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      01-13-2021, 05:18 PM   #1
medphysdave
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Cup 2 Tire pressure

I went to Costco today to add a bit of air to the tires. The door sticker recommends 32psi. Interestingly the track connect app for these tires suggest 38psi hot. What's everyone running?

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      01-13-2021, 06:21 PM   #2
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That sounds pretty close for an all-around recommendation. Recommended "cold" pressures assume a rise in pressure once driving. That's why I ask techs never to touch my tire pressures. I watch pressures on all of our cars and it drives me nuts when my wife or son get an oil change and their tires all get set to the recommended "cold" pressure even though they drove in with hot tires. The next morning, they are all 4-5 psi low.

In normal driving, warm tires probably rise 4-5psi above their cold pressure. In spirited driving, 6+ psi wouldn't be surprising at all. At the track with R-comp tires, I target 38-39 psi hot and usually start at 31-32 psi cold. I usually need to bleed pressure off after the second session, and a few more times as ambient temps increase through the day.
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      01-13-2021, 06:27 PM   #3
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I'm playing with the temp right now to balance around town and highway. For normal street driving in cold weather I would think running at the higher end of the optimal hot range would be of benefit so the pressure is a bit higher when starting out cold. .
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      01-13-2021, 06:39 PM   #4
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Quote:
Originally Posted by medphysdave View Post
I'm playing with the temp right now to balance around town and highway. For normal street driving in cold weather I would think running at the higher end of the optimal hot range would be of benefit so the pressure is a bit higher when starting out cold. .
In some ways, I am glad I can't watch while driving. On track, I watch oil and coolant temps and that's honestly enough to occupy time between shifts on the main straight at most tracks. I am happy to wait until I come off into the paddock to check tire pressures. I have settled on the best pressures for my set-up knowing that the pressures I measure after parking are probably already slightly lower than their peak in the last hot lap. I usually carry 90% corner speed on the cool down lap with minimal acceleration and braking, so the tires are still pretty hot when I get parked.
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      01-13-2021, 06:42 PM   #5
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When I ran Cup2s on the street I would be anywhere from 32-36 with only slight change of comfort and steering precision.

On track it's another story, when going over 37 they would desintegrate very fast.
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      01-13-2021, 07:21 PM   #6
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No need to monitor the pressure on track. It logs the temp and you can scroll through the time log and watch the tires as they heat up. Pressure and temp.
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      01-13-2021, 08:46 PM   #7
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Quote:
Originally Posted by medphysdave View Post
No need to monitor the pressure on track. It logs the temp and you can scroll through the time log and watch the tires as they heat up. Pressure and temp.
That's great. Does the app make suggested changes based on readings, or is it all left up to you?
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      01-13-2021, 08:54 PM   #8
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Quote:
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That's great. Does the app make suggested changes based on readings, or is it all left up to you?
In track mode it does. In street mode it does not. Yet. I keep sending them my suggestions. I think there is value in optimizing tire pressure on the street in various seasons. I'm sure it can prolong tire life. It's also a safety mechanism as I can see when the tires are up to temp when it's cold out. Since the app is optimized for these tires and the weight of this car I trust the numbers it suggests.
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      01-15-2021, 08:07 PM   #9
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Mine were around 33 or 34 cold from the PCD. Hmm.
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      01-15-2021, 08:32 PM   #10
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Are you guys reading the temps off the iDrive screen or on a phone app?
I was under the impression that the Cup2 option did not include the internally mounted sensor that feeds the Michelin App.
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      01-15-2021, 09:14 PM   #11
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Quote:
Originally Posted by DCC View Post
Are you guys reading the temps off the iDrive screen or on a phone app?
I was under the impression that the Cup2 option did not include the internally mounted sensor that feeds the Michelin App.
Track connect app. I bought the kit with the sensors.

It's incredible how much heat goes into the tires under mild braking. It can easily add 10 degrees F to tire temp. Then it cools back down after driving for a few minutes. I did roughly 130 hwy miles this evening and the tire pressure increased about 3psi per tire. I need to add another 2psi to the tires. I do notice the ride firm up a bit from when they were at 32 psi.
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      01-16-2021, 10:26 PM   #12
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Anyone have literature on the interplay between road temp and tire temp. How is traction impacted when tires are up to full operating temp on a cold road? I'm finding that even in cold conditions the tires come up to temp reasonably quickly.
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      01-17-2021, 02:34 PM   #13
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Definitely notice an increase in turn in sharpness between 34psi and 36psi.
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      01-17-2021, 06:15 PM   #14
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Quote:
Originally Posted by medphysdave View Post
Definitely notice an increase in turn in sharpness between 34psi and 36psi.
A positive change (better steering) or a Behance one with higher PSI?
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      01-17-2021, 06:46 PM   #15
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Quote:
Originally Posted by MadBimmeRad View Post
A positive change (better steering) or a Behance one with higher PSI?
The car changes direction like it's on rails. I'm really impressed. I still haven't pushed it hard enough to unsettle the chassis in corners with lower 33psi, or 37psi all the way around. I'm pushing cautiously, so this might be meaningless.

If you want comfort, the 32 to 34 psi is ideal. Matches very well with comfort setting on suspension. 36 to 38 psi and ride is much more firm. 36 to 44psi is considered the green zone on the app.
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      01-17-2021, 06:50 PM   #16
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On to the TPMS sensors. I'm not going to debate folks in their preference. My TPMS sensors show 15F-30F cooler at each tire. At this rate it is clear to me why poeple would say summer tires never get up to temp when cold. If you measure at the TPMS, they don't. If you measure the backside of the center of the contact patch they easily get up to temp. If you want to be cautious, then don't push your car until the TPMS tells you your tires are up to temp.
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      01-17-2021, 08:40 PM   #17
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Quote:
Originally Posted by medphysdave View Post
Quote:
Originally Posted by MadBimmeRad View Post
A positive change (better steering) or a Behance one with higher PSI?
The car changes direction like it's on rails. I'm really impressed. I still haven't pushed it hard enough to unsettle the chassis in corners with lower 33psi, or 37psi all the way around. I'm pushing cautiously, so this might be meaningless.

If you want comfort, the 32 to 34 psi is ideal. Matches very well with comfort setting on suspension. 36 to 38 psi and ride is much more firm. 36 to 44psi is considered the green zone on the app.
Thank you for the reassuring feedback
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