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Ranger wrote:
I would strongly urge for you to seek a psychoanalysis help about your unnatural fixation with brakes. There must have been some huge trauma in your life which has led to this condition.
oh, and I disagree completely with your assumption, by the way.
csrow wrote:
[quote]Ranger wrote:
I would strongly urge for you to seek a psychoanalysis help about your unnatural fixation with brakes. There must have been some huge trauma in your life which has led to this condition.
oh, and I disagree completely with your assumption, by the way.[/quote]
Re. needing psychoanalytic help. Let me introduce you to my teammate, SpecE30 series pshrink, Fred Switzer. He helps me with my fixations, and I encourage him to brake earlier into RA’s turn 1.
Re. brakes and tire temps. You don’t think that a 1000deg rotor is going to help heat up a directly connected wheel/tire? I would submit that there’s a lot more heat energy to be found in those rotors then a little scuffing of the rubber surface slipping on the turns.
During braking the kinetic energy of the car is largely transfered into heat. In contrast turning the car is a relatively efficient process, so there’s no reason for a large amount of heat energy to be absorbed by the tires. Sure, tire slip causes some heat, but accelerating the car in a turn(which is to say changing it’s vector, not speed) is a pretty darn efficient. Tire slip can’t add 10% to the acceleration. I bet brake rotors absorb the heat of 90% of the decceleration.
I’m gonna win this one.
In your universe, everything is less than six degrees removed from the almighty brakes.
I can not win.
Yes you are a wiener. oh I concede to your logic.
So all the people weaving left to right to heat up their tires are all stupid. Instead, they should be braking hard and heating up their tires that way.
155MPH wrote:
I do both. Breaking is the best way to get heat in the tires but zig-zagging around is fun, good at getting the crap off the tires and looks cool on the in-car video :X
155MPH wrote:
Yeah but…it is the friction of the tire scrubbing against the ground that heats the tread not the heat from the rotor.
Having said that, I can accept Scott’s theory that heat from the stinking hot rotors does contribute to pressure gain in the tire. How much so is debateable.
Carlton’s rotors (the left side at least) were glowing red hot as he braked for Sebring’s turn 7 last Thursady night. All that heat goes somwhere.
Don
Im not sure either but I think weaving helps to clean off and really heat up the outside edge of the tires that are not being worked as hard under braking. This is really the part of the tire you use in a corner… in our camber-challenged cars anyway.
Wow, this could bring up the whole brake cooling duct discussion again. Do you take them off to keep your tires hot? Or leave them on so your tires don’t get too hot???
DB
csrow wrote:
[quote]In your universe, everything is less than six degrees removed from the almighty brakes.
I can not win.
Yes you are a wiener. oh I concede to your logic.
So all the people weaving left to right to heat up their tires are all stupid. Instead, they should be braking hard and heating up their tires that way.[/quote]
I’m a wiener? lmao. That’s the kind of thing that ought to go on a big rear widow decal. But maybe “Ich bin einer Wurst.”
Dude, you just are too decent of a guy to effectively harangue another with disparaging names. This is clear because you have developed no skills in childish criticism and tauntage. Let me help:
Scott, you are full of shit.
Scott, you arrogant douchbag.
Scott, you are stinkee.
But back to the subject at hand. My perception is that on the warm up lap folks warm up their tires largely by repeatedly accelerating and braking. And that turning left and right, or scrubbing the tires, is intended to scrub off paddock gravel and dirt.
I don’t pretend that I have all the answers. Hmm. Ok, well maybe I do. But anyways, I’ve not tested all these ideas, but a 1000deg rotor is going to heat up an air mass only a couple inches away. The surface of the tire may only be a 1/2" from the air mass, but that surface might only be 200deg. So I’d contend that the heat of the rotor contributes significantly to heat of the air in the tire.
Sounds like this would be very likely hard to measure. It’s an interesting thought though.
