wide vs. narrow wheels/tires

[NoHaveMSG]

Originally Posted by nikitopo

Yes but more mechanical grip doesn't make you ALWAYS faster given that power is the same.

Yes we know. I have never disagreed with this statement. It's the way you presented the information.

2 cars setup vastly different with two different compound tires and drivers of unknown skill differences. The diameter of the tires are even different.

Icecreamtruk In todays topic: a bunch of people who have no idea how grip works and some who do (at least partially) but get flamed for trying to share the knowledge.

Grab your popcorn, and start from page 9.

This thread has been great from the start.

[rvoll]

Originally Posted by RayRay88

Ofcourse, but the original argument stemmed between track testing of two different widths. Generally speaking a wider tire gives more mechanical grip than a narrower tire of equal construction and compound.

This is a myth and is just not true. I've had a number of track experiences where the narrower tire was faster. The tire/wheel combo is one where the ONLY way to find out is to do a real world test. Adhesion is a combination of contact patch and contact pressure -- not just contact patch. Wider tires have less contact pressure. In addition, it is a function of the majority of directional forces. So for autocross, where you are exerting a lot of lateral forces, wider is generally better because of the squarer contact patch and the forces against that patch. On a road course, or on the road in general, where 95% of the travel is just forward, and not turning, the narrower tire tends to be faster because it is generally lighter and there is less drag. Have you ever seen a dragster with wide front wheels? On the other hand, if you have to put a lot of hp on the driving wheels (something that is not necessary with the Twins), then wider ON THE DRIVING WHEELS makes sense as you are putting more rubber on the road during acceleration. However, once you are at speed, those wider tires are a negative. None of this takes into account other factors like mpg where narrower tires are clearly better.

There are no simple axioms that can determine what is better. Manufacturers spend a lot of time getting balance for their cars and once you significantly deviate from that balance, you cannot be sure of the results.

[strat61caster]

Originally Posted by rvoll

Have you ever seen a dragster with wide front wheels?

[RayRay88]

Originally Posted by rvoll

This is a myth and is just not true. I've had a number of track experiences where the narrower tire was faster. The tire/wheel combo is one where the ONLY way to find out is to do a real world test. Adhesion is a combination of contact patch and contact pressure -- not just contact patch. Wider tires have less contact pressure. In addition, it is a function of the majority of directional forces. So for autocross, where you are exerting a lot of lateral forces, wider is generally better because of the squarer contact patch and the forces against that patch. On a road course, or on the road in general, where 95% of the travel is just forward, and not turning, the narrower tire tends to be faster because it is generally lighter and there is less drag. Have you ever seen a dragster with wide front wheels? On the other hand, if you have to put a lot of hp on the driving wheels (something that is not necessary with the Twins), then wider ON THE DRIVING WHEELS makes sense as you are putting more rubber on the road during acceleration. However, once you are at speed, those wider tires are a negative. None of this takes into account other factors like mpg where narrower tires are clearly better.

There are no simple axioms that can determine what is better. Manufacturers spend a lot of time getting balance for their cars and once you significantly deviate from that balance, you cannot be sure of the results.

You seem to be running in circles. I was quite clear from my first comment that this was all related to circuit racing. You keep bringing up daily driving to argue your point.

Let me try to simplify.

All things being equal on a track.
Wider tires will generally give you more lateral G.

This does not take into account drag, weights or temperature.


In terms of contact patch pressure, it's not that simple. Rubber is deformable and so is the contact patch so tires can't be simply looked at as F=ma or even F-mu*r.

Contact patches remain relatively the same for both wide and narrow tires of equal compound and construction, the wider one will have a wider and shorter patch, and the narrow one will have a narrow taller patch. Wider contact patches create more lateral force per slip angle than a narrower patch. Simple.

The balance is about finding the point of diminishing returns, where you try to see how wide you can go before one or more of the mentioned variables start overcoming the increase in lateral grip.

I suggest you read up on tire load sensitivity. Your real world experience is limited to your knowledge about what is actually happening to your tire.

In response to your drag racer theory, funny cars actually require tall narrow tires for the longest possible contact patch (tall narrow patch is always better for linear acceleration). Why do they still use huge wide tires? Because tall narrow tires can't cope with the heat 5000hp puts into them.

Also I question anything you say simply based on the fact that you think a road course is 95% forward travel. Maybe you mean drag racing?

[NoHaveMSG]

Originally Posted by rvoll

This is a myth and is just not true. I've had a number of track experiences where the narrower tire was faster.

Huh?? I think we need to back up a sec and rethink what was said. There is a constant disconnect between what is quoted vs the argument being made.

RayRay88

Ofcourse, but the original argument stemmed between track testing of two different widths. Generally speaking a wider tire gives more mechanical grip than a narrower tire of equal construction and compound.

