Tire temperatures on different sides of the car.

[Jersey Tom]

I'm an engineer in pro level American racing, yes.

Cool man. NASCAR I take it?

Correct.

The "positive feedback" you mentioned is likely to be stabilised somewhat by the fact that the effective tyre damping coefficient reduces as the temperature rises (all within limits, of course).

Depends what you mean by "damping coefficient" here, i.e. the loss modulus (which I agree should drop with temperature) or tan delta (effectively a normalized measure of loss rate to stiffness). In any event I don't particularly agree with adhesion always being better hotter. For that matter, depends what one calls adhesion.

Is there sensors or some other device readily available that can track the tyre temp real time and display that?

As mentioned, IR sensors on the tread surface are a popular item. Some people swear by them. Others think it's meaningless. Can put IR sensors inside the wheel too looking at the carcass - but that's just that, you have the liner (if there is one), plies, belts, and overlay between that sensor and the base of the tread.

Then yes, a tire company CAN put thermocouples cured inside a tire. A quick Google search reveals common uses of this. Think about how much strain a tire sees while driving... not an ideal situation for a sensor inside the thing.

In any event, as with most things... measuring tire temperature isn't necessarily about the "perfect" solution as it is "work with what you've got, it's better than nothing."

[hardingfv32]

Then yes, a tire company CAN put thermocouples cured inside a tire.

Could your develop a scale or data points of these thermocouples in the tire verses the exterior IR sensors in the lab?
Would you expect such data to holds it's correlation when using it on a normal tire, no thermocouples, on the track?

Brian

[Jersey Tom]

Then yes, a tire company CAN put thermocouples cured inside a tire.

Could your develop a scale or data points of these thermocouples in the tire verses the exterior IR sensors in the lab?
Would you expect such data to holds it's correlation when using it on a normal tire, no thermocouples, on the track?

Brian

Short answer - no, I don't think so. Long answer may have to wait until later.

[olefud]

IR vs. thermocouple got me to thinking. It would seem that a thermocouple piercing the surface would be better for pit tire temps since the surface temps are probably affected more by pit entry. On the other hand, an IR array recording surface tire temps in real time while running in anger would seem to be overall the better approach.

Does this at all correlate with reality?

[Kambu]

There are many systems that are available to measure tire temperature.
When I was still kart racing, I used a system that would mount on the inside of the wheel and attach where the tire valve would go. It showed the air temperature inside the tire, and tire pressures in real time on the dash. The problem with set up was that often it would take time to get to the mechanics after the race and it is impossible to measure tire pressures then, since the tires had already cooled down. The system also had the function to let out air by the press of a button. It was not allowed in many larger championships though, but you could still use it in practice.

I know that F1 teams and some lower formula class teams have experimented with thermal cameras at the side of the track, I am not aware if they started using it though.

[Jersey Tom]

IR vs. thermocouple got me to thinking. It would seem that a thermocouple piercing the surface would be better for pit tire temps since the surface temps are probably affected more by pit entry. On the other hand, an IR array recording surface tire temps in real time while running in anger would seem to be overall the better approach.

As I was saying.. some people still subscribe to needle pyrometers and pit measurements, because it's either what they're used to or it's all they've got. Personally I can't think of any good reason to use an IR gun in the pits though I see people do it here and there.

Some subscribe to the IR sensor and camera thing while driving on track. Others say that's a load of BS and not really telling you an awful lot of what's really going on.

I know what my opinion is, based on my experience and the hard data I work with. Some agree with it, some (including some of my competition and other "big names" out there) don't agree with it. So be it.

There aren't many universal truths in this gig. Which is good, as it keeps me employed!

[Cam]

JT, do you have thoughts on how to get and keep the tyres on the right window? Could this be done with better data acquisition on the fly during a race or is simply trying to make a car right in the first place then try to build speed second?

[Jersey Tom]

Ahh yes, staying in "the window." A good topic.

First, how are you even going to know what the "window" is? Where is it centered? How big is it? What is the window FOR? Traction? "Grip" (a four letter word mind you) ? Lap speed? Speed over one lap? Speed over many laps? Not all synonymous things, and are often fighting each other. IMO the line of "race tires work best within the range of X to Y degrees" is a crock because it's so vague and non-specific. "Best" is often subjective and is by definition a relative term.

