Tires seem to be getting way too hot

[Hotrunner]

New to me 2015 335i XDrive Sport Line 49 K miles with 4 new Pirelli Cinterato P7 run flats (OEM tire size). I am concerned that the tires are heating up too much even when driven gently. Using an infa-red thermometer, I have measured front tire temperatures as high as 135 F after moderate driving for an hour or so on a typical warm summer day (85 F ambient). The brake rotors are staying relatively cool and are definitely NOT contributing to the elevated tire temperatures. The rear tires are getting hot also but generally are about 10-20 degrees cooler than the fronts. I am running the BMW recommended pressures plus 1 psi in all 4 tires (so that's 33 front and 39 rear, cold) and these pressures are verified using 2 separate tire gages. To further test my concern, I drove gently for 15 minutes early in the morning (overcast, no sun) with a pavement temperature of 58 F and ambient air temperature of 59 F. Beginning tire temperatures, taken in the garage which was a bit warmer inside, were 69 F on the front tires and 68 F on the rears. I drove gently at 60 mph and returned to the garage where I measure both front tires at 88 F and 75 F on the rears. So that's a 19 degree increase on the fronts after driving gently for just 15 minutes on cool pavement. The brakes were barely used so the rotors remained cool.

So here are my questions:
1. Is it normal for tires to get this warm this fast? My X5 has Goodyear run flats which don't get nearly as hot.
2. Is 135 F too hot for these tires? How hot is too hot?
3. This would also result in a corresponding increase in air pressure. How much is too much?
$. If this is not normal, what could be the cause?

Thanks in advance for your thoughtful answers!

[circuit.heart]

85F ambient and sunny means the tarmac will easily be over 100F. On top of that, friction in the wheel hub heats up the wheel, heat from brakes heats up the wheel to well over 150F in "moderate" mixed driving and wheel temp will try to equalize with tire temp even if you're not adding heat to the tire. The only thing removing heat from the wheel/tire assembly is airflow when you're driving. Rough guesses, the tire shouldn't be cooler than the road but I would expect it stays within 20F of the surface temp.

If your front alignment is off (toe in or toe out) you will be either flexing the sidewall more (long explanation) or worst case actually scrubbing the tread against the road, which will absolutely heat up the tire beyond desirable. Since you were able to heat up the front tires much faster than the rears, my first assumption is that the heat is coming from rolling the front tires. You can check the front toe alignment yourself.



Sub out the fancy plates for fast food trays or whatever, we're not looking for perfection just a cheap check. If the tape measures don't come close to reading equal (for example, 70" on one and 71" on the other), there's your problem.

If the front toe is fairly close to 0 (the difference between the tape measure readings), at least you've ruled out the obvious source of heat and can look into other possibilities like a faulty cord, faulty wheel bearing, dragging brake pads, etc.

[Hotrunner]

This is good, it did not occur to me that I could do a rough check of the toe myself. I took the measurements a couple of times and each time I saw about 1/8" difference 71" in front of tire, 71 1/8" behind so I guess that would indicate toe-in but I don't know how that would equate to degrees The alignment performed by the dealer (Not local, not a BMW dealer) at the time of sale with the new tires installed shows that the front toe had been out of spec and was adjusted to 11 degrees on both left and right wheels, but I don't know how that compares to the BMW spec. I should mention that the car goes perfectly straight and does not have any noise or symptom of a bad wheel bearing. It seems I would have to have bad bearings on both sides as both front tires are heating up about the same. It would be quite a coincidence to have faulty cords on both front tires, but I could swap the front with the rears to see if that changes anything. I had already ruled out a brake issue as the rotors and calipers are staying cool as evidenced by the IR temperature readings on those parts. Even the wheels were still cool following my short early morning drive. Only the tires that were getting warm, so I am sure the heat is being generated by the tires.

I think my next step will be to swap the fronts and rears, then depending on the results I may take it to our local reputable alignment shop to have it checked.

If anyone has any additional thoughts or insights - I'm listening!

[MarcoZandrini]

The primary cause of heat in a tire is internal flexing of the tread area plies. There’s a vid on YT in which a guy put a GoPro camera on the inside of the rim, and then mounted the tire. He put the tire on the car and drove the car. He then remove the tire from the and removed the tire. He removed the camera from the wheel.
The amount of flexing of the tire’s tread material is impressive. With the flexing comes the movement of the material plies-the tire’s “body” plies and the tread’s belt(s). This internal flexing causes friction as the layers flex in different directions.