This is absolutely true, up to a point obviously. If you have evidence to prove otherwise please present it, but in general this is a genuinely accepted fact.

Then we go to your second line.

I've had a number of track experiences where the narrower tire was faster.

That is not what is being argued by RayRay88. He only commented on the lateral grip capability of a wider tire.

No one is disagreeing with this statement. We can break down this thread to simply say "more lateral grip does not always equal improved lap times." Then of course we wouldn't have this 11 pages of glory

[fatoni]

Originally Posted by rvoll

This is a myth and is just not true. I've had a number of track experiences where the narrower tire was faster. The tire/wheel combo is one where the ONLY way to find out is to do a real world test. Adhesion is a combination of contact patch and contact pressure -- not just contact patch. Wider tires have less contact pressure. In addition, it is a function of the majority of directional forces. So for autocross, where you are exerting a lot of lateral forces, wider is generally better because of the squarer contact patch and the forces against that patch. On a road course, or on the road in general, where 95% of the travel is just forward, and not turning, the narrower tire tends to be faster because it is generally lighter and there is less drag. Have you ever seen a dragster with wide front wheels? On the other hand, if you have to put a lot of hp on the driving wheels (something that is not necessary with the Twins), then wider ON THE DRIVING WHEELS makes sense as you are putting more rubber on the road during acceleration. However, once you are at speed, those wider tires are a negative. None of this takes into account other factors like mpg where narrower tires are clearly better.

There are no simple axioms that can determine what is better. Manufacturers spend a lot of time getting balance for their cars and once you significantly deviate from that balance, you cannot be sure of the results.

Can you explain this?

[venturaII]

Originally Posted by fatoni

Can you explain this?

Tires hold cars off the ground by volume, not pressure (at least, not directly). A larger tire has more volume than a smaller tire at the same pressure, so increasing the tire size on a vehicle means you need less pressure to achieve the same load capacity.

[RayRay88]

Originally Posted by venturaII

Tires hold cars off the ground by volume, not pressure (at least, not directly). A larger tire has more volume than a smaller tire at the same pressure, so increasing the tire size on a vehicle means you need less pressure to achieve the same load capacity.

100% true. The only thing he fails to grasp is that contact pressure, for two equal tires of different widths, really only starts to truly matter when you’re talking about snow or rain where you want as much pressure dowards to cut through whatever medium you’re driving on. Hence why rally vehicles have super skinny tires. On the pavement contact patch deformation and shape dictate lateral grip the most.

[fatoni]

Originally Posted by venturaII

Tires hold cars off the ground by volume, not pressure (at least, not directly). A larger tire has more volume than a smaller tire at the same pressure, so increasing the tire size on a vehicle means you need less pressure to achieve the same load capacity.

it can change the pressure per square inch but not the pressure. if a car weighs 2800lbs, its going to exert 2800 lbs of pressure on the ground no matter what the tire volume is.

[nikitopo]

Originally Posted by NoHaveMSG

No one is disagreeing with this statement. We can break down this thread to simply say "more lateral grip does not always equal improved lap times." Then of course we wouldn't have this 11 pages of glory

I think it is a good discussion

[why?]

Originally Posted by fatoni

I think it's at least as inaccurate to say that a 300 width would actually give more mechanical grip to begin with.

and yet that is absolutely what the wider tire is always better crowd is arguing. Of course it is absurd.

[switchlanez]

Originally Posted by fatoni

it can change the pressure per square inch but not the pressure. if a car weighs 2800lbs, its going to exert 2800 lbs of pressure on the ground no matter what the tire volume is.

Pressure is defined as force per unit area (lbs/in^2 or N/m^2). You're describing 2800 lbs of force to the ground, not pressure. Saying "pressure per square inch" is like saying (lbs/in^2)/in^2 or lbs/in^4 which is not a unit of pressure.

Pressure is inversely proportional to the area so if you apply the same amount of force (2800 lbs) to a smaller area, pressure goes up:
2800 lbs/area (in^2) = some pressure (psi)
2800 lbs/smaller area (in^2) = some bigger pressure (psi)

[why?]

Originally Posted by RayRay88

How is that 100% false?

Because there are other factors. It is all about balance. You can have too much mechanical grip for a car to overcome. And that will absolutely slow a car down. Because grip=friction. Now if the car has a massive engine and can never get enough grip, that is one thing. But out cars have 200 hp, if that, to the wheels. And every bit of extra grip means the engine has to work harder to do everything.

Now maybe that is just a regurgitation of what you meant. It just felt like you were arguing that no matter what the wider the better, and all track cars should run as wide a tire as possible and the most aggressive aero they can possibly create.

[Tcoat]

Originally Posted by strat61caster

"DAMNIT FRED you put the body on backwards again!"