Should Champcars go to a wider tire for '05?

[ChrisB]

AFAIK the current rear Champ tires are 14.5" wide. For comparison, the rear tires at the peak of F5000 in the mid 70's were about 16.25" wide. (F1 also about the same then) That's about 12%

I guess there's 2 ways to go with this...

1. Wider with about the same compounds as now

2. Wider with a harder spec compound

Going with the first means increased mechanical grip. As we've seen in the threads about undertrays, we want to lessen the things that are more affected by aero disturbance, and increase the things that aren't. Obviously mechanical/tire grip is not affected by aero disturbances, so having more of it would be a GOOD thing, right?

Going with the second idea... a harder spec compound would greatly reduce the marbles, lessen the variance between "the line" and "off line" because of less rubber getting put down, and increase the distance the tires can go between stops. However, a harder compound will lessen mechanical grip, and we may not want that... thus a wider tire would help preserve that grip lost by a harder compound.

Either way, a wider tire seems the way to go. Comments anyone?

[DaveL]

"Obviously mechanical/tire grip is not affected by aero disturbances, so having more of it would be a GOOD thing, right?"

You bet.

Wider tires would make for better racing at all tracks. The only drawback is an increase in unsprung weight.

[RacinM3]

A wider tire with the same compound would be good. A wider tire with a harder compound could just have as much grip as todays tires. I'm sure the tiremakers don't need mould-building practice.

[damiandoan]

And the associated increase in drag from the wider tires would have what effect?

DD

[Lizzerd]

ChrisB, I don't necessarily disagree with your conclusion, but how you got to it. And this is just my gut feeling. It doesn't come from someone who designs or works on racecars.

Firstly, you're right (as far as I know) about mechanichal/tire grip not being affected by aero disturbances, but a wider tire will indeed cause more aero drag on the car and more disruption of air at the trailing end of the car, hence making life a little more difficult for those who follow. Whether the increased grip of wider tires outweighs the decreased aero performance of a following car is for the people who are smarter than me to figure out. Obviously, higher speed worsens the consequences.

Secondly, I recall hearing more than a couple drivers last season comment that Bridgestone has developed such a good tire that marbles are no longer an issue. The lack of competetion with Goodyear is the culprit. Bridgestone's interest has gone from being faster, to being reliable, durable, and consistent throughout a stint. Changing a compound that works wouldn't make sense for them.

So, my conclusion would be don't try to fix something that doesn't seem to be broken.

[Mike Kellner]

I would opt for wider tires, because they will slow the cars in fast parts and give more grip in slow sections. Wider ruber has been on my list of changes for years.

[mnkywrch]

I'd take a harder spec capable of lasting the entire race.

[pchall]

I'd like to see a narrower rim and a lower profile tire.

A champcar driver won't be needing to get a 1000HP down on a street course in the forseeable future. Both the tires and the drivers need to be made to work harder.

[Napoleon]

I am strongly in favor of a narrower/lower profile tire, if any change is made. Less grip = more driver talent needed to extract 100% from the car.

[ChrisB]

I agree with a lower profile too.

I posted this also on AR1 and Peter O. made a good point about wider widths mainly allow for softer compounds. (Pete, if you're lurking...)

Question for anyone... if you have 2 tires of different widths but the same soft compound, given the same application, will the wider tire produce less marbles, or about the same as the narrower one? (the point being that tire grip could be increased by going wider & softer w/o increasing the marbles)

[Peter Venkman]

"The only drawback is an increase in unsprung weight."

That, and an increase in frontal area.

Not that that is that bad. In fact, increasing frontal area directly influences max speed naturally, by physics.

I still would like a reduction in both free air wings and the tunnels.

I would want less tire loading so that corner speeds are reduced, and require "precise balance" that separates the drivers from the poseurs, and further reduces the low-to-high turbulence that comes off the back of today’s' cars, at speed, that can abruptly lighten the front end of the car behind, thus reducing the potential for passing under braking into the corners late.

I'm not avocating returning to yesteryear, but some of the most exciting racing extant was practiced during the Can Am series in the 70's, where aerodynamics was is its infancy.

