Pirelli 18 inch tyres - visualization

[PhillipM]

I wouldn't be so sure about wheel mass only affecting longitudinal acceleration, there's a gyroscopic component in a spinning wheel...

[Jersey Tom]

I wouldn't be so sure about wheel mass only affecting longitudinal acceleration, there's a gyroscopic component in a spinning wheel...

Tire load variation / mechanical grip is another one. I've known open wheel guys in lower levels than F1 go to the expense of titanium bolts and silver-plated nuts to save a few grams of unsprung mass. Going to 18" wheels, that's orders of magnitude more. Kilos.

[Andres125sx]

From first hand experience, yes. Cars in the UHP category with the big price tags are heavily driven by marketing. Don't forget that the vast majority of those cars don't see track time - they're on display. The tire companies involved usually don't even have any say in it. They're told, "Okay here's our prototype car.. we've already picked the springs and bars, kinematics, etc.. already have picked the rim and tire size.. figure out a tire design in that box which will give us the handling we want."

Fashion. If you had a choice between comfy runners or skinny high heels, your choice depends on what you want others to think, not performance. James May:

Anyway - tyres. I'm not suggesting this is a directly related topic and yet, in a way, it is. A few days ago, I was looking at a slightly tricked-up Nissan sitting on tyres that had about as much give in them as a supermodel's elbow, and I just didn't fancy it at all. Didn't look like it would keep you warm at night.

Then, in America a few weeks ago with Jeremy, we saw a Dodge Charger (the new one) on tyres that had obviously been up vomiting all night, and that looked really uninviting. I mean, the wheels looked positively unwell. Terrible, it was.

It's been going on for years, this sort of thing, and I think it's time we cried ‘enough'. Some tyres are now so thin it's difficult to tell what they actually are. It's fashion, obviously, because really low-profile tyres are of no benefit outside of the racetrack and only make the car steer and ride badly, so it will probably pass. I think this may be about to happen, and I do hope so.

You both are going the same route... no benefit outside the track. Ok, I may agree but, who was talking about that?

We´re talking about F1, and I used the example of supercars. Both are designed for the track

1000hp are of no benefit outside the track either, but they still build cars with that insane power. That´s the point of those flagships, building the fastest car they´re able to design, and that obviously means designing the car for track use. If we/they don´t think about the track then all those cars (LaFerrari, P1, Veyron, Zonda....) have no sense at all so, why building a car for track use, but using tyres for outside the track?

They all are designed for the track, and that obviously includes the tyres

F1 has proven for years that 'really low-profile tyres' are not required at the top level of Motorsport. The cars zip around quite fine. So why change? Fashion. Gucci needs to sell more hand bags.

F1 has also proven for years active wings are not required at the top level of motorsports...

Does that mean active wings are not faster?

You´re implying F1 rules are written to ensure the cars are as fast as possible..... When you´re kidding please use some smilie, I´m spanish and struggle to notice when you´re joking

[Ciro Pabón]

I feel sorry for all the drivers riding on such thin tyres with essentially no suspension.

I also feel sorry for the people who will get a puncture by riding kerbs.

Finally, more money thrown at pulled-out-of-my-ass specifications?

Thermal sensitivity will rise because the tyres will have less volume of air inside, so less affluent teams will get even more abysmal times.

Not to mention they are ugly: we saw it coming.

... and puhleeze, don´t explain to me these stupid tyres will give you better handling.

If you want even higher lateral g´s there are a million ways to get it, most of them prohibited.

People, F1 is run by ricers

There is nothing more uncool than trying to be cool.

But mommy says I'm cool!

[henry]

Humble pie time.

I did some calculations using a spreadsheet rather than lying in the bath.

I got:

Increased mass of front wheel assembly - 2.4kg plus 5.3kg of referred mass from inertia.

Increased mass of rear wheel assembly -- 2.5kg plus 5.7kg of referred mass

That makes an additional 31.8kg of mass to be accelerated. Using the 0.4 secs per 10kg rule that woul put the lap time loss at 1.3 seconds due to mass and inertial effects.

I would expect teams to trade ballast to get rid of the increased mass so we are left with the inertial effect from the 22kg of referred mass. If the 0.4 rule applied to this the maximum lap time loss would be 0.88 seconds. Since the loss only applies to straight line acceleration when not traction limited my guess would be a lower loss, maybe 0.6 seconds from inertial effects alone.

[henry]

I wouldn't be so sure about wheel mass only affecting longitudinal acceleration, there's a gyroscopic component in a spinning wheel...

Indeed there is. Can you propose a mechanism by which the gyroscopic effects would affect lap time?

[henry]

I wouldn't be so sure about wheel mass only affecting longitudinal acceleration, there's a gyroscopic component in a spinning wheel...

