[flash]

sure it feels that way. it's completely logical. you don't push lateral Gs. soft tires will "feel" more planted until you push them toward the edge. once you do, you'll quickly find out that they have lost a lot of their ability. tires grab better at low speeds with low air pressure, but better at high speeds with high air pressure. that's another reason autocrossers run low pressure. they aren't going very fast. if they took that same car out on a track, they would be spinning and sliding all over the place.



i reiterate that i will take you to a skidpad, at my expense, and show you.

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[Rap]

I just did the skidpad and started my temps at 32. They heated up to around 36. Once you go too fast there is no catching it and you spin. Tire temps are the most widely varied piece of info that I have ran across. It seems that everyone has an opinion as to correct tire pressure. My experience from 30-96 degrees is a 4 psi spread. Now mind you this is from a limited experience, but I do have those temp extremes. This also includes autocross and DE. My instructor told me he wanted me to spin to feel it. Never had a steering wheel yanked out of my hands. Sort of neat as long as you let go and don't lose your hands!

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[Cloud9...68]

I have also read that newer generation tires perform better at higher pressures than a lot of people are used to from past experience. But rather than speculate and spend a ton of time (and rubber) experimenting, it seems like this gadget would provide some very valuable data to answer what is really the optimal tire pressure (and alignment settings as well):



http://www.opti-grip.com/optigrip/Opti-Grip.html



It places three infrared temperature sensors inside each of your fender wells, allowing you to monitor the temperature across the face of your tire in real time. Seems like a great idea, but I couldn't find any legitimate reviews on it - just lots of people asking if anyone else had used it. I guess the price would put a lot of people off, but I'm sure the pros use this kind of stuff all the time. Thoughts?

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[MB968]

[quote name='craigawoodman' timestamp='1368437830' post='142663']

Sorry to highlight it, but every time your tyre heats up and cools, it spells and draws in a small amount of external air, hence why tyres lose pressure. The liner and bead are not perfectly sealed, etc.

[/quote]



craig, what is the mechanism that causes the tire to draw in air molecules (is it all the constituents of air, or just some). The inside of the tire is always about 2 bars above atmosphere. So, it can't be pressure, as it is going the wrong way. Do you have any technical ref./papers I could read.

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[craigawoodman]

It is the movement of the tyre bead, valve, etc as it rotates. Some pressure in, some out, along with a bit of osmosis. The tyre is not a perfectly sealed environment. The bead and valve stem move as the tyre rotates and heats up. Moisture that gets into this area can be drawn in by the movement of the bead/rim interface (most tyre beads are angled, along with the rim). Same if you do not run a valve cap, moisture can sit in the valve when stopped and be drawn into the tyre. Same as the rubber valve spins around and moves and the surface between it and the rim can draw moisture in.



We are not talking a lot of moisture/water, but then you don't need a lot to create a saturated environment.



With earthmover tyres, as most haul roads are watered, you can put a tyre onto a brand new rim and remove it 18 months later and the combination of moisture in the air and an elevated temperature will have corroded the internal metal surfaces of the rim - but the external surfaces are fine. This is on a tyre with a bead width of 4" and an operating pressure of 110psi cold and 135psi hot. The rubber expands and moves and this can draw in moisture like any capillary action through a very small or microscopic opening.



The liner itself is also not totally impervious to leakage. For this reason, liners exposed to chemicals or even sunlight for too long can embrittle and become porous - but this normally leads to mechanical separation. In earthmover tyres, this can lead to a major tyre fire.



Craig

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[Samariter]

Tyre pressure makes a big difference

For Street tyres on 17 inch I prefer 33 front 36 rear PSI and I am adjusting +3 for Autobahn and -3 for Mountain passes. If you are tracking with street tyres you may have to adjust even way below 33 depending on the course layout.

The semis I run with 23 and 26 PSI.

In any case you have to play around a lot to find the setting that is right for you.