In general though, I'd say the tire supplier has infinitely more control over how hot the tires run than the teams do. Easy to bring a tire that's just impractical and unworkable. Sometimes the tire company struggles to even control that heat, and so by comparison a race team engineer hasn't a shot of changing it at all really. You're just stuck with what you've got and are grasping at straws because it's the only thing you can do.

There's no magic to heat in tires. It's proportional to three things: (a) material properties, (b) deflection, (c) rotational speed.

For material properties we already know this is almost entirely in the hands of the tire supplier, aside from what you can do scuffing tires in practice. A very lossy or hysteretic material loses more energy to heat in a given strain cycle than something that isn't.

Deflection... well you're already piling on as much downforce as you can get away with, and your driver is already going as fast as they can, so those knobs are already bottomed out. With setup you can change how that load is distributed at any point in time a little bit, but if you want to add somewhere it has to go away somewhere else. That leaves tire pressure. Can't run too low or you blow the things out. Also with a high stiffness suspension if you're relying on tire spring rate for your suspension rate you can't just arbitrarily go up and down in pressure just to move the temperature needle as you're going to hurt yourself elsewhere with aero attitude or wherever.

Then there's rotational speed, where again you're already trying to go as fast as possible so it's not like you can tell the driver to "just drive faster" if you really think your temps are too low, and it's not good for finishing position if you tell your driver to slow way down if you think you're too hot. Though you can tell your driver to stop being an ass and killing the tires with throttle or brake if they are indeed doing so.

For the most part I'd say you're stuck where you're at with some small range of adjustment. But if the tire you choose (or are given) is way off for running temperature on a given platform... you're stuck. You can crank up the tire blankets I guess but as you take them off and drive, the tires are going to settle to wherever they want to be. As I say.. there are some problems for which there is no practical solution. IMO a big part of "for real' engineering is accepting that and identifying which battles you can fight and which you can't.

[Cam]

Awesome reply.

So are you saying that there's really no way the teams can ever really understand or get on top of these tyres?

[Jersey Tom]

Awesome reply.

So are you saying that there's really no way the teams can ever really understand or get on top of these tyres?

"Understand" is a vague term. Understanding is one thing, being able to make things happen is another. I understand quite well that some millions (billions?) of years from now the sun will expand as it dies off, engulf the Earth and incinerate it. Nothing we can do about it, just it what it is.

Perhaps that's an extreme example.

But I'd say that yes it's important to note that some aspects of tires / vehicle dynamics / whatever can't be "figured out" or "sorted" or "gotten on top of" by just noodling on it for a long enough time. Some things are what they are.

Want more heat in the tires... ring up your aero group, ask them for more downforce!

[Belatti]

Using a simple IR pistol for measuring tyre temp in the pits may not be considered sophisticated but gives you some info and its better than nothing. And maybe it can be all you have for some amateurish series.

You may not know whats exactly happening in the specific moment you need to know, but after all the process is an accumulation one.

I have good statistics about tyre temps measured in the pits, the correlation with pressure increase its good and matches. The camber, too.

Regarding the "window" problem JT mentions, well, at least in my case I have solved a couple of issues aided with that simple and cheap IR gun: a new junior formula chassis that was succesful qualifying but not showing strong pace for the whole race. Arround lap 10 it begins to oversteer quite a couple of drivers agreed. The issue was, rear tyres temp increased more than fronts, according to pit tyre temp measurements. But the effect didnt show up in the pace fo the 5 qualy laps. The solution was a to move weight to the front, not an easy task as there is no ballast. Althoug we could change a little bit gearbox, driver, battery and radiator position, enough to shift arround 2%.

[flynfrog]

Using a simple IR pistol for measuring tyre temp in the pits may not be considered sophisticated but gives you some info and its better than nothing. And maybe it can be all you have for some amateurish series.

You may not know whats exactly happening in the specific moment you need to know, but after all the process is an accumulation one.

