What's a good temperature spread along the tire?

I bought a thermal thermometer (one of those point and shoot things) and took readings on all 4 tires tonight immediately after a 1 hour drive. I was told that if the tire is hotter in the center than the sides than the tire is overfilled, and if it's hotter on the sides than the center that it's under-filled. But here's what I got:

The fronts read pretty consistently between 96-98F across the tire. Was about 1-2 degrees hotter at the center. Is that enough to indicate pressure overfill?

The rears read consistently between 98-100F, and was about 1-2 degrees hotter at the center.

But interestingly, the driver rear was about 7-9 degrees hotter at the inner most edge (inner = closest to the center of the car) and the passenger rear was about 4-6 degrees hotter at the inner most edge. And the fronts were both about 10 degrees COOLER (87F) on the inner most edge. Is that temperature difference related to camber? Is that good/normal, or bad? I've got -1.5 camber in front and -1.8 camber in rear. Any idea what is attributed to the fact that the rears were 4-9 degrees hotter at the inner most edge as opposed to the fronts being 10 degrees COOLER at the inner most edge?

Thanks in advance for any insight!

 

On the street or on the track? It doesn't really mean much if you are driving street. Most important is have your tire pressure set correctly. If you are driving on street where a lot of straights, you will see tire hit up the inner more as you have more negative camber. The negative camber is really put to use when you drive hard around corners, so if you are just street driving, it will only put the inner tire to use more. Not to mention you probably have more toe in the rear.

 

This was after driving on the street.

I recorded temperature like this because I had the understanding that the way to "have you tire pressure set correctly" is to find at which PSI you get uniform temperatures across your tire. Considering that different tires like different PSIs and the temperature your car recommends isn't always the ideal PSI if you swap tires from OEM, and especially if you drive aggressively.

So I'm just trying to put some sense to the temperatures I recorded.

I only have 1/16 toe-in in rear (each side -- 1/8 total). 0 toe in front. I can't imagine just that 1/16 toe-in in the rear would be the cause for the rear inner edge being considerable hotter and the front being considerably colder at the inner edge.

 

It's good that you are experimenting stuff, but as I mentioned earlier, you are not benefiting much on street. As long as you have proper pressure in the tires, you are fine on street most of the time. The method is really intended for track/autocross use. First of all, point and shoot thermostat will not give you an accurate data (It only get surface data which will cool off too quick, and you need temperatures that are stored in the tire). You will need a stick in style such as http://www.longacreracing.com/catalo...id=200&catid=7 in order to read the data accurately.

You have an alignment setting that is not within factory alignment range. Your alignment setup is good for track/autocross, but not so optimal for street use. The reason you are getting the inner tire hotter is because you use the tire on straights most of the time which the inner tire contact the road the most.
Sure your tire pressure can play a big rule on how you want the tire to contact the road, other than proper inflation, there are over and under inflation Over inflation, you will see the tire temperature on the middle of tires, and the middle tire will wear out quicker than the sides. Under, you will see the sides gets chewed up faster.

With that said, tire pressure play a big rule how the car can handle. Lower front tires pressures generally induce under steer, while more front than rear will introduce over steering. If you want the car to turn quicker, want to bump some pressure in the front tires.

Street and track condition are totally different conditions. On the track, there is no stop lights, you don't get a 5 mins straight ways without corners, you are pushing over 1.0 lateral g force on the corners, thus, the tires are always be happier with more negative cambers where they will give you more grip on the corners, and tire temperature will be even distributed out when around the corner. Tires on track will heat up very quick and generate pressure fast, thus most of the track guys will start the temperature a little lower than what they use on street, so the temperature will stay in the optimal grip range for the tires.

Just my 2 cents. If you want learn more info, read up tirerack articles. Have fun!

EDIT: I was based on 987 alignment, seeing your screen name as 981WC, I guess yours is a 981, so I don't know if the factory alignment settings are the same or not.

 

Thanks, boostpower! Yes, I have a 981. It's a 2014 Boxster with 19" Michelin Pilot Super Sport tires.

The only thing about my alignment that's very different than spec is the front camber. Front camber from factory was -0.5 and I changed it to -1.5. Rear camber is about the same (I actually lessened it slightly from -1.9 to -1.7) and gave it slightly less toe-in on the rear and front. So the rear should be behaving no differently that stock.

I've already read almost all of the TireRack articles. I do my research before asking questions to live people.

I drive aggressively on the street so that's why I set my alignment as such. My car gets redlined every single time I drive it and there's no highway on or off ramp that I don't tackle with a little bit of tire squeal (when there's no traffic holding me back). Still, those high G corners are maybe 2-5% of the entire driving and you're right, 90% or more is just driving in a straight line. But I want the performance alignment settings for those moments when I decide to have a little fun.

Previously, I was running the OEM tire pressures recommended on the door sticker: 29F 30R cold. I just changed to 33F 30R cold to try and get a little more oversteer out of it (I like oversteer!). I haven't taken enough corners with it yet to get a good feel for the difference, but at first brush the only real difference I seem to notice is a firmer (less comfortable) ride over bumps in the road. Should a 4 PSI increase make enough of a difference in handling that I should be able to tell instantly, or would I need a bigger increase to notice it? I definitely notice a slight difference in the ride firmness though.

This is the first car I've decided to play with tire pressure differences with so while I've read a ton about the theory of it, I'm new to putting it into practice and actually seeing first-hand how pressure differences affect performance.

 

I do the same when i see an on/off ramp, but cops here has been working very hard to earn their bonuses, so I have behave a bit lol. Generally higher pressure will stiffen up the tires, and could cause a bit more bumpy on the road. Normally with 4 psi increase, you should be able to see a difference. Other options to increase over steering would be increase front tire size, increase rear springs, stiffen rear sway bar...

 

Sounds like you have a good understanding of these concepts. You have too much negative camber for these driving conditions, unless you are driving straight for a good while before you measure tire temps. You should also closely monitor tire wear to see where you are getting the most wear. You want to set up your car for the most frequent driving you do, deviations from this standard course will be a compromise from the ultimate setup.