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Professional Motorsport Data Analysis: IR Tyre Temp Sensor

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IR Tyre Temp Sensor

09.25

00:00 - While we can get internal tyre temperature data with our TPMS sensors as discussed in the previous module, this is only part of the story and with tyres being so critical to a car's performance, the more real time live data we can get about them, the better.
00:15 This is where measuring the external surface temperature of the tread comes in.
00:19 Which is usually done using a single or multiple infrared sensors pointed at the surface of each tyre.
00:26 In the past, infrared sensors were only capable of measuring a single surface temperature over a relatively small area.
00:33 This meant that in order to measure the surface temperature distribution of a tyre, we would need to have an array of sensors looking at each tyre in order to understand the temperature difference across the tyre surface from inside to outside.
00:46 These days, sensors that can scan the whole surface of a tyre, with a single sensor and output the surface temperature distribution are commonly available.
00:55 Obviously the tyres are moving with respect to the chassis, particularly with the front tyres turn in during cornering.
01:02 This presents a challenge to packaging the sensors as the ideal scenario is for the sensors to be mounted to the suspension such that it moves with the tyre and can be pointing at the same area of the tread at all times.
01:14 Having a single sensor per tyre simplifies this requirement as well as reducing the cost and wiring complexity by needing to buy less sensors.
01:23 At the end of the day, it's the layout and configuration of the car that will determine whether it's practical for the sensors to be chassis or suspension mounted.
01:31 It might also be practical to only mount the sensors for testing but not for competition.
01:37 These days, as with a lot of sensors on the market, it's becoming more common to use infrared sensors that communicate to the logger over CAN as opposed to connecting them directly to an analog input of the logger.
01:49 As with every other system that uses CAN, this simplifies the wiring but at the expense of a bit more initial configuration time of the system.
01:57 In a similar way to tyre pressures, the traditional way to measure the tyre temperature distribution is to measure in the pit lane after a run with a hand held pyrometer.
02:07 And it's important to understand that having infrared measurements doesn't remove the need for that manual check with the pyrometer, it just makes up for the traditional method's limitations and supplements it.
02:19 The problem with checking the temperatures in the pit lane is it's just a single snapshot in time and is inevitably recorded a while after the tyre was fully loaded on track.
02:29 Not only does this time delay have the effect of giving the tyre time to cool but the heat will also tend to bleed away from the hotter parts and into the colder parts, making the temperature split seem less drastic.
02:42 At this point, we also need to make the distinction between infrared and tyre pyrometer measurements.
02:49 An infrared sensor measures the outer surface temperature of the tread, whereas a pyrometer when being used correctly, while being affected by the temperature of the tread, also partially measures the temperature of the construction of the tyre.
03:02 Temperature generation within a tyre is the result of hysteresis which occurs both within the carcass and the tread of the tyre.
03:10 You can think of this as internal friction that generates temperature within the tyre.
03:15 The materials, manufacturing method differences for the tread, carcass of the tyre and ways they're loaded are vastly different and as a result the way the temperature builds up and is stored within different parts of the tyre is quite complex.
03:29 When we use a pyrometer to check the temperatures at the end of a run, it can tell us something more about the energy distribution inside the construction of the carcass while the infrared readings are telling us something closer to the way the energy is being distributed within the tread.
03:43 Obviously these two things are closely related as they're physically connected so temperature will flow in both directions between the tread and the construction.
03:52 When we measure the temperature distribution of the tread in real time on track, this can give us an indication of how the surface of the tyre is being stressed.
04:01 This is a function of many things but usually we're most interested in this temperature distribution in terms of wheel alignment, kinematics and tyre pressure.
04:11 If we're focusing on the wheel alignment, the 2 parameters we're generally going to be most interested in are the camber and the toe.
04:18 The static camber is what we measure with the car during setup, when the car is at rest.
04:24 When the car is on track, the static camber numbers go out the door, instead being replaced by dynamic camber.
