidewall max rated winter tires, year round. I've got 50 PSI in them. Other than the bone shaking ride over bad bumps (railway crossings), no adverse news to report.

Hi,

The Michelin X-Ice snows I have have a 51PSI sidewall max, and they roll better than my summer (Yokohama Avid) tires. They are top notch snow & ice tires.

What I have noticed, regardless of if the tires are snows or not, is the quality of the tire usually dictates the max psi.

The cheap tires are usually labeled at 35 PSI. This is the case of my cheap Trivent (touring) tires and the Pacemark Snowtrekker tires (from Walmart) on the van, as well as the Dayton all seasons I used to have. One of the Snowtrekkers blew a sidewall out with less than 10k on them. I replaced them with some more expensive tires I bought used from my friend, they are rated at 44 psi. I could have sworn the Blizzaks on my old 6k wagon were 44 PSI too.

The better tires seem to be rated at 44 PSI. This is the case for the Viva Touring tires (rebranded Goodyear Regatta) tires on my Celebrity, the Goodyears on my friend's Bonneville, and quite a few others. Also the Winterforce snows on my 89 6k wagon are 44 PSI.

I can usually tell just by looking at them. The 44 PSI tires seem to have a heavier sidewall and they just LOOK like a better tire. The 35 PSI tires have a sidewall that seems pretty wimpy but probably gives a softer ride.

The Michelin Ice X tires on my wifes 93 Topaz have a max rating of 51 PSI. So when the weather was good all summer I ran them at fifty (from the previous 32). It made almost 2 mpg without any appreciable wear abnormalities. The ride is harsher but the wear and mileage are great.

Note, I have experimented in snow, ice and rainy weather and from experience hard tires make great sled runners in the white stuff. So whenever the weather is bad a lower softer more compliant tire makes a world of difference. By the way I drive about ten K miles per year in the snow alone in my work. About thirty K total on my work car so mileage is important. :thumbup: