Rolling Resistance of F1 Tires

[MerlinC]

Although there is a lot of information on rolling resistance in the forum I have not been able to find an answer to the following below. Ideally somebody will provide firm numbers of the rolling coefficient – if this information can’t be made available to the public I would be interested relative numbers for the different compounds.
(A) How big is the difference of the rolling resistance for available compounds (SuperSoft, Soft, Medium, Hard, Intermediate and Heavy Wet)?
My understanding is “softer” compounds have higher rolling coefficient?!

(B) Is the rolling coefficient different for front- and rear tires?
From literature I would assume that the width of the tire does not impact the rolling coefficient because there is no surface in the equation for rolling resistance

F = Crr N

with F is the rolling resistance, Crr is rolling resistance coefficient (CRF) and N is the normal force.

Any advice is highly appreciated.

[Jersey Tom]

My understanding is “softerer” compounds have higher rolling coefficient?!

"Softer" in the sense of more "grip" through higher hysteretic loss tread formulations - yes, I'd expect higher rolling coefficient.

Is the rolling coefficient different for front- and rear tires?

I'd certainly expect so.

From literature I would assume that the width of the tire does not impact the rolling coefficient because there is no surface in the equation for rolling resistance

Ah yes.. "the" equation. What you present is one model for rolling resistance. In the real world most things don't fit just "some equation." In any event I'd expect width of tire to make for a higher rolling coefficient since you have more tread rubber. The tread rubber is the biggest contributor to rolling resistance, typically.

I'd have to guess there are some SAE papers around on this, though I haven't looked.

[Tim.Wright]

Your equation is correct, but Crr will change for a different tyre. Intuition tells me a wider tyre will have a higher Crr because you are deforming more tread (therefore losing more energy) in a wider tyre.

Why are you looking at this anyway? Coast down tests or something? Its normally neglected because its such a low force compared to typical operating forces in the longitudinal direction.

[MerlinC]

Why are you looking at this anyway? Coast down tests or something? Its normally neglected because its such a low force compared to typical operating forces in the longitudinal direction.

Well. The reason why I'm looking for this information is that I'm re-doing a tire model for an F1 simulation in rFactor. The tire model is requesting this parameter to calculate the heat caused by rolling and friction.

Having in the simulation 6 different compounds I'm trying to get them done as accurate as possible. But there is very limited information on technical data of F1 tires. I can understand that this information is not available for the 2014 tires - but it's a little bit surprising that nearly no information is available of the 2013 tires.

By the way another question came up this afternoon. The tire model considers 3 effects of cooling the tire. Heat transmission to the road, convection in static air and in moving air. I'm assuming that the dominating effect is cooling through moving air and conductive heat transfer to the road is limited. Does anybody have some numbers / percentages how the 3 effects will be participate in tyre cooling?

[Greg Locock]

Your equation is correct, but Crr will change for a different tyre. Intuition tells me a wider tyre will have a higher Crr because you are deforming more tread (therefore losing more energy) in a wider tyre.

Up to a point. A wide tire has a short contact patch and therefore there is less deformation of the rubber in the patch (ultimately the pneumatic trail for vertical forces must be related to the length of the contact patch, and the PTfor Fz is the cause of rolling resistance)

Michelin did some nice work on this and reckoned for a 90 kg axle loading a 60mm wide tire was about right, and you will notice that the size of road bike tires is increasing rather than decreasing.

For passenger car tires the most significant contributor to rolling resistance is tread and subtread compound, not tire size.

[Tim.Wright]

Why are you looking at this anyway? Coast down tests or something? Its normally neglected because its such a low force compared to typical operating forces in the longitudinal direction.

Well. The reason why I'm looking for this information is that I'm re-doing a tire model for an F1 simulation in rFactor. The tire model is requesting this parameter to calculate the heat caused by rolling and friction.

Having in the simulation 6 different compounds I'm trying to get them done as accurate as possible. But there is very limited information on technical data of F1 tires. I can understand that this information is not available for the 2014 tires - but it's a little bit surprising that nearly no information is available of the 2013 tires.

