Tyre Width Vs Grip

[Jersey Tom]

Like anything else its a model, not a rule. The typical school room frictiom model is the Coulomb one. Sadly, most think that it is the only one.

[xpensive]

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The amount of in-plane force the tire can generate is directly proportional to the vertical force, sure.
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Why we perhaps should be careful with statements like the above, from another thread, as it refers to the "mu" model ?

[raymondu999]

There's something I cn't quite get my head around now. So when F1 transitioned from grooved to slicks in 08->09, and Bridgestone decreased the width of the fronts from 09->10 to shift the balance rearwards, barring any change in compounds, wouldn't they then give the same grip given that the load is still distributed anyways, and the narrower treads of the 10/08 tyres would have more pressure applied anyways?

[Jersey Tom]

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The amount of in-plane force the tire can generate is directly proportional to the vertical force, sure.
...

Why we perhaps should be careful with statements like the above, from another thread, as it refers to the "mu" model ?

Like it hell it does. The amount of traction a tire can generate isn't just random. There's most certainly proportionality to normal load. It just isn't a constant linear proportionality through the whole load range (Coulomb model), nor are the forces purely generated by "dry friction."

There's something I cn't quite get my head around now. So when F1 transitioned from grooved to slicks in 08->09, and Bridgestone decreased the width of the fronts from 09->10 to shift the balance rearwards, barring any change in compounds, wouldn't they then give the same grip given that the load is still distributed anyways, and the narrower treads of the 10/08 tyres would have more pressure applied anyways?

Not following this line of reasoning. Might have to run it by me again in different terms. Bear in mind also when Bridgestone narrowed the front slick mold it looked like a pretty substantial mold profile change, not just "narrower."

In other news I hate the word "grip." So vague. There's traction and there's response, and some linking between the two.

[xpensive]

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There's most certainly proportionality to normal load. It just isn't a constant linear proportionality through the whole load range (Coulomb model),...
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Sometimes even the most prominent name-droppers on this forum manages to confuse the simplest mathematical concept.

[Jersey Tom]

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There's most certainly proportionality to normal load. It just isn't a constant linear proportionality through the whole load range (Coulomb model),...
...

Sometimes even the most prominent name-droppers on this forum manages to confuse the simplest mathematical concept.

Yeah yeah that's cute and all. Does "direct" proportionality imply pure linearity? If so, my bad - wrong term. If you want to dick around with verbiage, be my guest.

Though if we want to go down that road, I still hate the word "grip." It is incredibly vague and imprecise and interpreted in significantly different ways between certain drivers and/or engineers. Dislike it almost as much as saying a car is "understeer" or "oversteer"

[Richard]

Perhaps the amount of in-plane force the tire can generate is a function of the vertical force? A complex function, but more vertical load results in more in-plane force than one would get with less vertical load.

No need to get personal about it.

[DaveW]

Just for interest, perhaps, here is an updated rig test view of tyre vertical stiffness, including some from 2011 (allegedly, GP2 & F1 tyres were the same). Before anybody comments, apologies for the number of significant figures in the slopes of the trend lines.

[hardingfv32]

Dislike it almost as much as saying a car is "understeer" or "oversteer"

Please expand.

Brian

[xpensive]

Perhaps the amount of in-plane force the tire can generate is a function of the vertical force? A complex function, but more vertical load results in more in-plane force than one would get with less vertical load.

No need to get personal about it.

Quite obviously, there's a relation between vertical force and the maximum horizontal such, which is why the car's downforce is so paramount in Formula one these days, but that does not mean that we have a direct proportionality.

Speaking of which, mathematically there's a distinction between proportionality and linearity;

http://en.wikipedia.org/wiki/Proportion ... thematics)

[hardingfv32]

Just for interest, perhaps, here is an updated rig test view of tyre vertical stiffness, including some from 2011 (allegedly, GP2 & F1 tyres were the same).

Thanks...

Is tire 'vertical stiffness' the same as tire spring rate?

Brian

[DaveW]

Is tire 'vertical stiffness' the same as tire spring rate?

Lots of pointless semantics hereabouts (if I may say so)... vertical stiffness is the local rate of change in tyre vertical load per unit deflection, otherwise known as the "tangent stiffness"... Units are shown.

[xpensive]

Come now Dave, "Spring rate", hasn't that something to do with "spring break"?

[hardingfv32]

Just for interest, perhaps, here is an updated rig test view of tyre vertical stiffness, including some from 2011 (allegedly, GP2 & F1 tyres were the same).

Are the provided tire vertical stiffness values in a similar range to other road racing slicks found in other classes?

Brian

[DaveW]

Are the provided tire vertical stiffness values in a similar range to other road racing slicks found in other classes?

Not really. From my point of view, the objective of setting the suspension of a race car is to match the vehicle to the tyres (mechanically). From the tyre designers point of view, arguably, it is about matching the tyre characteristics to the vehicle (amongst other things, no doubt). It might be argued that a good first attempt would be to match vertical stiffness distribution to the "natural" position of c.g. of the vehicle.

Clearly, neither of the two last Bridgestone tyres satisfied that criterion, which might explain why F1 teams were intent on pushing the c.g. as far forward as they could, also why FOTA decided to limit teams scope for changing c.g. position.

I leave you to work out the ideal position for the 2011 Pirelli's.