The Porsche Manual says 36 PSI all round if I am not mistaken ...



PS all values cold

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[lbpesq]

INteresting

[quote name='Cloud9...68' timestamp='1368587277' post='142725']

I have also read that newer generation tires perform better at higher pressures than a lot of people are used to from past experience. But rather than speculate and spend a ton of time (and rubber) experimenting, it seems like this gadget would provide some very valuable data to answer what is really the optimal tire pressure (and alignment settings as well):



http://www.opti-grip.com/optigrip/Opti-Grip.html



It places three infrared temperature sensors inside each of your fender wells, allowing you to monitor the temperature across the face of your tire in real time. Seems like a great idea, but I couldn't find any legitimate reviews on it - just lots of people asking if anyone else had used it. I guess the price would put a lot of people off, but I'm sure the pros use this kind of stuff all the time. Thoughts?

[/quote]





Interesting. Anyone ever tried the remote pressure sensors?

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[ds968]

[quote name='lbpesq' timestamp='1368632085' post='142737']

Interesting. Anyone ever tried the remote pressure sensors?

[/quote]



give it a week, I have a feeling someone we all know will likely hve these installed on his car..in a flash <img src="/forum/images/smilies/968/rolleyes.gif" class="smilie" alt="" /> . it's probably the only gauge ever made to measure and monitor anything car related that's missing in that vehicle <img src="/forum/images/smilies/968/tongue.png" class="smilie" alt="" />

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[flash]

lol - i've used others, and have something like them in 2 cars. never thought about it on the 968 though



hmmmmm..........

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[ds968]

O.T. somewhat, but I rented a SUV not too long ago ( on one of my trips to LA) and it was either a Ford or a Chevy, which had a warning system for low tire pressure. A great thing to have, except this one did not identify which tire it was ( and with the systems being as sensitive to trigger the light to me on for as little as a 2 psi deviation ) good luck trying to figure out which of the four tires you need to fill, unless it's obvious. Well, it was not ! Drove me insane - I filled what to the best of my guess was the culprit tire, got in, the signal was still on, so I filled all of them and then the friggin' warning indicated the psi is above the recommended level !! Arrggh . Now, before you ask why I did not fill them all to the same psi, its because I don't carry a tire pressure guage when I rent a car, the gas station air pump did not have a pressure indicator, and I was not about to go in search of an auto parts store or a gas station that sells those things. Lucky it was a rental and I could not care less about what I'm riding on unless the tires were completely flat, but imagine someone buying that car and having to deal with that crap . What brilliant engineer designed that feature ?!

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[Cloud9...68]

I haven't found any reviews of the opti-grip - just a bunch of people on various forums asking the same question - "Anybody try these...?" I think it would be a total waste of money on a street car, but for a track car, if it works as advertised, it seems like a great way to dial in tire pressures and alignment settings to prioritize the car's speed through the most important corner or corners on a particular track, since it records tire temperatures in real time, as opposed to after they've had a chance to cool down after the car is in the pits.

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[Rap]

Which one of he three are we talking about? DS how did you know I was thinking of ordering this. Are you like pysco or something? Lol

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[flash]

the SL550 has two different types of systems it can come with. one reads pressure. the other only reads if it is "out of spec". the latter can be "adjusted" by the dealer so it will read the range you want. i set my range for where i want to run the tires.



the denali actually reads pressure in all 4. i really like that feature. when i was towing, it was very helpful in determining the correct pressure for the load.

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[Inkedupfatboy]

My element and Ridgeline both have tire pressure monitor systems. Every time it gets to a certain very low temp for Floirida, the wife's Element sets off the warning system. Since it is cold, the air "shrinks" (I guess is the easy way to 'Splain it) and the tire looses pressure. The element takes a 140MPH speed rated tire (believe it or not) Once I check all the tires and fill them as needed, I have to drive the car to get the tires warmed up, so the sensors reset. They don't just sense the new pressures just by adding air.



