tyre temperature - the only thing that matters

[Belatti]

Here another question to tyre experts regarding tyre temperature.

Can you determine tyre damping coefficients measuring temperature? If not, how does tyre engineers determine it?

From all the suspension models I have seen (1/4, 1/2 or 7DOF full models) all neglect this important aspect. And I say important because, even if tyre damping may be small compared to shocks damping, in the present state to competitiveness that may be the gap for suspension and tyre tunning that can get you from the middle to the front.

[ubrben]

You can't determine it by measuring tyre temps.

If we do measure it, it's on a dedicated rig. Even then it's not done as a matter of course. It's of academic interest but has minimal practical use to be honest.

Ben

[DaveW]

Here another question to tyre experts regarding tyre temperature.

Can you determine tyre damping coefficients measuring temperature? If not, how does tyre engineers determine it?

Ben is correct, temperature cannot be used to estimate damping coefficient. However, it is possible to estimate tyre damping using a multi-post rig.

The solid lines on this frequency response function were obtained from measurements of a vehicle being excited by a swept "sine", constant peak velocity input to the tyres. The magnitude represents the gross stiffness of the front tyres of the vehicle (averaged left & right), whilst the phase describes how the gross stiffness is split between "spring" & "damping" (magnitude * cosine(phase) = spring & magnitude * sine(phase) = damping). The response function probably can't be trusted much below 3 Hz.

I have fitted a model spring & damper to the response function over the frequency range 6 - 10 Hz (as it happens). Model parameters are shown in the legends (Ks = spring stiffness (N/mm), Cs = viscous damping coefficent (N/mm/sec), & Cc = hysteretic damping coefficent (N/mm)). As you can see, stiffness varies with frequency (&/or amplitude), and damping is a mixture of both viscous (which can be included in a time-domain model) & hysteretic (which can't). Fortunately, perhaps, the damping component is relatively small compared with the stiffness component. That (in my view) doesn't make it unimportant, because damping is the mechanism that injects heat into tyres on-track.

To provide a "foot-to-earth", here are two-cycle "snapshots" of load-displacement trajectories (with mean load removed) taken at various times (frequencies) from the same recording. Parameters estimated from the trajectories are shown in the legends. Hopefully, the trajectories will help to understand the response function.

It is probably worth noting that tyre stiffness and damping of tyres varies with almost any parameter you care to think of including pressure, mean load, camber, input amplitude, frequency & temperature. The variation with temperature is interesting because both stiffness & damping decrease with increasing temperature. The reduction in damping with increasing temperature is important, because it explains why race tyres can be "worked" to achieve relatively consistent performance on-track.

[marcush.]

Here another question to tyre experts regarding tyre temperature.

Can you determine tyre damping coefficients measuring temperature? If not, how does tyre engineers determine it?

Ben is correct, temperature cannot be used to estimate damping coefficient. However, it is possible to estimate tyre damping using a multi-post rig.

The solid lines on this frequency response function were obtained from measurements of a vehicle being excited by a swept "sine", constant peak velocity input to the tyres. The magnitude represents the gross stiffness of the front tyres of the vehicle (averaged left & right), whilst the phase describes how the gross stiffness is split between "spring" & "damping" (magnitude * cosine(phase) = spring & magnitude * sine(phase) = damping). The response function probably can't be trusted much below 3 Hz.

I have fitted a model spring & damper to the response function over the frequency range 6 - 10 Hz (as it happens). Model parameters are shown in the legends (Ks = spring stiffness (N/mm), Cs = viscous damping coefficent (N/mm/sec), & Cc = hysteretic damping coefficent (N/mm)). As you can see, stiffness varies with frequency (&/or amplitude), and damping is a mixture of both viscous (which can be included in a time-domain model) & hysteretic (which can't). Fortunately, perhaps, the damping component is relatively small compared with the stiffness component. That (in my view) doesn't make it unimportant, because damping is the mechanism that injects heat into tyres on-track.

To provide a "foot-to-earth", here are two-cycle "snapshots" of load-displacement trajectories (with mean load removed) taken at various times (frequencies) from the same recording. Parameters estimated from the trajectories are shown in the legends. Hopefully, the trajectories will help to understand the response function.

It is probably worth noting that tyre stiffness and damping of tyres varies with almost any parameter you care to think of including pressure, mean load, camber, input amplitude, frequency & temperature. The variation with temperature is interesting because both stiffness & damping decrease with increasing temperature. The reduction in damping with increasing temperature is important, because it explains why race tyres can be "worked" to achieve relatively consistent performance on-track.

dave...there is a clear change in charecteristic when a tyre works or better said is worked correctly.
I assume or think it is possible that its damping charecteristics are quite different when the tyre is in the " window ",but for sure on a rig there is no way to get the tyre working as it is simply a tool not meant to be working tyres...
So again an area were vast experience and a nose for important things will pay out as you surely have ideas about this..
Do the tyres even get warm on the shaker?

