Understanding tire pressure
08-15-2006, 09:44 PM
#16
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I have found that quality gauges that read off a pound or two from perfect calibration, when treated properly, continue to read "off" by the same amount. Barring a serious brain fade, it is simple to make the same allowance each time for me. I have found they don't wander from their readings any faster than a quality gauge that happens to calibrate right on the mark. I'm NOT talking about cheap, crap gauges.
I like these:
http://www.longacreracing.com/catalo...id=982&catid=8
http://www.longacreracing.com/catalo...d=1168&catid=8
I like these:
http://www.longacreracing.com/catalo...id=982&catid=8
http://www.longacreracing.com/catalo...d=1168&catid=8
08-15-2006, 10:32 PM
#17
Nordschleife Master
I had an analog gauge that seemed to work fine all season. Then one day it all of a sudden read very low. The reading just didn't seem to make sense. I checked it with DrJupe's super-duper gauge, and sure enough, the calibration had literally changed overnight. Before that I had never noticed an issue, but I suspect I had unknowingly had incorrect TPs all along.
08-16-2006, 09:30 AM
#19
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Originally Posted by 38D
I had an analog gauge that seemed to work fine all season. Then one day it all of a sudden read very low. The reading just didn't seem to make sense. I checked it with DrJupe's super-duper gauge, and sure enough, the calibration had literally changed overnight. Before that I had never noticed an issue, but I suspect I had unknowingly had incorrect TPs all along.
08-16-2006, 09:31 AM
#20
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Originally Posted by Gary R.
Sheesh... I bought a Pyrometer (used) for less than that figgin tire pressure guage! You guys hava a sponsor?
08-16-2006, 09:38 AM
#21
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Originally Posted by Bull
So now you are convinced that his new gauge is correct, and always will be so......
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Larry Herman
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Larry Herman
2016 Ford Transit Connect Titanium LWB
2018 Tesla Model 3 - Electricity can be fun!
Retired Club Racer & National PCA Instructor
Past Flames:
1994 RS America Club Racer
2004 GT3 Track Car
1984 911 Carrera Club Racer
1974 914/4 2.0 Track Car
CLICK HERE to see some of my ancient racing videos.
08-16-2006, 11:00 AM
#24
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Comp Tire East (Goodyear Guys) have a calibration machine at just about every SCCA regional and national. You'll be surprised that almost nothing is accurate to it.
It's also important that you are using tire pressures as a means to get good wear / even heat. That being said, the actual pressure doesn't matter. As long as you can repeatably start at the same pressure, it doesn't matter what the number is. We are back at the point of large window of operating pressures.
As far as a guage being so far off that it is unsage, I've never had a guage go more than 2-3 lbs. out. On a FC car, that brings you at worst down to about 15 lbs. which won't result in tire failure.
Matt
It's also important that you are using tire pressures as a means to get good wear / even heat. That being said, the actual pressure doesn't matter. As long as you can repeatably start at the same pressure, it doesn't matter what the number is. We are back at the point of large window of operating pressures.
As far as a guage being so far off that it is unsage, I've never had a guage go more than 2-3 lbs. out. On a FC car, that brings you at worst down to about 15 lbs. which won't result in tire failure.
Matt
08-16-2006, 11:11 AM
#25
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Originally Posted by Larry Herman
Well, Charlie is faster than Colin, so Colin kinda looks up to him.
08-16-2006, 11:15 AM
#26
What about this gauge?
http://www.longacreracing.com/catalo...id=213&catid=8
Why is it necessary to get any fancier than this?
http://www.longacreracing.com/catalo...id=213&catid=8
Why is it necessary to get any fancier than this?
08-16-2006, 11:39 AM
#27
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That's the one I have now, seems to work very well. Along with the new Pyrometer I just picked up I should be able to tell what is going on with my tires and relate it to my shop for any possible adjustments (per track of course)..
08-16-2006, 12:55 PM
#29
Originally Posted by Bull
Todd, I would look for a guage with a swivel chuck. That one doesn't appear to have one.
08-16-2006, 12:59 PM
#30
Burning Brakes
Originally Posted by Larry Herman
... I couldn't help wondering (there I go again 
) if the car setup has more impact on tire pressures than we realize. For a specific tire and wheel combination, will different spring rates and camber/toe setting require different pressures in order to get the optimal tire performance from that setup?
My theory is that it will. In layman's terms, if you have a no-compromise racecar where you can set the camber for optimal temps across the tire, then you should be able to run the tire a little harder, because you are using more of the tread equally. That extra bit of pressure will help the tire to maintain it's shape and stay firmly planted on the road, getting all of the grip that it has to offer.
If you have to run less than optimal camber because of other reasons, like you have to live with it on the street, then I would think that you may have to run a little less pressure to allow the tire to distort a little more. This may allow the outside edge of the contact patch to grow in length a little, and also may help keep the inside part of the tire from unloading quite as much. This would help to keep as large a contact patch as possible, maximizing the grip. Even though the tire is not performing as well as it ultimately can, it actually works better in this particular setup with a little lower pressures.
I am talking about a range of 3~5 lbs hot pressure. Since this is pretty much conjecture on my part, I would like to know what your experiences have been, especially if you have any testing data to back up your conclusions.
) if the car setup has more impact on tire pressures than we realize. For a specific tire and wheel combination, will different spring rates and camber/toe setting require different pressures in order to get the optimal tire performance from that setup?My theory is that it will. In layman's terms, if you have a no-compromise racecar where you can set the camber for optimal temps across the tire, then you should be able to run the tire a little harder, because you are using more of the tread equally. That extra bit of pressure will help the tire to maintain it's shape and stay firmly planted on the road, getting all of the grip that it has to offer.
If you have to run less than optimal camber because of other reasons, like you have to live with it on the street, then I would think that you may have to run a little less pressure to allow the tire to distort a little more. This may allow the outside edge of the contact patch to grow in length a little, and also may help keep the inside part of the tire from unloading quite as much. This would help to keep as large a contact patch as possible, maximizing the grip. Even though the tire is not performing as well as it ultimately can, it actually works better in this particular setup with a little lower pressures.
I am talking about a range of 3~5 lbs hot pressure. Since this is pretty much conjecture on my part, I would like to know what your experiences have been, especially if you have any testing data to back up your conclusions.
Besides the discussion around gauges, all of the talk in the paddock generally seems to be centered around static setup; such as cold/hot tire pressures, camber settings, spring rates, etc. However I would suppose that racing tires are very sensitive to dynamic setup. Again, not knowing setup details, but looking at the pictures of the cars in discussion, they all have large front splitters and various types of wings at varying angles, may be some even have diffusers - I don't know. Since, tire pressure, beyond it's under-dampened spring rate, should perform differently under varying load. The load is not only the car's weight (a static component) but also the downforce exhibited on each corner (road speed^2), which is to say that over road courses, that dynamic load should change considerably over a single lap. What do you think of this general unknown in the equation, or is this actually a known quantity helping racers setup tire pressures in a similar manner? Otherwise, it is quite understandable that a wide range of pressures would work for different cars.
Of course this does not take into account any tire break-in procedures that may or may not be followed, which may also completely change the picture.