By the way another question came up this afternoon. The tire model considers 3 effects of cooling the tire. Heat transmission to the road, convection in static air and in moving air. I'm assuming that the dominating effect is cooling through moving air and conductive heat transfer to the road is limited. Does anybody have some numbers / percentages how the 3 effects will be participate in tyre cooling?

Whats the point of redoing the tyre model if you are just populating it with rules of thumb? In other words, if you don't have the actual data for these tyres, how do you expect to get a better result than what is already there?

[MerlinC]

Whats the point of redoing the tyre model if you are just populating it with rules of thumb? In other words, if you don't have the actual data for these tyres, how do you expect to get a better result than what is already there?

You are making a valid point. First my hope was that somebody in this F1Technical forum can tell me a source where I can get the tire data - but that does not seem to be the case.

Given this, going forward with rule of thumbs is the only way of improving the model (although it's not going to be perfect). Wouldn't you agree that a tire model reflecting correct relations-ships is better than one where the hardest compound has the highest grip ?

By the way do you have an answer to the questions I raised as well?

[Lycoming]

Where to the values for the model you already have come from and why do you think that numbers derived from rough estimations and rules of thumb will be better?

As for the heat transfer thing, natural convection is basically negligible once you get the airflow moving fast enough. Basically at high speed, forced convection dominates and at low speed or no speed, natural convection dominates. Can't say anything about the actual numbers involved, but have a look through a heat transfer textbook.

[mcjamweasel]

This video is a nice comparison of (admittedly not current Pirelli) F1 tyres vs others.

Tire ski jump.: http://youtu.be/f62Z8Ev9OXA

[MerlinC]

Where to the values for the model you already have come from and why do you think that numbers derived from rough estimations and rules of thumb will be better?

That is not clearly documented. There is some indication that the tire model is just derived from an standard race tire by adding factors.

Why do I want to do an own model? Issue is that the current tires in the simulation behave in regard wear and temperatures very much different to what is being observed in real Formula1. So what is wrong trying to gather the available information do a new approach? If it is not going to be better than what we have today we can still use what is there

[MerlinC]

This video is a nice comparison of (admittedly not current Pirelli) F1 tyres vs others.

Tire ski jump.: http://youtu.be/f62Z8Ev9OXA

I wished my Japanese would be better

[Jersey Tom]

The "tire model" in rFactor is so hokey / poor from my recollection... you might as well just tune the model parameters by feel rather than trying to find hard data on it.

[tok-tokkie]

It is strange that tire data is not available. The teams put a huge effort into collecting tire data. Mercedes were renowned for having really poor data resulting in terrible tire heating and wear performance the last 3 or 4 seasons. Obviously it is vital and critical information for each team which they will want to guard and keep secret but each year the data changes since the tires change. Plus Pirelli (nowadays) issue the teams with tire data for the next season's tires. With all this information floating about I am surprised none is available - particularly for past seasons.

[Jersey Tom]

It is strange that tire data is not available. The teams put a huge effort into collecting tire data. Mercedes were renowned for having really poor data resulting in terrible tire heating and wear performance the last 3 or 4 seasons. Obviously it is vital and critical information for each team which they will want to guard and keep secret but each year the data changes since the tires change. Plus Pirelli (nowadays) issue the teams with tire data for the next season's tires. With all this information floating about I am surprised none is available - particularly for past seasons.

I suppose I can kind of see your line of reasoning... but it's not that simple.

I had a long, detailed reply written up but.. gonna scrap it. Ultimately there's a lot of cost and intellectual property involved in all parties, regardless of if the tires are current are not. For that matter, I feel pretty confident that some of the data and analysis work I did a couple years ago is better than where some of my competitors are at today. I suppose a lot of people think that of themselves though. In any event "old" doesn't mean bad or out of date... so you're never really inclined to give things away, not knowing where the competition is at.

And even if all the data were released to the public I think it would mislead and confuse even the more "technical" fans more than anything.

It is a very challenging topic, one where the more experience you get the more you question everything and are very wary of the numbers you are presented.