Tire load variation / mechanical grip is another one. I've known open wheel guys in lower levels than F1 go to the expense of titanium bolts and silver-plated nuts to save a few grams of unsprung mass. Going to 18" wheels, that's orders of magnitude more. Kilos.

I was only addressing the inertial effect raised by flyboy. I don't have any background to have a feel how different, better or worse, the change to a stiffer tyre with higher unsprung mass would be.

I wonder if the titanium bolt guys have ever measured the benefit.

[flyboy2160]

Humble pie time.

I did some calculations using a spreadsheet rather than lying in the bath.

I got:

Increased mass of front wheel assembly - 2.4kg plus 5.3kg of referred mass from inertia.

Increased mass of rear wheel assembly -- 2.5kg plus 5.7kg of referred mass

That makes an additional 31.8kg of mass to be accelerated. Using the 0.4 secs per 10kg rule that woul put the lap time loss at 1.3 seconds due to mass and inertial effects.

I would expect teams to trade ballast to get rid of the increased mass so we are left with the inertial effect from the 22kg of referred mass. If the 0.4 rule applied to this the maximum lap time loss would be 0.88 seconds. Since the loss only applies to straight line acceleration when not traction limited my guess would be a lower loss, maybe 0.6 seconds from inertial effects alone.

You've got only part of the answer (the delta from increased translation mass) in guesstimating the acceleration delta. You still have to address the extra work you have to do to overcome the increased rotational inertia. Despite what's in other posts above, this delta will get added to the translation inertia guesstimate.

You reduce the rotational inertia of the wheel and tire for same reason you try to lighten the engine flywheel: that added rotational inertia wastes energy you could otherwise use to accelerate the car in translation.

[henry]

Humble pie time.

I did some calculations using a spreadsheet rather than lying in the bath.

I got:

Increased mass of front wheel assembly - 2.4kg plus 5.3kg of referred mass from inertia.

Increased mass of rear wheel assembly -- 2.5kg plus 5.7kg of referred mass

That makes an additional 31.8kg of mass to be accelerated. Using the 0.4 secs per 10kg rule that woul put the lap time loss at 1.3 seconds due to mass and inertial effects.

I would expect teams to trade ballast to get rid of the increased mass so we are left with the inertial effect from the 22kg of referred mass. If the 0.4 rule applied to this the maximum lap time loss would be 0.88 seconds. Since the loss only applies to straight line acceleration when not traction limited my guess would be a lower loss, maybe 0.6 seconds from inertial effects alone.

You've got only part of the answer (the delta from increased translation mass) in guesstimating the acceleration delta. You still have to address the extra work you have to do to overcome the increased rotational inertia.

Sorry, I'm not making myself clear.

The figures I have computed are the extra mass of the wheel, what you call translational mass, PLUS the mass which, at the contact patch, represents the inertia of the wheel. That mass has the same relation to the linear acceleration of the wheel as the inertia itself has to the rotational acceleration. This inertial mass only affects the longitudinal acceleration of the car whilst the translational mass affects accelerations in other planes.

This means that the rule of thumb for evaluating translational mass effects will overestimate the loss of lap time for the inertial effects.

[flyboy2160]

....

Sorry, I'm not making myself clear.

The figures I have computed are the extra mass of the wheel, what you call translational mass, PLUS the mass which, at the contact patch, represents the inertia of the wheel. That mass has the same relation to the linear acceleration of the wheel as the inertia itself has to the rotational acceleration. This inertial mass only affects the longitudinal acceleration of the car whilst the translational mass affects accelerations in other planes.

This means that the rule of thumb for evaluating translational mass effects will overestimate the loss of lap time for the inertial effects.

What is this "reference mass" you are adding at the tire contact patch?

[Andres125sx]

Just an uninformed question

Would the increased rotational inertia improve traction?

Since it´s more difficult to change rotational speed quickly....

[henry]

What is this "reference mass" you are adding at the tire contact patch?

If you accelerate the wheel there is a fixed relationship between the linear acceleration and the rotational acceleration based on the rolling radius. The accelerating rotating inertia can be equated to a mass accelerating linearly. Actually it doesn't need to be at the contact patch.

There is a better explanation here - http://hpwizard.com/rotational-inertia.html

[xpensive]

Xcuse my ignorance, I must have missed something, but what is the official reason to switch to these silly looking wheels?

Just "Pimp my ride"?

[Andres125sx]

Xcuse my ignorance, I must have missed something, but what is the official reason to switch to these silly looking wheels?

Just "Pimp my ride"?

http://www.fastcoolcars.com/images/wall ... pi-big.jpg

Don´t know, try asking WRC teams...

Find the difference

[xpensive]

So why did not anyone go that way when tire-development was free and there was something called competition?

I don't think anyone has asked for this, just the FIA thinks it looks cool, another stupid rule-change for the sake of it.

As Ciro said, I pity the drivers.