That said under braking the friction of the tire (before slip) will generate heat which will warm the tire but I would think that PSI gain/loss would be very small/transient since you’re (in most cases) mostly on the gas and not the brake. Thus the majority of PSI gain/loss is from acceleration and turning. Not the rotors.
My $0.02. 
Ranger,
My apologies if my obscure humor has missed the mark. It’s a personal habit to always pronounce the word ‘winner’ as ‘wiener’ and it did not translate too well online.
This idea that hot rotor is bring up the temperature should be easy to test if there was a long straight that could be used.
Drive three times with the same starting tire temperature.
1)As a base line, drive at a fixed speed in a straight line and then measure the resulting temp.
2)Drive in a straight line at the same speed but with your left foot resting on the brake to bring up the rotor temperature. Measure the tire temperature.
As I stated before I disagree that the rise in tire temperature is mainly caused by the heat from the rotor. I believe it is due the the friction as the tire slides on the track surface.
Clearly the radiant heat from the rotors affects the temperature of the wheel and, in turn, the temperature/pressure of the air in the tire.
I will have reached se30.com nirvana when I can convince Ranger to do some side-by-side testing on black versus silver wheels.:laugh:
Steve D.
How about 5 spoke vs. 12 spoke wheels?:ohmy:
When I went to Driving Concepts racing school, they taught us to do both (brakes and scrubbing) and said that a lot of tire heat came from braking.
What about the heat that is transfered from rotor to wheel to tire…I have burnt myself changing tires without gloves…Just another angle…
Ok, I was wrong.
The friction does play a roll in heating up a tire but the main force behind the heat generation is the deflection of the tire as it is rolling.
Amount of the deflection and the speed of the deflection are the two main factor behind the tire temperature rise.
Higher the load and the faster the speed, more heat will be generated. The temperature rating of a tire is a rating of how fast the tire can dissipate the generated heat.
This report shows tire temperature measurement as a function of distance traveled twice around (about 4.4 miles) the Top Gear test track.
Starting from an ambient temperature of about 80 degrees, you can see the rise in temperature to about 200 degrees (front tires) at the end of two laps.
On the last graph, note the different temperature rise bumps on the left side tires verses the right side tires as the car take a tight left turn first followed by the two tight right corners (Chicago and Hammerhead).
There is no correlation between the rise of the tire temperature to the rotor temperature.
As a side note, it’s also interesting to see the temperature gradient across the tire at three spots.
csrow wrote:
[quote]Ok, I was wrong.
The friction does play a roll in heating up a tire but the main force behind the heat generation is the deflection of the tire as it is rolling.
Amount of the deflection and the speed of the deflection are the two main factor behind the tire temperature rise.
Higher the load and the faster the speed, more heat will be generated. The temperature rating of a tire is a rating of how fast the tire can dissipate the generated heat.
This report shows tire temperature measurement as a function of distance traveled twice around (about 4.4 miles) the Top Gear test track.
Starting from an ambient temperature of about 80 degrees, you can see the rise in temperature to about 200 degrees (front tires) at the end of two laps.
On the last graph, note the different temperature rise bumps on the left side tires verses the right side tires as the car take a tight left turn first followed by the two tight right corners (Chicago and Hammerhead).
There is no correlation between the rise of the tire temperature to the rotor temperature.
As a side note, it’s also interesting to see the temperature gradient across the tire at three spots.[/quote]
There isn’t enough in those charts to support any conclusions.
The rotor, hub, wheel, air and tire all all separate components of a system. Each has different heat conductivity, retention, mass, surface area and is subject to different amounts of convective cooling.
All these charts show is temp changes on the surface of the tire during a couple laps. Of course hot laps increase the temp of the tire’s surface. But that wasn’t the issue. The question was, do hot rotors contribute to air pressure changes?
It takes time for heat energy to flow. Red hot rotors won’t translate to 200deg air in the tires immediately. Heat energy has to flow from the hot rotor thru the hub and wheel and then to the air in the tire. Eventually, an equilibrium will be reached where the changing rotor temps and changing tire surface temps no longer change the air inside the tire.