I have good statistics about tyre temps measured in the pits, the correlation with pressure increase its good and matches. The camber, too.

Regarding the "window" problem JT mentions, well, at least in my case I have solved a couple of issues aided with that simple and cheap IR gun: a new junior formula chassis that was succesful qualifying but not showing strong pace for the whole race. Arround lap 10 it begins to oversteer quite a couple of drivers agreed. The issue was, rear tyres temp increased more than fronts, according to pit tyre temp measurements. But the effect didnt show up in the pace fo the 5 qualy laps. The solution was a to move weight to the front, not an easy task as there is no ballast. Althoug we could change a little bit gearbox, driver, battery and radiator position, enough to shift arround 2%.

why not run lower starting pressure in the rears for the race or a softer spring? I do follow your school or race car tuning. When I worked on stock cars we has max shock travel tire temps in the pits with a needle, a scale to get the balance correct and a tire pressure gauge. I am no JT when it comes to suspension but this can get you pretty close.

[DaveW]

Depends what you mean by "damping coefficient" here, i.e. the loss modulus (which I agree should drop with temperature) or tan delta (effectively a normalized measure of loss rate to stiffness). In any event I don't particularly agree with adhesion always being better hotter. For that matter, depends what one calls adhesion.

Specifically, the imaginary component of tyre stiffness, evaluated as the frequency response function of CPL per unit tyre deflection averaged over a nominated frequency range.... The numbers are converted to an "effective" damping coefficient for conveniece. As an example, here are the estimates of the first few runs of a test. Run1 was with tyres at rather less than ambient, Runs 2&3 were for "hot" tyres (run3 slightly cooler than 2), & the remainder were with "cold" tyres that were more close to ambient (one would guess) - and had tyre pressures modified to match the vertical stiffness of the hot tyres..

It is easy to build a picture, with all else constant, of a tyre being heated rather less with each succeeding revolution as the temperature builds, reaching an equilibrium condition at some temperature that is not far away from optimum (whatever that may be). The perennial problem with a race car is that there are two sets of tyres, both of which have to be looked after, managed by a driver, who will happily lean on the "working" axle at the expense of the non-working axle. This can lead to the destruction of one, the other, or both, sets of tyres if they are not well matched to the car (or, more correctly, if the car is not well matched to the tyres).

Belatti mentions one (c.g. position) & flynfrog another (tyre pressures) way of matching a car with its tyres. I could add springs, bars and dampers to those that I normally look at closely on a rig. Actually, there are any number of others, normally taken care of by competent design engineers & mechanics (the current craze seems to be semi-seized CVJ's, for example). To follow on from Belatti's example, I once helped to set-up an open wheeler (F2000, if I recall correctly). The engineer reported that, actually a "rig setup" didn't improve lap time, but it did make the tyres "60 laps tyres, rather than 6 laps". It follows, I think, that I matched the vehicle better to its tyres - I am still working to understand fully the why.

[Jersey Tom]

Belatti mentions one (c.g. position) & flynfrog another (tyre pressures) way of matching a car with its tyres. I could add springs, bars and dampers to those that I normally look at closely on a rig.

For sure, those and others (differential, aero balance, etc) are all typical adjustments to get the tire / vehicle system to behave as you want it to. However, they all require the tires to still be "close" to begin with. Most of the time that's the case - be it an OE submission or a professional race car, and on the chassis side of things we generally get used to feeling like you can tune the car to the tires.

Sometimes it isn't the case. There are things a tire company can do (intentionally or otherwise) which will just absolutely blow away any realistic chassis adjustment, no matter what you throw at it. I've seen that from both sides of the fence now.

The other side to this, is that even if your car and/or tires are crap... so long as you're less crap than the competition - then you've won!

[Belatti]

Right now Im far away from office and have little time to analyse properly the posts above. The thing I wanted to point out is that there were reasons for changing the weight rather than tyre pressures and springs, being the first that cold pressures are low and I would not like to make the thing "cheesy" (let alone dangerous) on the first laps and the second being aero, lateral balance and traction wich was superb. Now I know those change with weight distrib, but in this case the thing kept the good overall balance and started to treat the tyres better.