[Peter Venkman]

" Question for anyone... if you have 2 tires of different widths but the same soft compound, given the same application, will the wider tire produce less marbles, or about the same as the narrower one? (the point being that tire grip could be increased by going wider & softer w/o increasing the marbles)"

I may be all wrong on this, but here's my opinion on your question.

A racecar has a certain front to rear, and side-to-side (and cross weight bias) weight distribution.

Each tire takes their share, based on the local car weight assigned to it, both statically and dynamically.

If you have a wider footprint, the areal (area) loading is decreased (same load distributed over a larger area), and the work any square inch of that tire is reduced, given equal shear loads (forward or lateral).

In a car with sufficient down force acting on the car, and you present more “footprint” by wider tires, and the flattening of the tire patch by the download, you actually increase the grip further simply as a function of the increase in effective area due to the downforce. Of course nothing comes for free, so you also lose some energy to the greater deflection of the tire.

I think that the primary factor in “marbles” is the rubber’s vertical and transverse shear capability (softness, measured by a durometer test). If you think of the tire as a column of stuff with the anchorage point at the tire carcass and the load being applied at the end that contacts the track surface, the hardness or strength (in bending or shear) of that column or beam is predicated on how strong that column can react the shear loads, and if the rubber is soft enough (as in weak in bending and can be separated from the carcass) then you produce “marbles”.

Although that may not be the only reason, I do think that it is the primary reason for “marbles”.

[ChrisB]

Just to illustrate the approximate widths I'm talking about, here's a photo of Mario at Pocono '75 in the F5000 Lola

http://www.netaxs.com/~gg1/race/mapoco75_smaller.jpg

(this photo is copyright Jon Reynolds, but I made a smaller version to load faster in a forum)

[RARules]

Originally posted by Peter Venkman

"Question for anyone... if you have 2 tires of different widths but the same soft compound, given the same application, will the wider tire produce less marbles, or about the same as the narrower one? (the point being that tire grip could be increased by going wider & softer w/o increasing the marbles)"

I think that the primary factor in “marbles” is the rubber’s vertical and transverse shear capability (softness, measured by a durometer test).
...
and if the rubber is soft enough (as in weak in bending and can be separated from the carcass) then you produce “marbles”.

Although that may not be the only reason, I do think that it is the primary reason for “marbles”.
Comments about marble formation seem reasonable so far, but they all seem to miss one point:

With a wider tire, the loading is less for a given speed / turning radius. But of course, with the increased traction everyone would be cornering faster. I'd posit that the cornering speeds would increase until the tire loading reached the same as with the narrower tire. So we'd be at the same marble-producing point, right?

In other words, I'm assuming that (given identical rubber compound) the critical point for cornering is roughly the same as the critical point for marble producing. So wider tires wouldn't significantly impact marble production.

I think the rubber compound is the main factor here. With tire competition, it's an advantage to use a tire with marble-producing parameters. But this makes races more like a parade because no one can go off-line at all. I don't see how one could set up rules that allow tire competition yet reduce marble-formation.

Therefore, the conclusion is that tire competition is generally bad for passing.

[Mike Kellner]

"I don't see how one could set up rules that allow tire competition yet reduce marble-formation."

It is my belioef, that if you are willing to do the work, you can test for almost anything mechanical. What if they developed a standard abraision test? Heat the tires to 100°C and then put them on a lathe and grind then with a specified rough surface, pressing against the tread at a specified force, for a specified length of time. Weigh the tires before and after, and have some maximum material loss that is allowable?

[RTKar]

Hard compound less grip, less marbles, maybe. Soft compound spec, No.

[Peter Venkman]

"I'd posit that the cornering speeds would increase until the tire loading reached the same as with the narrower tire. So we'd be at the same marble-producing point, right?"

Yeah, I think I agree with you to a point.

There's two significant actions that happen with tire loading: one, friction of tire compound to track surface which in physics, it's been taught that that is insensitive to area (which is BS in this case).

