F1 tyre slip angle?

[PlatinumZealot]

THis is my first time seeing such a graph and hearing of this topic off slip Angle..

So thanks for posting..

What i gather from the graph is that the importance of the Force Vs slip angle graph (Red) is to see how it relates to the Aligning moment graph (green).. i don't think it is possible for a driver to know the slip angle while driving (unless his steering wheel tuns at 1:1 with the front wheels of the car itself).. but the "Feed back" from the wheel after passing the peak resistance will let the driver know he is the peak of the Lateral Force since they coincide at roughly the same Slip angle.. Correct?

[Jersey Tom]

To a degree, yea. In a simple steering system aligning torque counts for a lot, though with mechanical trail the tire lateral force gives some steering wheel kickback as well. Ideally you'd have em peak at the same point, but I'm pretty sure that's impossible. Aligning torque always peaks first.

Though with power steering systems, as you'd find in a F1 car, Nascar, or passenger car, the steering feel is dramatically changed. From what I've seen.. you get the same linear buildup but then it just saturates.

Driver has a lot of feedback available... steering wheel torque... how much vehicle response he's getting from more steer angle... g forces... and visually how much the car is rotating.

[Ciro Pabón]

All right, so modern tyres are more responsive. Wow, it must be really difficult for the driver to feel the "breaking point" (that is, when the tyre starts to slide noticeably).

Now, can anyone write two paragraphs about what in heaven is cornering stiffness? I've read an heard about it but I've never really understood the concept.

I know I'm kind of dragging the thread beyond the initial purpose, but it would become a "first time thread" if we could explain in plain english some things that drivers need to know, as Jersey Tom points. It would be even nicer if someone could show another curve for racing tyres with a more "acute" slip angle.

Of course we trust in you, Tom, it's just that I think that a good engineer or technician hardly believe the things he sees, imagine when he just hears something...

Engineering Tip: don't fall in love until you see him/her, next morning and with your own eyes!


So, I follow Belatti's idea of do-it-yourself: nothing substitutes first hand experience. What about the castors, Belatti? They could work.

Oh, welcome, n smikle, and thanks (again) for your kind words, this is a little forum with big posts. I would say your proposition is not correct. The peak of the steering force happens "before" the peak of the lateral force. So, in the end, you have to push the wheel beyond it's maximum momentum (I think) to get maximum grip. It works for me in karting. BTW, do not trust me, I'm not a champion driver...

So, Fz is downforce, isn't it, Downforce?

[Gecko]

Now, can anyone write two paragraphs about what in heaven is cornering stiffness? I've read an heard about it but I've never really understood the concept.

On the graph of the lateral force vs. the slip angle, it is the slope of the graph at the point where the lateral force reaches 0 (or when slip angle is 0, usually there is not much difference). It is therefore the gain of lateral force per change of slip angle, but in the regime far below the actual peak cornering performance.

The cornering stiffness therefore plays an important role in areas where the tyres aren't yet loaded fully in the lateral direction, such as braking stability and turn in.

The cornering stiffness (as well as the whole lateral force vs. slip angle graph) of course changes when the tyres are loaded longitudinally, such that under braking it may even increase for certain longitudinal forces, but then drop off when you approach the limit. That is why the car may feel like it's "dancing" when braking very hard.

[Downforce]

So, Fz is downforce, isn't it, Downforce?

Yeah, my favorite.

Fz is part of the weight that falls on particular tyre + part of the downforce that falls on her.

[Belatti]

Ciro, thanks for your omipresent answers!
I always prefer a "I dont know but try this" than mere silence

I was thinking in testing the tyre with homemade instruments inside a "lab" because:
a. there is a huge lack in manufacturer data and there is only one manufacturer permited (cost cutting)
b. there are only two test sessions permited in the whole year and there are a thousand items to test...
c. as you already said, we have no money (or extra eyes) to get fancy instruments

So, thanks anyways because, you know, one idea carries to another carries to a solution

[sdimm]

Thank you very much, Downforce and welcome to the forum. Do you have any idea what's F2? Normal force?

I've never seen a 25.0 x 9.0 tyre reference, btw.

Sdimm, I agree with your idea. On the track you want the tyres to sound (squeak), but not too much. In my case, it depends a lot of my ear, that's why simulators annoy me.

When I drive simulators I always make sure to get the sound of tyre scrubb and skid as high as possible. Sometimes even lowering the sound of the engine and soundeffects to get it right. When you drive a real car or for instance a gokart the sound of the tyres is very obvious.

When I for instance brake with my Sport2000 kart I try to get the right brakingpoints by listening to the sound of the tyres scrubbing. When a really good driver is in a gokart and brakes you can always hear how the backwheels are screaming al the way up to the apex which is key to drive fast.

In the last few months I have really gotten intrested in tyres, how the behave and is different to eachother.
And it seems that this slipangle deal is quite important to understand a tyre.