04:30 This is a function of the static camber, suspension stiffness and kinematics of that particular suspension.
04:36 It's intuitive that the part of the tyre that is most heavily loaded will be generating the most temperature and clearly the more dynamic camber we have, the more vertical load will be applied to the inside shoulder of the tyre.
04:49 Using the tread temperature, we can get some idea of how the tyre is loaded, from inside to outside and therefore which part of the tyre is doing the most work.
04:59 Toe also influences the tyre tread temperature but thanks to a different effect.
05:04 Apart from being related to the dynamic slip angle the tyre experiences, toe affects how much of the face of the tyre, scrubs across the surface of the road which in turn affects the heat build up in the tread.
05:15 If the tyre is aligned with the direction of travel, which would be a zero toe angle while travelling in a straight line, there is no toe induced scrub and therefore no additional heat buildup.
05:26 With excessive toe angles the tyre will generate significant tread temperature on the inner or outer edges as a result.
05:33 Not only does this create extra drag on the car while it's accelerating, it will tend to wear and potentially damage the tyre on the edges with excessive tread temperature.
05:44 There are many reasons for running different levels of static and dynamic toe related to handling.
05:49 But being able to measure its effects on the tyre can be helpful.
05:52 It tends to get less of a consideration when discussing tyre temperatures but air pressure has an indirect effect on the heat of the tread in the construction.
06:01 The lower the pressure, the more internal deflection will be present in the tyre while it's being used on track.
06:08 This deflection leads to hysteresis which in turn generates additional internal temperature or to put it another way, the lower our tyre pressure, the more strain energy is absorbed by the tyre and the less by the suspension.
06:22 That carcass temperature is partially transferred to the tread which is what we can read with the infrared sensors.
06:28 This isn't the only way pressure affects the temperature though because the lower the tyre pressure the more stress will be placed on the inner and outer edges of the tyre as the carcass provides a higher proportion of the total vertical stiffness of the tyre.
06:43 This results in more heat buildup at the edges of the surface of the tyre so with higher tyre pressures, the carcass becomes more uniformly loaded and the centre of the tread tends to take more of the vertical load.
06:56 This results in more heat buildup in the middle of the surface of the tyre and obviously this has a relationship to the surface pressure distribution that the tyre's experiencing as well.
07:07 So what is the right temperature distribution to tune for? Very simply put, it's the one that makes the car fastest while remaining reliable.
07:15 As you probably guessed, there's no simple answer that covers all situations because there are just so many variables at play, even just looking at a specific model of tyre.
07:25 With that said, and as a general guide and starting point for road racing, it's normal to aim for a hotter inner edge relative to the outer edge when mid corner.
07:35 This comes from the fact that modern tyres always make more lateral grip with negative dynamic camber during cornering.
07:42 We know that when we have more dynamic negative camber, we're applying more load to the inner edge of the tyre which we'll see through the temperature buildup of the infrared sensors.
07:52 Every chassis, driving style, road surface type, track configuration, specific tyre, weather, ambient temperature and session type will have different optimum targets.
08:04 In reality, it's impossible to find the optimum settings without extensive tyre testing.
08:10 Unless you're involved in very high levels of racing, even the tyre manufacturer will only be able to give you broad recommendations or targets for inflation pressure and temperature distribution.
08:22 Unless you're competing in a series with multiple tyre manufacturers fighting with each other, the tyre manufacturer's primary concern is going to be geared towards reliability over peak performance.
08:33 So we also have to take this into account when they give out advice.
08:37 However as a ballpark target for tyre temperature distribution, a good starting point is to aim for a rough difference in external temperature between the inner and outer edges of 10-20°C on average at mid corner.
08:52 This is a safe place to start and from there, we can experiment with our tyre pressure and wheel alignment settings to see what's most suitable for each individual situation.
09:01 It's worth noting that anything that adds stress to the tyre, particularly low pressures and high camber, is increasing the risk of a tyre failure.
09:10 In the case where sustained high speeds are involved, this increases the risks even further.