tyre temperature - the only thing that matters

[speedsense]

Good question, & one I can't answer simply. However, it is worth noting that a spring doesn't have a "frequency", as I'm sure you know. The comment is worth making, however, because your statement implies, perhaps, that a quarter car model can be used to set springs & dampers. The technique certainly is used in the road vehicle world to decide on spring selections (spring_stiffness / corner_spring_mass). The concept is flawed, however, because tyres do affect vehicle natural frequencies & the two axles of a vehicle are not isolated from one another, but are connected by the sprung mass.

I did mean in use, on a road race car, the springs (all four), the springs will acquire a frequency cycle, which the dampers react to and attempt to control. If this frequency cycle comes into the same "percentage of range" or "equal" for the front and the rear, the chassis ride will be affected negatively, increasing the potential for handling problems and negative, inappropriate reactions to bumps. This can be canceled out by simply changing the spring rate to alter the frequency.
With tires, shock technology (and the J damper) has come to the point of controlling not only the frequencies of the chassis (mostly at the spring level), but also the frequency cycles of the tire. As we can't change the spring rates of the tires except through tire pressure (easier done with radials as they don't have tire center growth problems with pressure. Almost impossible with bias.)

It is interesting to note that your finding of the ratio of tire ratio spring rates have a "sweet spot", that in my opinion has a correlation to this frequency balance.

In other words, the mechanical suspension set-up problem is not one of optimizing two second order systems (or even two fourth order systems if tyres are included), it is one of optimizing a single eighth order system, with (actually) many non-linear parameters. An asymmetrical vehicle (e.g. NASCAR) raises the complexity yet again. A satisfactory solution to the problem (in general) can only be obtained using a full vehicle model or a hardware-in-the-loop test using multi-post rig.

To illustrate, start with a completely symmetrical vehicle (c.g. at 50%, same springs, dampers & tyres at each axle). If the front springs are required to be increased, then a quarter car model would suggest that the front dampers should also be increased. Usually, however, increasing the front springs will imply that the rear axle will dissipate more of any disturbance energy, so the correct change would be to increase the rear dampers. When the ratio of tyre/spring stiffness is small, the spring change would probably require some combination of increased rear damper settings, reduced front damper settings, reduced rear springs, & increased rear tyre stiffness. Parameters very definitely become highly "coupled".

Wouldn't a rise in spring rate require a reduction in shock dampening? And on the other end, a lower spring rate, an increase in dampening?
Wouldn't increasing both the dampening amount and the spring rate, result in an "undershoot" of the spring (by over dampening the spring) in restoring it to rest?
****As the natural frequency of a stiff spring (without a damper involved), returns to rest quicker and in less cycles than a softer one.***

Why is tyre stiffness important? Because they have to support the suspension & transmit suspension loads to the road surface. It follows that tyres (or, more accurately, their vertical stiffnesses) are an integral part of the suspension of a vehicle. It turns out that having a stiffness split that corresponds with the sprung mass c.g. position is a good starting point. Tyres that don't have the "correct" stiffness split can be accommodated by making suspension adjustments; if other (usually driver or aero) requirements mean that this in impractical, then the alternative is to move the sprung mass c.g. position, which is what F1 teams have been doing for the last few years. There is a compromise to be made in that case, however. Moving the c.g. (& centre of pressure) forward improves vehicle "mechanical" control & tends to increase front tyre temperatures, but it will reduce traction...

Tyre lateral stiffness split is also important, principally for the driver. A vehicle that sideslips under lateral loads affects a driver's ability to operate close to the "lateral limit" of the vehicle (& its tyres).

Are the current F1 tires and their alternate compounds,IE: Soft, supersoft etc. all of the same construction with different compounds or do they alter the construction as well?

As I said at the start, your question is difficult to answer. I hope the above will help a little.

Yes it has. Having spent a lot of time with the cars you mention, except F1, and time at 7 posters with assorted cars, I'm interested in your view, as someone who appears to have spent a lot of time around poster rigs.

[Jersey Tom]

More spring does require more damping, if you want to keep the same damping ratio. Otherwise you will be increasingly underdamped.

Oh, and be careful with your terminology between "bias" and "radial" tires.

[speedsense]

More spring does require more damping, if you want to keep the same damping ratio. Otherwise you will be increasingly underdamped.

??? If I apply 500lbs of force to a 1000lb spring I will compress it .5 inch. If I apply 500lbs to a 500lb spring, I will compress it 1 inch.
Let's say I take both springs, apply the same load to each and remove the load at the same time, the springs will extend and compress (cycle) until they come back to rest. The stiffer spring will return to rest, on it's own, before the softer spring returns to rest. Correct?