[Hotrunner]

Yes I have seen that video.

[Hotrunner]

Well now I have swapped the tires front to rear and adjusted the air pressures accordingly (33 front and 39 rear). Then I did the same gentle early morning drive for 15 miles on cool pavement with no sun resulting in an 18 degree rise in the rear tires and a 30 degree increase in the fronts. The last thing I will try before getting an alignment check will be to increase the front tire pressure to equal the rears and repeat the drive. This should reveal if the 6 psi difference between fronts and rears results in that much more flex to increase the temperature that much.

If anyone else could get me a read on your front vs. rear tire temperatures after driving I would be curious to know if you are seeing such a large difference.

Thanks.

[MarcoZandrini]

The iDrive tire pressure and temperature readout in my car shows the front tires getting 20 or 30 degrees warmer than the rears. This makes sense as the fronts steer the car. I wouldn’t worry about the temps.

[Hotrunner]

The iDrive tire pressure and temperature readout in my car shows the front tires getting 20 or 30 degrees warmer than the rears. This makes sense as the fronts steer the car. I wouldn’t worry about the temps.

Thank You Marco, that's exactly what I was hoping someone would confirm. My display only shows tire pressure, not temperatures, so that's the next thing I will go after to resolve (I was checking tire temperatures using an IR thermometer). In the meantime I had already gone ahead and increased the front tire pressures equal to the rears, but still measured similar temperature increases. Then today I had the alignment checked which verified the front toe is in spec. So I'm glad to have another data point from Marco because I was out of ideas for possible causes.

[MarcoZandrini]

You’re welcome.

[circuit.heart]

The fronts may steer the car, but you're not doing a whole lot of steering on the street + all four tires do cornering work if you are doing that kind of driving. What is the rear toe for comparison?

Front toe 1/8" in is within spec, but it's a lot - if you wanted to optimize, I keep all my cars (road, track) within 0-1/16" with passengers and fuel. Rear toe is often higher for stability under braking.

[Hotrunner]

The fronts may steer the car, but you're not doing a whole lot of steering on the street + all four tires do cornering work if you are doing that kind of driving. What is the rear toe for comparison?

Front toe 1/8" in is within spec, but it's a lot - if you wanted to optimize, I keep all my cars (road, track) within 0-1/16" with passengers and fuel. Rear toe is often higher for stability under braking.

The alignment performed by the dealer at time of purchase shows rear toe at LR 0.15 degrees and RR at 0.16 degrees with a resultant thrust angle of 0.00. This puts both The recent alignment (1,000 miles later) at a local shop shows LR at 0.21 degrees and RR at 0.12 degrees with a thrust angle of 0.05. In both cases the rear toe is in spec per the printouts, but the specs are different between the 2 shops which of course raises more questions. The printouts are in different formats so that means 2 different type alignment machines and software were used. I don't know much about alignment machines but the most recent one performed by the local shop was on a Hunter Hawkeye with full fuel / no passengers.

BTW front toe results and specs were also different between the 2 shops, which makes this all a bit more puzzling. I wouldn't think alignment would change much in 1,000 miles of highway driving.

[MarcoZandrini]

Different alignment machines, different results. I’d go with the dealer machine.

[autosecret]

When the temperature is high, the air in your tires takes up more volume, whereas when the temperature is cold, the air takes up less volume. Thus, when temperatures plunge, the computer in your car believes that your tires are low on air.

The inflation pressure in tires generally drops by 1 to 2 psi for every 10 degrees the temperature lowers. Also, when you drive your car, and the tires warm up, the pressure in the tires will increase one psi during each five-minute interval in the first 15 to 20 minutes you drive.

Tire manufacturers have a recommended psi, which dictates an optimal pressure level for your car and its tires.

However, that psi number is set for when your tires are cool. Ideally, when you add air to your tires in the wintertime, you should fill them up when they are still cool
If you leave your tires underinflated, it will cause you to lose some control of steering, increase friction, cause more wear on your tires, and decrease your car’s efficiency in using gas. However, if you overinflate your tires, your ride will be bumpier.