Transient tyre characteristic

[timbo]

When we talk about tyre characteristics (softness/stiffness, c of friction etc) I assume static (e.g. when all forces are in equilibrium) measurements are discussed.
But what about transient response?
Can you make soft tyre that would come to equilibrium slowly, so it would be stiff when sharp input is applied.

I imagine it would depend on relaxation time, which in effect would depend on rubber physico-chemical properties. Would relaxation time be too short for transient characteristics to play any role?

[DaveW]

Drivers are sensitive to the way steering loads build up when turning the steering wheel. For a given set of springs & bar, linear front dampers cause a slow build up of vertical load transfer, & hence a relatively slow steering time constant. Increasingly "digressive" damper characteristics cause ever more rapid vertical load transfer & a reduced steering time constant, which drivers tend to appreciate.

Dampers can be too digressive, however, & then drivers complain that the tyres "buckle". I think this is driver-speak for transient under-steer when load build up becomes too fast for the tyres to "relax" into their loaded "shape". JT &/or Ben may well have a more rational explanation for the effect.

[speedsense]

When we talk about tyre characteristics (softness/stiffness, c of friction etc) I assume static (e.g. when all forces are in equilibrium) measurements are discussed.
But what about transient response?
Can you make soft tyre that would come to equilibrium slowly, so it would be stiff when sharp input is applied.

I imagine it would depend on relaxation time, which in effect would depend on rubber physico-chemical properties. Would relaxation time be too short for transient characteristics to play any role?

This is a fundamental difference between a "bias ply" formed construction and a "radial" formed construction tire.
However to do this with the same construction tire would be difficult (if not impossible) because a tire is "velocity dependent" in it's actions and essentially an uncontrolled spring. Though fairly recent shock technology deals with some of this, overall the tire is still uncontrolled in it's response and transient behavior. Also tire pressure difference (changing the spring rate) has some effect in control, but here again only to small changes of control.
Applying two very different velocities to the same construction tire will result with inconsistent results not "controlled" ones or differing responses.
Difference in tire construction may suit one driver and not another, and changes to a different construction (same type of tire,altering the construction and with same compound) may reverse this result. Ultimately it boils down to the driver adapting to the tires on the car. IMHO

[ubrben]

This is a fundamental difference between a "bias ply" formed construction and a "radial" formed construction tire.

Can you explain more about what this fundamental difference is?

Ben

[Jersey Tom]

I'd like to hear this 'fundamental difference' as well.

With regard to tire transients... many or most vehicle dynamics engineers have a hard time fully grasping the full scope of steady-state tire mechanics, the implications of test data, etc. Testing race tires is 50% of my job and I don't even have it 100% nailed. (No one does).

Transients are a while separate can of worms. You don't wanna go there Or at least I don't!

[timbo]

Transients are a while separate can of worms. You don't wanna go there Or at least I don't!

Well, a part of my question is if they do play a role.
It must be totally dependent on relaxation and "stimulation" time-frame.

[speedsense]

This is a fundamental difference between a "bias ply" formed construction and a "radial" formed construction tire.

Can you explain more about what this fundamental difference is?

Ben

Same car,same driver,same setup running two sets of the same size tires, alike compounds. One set bias formed the other radial formed.
Both tires are driven over the limit, at a point between the apex and exit of the corner (throttle on). The Bias formed tire, will reform it's grip level at a much higher velocity and more abruptly than it's radial counterpart, which will delay slightly longer before gripping the road once again.
The same differences happen on entry where a bias formed tire can be driven more abruptly on turn in (rotating or "pitching" the car into the corner} where the radial formed responds favorably to a smoother transition of change of direction and responds unfavorably to rotation or "pitching" in part due to delay of transient behavior.
Both are examples of horizontal loadings with "almost" opposing results.

With vertical loadings, a radial formed tire will respond favorably to a reduction in spring rate allowing a slower loading of the vertical weight, with an increase in total load. The Bias formed tire will respond favorably to higher spring rates with higher a velocity loading of vertical loads.

IMHO

[bill shoe]

I tread carefully here because others probably have more detailed tire knowledge than I do, so I'm reduced to bad puns and tire generalizations. My experience is from testing relatively generic street tires.

A simple way of thinking about tire stiffness is to think about sidewall stiffness vs tread stiffness. It is possible to make a tire with high steady-state gain (cornering force relative to steering angle) by using soft sidewalls and stiff tread. However, this kind of tire will have slow and awkward transient response.

Sidewall stiffness has more subjective influence on transient feel than steady-state response gain. If you bump up the sidewall stiffness to match the tread stiffness then the tire may feel strong and well coordinated. If the sidewall stiffness is too high compared to the tread stiffness then the tire can feel a bit numb, and I think this relates to the buckling feeling DaveW describes.

In street tire development programs the typical priority is to first decide on tread compound, next find a good balance of sidewall stiffness to tread stiffness, then fine tune other attributes. What constitutes a good balance of stiffness depends heavily on the car.

[Jersey Tom]

This is a fundamental difference between a "bias ply" formed construction and a "radial" formed construction tire.

Can you explain more about what this fundamental difference is?