The other is a molecular attraction that would be different as a function of tire compound material and how much of the tire surface can conform to the irregularities of the track surface, which would be more, with a "softer compound" (local area deflection).

[ChrisB]

Something else to throw in here...

Who here wants to keep it to ONE tire manufacturer, and who'd like to see two? (tire war)

And if just one, who's in favor of having just one spec compound for all, and who's in favor of having 2 or more compounds available?

(FWIW, my vote is for a single supplier with the same spec compound for all)

[RTKar]

Agreed, single supplier, same spec at least until things stabilize.

[Lizzerd]

You can't spec a compound. They are proprietary to the manufacturers. That's like telling Coke and Pepsi to make cola to the same formula. Can't be done.

If there is another tire war (and I'm not necessarily against that), the war will be for speed. That Bridgestone (Firestone then) was able to drive Goodyear away from the series was they were able to come up with a fast tire that happened to be longer lasting than Goodyear. But to be faster, both manufacturers had to make softer tires. The tire war turned into a war between the drivers and the marbles. Now, Bridgestone makes a tire that does not "go off" during long runs, but I guarantee you, if another manufacturer enters the fray, that it will be the same old, same old... Tires will get softer and faster, and we'll have the marble problem again.

[Lizzerd]

Okay, I think I misread ChrisB's post.

If there is one manufacturer, then yes, allow them to bring two compounds. I though he meant a spec compound for two or more manufactures.

But, two or more with two compounds available would be great. I would even say let them use both during a weekend or even a race, if they choose, which would create a whole new variable. How do you set up your car? Surely, the setups would be different for "soft" and "hard", so do you commit to one or the other before the green? Start with a compromise setup? Okay, I'm just thinking out loud, I guess. Just more food for though to we, the people on the other side of the pit wall.

[Peter Venkman]

"'d posit that the cornering speeds would increase until the tire loading reached the same as with the narrower tire. So we'd be at the same marble-producing point, right?"

Yeah, I agree that the tire lateral (and fore/aft) capability would increase with the increase in tire width, but because the tire tread stiffness (not the carcase stiffness) is greater, it would still retard "marbles" at the maximum possible slip angle and tractive load because the tread rubber would be stronger, or more capable of taking deflection before failure.

[Peter Olivola]

This is all very well, Mike, but tire compounding is still not entirely scientific. Even within your limitations there will be large variations in behavior. Abrasion testing is meaningless. Tire performance is related to temperature and loading over time but it also relates to how tread surface deflection is controlled by the carcass and sidewall which your test wouldn't even touch. I would add, that surface abrasion isn't nearly the source of heat you seem to imply. Most tire heat is a function of hysterisis, not direct surface abrasion. Your test won't touch that at all.


Originally posted by Mike Kellner
It is my belioef, that if you are willing to do the work, you can test for almost anything mechanical. What if they developed a standard abraision test? Heat the tires to 100°C and then put them on a lathe and grind then with a specified rough surface, pressing against the tread at a specified force, for a specified length of time. Weigh the tires before and after, and have some maximum material loss that is allowable?

[RARules]

Originally posted by Peter Olivola
I would add, that surface abrasion isn't nearly the source of heat you seem to imply. Most tire heat is a function of hysterisis, not direct surface abrasion. Your test won't touch that at all.
If you could clarify, please. I know what hysteresis is in electromagnetics and related phenomenon, but I'm not an ME, so I'm not familiar with how it relates to tires and rubber compounds. Is this simply the tread flexure coming on to and off of the contact patch? (which I wouldn't normally think of as hysteresis, but what do I know?)

[Mike Kellner]

Re Peter Olivola,

My goal isn't to equalize tires or slow cars. The biggest complaint about tires is marbles. I was suggesting a standard abraision test as a way of controlling marbles. You could run any tire as long as it met the standard. (Of course I would include size and safety rules) While no test is perfect, I am wondering if you couldn't run some test that aproximatly showed the marble creating potential of a given tire. The weight removed from the tire in the test would be more or less relative to the rate at which it would shed marbles in a race. The reason I suggested heating the tire to 100C is that is about the working temperature of a racing tire. I thought it would be better to test it near it's working temperature. If that temperature is different, change the test temperature.

