50 years different

[island911]

Good stuff, Steve, but tires don't absorb heat as much as they create heat from dynamics.

Increasing surface area (width or circumference) will decrease dynamic heating and increase cooling.

[Sooner or later]

A 245 50 17 tire is significantly different than a 265 50 17 tire.

It ain't just the tread width that changes. The only component that will probably stay the same will be the bead. Tread, plies, liner, apex, sidewall, overlay (if used) will all be of different width and slightly different contour (fabric components will only have width changes). The 265 will be taller. SW deflection will differ. Contact patch will change and not just due to tread width.

So when you say you want the same tire with only a different width you ain't gettin' that.

[RWebb]

Originally Posted by masraum

Contact patch doesn't increase as tire width increases. The contact patch just changes shape.

Exactly.

Note the width increase.

[masraum]

Originally Posted by island911

Good stuff, Steve, but tires don't absorb heat as much as they create heat from dynamics.

Increasing surface area (width or circumference) will decrease dynamic heating and increase cooling.

OK, night, they heat up due to deformation, and then hold the heat that is created in them. I assume the process is similar to how if you're trying to break a piece of metal by bending it back and forth, the metal heats up where you're bending it.

[masraum]

Originally Posted by RWebb

Exactly.

Note the width increase.

right, width increase, and length decrease (what? it was cold!).

[john70t]

Small skinny tire:
1). Lighter weight = Faster suspension response.

2). More consistent and faster sidewall flex = Outer tire drags on the ground to provide traction and driver feedback through the frame.

3). Some traction is always better than none..... i.e. sporadic skipping and hopping.
(unless of course you are at cars and coffeve.)
Please refer to #2 above.

4). No high-speed pressure area is created at the tire-to-surface arc zone..which creates lift at high higher speeds.

5). Smaller contact area = More psi = More traction

[Jack Olsen]

Originally Posted by pwd72s

Jack's poster is nice, but a bit of a misnomer. There are plenty of people who would accept that challenge. Especially if it involved timing on a track other than the one he knows like the back of his hand. Guess you could say he's an amateur specialist...very skilled, but not really the ultimate.

Not trying to denigrate what he's done to his car, or his skill on Willow Springs. To each his own.

Yes. The list of particular situations where a modern 911 would beat my car is pretty long. It will accelerate faster. It will probably brake faster. These are two areas where the newer car's weight can be overcome with power or technology.

But the reason I'm quicker than some of the new Porsches at Willow Springs isn't because of how well I know that track. What's particular about Willow Springs is that it doesn't have any 5th-to-2nd (or even 4th-to-2nd) corners. In a fast lap, the lowest speed my car ever drops to is 60 mph. This means I never need to 'dig myself out of a hole' in terms of acceleration -- which would give a huge advantage to a 475-hp GT3 or the 870-hp 918. Willow has very-high-speed (often steady-state, sweeping) corners. So sustained cornering speeds are hugely rewarded, with hard braking and hard acceleration performance not so much.

Through a long 100-mph sweeper, the weight advantage my car enjoys means I can go through that corner faster than a GT3 or even the 918 -- even with all of their technological innovations (four-wheel steering, suspension sophistication, torque vectoring, whatever). Lateral acceleration is where 'plain old weight' is a huge factor. 'Power-to-weight' really only applies when you're talking about straight-line acceleration (or deceleration). Power and cornering speed are not directly related at all.

As it happens, the 918's power advantage is so great that it ultimately buries my lap time by being so awesome on the straights. But I'm quicker through it in just about all of the corners -- which, considering the march of tech progress, is something that still surprises me.

I believe that if it were possible to drop a 918 powerplant (or the equivalent horsepower) into my 911 without adding any weight, I'd be able to navigate Willow Springs faster than the modern car. But of course, it's not possible to do that.

So to be clear: the laws of physics are the laws of physics, and my car is not magically able to best the efforts of 50 years of work by Porsche AG in many ways. But going through a corner, there are some hurdles caused by total chassis weight that technology has still not made irrelevant.

[masraum]

Originally Posted by Jack Olsen

Yes. The list of particular situations where a modern 911 would beat my car is pretty long. It will accelerate faster. It will probably brake faster. These are two areas where the newer car's weight can be overcome with power or technology.