The ridgeline having bigger all terrain tires have only ever set the sensor off once since both cars were new in 2007. The Element usually is good for setting off the sensor once a year in the late winter early spring.



I am sure that tread differences make a huge differences as the nascar and other drivers wiggle down the road to heat their tires up to get them sticky for the high speeds.



Just throwing it out there and seeing what sticks - lol



Ed

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[Kim]

The Carrera is like Flash's SL550. The "real" measurement, specific for each tire, works when the car is moving. The second system, working only where the car if stationary, compares each tire to the specs for that size and type (which is prgrammable, eg 19 inch summer, 18 inch winter, etc). The latter simply shows deviations - FL is -0.5 pound low, RR is +1.0 pound high, etc.

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[Cloud9...68]

OK, I just sent an email to the editors of Grassroots Motorsports magazine suggesting they run a test of the Opti-Grip in-wheelwell tire temperature monitoring system. Will be interesting to see if they respond. Since most questions about tire pressures and alignment settings can be answered by accurate measurement of across-thread tire temperature (or so I've read), a system like this should theoretically settle a lot of arguments with actual data.



But to be clear, I'm talking about the system that aims wheelwell-mounted infrared sensors at three points across the thread of each tire, not the in-wheel tire pressure monitoring systems a lot of new cars come with.

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[ds968]

I was trying to figure out on which thread I should post this, and since I have little patience for doing any search, I picked the first one that I thought was " eh, close enough " , lol.

So my six speed often sits for weeks on end at times, but even when it was driven regularly the tires never lost air. It still does not. Ever. And I mean not even half of a psi in an entire year ! By contrast, both my tip, and my MBZ and the other cars we have ( Nissans ) , all of which have different make and size tires on them, lose one psi or two every month or at least every other month . The six speed is the only car with Pilot Sport PS2 on it. Whether it's the tires themselves , or whether it's the valves and it has nothing to do with the tires is the question. I do remember one time when I had the PS2s installed the shop asked me if I want regular valves or the " premium " valves for an extra $ 2 or $ 4 or something negligible like that . The first thought was : seriously ?! I'm spending around $ 1,200 for the the set and you think I'm going to cheap out on crappy valves ? The second thought was : seriously ?! I'm spending $ 1,200 on the tires and you're going to charge me an extra couple of bucks for throwing in some decent valves to go with that ?

So I had not realized that some valves are better than others and you can ask for premium ones when you change tires. But still wondering if that's just a coincidence as to why the PS2s are not losing any pressure or if it has more to do with how the tire seal on the rims, vs other tires..? And I keep forgetting to ask for " premium " valves when I replace the tires on my other cars, thus unable to test the psi loss phenomenon :-) .

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[Bulti]

I've got to ask: are the tires of the 6-speed also filled with plain air? All tires should loose pressure over time because the air molecules go straight trough the fabric an rubber of the tire itself...

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[ds968]

Yes, plain air . No nitrogen or other fancy stuff . But hey, maybe California air is warmer than other air, and thus has bigger molecules , lmao. Incidentally, I just measured the PSI again on the blue car this morning - ( I had to inflate the Nissan Sentra tires because they lost a couple of psi in the last month or two and the low pressure warning light came on , so while the air pump was out anyway, I checked the other cars as well ) - still at the exact same 32.5 cold pressure I keep on all tires which it had in early springtime when I last put air in them. Ok, I know one of you wise guys is going to suggest the digital gauge is broken and stuck at 32.5 for the last six months , but it's just fine - I have six cars all with different readings using that gauge

Btw, I mentioned this psi thing earlier in the thread but the 2011 Nissan Sentra is another one of those cars which does not indicate WHICH tire is low on air when the alert light comes on. And just 2 or 3 psi below spec triggers the damn thing, so you can't tell which tire it is with such a small loss of pressure . So I have to inflate all and then set all four at the right psi - PITA !

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[Rap]

Air pump? Don't you mean compressor! Lol

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