In simple terms. We want to control marbles because they are a detrement to competetive races. Marbles are tire material abraided off of the tire. So, test tire by abraiding it and measuring how much material it loses in a standard test. Set limits to control marbles, based on that test.

[Peter Olivola]

In tires, hysteresis is internal friction and the resulting heat caused by it.


Originally posted by RARules
If you could clarify, please. I know what hysteresis is in electromagnetics and related phenomenon, but I'm not an ME, so I'm not familiar with how it relates to tires and rubber compounds. Is this simply the tread flexure coming on to and off of the contact patch? (which I wouldn't normally think of as hysteresis, but what do I know?)

[Peter Olivola]

Mike,

Heating tires externally does not produce the same behavior as the heat generated by the tires internal friction (hysteresis.) That's why it won't work as you want it to.


Originally posted by Mike Kellner
Re Peter Olivola,

My goal isn't to equalize tires or slow cars. The biggest complaint about tires is marbles. I was suggesting a standard abraision test as a way of controlling marbles. You could run any tire as long as it met the standard. (Of course I would include size and safety rules) While no test is perfect, I am wondering if you couldn't run some test that aproximatly showed the marble creating potential of a given tire. The weight removed from the tire in the test would be more or less relative to the rate at which it would shed marbles in a race. The reason I suggested heating the tire to 100C is that is about the working temperature of a racing tire. I thought it would be better to test it near it's working temperature. If that temperature is different, change the test temperature.

In simple terms. We want to control marbles because they are a detrement to competetive races. Marbles are tire material abraided off of the tire. So, test tire by abraiding it and measuring how much material it loses in a standard test. Set limits to control marbles, based on that test.

[RARules]

Originally posted by Mike Kellner
In simple terms. We want to control marbles because they are a detrement to competetive races. Marbles are tire material abraided off of the tire. So, test tire by abraiding it and measuring how much material it loses in a standard test. Set limits to control marbles, based on that test.
Well, it wouldn't be perfect (or even feasible), but consider this possibility:

Run the tire on a fixture ala a dyno testing rig - against a reasonable diameter cylinder (i.e., not too small) with the surface *roughly* the texture and frictional coeffecient of asphalt (yeah, I know, how to keep the layer from flying off). Put enough power vs. resistance on the rig to heat up the tire and cause slippage (like the measurement used for traction control), and measure the spray of rubber coming off the tire after equilibrating.

True, this is only linear marble formation - not the side-force formation that we really care about, but it might be close enough.

What do you think of this as a starting point? Let's brainstorm a bit here as an intellectual exercise. What could you do to construct a meaningful test / simulation?

[ChrisB]

Would all this really be neccesary? I think it's highly plausable that Champcars are going to remain with a single-supplier tire situation, like Nascar & IRL. Even Bernard says he's in favor of going to a single-supplier in F1 to avoid tire wars. So... if you have one tire company supplying the field, do you make one compound available or two? If you consider that probably 90% of the teams all pick the same compound for a given weekend ANYWAY, having only one compound eliminates a lot of issues. Since everyone will be using the same thing, CART & the tire manufacturer can work together to make that compound what it needs to be for a given race.

(Does anyone know if Nascar & IRL have one compound or several available at their races?)

[ChrisB]

I just wanted to throw this back up to the top after the St Pete race.

We saw that having somewhat limited grip with a harder compound made for some pretty good competition.

You might think that going to wider tires would increase tire grip and that's not want we want... not neccessarily! The original idea of this thread was to increase grip in areas that are least afected by aero changes... and tires is one of them (undertrays being mainly the other). The overall grip could be kept at about the same as it was at St Pete... it would just be *even less* suseptable to aero changes, such as when trailing the car in front.

Nevertheless, even if they went to a wider tire with about the same grip as now, I suppose it would still *reduce the marbles* due to an increased size patch reducing the amount of wear per square inch.

Comments anyone?