Ben

Same car,same driver,same setup running two sets of the same size tires, alike compounds. One set bias formed the other radial formed.
Both tires are driven over the limit, at a point between the apex and exit of the corner (throttle on). The Bias formed tire, will reform it's grip level at a much higher velocity and more abruptly than it's radial counterpart, which will delay slightly longer before gripping the road once again.
The same differences happen on entry where a bias formed tire can be driven more abruptly on turn in (rotating or "pitching" the car into the corner} where the radial formed responds favorably to a smoother transition of change of direction and responds unfavorably to rotation or "pitching" in part due to delay of transient behavior.
Both are examples of horizontal loadings with "almost" opposing results.

With vertical loadings, a radial formed tire will respond favorably to a reduction in spring rate allowing a slower loading of the vertical weight, with an increase in total load. The Bias formed tire will respond favorably to higher spring rates with higher a velocity loading of vertical loads.

IMHO

I guess my follow-up question would be.. how are you defining "bias-formed" versus "radial-formed," and also how the compounds are "alike"

[speedsense]

I guess my follow-up question would be.. how are you defining "bias-formed" versus "radial-formed," and also how the compounds are "alike"

The "ply" as defined by the tire company and pointed directly at racing tires. A like compounds would the compound configuration number (IE a Goodyear 260 compound that comes in "bias" or "radial".)
Just like most that I know, if not all, that don't build their own tires, but purchase or lease them from the tire company, and pretty much go by what information they give us. If a bias ply isn't a bias ply, the company isn't saying so, yet represents them as so.

[ubrben]

I guess my follow-up question would be.. how are you defining "bias-formed" versus "radial-formed," and also how the compounds are "alike"

The "ply" as defined by the tire company and pointed directly at racing tires. A like compounds would the compound configuration number (IE a Goodyear 260 compound that comes in "bias" or "radial".)
Just like most that I know, if not all, that don't build their own tires, but purchase or lease them from the tire company, and pretty much go by what information they give us. If a bias ply isn't a bias ply, the company isn't saying so, yet represents them as so.

What Tom's getting at is that you clearly don't know what you're talking about. Your posts on this thread are full of lots of technical words and language but basically no genuine knowledge or insight... Should I add a smiley here? Go on then

Ben

[speedsense]

I guess my follow-up question would be.. how are you defining "bias-formed" versus "radial-formed," and also how the compounds are "alike"

The "ply" as defined by the tire company and pointed directly at racing tires. A like compounds would the compound configuration number (IE a Goodyear 260 compound that comes in "bias" or "radial".)
Just like most that I know, if not all, that don't build their own tires, but purchase or lease them from the tire company, and pretty much go by what information they give us. If a bias ply isn't a bias ply, the company isn't saying so, yet represents them as so.

What Tom's getting at is that you clearly don't know what you're talking about. Your posts on this thread are full of lots of technical words and language but basically no genuine knowledge or insight... Should I add a smiley here? Go on then

Ben

Really Ben? I'll put my racing experience up against anybody on this board, whether it's pro or club racing...
How many pro championships have you won?
How many race cars and types have you worked with?
How many races have you worked?



My knowledge comes from actually working in the field for 20 years...not from what I hope to do....

[Jersey Tom]

Ben's credentials speak for themselves. I'll let him elaborate if he cares to.

But for what it's worth.. particularly for race tires.. a "radial" versus "bias" construction doesn't have that much to do with the ply angle itself.

[speedsense]

Ben's credentials speak for themselves. I'll let him elaborate if he cares to.

But for what it's worth.. particularly for race tires.. a "radial" versus "bias" construction doesn't have that much to do with the ply angle itself.

Ben's credentials speak for themselves. I'll let him elaborate if he cares to.

But for what it's worth.. particularly for race tires.. a "radial" versus "bias" construction doesn't have that much to do with the ply angle itself.

Yes we've had this conversation in another thread, and the reason I resigned myself to "bias formed tires" made up the term. I never call tires by that name, but because of you I now find myself calling tires something else besides bias and radials. Tire engineers call them bias and radials when you buy them, but you point out to be "careful" in how the end users have always called tires.

I'll take your word for it Tom, I don't build tires I only go by what the tire engineers are telling me and my own experience running those tires and the many times I've run the two "types" of tires from the same company on the same car.
It has been consistent from what the tire company terms as "bias" and "radial" in the reaction of the tire to a) the chassis B) the driver and the setup change direction that followed in order to produce a front running or winning car.
Though the differences from a 1991-92 bias vs radials to now, are not as great, they still have the same characteristics coming from the end user point view. At least this one.
You could probably argue that construction or compound wise there isn't a difference, though on my end and the real time data I have, I see the differences every time, so far. To be fair the last time I did a back to back bias vs radial was four years ago, so if things have changed a lot since then, I won't know...
I have probably in my career been through some 2000 sets of tires with all the races and testing done. The most comprehensive test I ever did was 24 sets in two days with varied construction and compounds, all "radials", at least that's what I was told..

As far as Ben goes, making a blanket statement in a forum to a poster that he knows nothing about, speaks volumes of his credentials, hopefully his racing career isn't run this way, because it will be a short one if it is.

[ubrben]

I was simply commenting that your post didn't make a lot of sense.

Once again I'm really intrigued to know what this fundamental difference between cross-ply and radial tyres is. You made a blanket statement of your own in the first post on this thread and you haven't elaborated. I don't disagree with a lot of what you posted, but it was so vague and subjective. I'm sure you have a lot of experience but I'm guessing you didn't have a lot of data on these tyres you tested?

I'm a race car tyre designer, I'm not going to elaborate further, but this is one subject where I know what I talking about. Of course you can chose to believe what you want

Ben