Tire lateral properties 2

[sierra4000]

Hello ,
is possible (helpful) to measure and compare the tire lateral stiffness in garage conditions?

Thank You for ideas and opinions

Radek

 

[GregLocock]

The proprietary tire modeller I use does use the radial and lateral stiffness of the tire as inputs. I suspect that this is linked to the Mz/steer angle stiffness of the tire itself, which you can imagine is directly important. I don't know any more than that, and await @cibachrome's contribution!

Cheers

Greg Locock


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[sierra4000]

Thank You Greg,
i await also

 

[cibachrome]

OK, I'm game. What properties would you like to know about? With the right 3M ScotchWalk 'sandpaper', (It's not actually 'sandpaper', it's a carefully controlled surface suitable for calibrating tire test machines), you can measure Scrub Torque. That's the values and rate of Mz buildup related to parking effort. But, careful there, brakes on or off makes a difference. You can measure scrub radius if you are detail oriented. Static spring rate is there. On an alignment machine you could do some Mz compliance measurements of the whole quarter.

Displacement inputs can be managed. Force measurements are the problem for you.

But, what do you need or want? I've done tire properties from the statistical treatment of a large population of tire tests But it's thin ice. Honda wrote a paper on it. Basically neural network analysis.

If you happen to have a mid '80's HP analyzer lying around [garage, estate sale, and university overflow scrap sale items, you can do normal modes analysis of the tire and obtain the Kz, Fx, Fy, Mx and Mz from the resulting modal assembly. Thats a way to match tires and get consistent sets from pit stop to pit stop. Turns out 'Build Date' is the key sort variable.

If you can get ahold of a wide table mounted belt sander for wood working, you can rig up a rotating tin on a fixed frame, run the belt and feel the lateral stiffness. Actually now that I recall, I've done that on a chassis dyno with fairly large drums. You can run a sine steer test on it at the same time. If positioned properly, you will get identical results as a road test, just without the noise and crap in the signals. check this out:

https://www.youtube.com/watch?v=S4O7b0-epBo

Plus we got the same results from the same car shipped from Opel to Detroit ! Not bad for comparing stuff, but you need to have the stuff.
What's in your wallet ?

 

[gruntguru]

Cool stuff. I imagine sierra4000 wants to pull sideways on the wheel with a spring balance (or push with a suitable scale) while measuring the deflection. The numbers may be useful for comparing different tyres, pressures etc. I would suggest the opposite wheel be resting on a roller skate and the force be applied at the bottom of the rim (to minimise camber change).

EDIT. It would be useful to load and unload several times to identify deflections associated with tread "squirm" and static/dynamic friction.

je suis charlie

 

[cibachrome]

Either air bearings or 'grease plates'. But it's not a rolling tire, so If you had rolling tire data, you might try to correlate rolling vs. stationary properties. What's the brand, size, construction no., rim width and pressure?

Why do I believe we've been here before... And what do you expect to do with the information ?

 

[cibachrome]

Well whad ya no... Check this out. I suppose that if you had nothing and needed something, Probability could be in your favor. This is just a slab of ~360 (only) Continentals. Shift upwards is probably due to plysteer (so our headlight aim stays useful, at night, no moon, no stars, no streetlights, and no fireflies.)

Did I really call this pic "KY Jelly" ???

 

[sierra4000]

Yes, some like Gruntguru said,
my imagine was put rear wheel on plate and laterally push or rotate his contact patch

now i have simple compliance tool which shift one wheel contact patch to inward that i can see camber and toe changes and suspension parts deflections and here contact patch movement is quite significant.............but forces is not too high (around 2kN max) because grip is loosen early with only static car weight so now i try improve plate surface

 

[gruntguru]

If you are looking for suspension compliance, you can eliminate contact patch friction by loading the wheel perimeter directly like this.

je suis charlie

 

[sierra4000]

I know this, in fact i have feel that "caster effect" can be influenced for correct toe reading
in the past i use load direct to wheel center, but toe results was inaccurate

 

[sierra4000]

Of course I'm trying still to find some improvement for my racing car
some local reinforcement give nice handling gains (car is very accurate and fast in response and entries ) but still remain significant movement on tires
if different behavior with different rim or tread width can be find, it can be benefit
unfortunately i must hold same tire brand (AVON crossply)no exist alternative small diameter for final ratio

 

[gruntguru]

Racing slicks? Avon make some very compliant tyres for lightweight cars. Reducing lateral compliance may or may not be a benefit- there are many examples of stiffer tyres producing slower track times.

je suis charlie

 

[cibachrome]

Yeah but he's doing the rear of the car. Stiffer is always better there. Stiffer tires can cause slower lap times for reasons that would be pretty obvious to vehicle dynamics engineers who can analyze the whole car. It is rocket science.

