IR tire temps vs. temperature at the core

[Poe]

digging up a 2 year old thread for a sales pitch....followed by another in just minutes!

[Neil_Roberts]

Here is an example of the things you can learn from IR tire temp sensors:

http://thinkfastengineering.com/2012/08/solo-heat/

The surface is where the grip happens, so that's what I'm most interested in. Core temps are of primary interest to the tire manufacturers because they need to monitor the margins to blistering and carcass failure.

[Jersey Tom]

Originally posted by Neil_Roberts:
The surface is where the grip happens

Can't say I agree with that.

[rrobb]

Can you elaborate Tom, or is it top secret?

[Dash]

rrobb,

I'm not a tire expert, but it depends on the makeup of the whole tire.

Basically to get "grip", you have to stretch the tire in some direction. You then get a reaction force that is very, very, basically summarized into F = K * x where K is the spring force and x is the displacement and F is the force or "grip" the tire can put out.

Rubber can be referred to as black magic, because it behaves in a very unlinear pattern when stress is applied ( stress - strain curve is not straight ). Adding in temperature variations make this unlinear curve change shapes. Hotter generally means softer, and colder generally means harder. Really cold tires can go through a glass transition and become a brittle plastic. Really hot tires can become goop. There are then chords and stuff running inside this rubber to give it extra strength and shape. This whole big mess of stuff working together is whats going to give you grip.


Hope that shed a little light and didn't confuse you to hell and back.

[rrobb]

Thank you for your response.

Given the nature of my question, it was right for you to assume that I was looking for some tire basics.

I was looking for more of an understanding as to how temprature effected components other than the compound.

My assumption has always been that the belts and such are realtively immune to temp, while the compound is highly sensitive to it.

Given his background, and the nature of his response in this thread, I was thinking that Tom might be alluding to something along those lines that might be intersting.

[Dash]

I figured you meant you wanted a good explanation, but figured I could take a stab if you just wanted a little bit of info.

I'd like a good explanation myself.

[Jersey Tom]

Without getting much into it, as Dash mentioned and is available in the public domain (see the work of Persson)... in-plane (lateral, longitudinal) tire forces are not generated by a Coulomb friction model as we are taught with a block on an inclined plane in physics class, where the surface is really the only thing that matters.

As an aside, with whether or not the belts and things are temperature sensitive... everything in a tire is surrounded by "compound." There's tread rubber, there's rubber around the belts, the plies, the bead, you name it. The whole thing is a composite structure of a fabric or steel reinforcement within a rubber matrix.

I'll leave it to you all to consider how that reinforcement might be loaded, to what extent the surrounding matrix's mechanical properties are temperature sensitive, and what effect that would have on things.

But don't spend too much time on it, probably more important things to focus on. Just some academic food for thought when it's 2am and you're sick of welding terribly fit frame joints, take a break, have a beer, and contemplate the universe.

[Moop]

I would think that the temperature of the rubber on the surface would influence how much grip can be generated, as all the force has to pass from the road to the tire and hence through that rubber on the surface. In fact, the TaMe tire model(which has achieved a level of correlation that I think is pretty impressive) uses a surface friction coefficient dependent locally on contact pressure and temperature to calculate the lateral and longitudinal forces.

I would also think that as the core rubber heats up, it'll become more soft and compliant, so you'll have to stretch the tire more(or put it at a higher slip angle) in order to generate the same amount of grip(assuming that the tire surface temperature stays the same through the whole ordeal).

Am I missing something here?

On a side note, has anybody had any luck chasing down the paper by Fevrier and Le Maitre "Tyre Temperature Modelling: Application to race tyres"? Supposedly, it has more details on the model. I spent a good while trying to find it purely for interests sake. I even got a guy from the school's library to help me look for it, and even he couldn't get a hold of it.

[Jersey Tom]

My understanding is Tametire considers the bulk temperature of the entire tread - which should be a good clue. Been a while since I've gone through any documentation on it, so I could be mistaken.

In any event the bit about all forces having to be transmitted through the surface of the tire, to me comes across as still assuming that the tire/road interface is 2 dimensional - it isn't quite. It does have depth, and tire forces are not just a function of traditional friction. As I said earlier I think Persson's work goes over this well, as does Pacejka's (different aspects of it). Both readily available in the public domain.

Beyond the more academic side of things there are practical challenges to IR measurement, including varying emissivity of the tread surface.

Without a doubt there's plenty of hand waving and mixed beliefs when it comes to this topic. Some of it is arguable one way or another based on individual's own anecdotal evidence... some is flat out myth. Suffice to say that in my opinion IR / surface temperature measurement is far from the holy grail or "the answer." May work acceptably well for some people's requirements, and completely not for others. Like anything in engineering I'd say you have to know the strengths and limits of any data or process, or you can get yourself in trouble. Almost more important to ask yourself, "What CAN'T this tell me?" and not just "What CAN this tell me?"

Really not much black magic to this stuff, just an issue of (a) the public domain information available [of which there's a lot] isn't obvious to find unless you know what to look for, (b) concrete data is hard to come by because of IP and competitive advantage, which leads to (c) massive amounts of conjecture and speculation which once repeated enough times is assumed to be fact.

My 2 cents on it anyway. Individual opinions and experiences may vary!