So if I want the softer spring to return to rest at the same time as the stiffer spring, I need to add dampening to achieve it. Removing dampening will not achieve this result.

Oh, and be careful with your terminology between "bias" and "radial" tires.

Bias Ply vs a Radial ply tire, is that what you mean?

[Jersey Tom]

??? If I apply 500lbs of force to a 1000lb spring I will compress it .5 inch. If I apply 500lbs to a 500lb spring, I will compress it 1 inch.
Let's say I take both springs, apply the same load to each and remove the load at the same time, the springs will extend and compress (cycle) until they come back to rest. The stiffer spring will return to rest, on it's own, before the softer spring returns to rest. Correct?

So if I want the softer spring to return to rest at the same time as the stiffer spring, I need to add dampening to achieve it. Removing dampening will not achieve this result.

If you want to maintain a constant damping ratio in a simple 2nd order system... aka keep the system perfectly damped for example, or over- or under-damped to the same degree... as 'k' increases, 'c' must also increase. Just the way physics works.

Bias Ply vs a Radial ply tire, is that what you mean?

Just saying there are very few 'radial' race tires that actually have radial plies. Tire growth isn't as much a factor of being 'radial' or 'bias' as much as other things.

[Belatti]

Just saying there are very few 'radial' race tires that actually have radial plies. Tire growth isn't as much a factor of being 'radial' or 'bias' as much as other things.

I have never seen a racing radial arround here. Con you give an example Tom?

I recall reading somewere that, even if Bridgestone and Michelin F1 tyres were both bias, the later had more of "radial" properties. Was that because the angle of the plies? Hence the problems in the banked Indy?

[Jersey Tom]

Race "radials" ... F1, GP2, IRL, NASCAR, BTCC, DTM, WRC, Stock Car Brazil, Star Mazda, ALMS... etc.

Some people go by purely saying radial tires have plies with very little or no angle relative to each other... but there's a hell of a lot more to it than that.

I'm sure Bridgestone and Michelin have different design philosophies.. but to say one is more or less "radial" than the other is a stretch unless you've dissected them.. and to say that Indy problems were because of it is a huge leap.

[bill shoe]

DaveW, your posts are good enough to raise more questions...

To illustrate, start with a completely symmetrical vehicle (c.g. at 50%, same springs, dampers & tyres at each axle). If the front springs are required to be increased, then a quarter car model would suggest that the front dampers should also be increased. Usually, however, increasing the front springs will imply that the rear axle will dissipate more of any disturbance energy, so the correct change would be to increase the rear dampers.

I understand the rear will now dissipate a larger proportion of the overall energy, but why does this require a rear damper with higher absolute stiffness? Is this because the modified car in your example (stiff front, soft rear) will now dissipate more absolute pitching energy through the rear?

Tyre lateral stiffness split is also important, principally for the driver. A vehicle that sideslips under lateral loads affects a driver's ability to operate close to the "lateral limit" of the vehicle (& its tyres).

So the lateral tire stiffness relates to subjective car control feel more than theoretical car quickness. Is there a ratio of rear/front lateral stiffness that is good in the same manner as the vertical stiffness ratio? Any other useful rules of thumb for what lateral stiffness setups feel good to the driver??

[Jersey Tom]

Why screw around with lateral stiffness.. when you can go straight to what matters - cornering stiffness.

In which case yes.. relative proportion of front to rear cornering power is big.

[speedsense]

If you want to maintain a constant damping ratio in a simple 2nd order system... aka keep the system perfectly damped for example, or over- or under-damped to the same degree... as 'k' increases, 'c' must also increase. Just the way physics works.

My bad, must of wrote this without coffee, my hair probably looked like Newton's, so did my attempt at changing physics...LOL
While my thinking (in my head and not here) did involve a series sprung car, (tire spring rate, and "normal" spring and shock located within a rocker. High down force numbers present... and for simplicity, the absence of inertia.
If you solve for the tensile forces for each spring, and consider a forced sinusoidal motion, point 1)as a mechanical analog of rubber materials because it's mean power dissipation is frequency-dependent, with a peak, in a similar fashion to viscoelastic materials.
And point 2)It is revelvant to suspension behavior,in which compliances not in parallel with the damper are subsantial. These non-parallel compliances arise in the tire and in the suspension structure and mountings. For a passenger car the value of the tire may be ten times what it is for the car's spring. In ground effect cars, may be more of a similar value.

You eventually arrive at a mean power dissipation in this system, partly due to the peak of the tire frequency-. At small frequencies, the dissipation rises. At high frequencies it falls.
If you insert mathmatically, a relative dampening parameter, you will come to realize that an increase in the dampening coefficient becomes declining in comparison to the "peak".
While increasing and perfecting your control over the car's spring, the series spring can cause an over-dampening effect as result on the whole system.

