What tire pressure should I run?

[oldtamiyaphile]

Placard says 28psi.

Here we are at 31psi:



Here we are at 39psi (temperature delta is 0.2*C!):



I know which looks happier.

[California98Civic]

Originally Posted by oldtamiyaphile

Placard says 28psi. ... I know which looks happier.

Interesting test. Thanks. But maybe you could sharpen it a little and make a thread? What were the methods and conditions of your test? There are a lot of variables here that you are not describing: starting tire temp, outdoor temp, road temp (hours of sunshine), how many minutes you drove... heck, even the number of times your turned these front wheels and the speed at which you took turns might affect these results a little.

Also, do your results matter for tire wear? Who says the resulting temperatures are a problem? Tirerack claims a 50* F increase after 30 mins driving is normal. These two temperatures might be functionally meaningless if they are well within the design limits of the tire.

I'm not trying to snipe at you. I think you have the start of a really interesting thread more rigorously testing these things.

[Jez77]

I agree those test mean nothing with out some context, even then a laser temp gun would give a more accurate readings at each tread block for comparison.

Are they pics of the same tyre even?
Front tyre will generally be hotter than rear due to wheel alignment and steering force.
Pics are in different locations and very different road temps.

Which one do you think is happier? You don't make that clear.
To me the lower pressure pic looks far more even, the higher one is much hotter on inside edge

[RedDevil]

All I know is that I noticed a problem once because my instant FE readout was showing lower economy than the situation called for. I went over bumps and through corners and all felt fine until the very last corner before arriving at work, where the back suddenly stepped out.
There was a screw in the middle of the thread of my rear right tire and the pressure was down to 10 PSI.
I immediately aired it up (motorized pump aboard) and drove it to my nearby dealership to get it plugged properly.
Airing up was tricky because the tire was almost too hot to touch...
The other tires at 40 PSI were ambient.

Low pressure heats up and damages tires.

[oldtamiyaphile]

Originally Posted by California98Civic

Interesting test. Thanks. But maybe you could sharpen it a little and make a thread? What were the methods and conditions of your test? There are a lot of variables here that you are not describing: starting tire temp, outdoor temp, road temp (hours of sunshine), how many minutes you drove... heck, even the number of times your turned these front wheels and the speed at which you took turns might affect these results a little.

Also, do your results matter for tire wear? Who says the resulting temperatures are a problem? Tirerack claims a 50* F increase after 30 mins driving is normal. These two temperatures might be functionally meaningless if they are well within the design limits of the tire.

I'm not trying to snipe at you. I think you have the start of a really interesting thread more rigorously testing these things.

These are just some preliminary results - this thread got me thinking about measuring tyre temps, rather than just going by OEM recommendations, which I've always found to lead to shoulder wear. It's not so much the overall temperature that's in play, just the temperature delta across the tyre. Overall temp will be influenced by the factors you mention, the deltas less so.

An even temperature across the tyre means each tread block is doing the same amount of work - that should be good for wear. I'll air up to max side wall next and see what happens.

Frankly, it would take weeks for testing to arrive at a rigorous conclusion - probably why no one on the internet seems to have done it. I find dozens of references to how tread wear affects dry/wet braking distances, but nothing for pressures.

Remember, the OEM placard says 'recommended' there's no possible way they can give you optimum pressures for every possible scenario.

http://www.rarespares.net.au/rarespa...oduct=92048297

If your placard lists only a single pressure (as my test car does) and you're running at high load and high speed, you're actually running much too low pressures. In my case the OEM tyres were 175's, but the car was fitted with lower profile 205's so the OEM number becomes meaningless. Even if I air up to max side wall, I'll still have more contact patch than the 175s.

[oldtamiyaphile]

Originally Posted by Jez77

Are they pics of the same tyre even?
Front tyre will generally be hotter than rear due to wheel alignment and steering force.
Pics are in different locations and very different road temps.

Road temps are the same, you can't read thermal images like that - the colours mean completely different things across two images. They are of the same right front tyre. The second pic shows a much more consistent temperature across the tyre (outright temps I'm less interested in). More testing and a proper thread is planned.

[Jez77]

Originally Posted by oldtamiyaphile

Road temps are the same, you can't read thermal images like that - the colours mean completely different things across two images. They are of the same right front tyre. The second pic shows a much more consistent temperature across the tyre (outright temps I'm less interested in). More testing and a proper thread is planned.

I certainly don't see what you do.
If you say road temps are the same why would the colours not be similar that seems ridiculous and makes the images pretty much useless to compare if that is true.

You say the bottom image is more consistent temps yet it is much lighter on the inside of the tyre. Top image is a little lighter on the outside if anything but I'd say that would change depending on if you went around a left or right hand corner before you took the pic.

The bottom pic also shows the tyre hotter in the middle than the top and bottom making me think the camera is seeing it hotter because it is closer to the lens.
Meaning if your not exactly perpendicular to the tyre when you take the pic results will be inaccurate.
I'm sorry mate but I don't think that camera is going to give you the accurate results you need.
A laser temp gun would be able to give a block by block temps that you would be able to log onto a chart temps vs pressure which would give you the most accurate idea of what is going on.

[oldtamiyaphile]

Originally Posted by Jez77

I certainly don't see what you do.
If you say road temps are the same why would the colours not be similar that seems ridiculous and makes the images pretty much useless to compare if that is true.

No it doesn't work that way. What would be ridiculous would be to have a single colour scale across all your images. My camera operates at -272 to +250*C. If black always meant -272 and white always meant 250, then the vast majority of images would have next to no definition and the whole thing would be useless.

The temp scale can be locked, but is normally dynamic. These pictures are really only intended for my own use, they don't really mean much without access to the raw point data.

Also, the road temps are similar, that's not to say the temp of my driveway is as high as the road temp.

I can always come back to an image and get spot temperatures using the software, weeks, months and years later. Again, the second image only varies by 0.2*C across the whole tyre - even if the colouration is a quite stark. If you understand about emissivity there's no non contact method that's going to be 100% perfect. My FLIR camera tells me the boiling point of water is 99.9*C- I'm pretty happy with that. The IR temp gun has the same limitations except I can see where my potential errors are, as well as save that point in time for future integration.

I also have a durometer that can be used to verify results.

[oldtamiyaphile]

Just to help every one get their head around how an IR camera works, this is the inside of my freezer:



Even if there's next to no temperature variation, the camera will make it look like there is.

[CapriRacer]

I guess I have to say it again:

Inflation pressure is just one of many variables when it comes to tire wear - and it isn't the most important. You can get even wear on underinflated tires as well as overinflated tires. You can also get uneven wear on properly inflated tires.

So even wear is NOT an indication that the inflation pressure is where it ought to be. And uneven wear is NOT an indication that the pressure is wrong.