Tire surface temps don’t tell us about what is going on with tire air temp or pressure. IR sensors oriented on the rubber’s surface don’t even tell us what is happening 1/8" deep in the rubber, or half of a tire revolution later.
Rubber doesn’t conduct heat well, that is to say it has a low thermal conductivity. We can’t rapidly heat up the tire surface and then draw conclusions about the temp of the air inside the tire. If the air outside a house rapidly increases, the temp inside the house changes only slowly. The house’s walls are insulated so they have low thermal conductivity.
One is a high energy source and the other is a low energy source.
And energy transfer is proportional to temp difference. Once the air inside of the tire reaches 200deg, if the tire’s surface temp is cycling between 180-200deg (of course I’m making all these numbers up), then the direction of heat flow will reverse. The hot air in the tires will keep the tire’s surface warm and not vice versa.
So I stil submit that 1000deg rotors do have an impact on the temp of the air in the tire. And therefore the air’s pressure.
Ranger wrote:[quote]
…
3) We have an air volume who’s temperature is affected by two inputs of heat energy. The tire surface is heating when it’s under stress and cooling when it’s not under stress. Maybe it’s cycling from 180-200deg. And then the brake rotors are absorbing huge amounts of info and cycling between 350deg to 1000deg has they turn the kinetic energy of the moving car into thermal energy. In contrast the amount of heat energy produced by the deforming and slipping rubber is miniscule.
One is a high energy source and the other is a low energy source.
And energy transfer is proportional to temp difference. Once the air inside of the tire reaches 200deg, if the tire’s surface temp is cycling between 180-200deg (of course I’m making all these numbers up), then the direction of heat flow will reverse. The hot air in the tires will keep the tire’s surface warm and not vice versa.
So I stil submit that 1000deg rotors do have an impact on the temp of the air in the tire. And therefore the air’s pressure.[/quote]
Ranger,
I promise this will be my last post on this subject. I think we are just going to have to agree to disagree.
I do have couple of questions about your model of how tire is heated up.
Do I understand correctly that in your model, the tire does come up to the operating temperature (let’s say 200 degrees) without the aid of the heat from the rotors? So, if I drive 70 MPH on a highway and not touch the brakes, the tire will still be at or close to it’s operating temperature?
In the mean time, if the brake is used, then the rotor starts to heat up and eventually will heat up the air inside the tire which in turn will heat up the tire rubber.
Now, how does the air inside the tire know when to stop heating up tire? Why would it just stop at 200 degrees? As you say, if the rotor is a larger source of heat, would it not keep on heating up the air inside the tire which in turn will heat up the rubber? If I have a tire that is set to operate optimally at 150 degrees, will the inside air temperature stop at 150?
If the rubber is being heated by the air inside as the main source of energy, why is there a temperature gradient across the tire surface?
If you have a car with inboard brakes, will the tire still heat up?
csrow wrote:
[quote]Ranger wrote:[quote]
…
3) We have an air volume who’s temperature is affected by two inputs of heat energy. The tire surface is heating when it’s under stress and cooling when it’s not under stress. Maybe it’s cycling from 180-200deg. And then the brake rotors are absorbing huge amounts of info and cycling between 350deg to 1000deg has they turn the kinetic energy of the moving car into thermal energy. In contrast the amount of heat energy produced by the deforming and slipping rubber is miniscule.
One is a high energy source and the other is a low energy source.
And energy transfer is proportional to temp difference. Once the air inside of the tire reaches 200deg, if the tire’s surface temp is cycling between 180-200deg (of course I’m making all these numbers up), then the direction of heat flow will reverse. The hot air in the tires will keep the tire’s surface warm and not vice versa.
So I stil submit that 1000deg rotors do have an impact on the temp of the air in the tire. And therefore the air’s pressure.[/quote]
Ranger,
I promise this will be my last post on this subject. I think we are just going to have to agree to disagree.