Both springs most always be considered, in my experience, that is under damped at the car spring, to prevent over dampening the entire system. This is a small amount with high downforce present and a greater shift with lessening amounts of downforce, as the two springs are less equal in strength, and the peak generation becomes higher and falls more quickly...

BTW, again for simplicity, a linear dampener.

Bias Ply vs a Radial ply tire, is that what you mean?

Just saying there are very few 'radial' race tires that actually have radial plies. Tire growth isn't as much a factor of being 'radial' or 'bias' as much as other things.

Tire pressure growth, is what I should have said. Haven't found a "bias" tire that I could get away with over inflating without drastically changing it's size and ballooning, or worse yet blowing up. Found lot's of radials, I could however, even at 20 lbs over...

[DaveW]

Speedsense: JT is correct, I'm afraid. I can only suggest that some background reading would be helpful (with apologies).

I understand the rear will now dissipate a larger proportion of the overall energy, but why does this require a rear damper with higher absolute stiffness? Is this because the modified car in your example (stiff front, soft rear) will now dissipate more absolute pitching energy through the rear?

Given (the assumption) that an increase in spring stiffness will require an increase in overall damping levels, the purpose of my illustration was to suggest that the dampers to change might not be the "obvious" ones. I suppose this is the "mistake" I encounter most frequently when rig testing a vehicle for the first time. It is the case, by the way, that the spring selections for a typical "aero" race car mean that the front dampers control the vehicle pitch mode, whilst the rear dampers control the heave mode (both "mostly").

So the lateral tire stiffness relates to subjective car control feel more than theoretical car quickness. Is there a ratio of rear/front lateral stiffness that is good in the same manner as the vertical stiffness ratio? Any other useful rules of thumb for what lateral stiffness setups feel good to the driver??

I suppose I must acknowledge JT's correction (damn it). I believe that sideslip, or, more accurately, rate of change in sideslip is a primary cue that tells a driver how close he is to the vehicle lateral limit & what is likely to happen at the limit, & it makes some sense to me that there is likely to be a correlation between vertical & lateral stiffness. It is certainly true that, in one case (to repeat myself), a change in rear tyre construction (not size, shape or compound) suggested by a rig test yielded a 5% improvement in lap time & brought a smile to the face of the driver, who commented "I now know what the car is going to do".

A couple of additional comments. I have heard a respected (road car) vehicle dynamicist state that he uses rear compliance steer to "keep drivers away from the lateral limit". I also know that some teams change rim design to help drivers (I guess by modifying both vertical & lateral compliance). Both would lead me to suggest, somewhat hesitantly, that geometry & wheel compliance might be used to "recover" poorly matched tyres in a race car - but better, I'm sure, would be to get the tyre constructions "right" in the first place.

Back to a speedsense question. I haven't had the opportunity to compare F1 "prime" & "option" tyres on a rig, although it would astound me if there were construction differences across the range of slicks (but it wouldn't be the first time I've been astounded). However, I have been told that drivers very much prefer inters to slicks & I, in my one-eyed way, can find reason for that preference.

[speedsense]

Speedsense: JT is correct, I'm afraid. I can only suggest that some background reading would be helpful (with apologies).

No apologies needed, though you would have be afraid had you seen what I looked like when I wrote it.

Back to a speedsense question. I haven't had the opportunity to compare F1 "prime" & "option" tyres on a rig, although it would astound me if there were construction differences across the range of slicks (but it wouldn't be the first time I've been astounded). However, I have been told that drivers very much prefer inters to slicks & I, in my one-eyed way, can find reason for that preference.

Thanks. I had imagined that the driver's seem to like the inter's, seen several instances of them continuing to drive in the dry (as they wore out) and stayed quick on them... Have any idea on how much softer than say, the super softs, they are?

Oh, and Dave W, a comment you made earlier about a larger ARB increasing tire heat? Did you mean that? I could see stiff springs and adding a larger ARB as doing so, but adding an ARB and dropping spring rate, as cooling the tires. At least in my experience that has happened every time, even on a full ground effect car...

[DaveW]

I had imagined that the driver's seem to like the inter's, seen several instances of them continuing to drive in the dry (as they wore out) and stayed quick on them... Have any idea on how much softer than say, the super softs, they are?

Oh, and Dave W, a comment you made earlier about a larger ARB increasing tire heat? Did you mean that? I could see stiff springs and adding a larger ARB as doing so, but adding an ARB and dropping spring rate, as cooling the tires. At least in my experience that has happened every time, even on a full ground effect car...