There is no such thing as "Good" compliance as far as handling is concerned. If you have a ride problem or a durability problem, then you have to make a compromise.

 

[GregLocock]

From a steering feel perspective, camber stiffness of the wheel ( a lump of metal) is apparently detectable to those who claim to be able to feel such things. If we call that 9/10 bullshit, it still leaves drivers able to detect lozenging of the sidewalls. Plus one can actually work out the effect on linear range understeer. As a sort of estimate, the mechanical stiffness laterally of the contact patch due to the tire is about the same as the vertical stiffness, say 250 N/mm. So, with say 1200/800 kg weight distribution, the front deflects by 23 mm/g, and the rear by 16, so the understeer effect is 0.16 deg/g on a 2500mm wheelbase

That's the sort of number we do piss and moan about, when putting the budget together. It's not a program killer, but you don't want too many of those going the wrong way.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[GregLocock]

gg- don't know why you deleted your post.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[sierra4000]

If really we take into account that all stiffness comes more or less together then i have simple idea

see scheme please

for clarification, i can use tire 10"/15" or 10,7/15" same diameter 21,5" but is different construction kevlar versus nylon
set 4 pieces around 1500 euro
i can put to 10"" or 11" rim both is in manufacturer range

 

[sierra4000]

Or maybe only simple put two different tires for any each axle,then test front or rear change............so real understeer will tell everything about this tires??

Cibachrome, You said : "Stiffer is always better there" this rule also when car still is understeering?
is prefer rear stiffer tires and found balance n another place?
where? alignment?

again thanks for all comments

 

[cibachrome]

If you have both tire constructions, intermix front and rear, then reverse. Like eye doctor chart: "Better or worse?"

Understeering and rear is stiffened --> more understeer.

Rather than loosening the rear, stiffen the front: reduce Ackermann (Anti-Ackermann) to get more front grip. If power steering, increase pump flow rate/pressure. or change gear (torsion bar). Won't help at max lat but will feel more linear.
Wider front rim. Dynamic camber increase if tires have any camber grip left.

If tires are bigger than O.E.M., ADD more front bar because the high load capacity tires LIKE Fz and the pair with like the extra load transfer: Outside tire will increase more Fy and inside will give up less.

 

[NormPeterson]

Wider front rim.

This would be increasing the Mz/steer angle stiffness as well as lateral stiffness of the tire carcass, right?

If tires are bigger than O.E.M., ADD more front bar because the high load capacity tires LIKE Fz and the pair with like the extra load transfer: Outside tire will increase more Fy and inside will give up less.

The main reason I've heard for increasing front bar stiffness was to limit the amount of front tire grip loss due to strut suspensions' poor camber recovery and/or soft front suspension springing.


Norm

 

[cibachrome]

Rim increase normally does increase tire Mz stiffness but that's all gone near max lat. Usually goes negative if the caster is not set properly to align the peak Mz with the peak Fy. This is a 'feel' ingredient. But if you can work through it (as in ignore the negative torque gradient in the steering wheel), the front bite will keep going. The wider wheel will help relaxation distance/time constant which is a perception ingredient.

The higher load sensitivity (yeah, its sounds wrong, but we're stuck with it) means that the tire is more than willing to provide more force. As opposed to a pair of 'regular' pass car tires, with 90 - 95% reserve, which give up net Fy with a bar. Corvette TLLTD management is always faced with this situation. (typically 40% tire reserve). BTW: That's the max rated load molded into the sidewall but using only 60% of it..

Nobody mentioned weight distribution to change an understeer/oversteer regimen but that's effective. As for caster induced camber, the steered wheels have to steer. If you are hanging on at 20 degrees steering wheel angle, then that might mean 1 to 1.5 degrees at the kingpins. 20 degrees static caster will look pretty funny in a parking lot and sound bad, too, as the tires chew out the wheel house liners. There are some Cup cars that do this, but usually on the (always) outside front wheel because that has the highest load but not the Mu. (Inside tire has the extra Mu. Outside 1.5, inside 2.5.