But the reason I'm quicker than some of the new Porsches at Willow Springs isn't because of how well I know that track. What's particular about Willow Springs is that it doesn't have any 5th-to-2nd (or even 4th-to-2nd) corners. In a fast lap, the lowest speed my car ever drops to is 60 mph. This means I never need to 'dig myself out of a hole' in terms of acceleration -- which would give a huge advantage to a 475-hp GT3 or the 870-hp 918. Willow has very-high-speed (often steady-state, sweeping) corners. So sustained cornering speeds are hugely rewarded, with hard braking and hard acceleration performance not so much.

Through a long 100-mph sweeper, the weight advantage my car enjoys means I can go through that corner faster than a GT3 or even the 918 -- even with all of their technological innovations (four-wheel steering, suspension sophistication, torque vectoring, whatever). Lateral acceleration is where 'plain old weight' is a huge factor. 'Power-to-weight' really only applies when you're talking about straight-line acceleration (or deceleration). Power and cornering speed are not directly related at all.

As it happens, the 918's power advantage is so great that it ultimately buries my lap time by being so awesome on the straights. But I'm quicker through it in just about all of the corners -- which, considering the march of tech progress, is something that still surprises me.

I believe that if it were possible to drop a 918 powerplant (or the equivalent horsepower) into my 911 without adding any weight, I'd be able to navigate Willow Springs faster than the modern car. But of course, it's not possible to do that.

So to be clear: the laws of physics are the laws of physics, and my car is not magically able to best the efforts of 50 years of work by Porsche AG in many ways. But going through a corner, there are some hurdles caused by total chassis weight that technology has still not made irrelevant.

Pshhht, what do you know? Who's this Jack Olsen fella, anyway?

It's nice to see you slumming it, Jack! Nice write up.

[Jack Olsen]

Yeah, why is this in the off topic section?

It's a lot more technical than pictures of my car.

[island911]

Interesting write up JO. However I think that your conclusions on weight are a bit off the mark. (maybe purposely.) Yes, a heavier car takes more work (force) to round a corner (centripetal acceleration) but it also has more weight to stick the tires to the road. This is where aero comes into the weight equation. The heavier car will need much more aero down-force to have a weight-proportional affect.

[masraum]

Originally Posted by Jack Olsen

Yeah, why is this in the off topic section?

It's a lot more technical than pictures of my car.

I want to see BBII towing the camper. That would be quite a picture!

[Tobra]

Originally Posted by Jack Olsen

Yeah, why is this in the off topic section?

It's a lot more technical than pictures of my car.

Perhaps, but what tech section would be the place to put it?

[Porschist]

Originally Posted by Jack Olsen

I believe that if it were possible to drop a 918 powerplant (or the equivalent horsepower) into my 911 without adding any weight, I'd be able to navigate Willow Springs faster than the modern car. But of course, it's not possible to do that.

Indeed, mass is not an opinion. A track without dramatic decelerations and accelerations allows the contest to take place on centripetal forces. And lack of mass is the biggest element in centripetal efficiency. Most open wheel cars will lap a 918 on any track, even without aeros and even when way less powerful than the 918. In fact, many open wheels cars from thirty years ago will lap a 918. The only thing these cars all have, that the 918 does not, is the "added lightness".

Jack, I'd wager one would not need to match the HP of the 918 to beat it at Willows. I lapped a 918 hard and side forces were not as impressive as speed, acceleration and braking.
What if you added a turbocharger + modern rubber and rims to Black Beauty II?
Weight would probably go up notionally. Could even stay the same with some effort (recall the 934 homologation weight?).

I know you'll answer I already run modern rubber. I am saying more of it. To match the 918 contact patches.
And fresh, soft track rubber please. Like two grand per track weekend worth of it.
And a 600hp, turbo. To boost up to 700hp for when the press shows up to take the lap record.
I got a backdate with a 3.6 and a G50 itching to be converted to 918 beater.
It's black.
All you have to say is "maybe".
Sent you a pm by the way.

