Checking tire temps while driving

[Elp_jc]

Newer BMWs (with coding to turn on the option) will show tire temperatures (well, the air inside the tire, for the pedantic) along with pressures. Pretty cool.

That's nice. I've only seen them on MB GT-Rs, McLarens, Porsche GT3 RSs, etc.

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[Norm Peterson]

I agree. Overinflation is bad. But it takes more than just a few psi to get overinflation. If anything, the tires may even be a bit underinflated at the recommended pressures. The recommended pressure is the bare minimum that the manufacturer deems safe; not necessarily the best.

Recommended inflation pressures need to have adequate rated load at that inflation pressure to account for gross axle weight. That would put the tire placard inflation recommendations a little higher than necessary for lighter vehicle loading conditions, but they're not likely to tell you that.

Recommended pressures almost certainly account for 2 or 3 psi increases in inflation pressure due to normal driving, so a 32 psi cold number probably corresponds to designing for actual operating inflation pressures more like 34 or 35.


Norm

 

[kiksbutt]

1) Overinflation causes the center of the tire to wear more than the rest
2) Overinflation increases the spring rate of the tire assembly and will make it harsher and more bouncy
3) Overinflation will tend to reduce the grip level of the tire

Your vibration should be fixed by balancing, not by overinflating the tire. 34-35 warm is recommended for most OEM size tires.

Well that’s the thing, they tried to rebalance and that was the best they could do. Either deflate and have vibration or keep it at 39-40 and drive comfortably. I have a PP2 so I haven’t experianced any issued with PSI being at those levels. Albeit, I only have 500 miles on the car.

 

[kiksbutt]

I'd take it to another shop/dealer.

That’s my nightmare. Take it in for one thing, two more issues after that

 

[Bikeman315]

That’s my nightmare. Take it in for one thing, two more issues after that

If I may ask, why are you switching tires at 500 miles and what did you get? Also where did you buy them?

 

[kiksbutt]

If I may ask, why are you switching tires at 500 miles and what did you get? Also where did you buy them?

I got rid of SC2 tires and swapped them for all season tire Cooper GS3 from tirerack. This way I can drive it in almost all conditions.

 

[Bikeman315]

I got rid of SC2 tires and swapped them for all season tire Cooper GS3 from tirerack. This way I can drive it in almost all conditions.

OK, sounds reasonable. Did you use an installer from Tire Rack? If you did contact them immediately. They will assist you in getting this ridiculous matter resolved.

I am interested though. Why pay for the PP2 only to take off the packages most important part?

 

[WildHorse]

https://en.wikipedia.org/wiki/Cold_inflation_pressure

 

[Norm Peterson]

Well that’s the thing, they tried to rebalance and that was the best they could do. Either deflate and have vibration or keep it at 39-40 and drive comfortably. I have a PP2 so I haven’t experianced any issued with PSI being at those levels. Albeit, I only have 500 miles on the car.

For their rebalancing - did your shop at least break the beads and rotate the tires halfway around the wheel? One thing you can do on your own next is to jack each front tire off the ground and rotate it by hand, watching for anything that looks like out of roundness or non-uniformity in the sidewall. I'm not sure how to check rear tire roundness on a PP2.

Tire Rack has been pretty good about fixing problems like this. Been through it a couple of times over the last 30 years or so. Two of the tires on my granddaughter's car were out of round by enough to see if you held something up close to the tread and watched the gap looking for it to vary.


FWIW, I'd have first looked at Michelin's PS4S if driving in cold weather (anything much below about 40°F) isn't a concern, or PS A/S 3+ in 285/35-19 if you do need cold weather capability (285/35's are a legitimate tire size for 11" wide wheels, and a 2 mph difference at 80 mph compared to OE generally isn't worth worrying about). Either of these tires would probably be closer to the PSC2 tires in terms of overall behavior than a different brand's all-season tire.


Norm

 

[Norm Peterson]

https://en.wikipedia.org/wiki/Cold_inflation_pressure

This ^^^

Too bad those wiki tables are so coarse.


Norm

 

[Norm Peterson]

Here's a more useful table.

Norm

 

[Bikeman315]

Here's a more useful table.
View attachment 481266
Norm

Both this table and the Wiki article discuss PSI vs. outside temperature, not internal tire temperature. That’s why I asked about the importance of internal temperature.

 

[Norm Peterson]

Both this table and the Wiki article discuss PSI vs. outside temperature, not internal tire temperature. That’s why I asked about the importance of internal temperature.

Those are internal temperatures, because it's the temperature of the contained fluid that matters, not the outside ambient. The tables are based on pressures measured at 68°F and heated/cooled from there. What is being assumed is that the outside atmosphere remains at 14.7 psia (a good enough assumption for us but perhaps not for Formula 1).


Norm

 

[WildHorse]

Just a FYI my tires were set 32 psi cold. Today after 25 miles in 33*c heat (so obviously the road is much hotter) My front 255/40R19 tire pressure was 35 psi, & my rear 325/30R19 was 35 psi. So a 3 psi gain.

 

[Bikeman315]

Just a FYI my tires were set 32 psi cold. Today after 25 miles in 33*c heat (so obviously the road is much hotter) My front 255/40R19 tire pressure was 35 psi, & my rear 325/30R19 was 35 psi. So a 3 psi gain.

That sounds normal but what were internal tire temperatures. Still not quite sure why for day to day driving it matters.

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