Tire PSI Cold vs. Hot
- Thread starter MFP
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Kyle_E
Well-Known Member
When I was humping car tires for a living we were instructed to fill 4 PSI higher on hot tires.
Given my TPMS is accurate, normal hiway speeds increase pressure about 3 psi. Higher speeds, heavier loads, or hotter pavement can go higher. Recommendations are given for cold pressure. As stated by others, gages vary quite a bit, and I tend to rely on the TPMS.
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10% is the figure I've always heard.
Same here.
If > 10% under inflated
If < 10% over inflated
Not sure if there is extensive testing, and I've run tires at levels below my shops recommendations because they performed better.
Also varied between tire manufactures. I. E. Same bike and riding conditions required different pressures to perform their best.
gv550
Well-Known Member
According to my TPMS, rear Mitas E07+ at 42 psi cold often climbs to 47-49 when riding, front Mitas E07 dakar at 38 cold climbs to 42-44 psi.
bnschroder
2014 Super Tenere ES
Same here as gv550. I have the Orange TPMS that provides a constant read. My 42 PSI cold rear tire (Shinko 705) recently climbed all the way to 50 on the Interstate at 100 degrees ambient temperature and speeds of about 75 (solo rider, fully loaded). Front significantly less increase.
I'm sure weather and load play a (big?) part. But that's 10 to 20 %. Anything over that I'd be a bit concerned
Your matter of perspective about 8 psi not being much different is off, as that is more than 20% for a tire with under 40 psi. Ideally, the cold pressure should rise about 10% (some slightly more or less), so a properly inflated tire at 36 would rise to 40. btw, When the weather changes, tire pressures change by about 2% for every 10 degrees F.
Rubber flexing every time it makes a revolution creates heat and is good at holding the heat. Designers use this to give the right amount of flex for both speed and load/weight capability, which is why pressure is so important to getting the right wear pattern and longest life. If you start with too low of pressure, the contact patch with the road can (not always) be bigger to give better adhesion up to a point. However, the tread squirms more, increasing wear. The rubber flexing and creating heat in the sidewall softens the rubber in the thinnest portion of the tire, making it the weakest point of the assembly of fabric and rubber layers. Especially loaded down or going fast, that is about the last thing you want. It's why under inflated truck tires blow the sidewall, and why cargo planes blow them on takeoff, not landing.
Talk to the tire designers and they have a saying that the most important 3 things in tires are inflation, inflation, and inflation.
So if you start with max pressure allowable and you are within the bikes load limit, yet the pressures increase by 20%, what would you do?
Run higher than max recommendations?
The example above was for a tire at 42 psi, which is at the upper end.
Serious question, I don't what I'd do if encountering this situation on a road trip...
Probably keep riding but try to take it easy...
Super08
Well-Known Member
In June I took a 5,000 mile trip with mine quite heavily laden. Cold pressures were set at 34 front and 42 rear. On the hot days travelling on the highway I would see the rear go to 48-50 and the front around 38-39. Running around normally I see less than 10% increase.
Thanks, sounds like under heavy load a 20% increase happens.
I must be honest, on trips I check in the morning but not during the day when hot...
EricV
Riding, farkling, riding...
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That's a really good question. I'm no expert, but I would increase your pressure if continuing to travel with the same load.
Indirectly, max pressure can be confusing. Some tires are marked with the pressure they are tested at, which is NOT the max pressure. MotoZ is one of those. I think Mitas is also, but don't have one to look at. If you're not positive, ask the tire manufacturer or importer of your specific tire.
Remember that MAX Load is not MAX Pressure. MAX load means that was the load tested at the pressure marked on the tire! This is like DOT sound tests, they test at a specific distance from the exhaust and specific speed/rpm steady run. MAX load is just stating the test parameters.
Equally worth noting is tha the factory recommended pressures from the bike manufacturer are based on ONE specific set of tires. Sometimes two. Those are just recommendations and mostly based on a 'typical' load or sometimes unladen. My normal loads on the Super Ten are much higher than Yamaha's typical skinny Asian kid with a backpack. No way I would get the tire life I get running 33F/36R. For my fully loaded needs I run 36F/42R and have for a long time with good results for my riding needs. YMMV.
I wouldn't increase the pressure past 42 psi.
As long as the load on the tire is within its limits, and 42 psi is listed as the max pressure {cold}on the tire, that's what I'll inflate to.
Exception would be if I see cracks appearing around the knobs.
I'm not familiar with any tire that's got more than 42 psi listed as max (none of the ones I've run have had a higher value anyway)
There was a bit of tounge in cheek with this one. Everybody was giving their input, with only a matter of 4lbs between the high and low. Seemed we were all saying the same thing. I'm a bit anal about my tire pressure(s); used to get teased at work about my daily checks. I check the pressure before every ride, daily. That way, depending on any changes in weather, I will see the effect it has on the tire(s); correct if necessary. What does concerns me though, is that a tire's speed rating is certified at max pressure. There's not a manufacturer out there that recommends that a tire is ran at maximum pressure. I will assume....that occasional runs up into a tire's maximum speed rating zone has little affect on the tire's durability. How long can a tire be ran at it's maximum speed at a pressure lower than it was certified for? And, on some of the 50/50 tires the guys are using....what are their speed ratings?
Super08
Well-Known Member
Remember the tire pressure ratings are max "cold" pressure.
Most of the 50/50 tires I have seen have much lower speed ratings.
Most of the 50/50 tires I have seen have much lower speed ratings.