When talking to the f1 driver I know he said that it´s really intressting how the tyres change the way they lose the grip when they´re cold. For instance. They don´t loose alot of grip when they´re abit cold but what does change is the way it looses grip when you go over the "limit" of the tyres, that would be where the tyres slipangle is at it´s maxium. And also the way it looses grip in fast corners compared to slowcorners because of the wings. When you drive in a fast corner with them the wind actually have to have a sertain angle to the wings and the sharkwing on top of the engine to get efficient. Meaning that the car slides quite a bit if you think of the angle the car is having towards the path it´s going.

I thinks that's why F1 cars tend to have a setup that is a bit understeer in fast corners to not risk the car going into a oversteer scrubb which would damage he rear tyres alot. This characteristics of the f1 cars Bourdais has said is the problem for him this year.

It's fun to talk to other people who, like me diggs this technical stuff =)

// Mattias

[Ciro Pabón]

Thanks, master Gecko.

There you go, Belatti.

Sdimm, I think that when you use a simpler gokart, your rear tyres do NOT squeak or, at least, a lot less than front tyres. Your aim is to take the curves on three wheels, because you don't have a differential at the rear axle. When the rear inner tyre is silent (thus, it has lifted off the ground) your curve is perfect. I've never found a simulator that reflects that fine point in the sound.

[Jersey Tom]

Part of my job involves race tire F&M data, which is what I'm basing the slip angle stuff off. But I can't get specific. Anyway..

You can get some rudimentary tire plots from track testing.. but most of the benefit of having lab F&M data is to identify pressure peaks, Ackermann percentage, camber rates etc ahead of time. The benefit of getting tire traces at the track is minimal and/or harder to get.

Most simple and cheapest data to get is with a lateral accelerometer at the CG, and a steering angle sensor (get the steering angle of the front axle). You can plot one vs the other and see roughly where your lat g's are peaking as a function of steering input, and identify where you're overdriving the front tires.

That doesn't really tell you anything about force or slip angle though.. and the actual steered angle of the tire is going to be different than that of the steering mechanism from compliances, yaw rate, etc. To get the actual wheel/tire slip angle you'll need a slip angle sensor (~$25000 USD) on at least one wheel at a time.. plus an assembly to keep it on the wheel but stationary.

To get the forces and moments at each corner there's a few different ways. If its a SLA suspension you could probably put strain gauges on each element (2 in UCA and LCA, one in pushrod, one in tie rod) and if you know the geometry put together a math channel to get 3 forces and 3 moments.

Or, easier and more expensive would be to buy force hubs (~$500,000? USD) that bolt right on the car.

The most bang, for the least buck in terms of getting the most out of your tires are a needle pyrometer, and IR temp sensors. 3 on each tire. Set your camber and pressure to get an even temperature spread on each tire mid-corner.

[sdimm]

Thanks, master Gecko.

There you go, Belatti.

Sdimm, I think that when you use a simpler gokart, your rear tyres do NOT squeak or, at least, a lot less than front tyres. Your aim is to take the curves on three wheels, because you don't have a differential at the rear axle. When the rear inner tyre is silent (thus, it has lifted off the ground) your curve is perfect. I've never found a simulator that reflects that fine point in the sound.

Yes, but.

Even though you are lifting the inner tyre, which of course is how the kart is designed for, you are supposed to still use as much of the other tyres as possible. And how are the front tyres supposed to squeak into a corner?
The key is to under braking brake as hard as possible, often much more than people usually do, and then contiune doing so into the corner WITH the rear tyres squeakin. Then into the corner the front tyres which now is starting to take lateral forces and being used starts to also squeak and you´re of.

Just lifting the kart isn´t whats used to feel if your fast since you can when standing still kan lift the rear tyres if you jsut turn the wheel. Also in fast corners with a big radius you turn such a small amout the the kart isn´t lifting to you´re actually sliding the rear as well as the front tyres to turn.

// Mattias

[Ciro Pabón]

Well, I'm not sure how they do it, sdimm. My (rather old right now) tyres squeal into hard corners... even the front ones. Remember the old motto: a squealing tyre is a happy tyre. Don't make them sad.

[sdimm]

Ahh, you of course have brakes on the front tyres as well =) I only have it on the rear axel.

// Mattias

[Gecko]

for what its worth that plot looks like its from a very cold tire.

This quote made me curious; could you please tell a bit more about what are the typical main differences between such plots for a cold vs. warm tyre? Thanks

[Jersey Tom]

I can't, actually. But then again there really isn't a "typical" anything with tires.

But one thing that sticks out is the very low grip level (relative to what you'd expect to see from a F1 tire)... and basically no linear range. To me that says the tire is either on a really low grip surface or is cold, and the compound isn't sticking.

[PlatinumZealot]

unless the car is driving strait or has some extreme 4 wheel steering, there is always a slip angle right? what meaning does the slip angle have...(i know what it is) but what is the meaning to the driver/engineer.. is it just for reference to show how curved an arc the car is driving in?