The difference in vertical stiffness split of inters c.f. slicks is substantial & is caused mainly by the rear tyres.

Your comment on bars vs springs is interesting & logical, I think, because springs "work" the tyres everywhere, whilst bars have an effect (mostly) in turns. Have your tried simply increasing bar rates front & rear? If so, did you detect a difference in tyre temperatures?

[speedsense]

I had imagined that the driver's seem to like the inter's, seen several instances of them continuing to drive in the dry (as they wore out) and stayed quick on them... Have any idea on how much softer than say, the super softs, they are?

Oh, and Dave W, a comment you made earlier about a larger ARB increasing tire heat? Did you mean that? I could see stiff springs and adding a larger ARB as doing so, but adding an ARB and dropping spring rate, as cooling the tires. At least in my experience that has happened every time, even on a full ground effect car...

The difference in vertical stiffness split of inters c.f. slicks is substantial & is caused mainly by the rear tyres.

Your comment on bars vs springs is interesting & logical, I think, because springs "work" the tyres everywhere, whilst bars have an effect (mostly) in turns. Have your tried simply increasing bar rates front & rear? If so, did you detect a difference in tyre temperatures?

Yes and yes, the tire temps increased, as they put more loadings into the tires and less was absorbed in the suspension, with resulting increase in the compliance transferred to the tire.
With the limit of maximum tire heat being the point where the stiffness of the suspension is essentially "solid" and not compliant at all.
As I pointed out above, though the point being about dampening, the tire has spring properties that are very unlike the car's springs and are frequency dependent (yet mostly uncontrolled) and that as you make the chassis less compliant through stiffening ARB's and car springs. Furthermore, the "system" is a series spring system (containing) multiple springs, if we include chassis/suspension "piece" spring/flex, we are merely putting more reliance and the compliance on the uncontrollable springs, rather the ones we can control. (Outside of "up to date shock technology", J dampers, Mass dampers where some "forms" of vibration theory controls are used)

With a spring, it greatly effects that local corner (including that tire) of the car.
With ARB's you effect the loading "both" laterally and in cross weight loadings (even from one ARB) and that transmission of weight is one of subtraction (subtracting from one corner and adding to the other)

It's very interesting to note, that the tire type- an "assumed" Bias ply vs an "assumed" radial, have two very different reactions in vertical/lateral loadings at the tire,especially when the chassis is stiffened in compliance.

One more point for consideration, and that is the type of tracks that are run. Most of the tracks in Europe are very smooth and here in America tend to be much more on the bumpy side. There tends to a "fundamental" difference in approach to chassis setup from either side of the pond. In Europe the tendency is towards more importance on spring rate (to the higher side) and less dependence on ARB's. In the US the reverse tends to be true. Most US tracks demand compliance in the suspension to be quick. Sebring, for instance vs Miller, Alabama and recently Mid Ohio (which are the smoother tracks in the US)...

Yet, we have Nascar Cup cars running around tracks with no compliance in their front ends, which has resulted in several changes to tire construction/compounds. Ovals are an entirely different conversation.

[Belatti]

Just saying there are very few 'radial' race tires that actually have radial plies...

Race "radials" ... F1, GP2, IRL, NASCAR, BTCC, DTM, WRC, Stock Car Brazil, Star Mazda, ALMS... etc..

So race radials have not all radial plies... Are race radials just bias ply tires with, I dont know but lets say, from 0° to 15° from the plane of rotation?
Then (just as an example) race bias would have plies arround the 45° range?

Some people go by purely saying radial tires have plies with very little or no angle relative to each other... but there's a hell of a lot more to it than that.

Sure! that may be structural materials, their combinations, thicknes, angles, amount in the bead, etc...

[ubrben]

A pure radial tyre has ply cords running at 90 degrees to the beads. In practice if you have more than one ply you have to have some bias angle to stop them moving through each other when the tyre's cured. In practice if you have a two ply tyre they'll have a bias of at least 88 degrees.

But the reality for racing tyres is that the vast majority of "radial" racing tyres a more accurately called bias belted. With bias angles between ~60 degrees and 88 degrees. Conventional beltless bias (or cross) ply tyres have ply angles of 20 - 40 degrees.

Growth control in these "bias belted" tyres is achieved by a filament wound layer of aramid or other fibre. Variously called JLB (jointless bandage) spiral overlay, etc.

I (and I think DaveW) believe lateral stiffness is very important from a driver's perspective. In my experience drivers are quite sensitive to lateral deflection on rear tyres. To make a rear tyre laterally stiff enough for the driver to be happy it will almost always be vertically stiffer than the front. Particularly if the rear sidewall is taller than the front.

Ben