I do have couple of questions about your model of how tire is heated up.
Do I understand correctly that in your model, the tire does come up to the operating temperature (let’s say 200 degrees) without the aid of the heat from the rotors? So, if I drive 70 MPH on a highway and not touch the brakes, the tire will still be at or close to it’s operating temperature?
In the mean time, if the brake is used, then the rotor starts to heat up and eventually will heat up the air inside the tire which in turn will heat up the tire rubber.
Now, how does the air inside the tire know when to stop heating up tire? Why would it just stop at 200 degrees? As you say, if the rotor is a larger source of heat, would it not keep on heating up the air inside the tire which in turn will heat up the rubber? If I have a tire that is set to operate optimally at 150 degrees, will the inside air temperature stop at 150?
If the rubber is being heated by the air inside as the main source of energy, why is there a temperature gradient across the tire surface?
If you have a car with inboard brakes, will the tire still heat up?[/quote]
Tire’s heating up without the aid of heat from the brakes. Temp distro patterns have an important time element. If someone heads out for hot laps on cold tires the hot laps will heat up the surface of the tire, but the cold (non surface) rubber, cold air and cold wheel will help bleed off heat. It takes time for heat patterns to reach somewhat of an equilibrium. Of course they are never at a true equilibrium because stress on the tire (causing heat) changes one moment to the next, the contact patch that is being heated is revolving around the tire, and the brake rotor temps are constantly in flux. But the tire’s air temps will be a lot closer to an equilibrium 10min into the hot laps then they were in the first 2 min.
So it takes heat time to move around and find an equilibrium based on all heat energy inputs and outputs. Until that equilibrium happens we are just measuring localized temps. The temp on the surface of the tire, just after the contact patch leaves the road, is not the temp of the entire tire, nor the temp of the air inside of the tire.
A tire traveling at 70mph on the freeway probably won’t reach it’s operating temp, call it 200deg, at all. There’s just not enough energy consumed by the tire and turned into heat. When we pull into our homes at the end of a commute our tire feels only pleasantly warm to the touch.
How does the tire know when to stop heating up. It’s a matter of equilibrium. The movement of heat is proportional to temp difference. So as the tire and wheel get hotter their ability to shed heat gets better. At some point the heat energy “intermittant pulses” entering the tire/wheel system reach an equilibrium with the heat radiated by the tire/wheel system. At that point somewhat of an equilibrium is reached.
Temp gradient on the surface of the tire. Heat requires time to reach a temp equilibrium, especially in a material that transports heat energy poorly. So if we hustle we can get inside/center/outside temps of our tires, but if we dawdle the temps will all blend into the same temp. This is also why probes are better then IR sensors for taking temps. The IR sensors only get the temp on the surface of the tires, which cool so rapidly that it’s hard to get good data. The surface has been cooling ever since that last turn exit. But probes measure the temps under the rubber’s surface, where temp changes occur more slowly. That gives us another minute or so to get decent temp data before the differences in heat blend together in equilibrium.
Inboard brakes. Yes, the tires will still probably get some heat energy from the brakes, but less because they are farther away. By the time the heat has traveled a meter down the 2cm axle it has been exposed to convection cooling longer.
Lets make an imaginary cut at the axle to hub joint. Because of the additional cooling, the heat energy from the 1000deg rotor might only have a temp of 300deg at the end of the axle. The end of the hub might only be at 100deg because the tire doesn’t generate a helova lot of heat, and the tire/wheel has a heck of a lot of surface area for convective cooling.
Now we join the axle to the hub and a 300deg surface mates with a 100deg surface. Heat energy now flows to the hub, wheel and tire. The additional heat increases the temp of the hub, wheel and tire, which increases it’s cooling efficiency until a new temp equilibrium is found.
I agree that we’ve beat this one to death and should move on. I’ll admit error. I’ve no pride.