[pwd72s]

Jack:

"Through a long 100-mph sweeper, the weight advantage my car enjoys means I can go through that corner faster than a GT3 or even the 918 -- even with all of their technological innovations (four-wheel steering, suspension sophistication, torque vectoring, whatever). Lateral acceleration is where 'plain old weight' is a huge factor. 'Power-to-weight' really only applies when you're talking about straight-line acceleration (or deceleration). Power and cornering speed are not directly related at all."

Bingo! Colin Chapman had it right all along.

But Jack, you have to admit, your skill on Willow is higher than most...higher than many who run a variety of tracks. A well deserved skill earned through many hours of practice.

In a way, you're like the guy in a local pool hall named as the area "shortstop"...the guy called when a road hustler comes through town, lightening wallets. Call in the shortstop, and likely as not, the road hustler finds his wallet lightened, especially if he agrees to play on the shortstop's favorite table. On that table, the shortstop knows where a rail may bank funny, where a slow speed object ball will take a funny roll, etc.

I doubt there's a driver out there who knows Willow and it's nuances as well as you.

To get back to the original topic. Hell, let's face it...fat tires look much cooler than skinny ones.

[sammyg2]

You know how cars pick up speed when they slide off the track onto the grass.




lessee who remembers that reference.

[RWebb]

Originally Posted by Porschist

mass is not an opinion

Great Quote!

[Porschist]

Well, Jack certainly knows Willows like the back of his hands but Randy Pobst is not a stranger to that circuit either. Randy lapped a 918 in 1.23.54.
Jack is not far from that time, on less rubber and around 300hp.

If we assume Randy and Jack are equivalent hands behind the wheel (+/- a second?), Black Beauty II kicks ass, irrespective of driver's skill.

In the end, lapping a curvy track means pushing mass around corners against the grip of tires. There isn't much else to it. Electronics do not change physics.
1000 pounds of Mass lost are worth more than any electronic kit or, if you are not at Le Mans, 900 horsepower.

The comparison between Olsen's car and a 918 shows how cars have not really progressed. The evolution has been primarily in tires and contact patches.
The manufacturers "ate" tire progress to compensate for the obesity affecting their lineups. Minus a few seconds each year, baked in to show the new model was worth your cash because it was a bit faster than the last one. It's all engineered.
Put Jack's tires on the 918 and it'll careen into the desert at the first corner.
Put the 918 rims and tires on Jack's car, plus a booster, and Black Beauty would walk away.

A plank with four wheels is a plank with four wheels.

Or, as a Michelin engineer once said, 90% of a car is its tires.

[RWebb]

shows how cars have not really progressed on non-bumpy tracks...

also, near the limit & for skilled drivers

[pwd72s]

Originally Posted by Porschist

Well, Jack certainly knows Willows like the back of his hands but Randy Pobst is not a stranger to that circuit either. Randy lapped a 918 in 1.23.54.
Jack is not far from that time, on less rubber and around 300hp.

If we assume Randy and Jack are equivalent hands behind the wheel (+/- a second?), Black Beauty II kicks ass, irrespective of driver's skill.

In the end, lapping a curvy track means pushing mass around corners against the grip of tires. There isn't much else to it. Electronics do not change physics.
1000 pounds of Mass lost are worth more than any electronic kit or, if you are not at Le Mans, 900 horsepower.

The comparison between Olsen's car and a 918 shows how cars have not really progressed. The evolution has been primarily in tires and contact patches.
The manufacturers "ate" tire progress to compensate for the obesity affecting their lineups. Minus a few seconds each year, baked in to show the new model was worth your cash because it was a bit faster than the last one. It's all engineered.
Put Jack's tires on the 918 and it'll careen into the desert at the first corner.
Put the 918 rims and tires on Jack's car, plus a booster, and Black Beauty would walk away.

A plank with four wheels is a plank with four wheels.

Or, as a Michelin engineer once said, 90% of a car is its tires.

Can't argue with any of this...

[GH85Carrera]

The real difference is 90% of the racers at the track could drive the 918 with good lap times and not crash. Only a few could do it with Jack's 911. The computers do amazing things for average drivers. Jack's car is 100% driver controlled.

No ABS, traction control, power steering or rear wheel steering and the other nannies.

I would love to have a ride in either car around Willow Springs.