tomekz

How the heck do people inflate their cayman's? Tire pressure on my car is supposed to be 33 psi. Is this cold tires or warm tires? I have tried setting the tires to about 33psi but after driving for a while all four show 38 psi.

NightBlueTTS

33 cold is correct. It is ok that your pressures increase to 38 while driving.

OttawaSteve

I believe that cold is defined as 68F. As noted, a five degree rise is perfectly normal.

tomekz

thank you

Mike Murphy

Yep. Friction due to tires rolling under weight, plus massive torque from twisting, plus heat from the car will increase tire temps. Normal.

TMc993

Use a good gauge and don't depend on TPMS for exact cold pressure. As stated in another RL thread, TPMS is calibrated in BAR and rounded to PSI, so there may be a slight difference between gauge reading and the TPMS reading. Just set the pressures with your gauge, then use your TPMS to monitor inflation. As long as the ratios between "cold" inflation and "hot" inflation are uniform, you're good.

Mike Murphy

Here’s an interesting additional comment about tire pressure. I wondered how storing my car in a heated garage (55F) in the winter might affect tire temps when the outside temp is 0F, so I decided to test it out. After driving my car for about 45 mins outside and returning home, I noticed the tire pressure never changed at all. So 55 degree drop in outside temp was countered with the heat from driving, even with all that air cooling going on. Contrast this with track driving, where tire pressure can go up significantly in the same time period.

NightBlueTTS

Exactly. What I found helpful was to understand how this all works like as a system. My overly simplistic description:

What we are really managing are the “hot pressures” to ensure that they stay within a recommended range. For most street driving, starting with a cold pressure consistent with the door placard will keep you in the recommended range. There are of course exceptions to this rule, but generally you will be fine. It also depends on what you are optimizing for: longevity of the tire vs max grip.

On the track, we shoot for tire temps across the contact patch (measured in three locations) to stay within the tire manufacturer’s recommended temp range. This will typically correlate to a “hot psi” that can vary by tire eg some slicks I target 35/36 psi hot vs 32 for a different brand. To achieve these hot pressures, I’m usually starting a session with pressures in the 23-27 psi range depending on the tire and track temps. On track, the temps rise quickly through braking and lateral g’s — which are the activities that create the most friction/heat.


Hope this helps a bit. I’ve spent so much time managing tires for my track car that I’ve inadvertently gathered quite a bit of data.

absoluteczech

I've always done cold and under the impression stated pressure is to be done cold as well.
For those that want less of a swing in tire pressure, they should try nitrogen in their tires, It's a bit more stable. You can fill up for free at costco too

Mike Murphy

+1

Costco’s pure Nitrogen (compared with 78% air) is great because it has very little (if any) moisture, which can increase the life of the TPMS components inside the wheel, the wheel itself, and the tire itself. Together, these components are not cheap and there’s virtually zero premium getting nitrogen at Costco.

By contrast, air can have 20% humidity or well over 80% humidity, and that moisture can and will condensate inside the wheel and stay there forever. Granted, aluminum wheels and TPMS sensors that have anti-corrosion metals (brass, nickel, etc.) might not have much carbon-based steel, but oxidation and failures still occur, not to mention the wireless circuitry and battery are not bulletproof.

I just wish Costco by me had a road-force balancing system instead of the usual tire balancer. No biggie though.

Visual

Wow, I actually had no idea Costco had nitrogen filling stations. I looked into it and it seems like they're just right outside the tire center for anybody with a membership to use. I'll have to check it out next time I need to inflate my tires. Do you just completely deflate your tire filled with regular air there and fill it back up completely with nitrogen? I'd go during non-peak hours so I'm not taking forever filling up my tires and making people wait.

absoluteczech

Technically they don't even check if you have a membership. Yes, deflate and inflate otherwise you're mixing / diluting it. Now I have been told that they DO in rare cases run out of nitrogen, so if you completely deflate and it runs out mid way you could be left with a flat tire lol. Maybe bring a pump as a backup. But again it's rare. I recall it happening to a coworker of mine

Visual

Thanks for the pointer. I'll be sure to bring my portable inflator to make sure I'm not stuck there at the Costco parking lot lol.

MrMoose

The advantages of nitrogen filled tires on a street car are mostly just marketing and have been vastly overstated. If you're racing where ~1 PSI pressure variation matters to you then go for it, otherwise it's just a waste of effort. Definitely not worth losing the ability to top off your own tires at home.

You're not even getting pure nitrogen from the places that do N2 fill: it's like 90-95%. Plain old air is 78% nitrogen.

maschinetheist

I must say that I noticed the same during today’s cool down. PSI hovered around 30f/33r.

good point about using a proper gauge. Longacre has served me well.