[DaveW]

dave...there is a clear change in charecteristic when a tyre works or better said is worked correctly.
I assume or think it is possible that its damping charecteristics are quite different when the tyre is in the " window ",but for sure on a rig there is no way to get the tyre working as it is simply a tool not meant to be working tyres...
So again an area were vast experience and a nose for important things will pay out as you surely have ideas about this..
Do the tyres even get warm on the shaker?

Good questions....

I sometimes test heated tyres - which is why I know something about the effect of temperature on those tyre properties that I can "see". Interestingly (because the prime reason for rig testing is to set up dampers), tyre temperature affects all measurements, but not "optimal" damper settings for a vehicle. I did that test explicitly for a customer not long ago, when the difference in best damper settings hot c.f. cold tyres turned out to be 1 sweep (click) of damping (< 5% change).

Tyres do heat up a little (equivalent to between 1 & 2 psi of pressure), & I can plot changes in new ("sticker") tyre properties over time as they "run in", but any temperature change would tend to be localized (non-rotating tyres), & my test procedure attempts to gain maximum information with minimum energy input to the vehicle specifically to minimize temperature-related changes (damper characteristics, particularly).

It is easy to condemn rig testing as being completely unrepresentative of what happens on-track (which it is). However, it is surprising how useful such tests can be both for improving track performance directly & for developing an understanding of a race vehicle & what is (& isn't) important when refining a suspension set-up on-track.

[marcush.]

dave...there is a clear change in charecteristic when a tyre works or better said is worked correctly.
I assume or think it is possible that its damping charecteristics are quite different when the tyre is in the " window ",but for sure on a rig there is no way to get the tyre working as it is simply a tool not meant to be working tyres...
So again an area were vast experience and a nose for important things will pay out as you surely have ideas about this..
Do the tyres even get warm on the shaker?

Good questions....

I sometimes test heated tyres - which is why I know something about the effect of temperature on those tyre properties that I can "see". Interestingly (because the prime reason for rig testing is to set up dampers), tyre temperature affects all measurements, but not "optimal" damper settings for a vehicle. I did that test explicitly for a customer not long ago, when the difference in best damper settings hot c.f. cold tyres turned out to be 1 sweep (click) of damping (< 5% change).

Tyres do heat up a little (equivalent to between 1 & 2 psi of pressure), & I can plot changes in new ("sticker") tyre properties over time as they "run in", but any temperature change would tend to be localized (non-rotating tyres), & my test procedure attempts to gain maximum information with minimum energy input to the vehicle specifically to minimize temperature-related changes (damper characteristics, particularly).

It is easy to condemn rig testing as being completely unrepresentative of what happens on-track (which it is). However, it is surprising how useful such tests can be both for improving track performance directly & for developing an understanding of a race vehicle & what is (& isn't) important when refining a suspension set-up on-track.

of course with your testing it is possible to quantify the the tyre effect in the equation on track...

but of course the temp is not what is causing the effects it is the work of the tyres that produces the heat.....

[Belatti]

Thank you very much for your answers, again, Dave.

[DaveW]

of course with your testing it is possible to quantify the the tyre effect in the equation on track...

but of course the temp is not what is causing the effects it is the work of the tyres that produces the heat.....

I'm not sure I quite understand your question/statement, Marcus, but heat input is likely to depend on tyre cyclic_deformation * tyre_damping coefficient (without defining these too precisely), whilst heat loss is likely to be proportional to tyre temperature & the temperature & velocity of the air passing over the tyre. Hence, as tyre temperature increases, cyclic deformation will reduce (courtesy of increased pressure), and tyre damping coefficient will also reduce (as I noted above). Both will imply that heat input to the tyre will reduce with increasing temperature. At the same time heat loss will increase as the tyre temperature increases over ambient. A tyre will work "best" when the equilibrium temperature is equal to the optimum compound temperature (Pat Symonds called it the "glass transition temperature").

I think temperature is fundamental to understanding tyre operation, although I accept that it will vary both with time & location, so quantifying the effective temperature of a tyre is not a straightforward task. I recall colleagues of mine having endless fun drilling aircraft tyres to install thermocouples just above the carcass from bead to tread in order to quantify temperature build up during various phases of aircraft "ground operations".

[marcush.]

dave ,i only wanted to emphasize ,the ttrouble is not in the temp per se ,as you could just heat them up to the required temp..if that was the case.
The temperature window we see and wich is often talked about is the result of work done and loads aplied to the tyre correctly to conserve this equilibrium for as longas possible but not a thing of putting just heat into the tyre.
Or in other words:the term bringing the tyre into the correct temperature window or even stating to have issues with tyre temps is not correct.we should call it not working the tyres correctly ,so overworking or underworking the carcasss is what leads to the issues we see ...

ah someone read Racetech article..