Define: Tyre Grip

[ubrben]

Ok..because i am getting tired of this...if you even bothered to look in my blog you would see that i had put e note at the bottom mentioning his book...instead of going to my blog just to make fun of me or my copyright page or my donations page.

The graphs i posted yesterday in the previous page DO prove that the my second sentence IS correct...if you look at both graphs you will see that at zero slip angle the coefficient of friction developed is 0... If you don't see how this proves it then it is your problem..not mine...

The tires are elastic in twist...if you have ever handled a tire you will know what i am talking about...even with the tiniest changes in direction there is slip angle developed...this is basic theory about tires...

EDIT: unless someone comes up with a decent explanation or proof that I am wrong i will not answer because I refuse to take part in this kind of conversation

I've handled the odd tyre - I design and race engineer them... Greg simulates vehicle dynamics using ADAMS. JT analyses tyre data for a living.

Your graphs prove nothing of the sort. As I said in my previous post a vehicle will change direction as a function of steering and subsequent slip angle generation at the front tyres. The vehicle changes direction (heading angle) before any slip angle is generated at the rear tyres.

My previous post on this constitutes a decent explanation of why you're wrong. I'd like to hear your view on it.

Ben

[ubrben]

The graphs i posted yesterday in the previous page DO prove that the my second sentence IS correct...if you look at both graphs you will see that at zero slip angle the coefficient of friction developed is 0... If you don't see how this proves it then it is your problem..not mine...

Another example would be static toe on tyres. If you have static toe and a non-zero body sideslip angle, at some point you could have a tyre with zero net slip angle, whilst the other three have a non-zero slip angle.

Ben

[Tim.Wright]

You can have periods where the is no slip angle on a tyre but still have lateral force from the other tyres turning the car.

If you re-worded your sentance to say something like "disregarding effects of camber, ply steer and conicity, a single tyre requires a non zero slip angle to produce a lateral force" it would make sense.

Dont mention anything about the whole car. Its irrelevant to what you are trying to get across.

[amouzouris]

some people are missing the point of my explanation..i am trying to get people without any knowledge interested...if i factored in camber angles, toe angles etc...then they wouldn't understand a thing... even F1 engineers have a hard time figuring out a tire with all of its variables (see first half of 2012 season).

The graphs CLEARLY show that at 0 slip angle the CoF developed is 0. If you cant see and acknowledge that then it is not my problem

As far as toe angle is concerned, on the rear tires a negative toe angle is used which will only increase slip angle on the outer tire that needs traction..

I really doubt you design tires or any one of the other members does what you have described...this is my opinion which i am entitled to have...if however you really are engineering tires for a living then good for you...

EDIT: As i said before unless someone comes up with proof I will not answer again...And even posting my later post is a mistake..

[Tim.Wright]

I give up...

[GSpeedR]

amouzouris, the issue everyone has is with the following sentence:

For the vehicle to change direction, regardless of road speed, each of the 4 tires of the vehicle must have some slip angle.

Everyone is giving you examples of why this isn't necessarily true. So the keyword must is a problem.

[Jersey Tom]

if you look at both graphs you will see that at zero slip angle the coefficient of friction developed is 0

You're referring to this?


Is that raw test data or is that a model response? From the shape of it I would venture the latter, or a spline fit of some points in either case. You can make a tire model do whatever you want, to a degree it's arbitrary what you want to include or remove (in this case, rigidly specifying that Fy = 0 at SA = 0).

Suffice to say though, as Tim points out... you can generate lateral force at zero slip angle and zero camber through ply-steer and conicity. This is what real tires do. In fact, that tends to be an intentional design feature to have "residual" Mz or Fy for a variety of reasons. On consumer cars, part of that and alignment is to have a car travel straight on crowned roads.

For that matter, you can generate additional lateral force at a given state by changing vertical load or introducing longitudinal slip while keeping lateral slip at a fixed value (even zero).

Two supplemental points...
1. I'd make the case that F1 engineers having "a hard time figuring out a tire with all of its variables" is a function of (a) a product ill suited to the needs of the vehicle platform, in which case you are stuck without a way to engineering around it, (b) a product which degrades or changes so much over a stint that there's no shot at keeping it doing what you want, and/or (c) insufficient data provided by the supplier. I'd doubt it's for lacking grasp of what camber and toe do.

2. As an extension of Point 1, I could make the case that vehicle dynamics engineers in the consumer or OEM world need as much or broader fundamental understanding of tire behavior than a race team engineer. Turnslip, relaxation length, NVH, etc etc. A BMW or whatever has great handling because the tires are tuned well to the vehicle, and the designers and analysts have a good fundamental knowledge of vehicle dynamics. So it's not like tire behavior is some great expansive mystery that no one really understands. Is it challenging to characterize? It can be. But the knowledge is out there.

Beyond that, and not that it really matters, but Ben does engineer race tires. I used to work for a tire company and now specialize in tire data application at a race team. One of my competitors floats around here too! Suffice to say there are a fair amount of automotive industry and motorsport professionals around on this forum. Most of us know who each other are, and have pretty good working knowledge in their respective fields.

Whether or not you choose to believe that is inconsequential to me. I just want to win races. But I'd say if you keep an open mind and take in some of what's being said there may be potential to learn something.

[Lycoming]

You do not need nonzero slip angles on all 4 tires to change direction. Also, as somebody who has worked with real tire data, I assure you that a tire can generate a lateral force at 0 slip angle. I see and acknowledge that your graph shows 0 friction at 0 slip angle. But I have also seen real data where that is not the case.

[ubrben]

I really doubt you design tires or any one of the other members does what you have described...

"Reality is that which, when you stop believing in it, doesn't go away" - Phillip K. Dick

But by all means believe whatever you like if it makes you and your blog feel better

Ben

[raymondu999]

Isn't there a point, at the start of turn-in, however instantaneous, that the fronts have slip angle but the rears don't have slip angle, which is what begins the car's rotation (in terms of its heading)

[ubrben]

Beyond that, and not that it really matters, but Ben does engineer race tires. I used to work for a tire company and now specialize in tire data application at a race team. One of my competitors floats around here too! Suffice to say there are a fair amount of automotive industry and motorsport professionals around on this forum. Most of us know who each other are, and have pretty good working knowledge in their respective fields.

Whether or not you choose to believe that is inconsequential to me. I just want to win races. But I'd say if you keep an open mind and take in some of what's being said there may be potential to learn something.

What he said...

Ben

[amouzouris]

JT you keep referring to how camber and toe can generate lateral force with zero slip angle...just to clear this out...I do agree with you on this...what i wrote though is assuming that camber, toe etc. are 0.... The graph you re-posted must indeed be a model response, the other one however i believe is real life data...

putting our personal life and employment aside...which is an aspect that shouldn't really be discussed on a public forum...
i do take into consideration what you are saying..but i still disagree on some aspects...

this conversation is going nowhere..so instead of going on and on for pages about the same thing...why don't we refocus our energy on other aspects of a tire...a tire is a really interesting piece of engineering...and we would contribute a lot more to the forum and to the world by discussing another aspect of a tire instead of agreeing to disagree on a single aspect..

[ubrben]

.but i still disagree on some aspects...

Which ones?

Ben

[amouzouris]

whether or not with 0 slip angle lateral force developed is zero

[Jersey Tom]

whether or not with 0 slip angle lateral force developed is zero

See here. Not sure how Scribd managed to publish the contents of that book, but.. came up on a quick Google search for plysteer...