50 years different

[GH85Carrera]

What a difference.

It would be interesting to figure out just how much more traction that giant tire with modern compounds has compared to the little skinny Michelin "state of the art" street tire of 1970.

[brainz01]

Cool comparison

[flatbutt]

What would happen to a 1970 tranny trying to spin a 2020 tire?

[GH85Carrera]

The clutch would slip long before that tire spun. I have 255 summer tires on my 85 and no way I could spin them.

[Rusty Heap]

Originally Posted by flatbutt

What would happen to a 1970 tranny trying to spin a 2020 tire?

Back in 1970, Tranny was a n o r m a l different word than today.

[Sooner or later]

A few years ago someone posted an image of a pair of late model 911 tires behind and early 911. It was eye opening.

[island911]

weight and HP... body roll..

Wider tires do not provide more traction.

[GH85Carrera]

Originally Posted by island911

weight and HP... body roll..

Wider tires do not provide more traction.

What? So all the people putting bigger tiers on cars are just wasting their money?

There is zero doubt a new 911 is outperform an air cooled 911 in every performance test. 50 years of technology makes way more performance, and those big tires are a major part of it.

Jack Olsen has a great 911 that almost all of the air cooled owners lust after. It is far removed from stock.



If you notice he has tires much bigger than stock on his car. He can almost keep up with many modern 911s. But he has no AC, and it is almost a dedicated track only car.

I had to give up on my 15 inch Fuchs because there simply is no summer performance tire that I can drive on long road trips or in the rain. I bought Euromeister 17s and Michelin PS2 tires. I can promise you I have a TON more cornering grip than before.

[masraum]

Originally Posted by GH85Carrera

The clutch would slip long before that tire spun. I have 255 summer tires on my 85 and no way I could spin them.

You probably could, but you probably wouldn't want to.

[masraum]

Originally Posted by GH85Carrera

What? So all the people putting bigger tiers on cars are just wasting their money?

There is zero doubt a new 911 is outperform an air cooled 911 in every performance test. 50 years of technology makes way more performance, and those big tires are a major part of it.

Jack Olsen has a great 911 that almost all of the air cooled owners lust after. It is far removed from stock.



If you notice he has tires much bigger than stock on his car. He can almost keep up with many modern 911s. But he has no AC, and it is almost a dedicated track only car.

I had to give up on my 15 inch Fuchs because there simply is no summer performance tire that I can drive on long road trips or in the rain. I bought Euromeister 17s and Michelin PS2 tires. I can promise you I have a TON more cornering grip than before.

Right, but does your car have more traction because it's running 17" wheels with wider tires or does it have more traction because it's got a more modern tire with construction and rubber compounds that provide more traction?

From a static physics standpoint, if you could get the same exact tire in a 225 something 15 and a 275 something 18, and you took the same car with 2 different sets of wheels and put them on the car, the contact patches with the same air pressure would be the same size, and the static friction should be the same. Contact patch size is NOT a part of the formula for frictional force, only the coefficient of friction and the force applied.

But I believe most science/engineering types agree that the traction that you get from a tire is not all down to the force applied times the coefficient of friction. There are other factors at play in how a tire provides grip. The tire carcass deforms and how it deforms and how it contacts the road, and the shape of the contact patch and etc.... all make small differences that add up to big differences.

so, yes, from a certain point of view, a bigger tire isn't necessarily going to mean more traction. Also, a different tire will probably provide different traction, maybe more, maybe less, maybe both depending upon the conditions and setup of the car.

[GH85Carrera]

I certainly have never done any real measurements of the cornering forces, just seat of the pants. The last two sets of 15 inch tires I had were rated as mud and snow tires, simply because there is such limited choice in 15s. They were OK for normal driving and marginal for autocross. I went from 205-50-15 front and 225-50-15s rear because it was all that I could get, to 225-45-17 front and 255-40-17s rear and summer performance Michelin PS2 tires. It is hard to stay in the seat now at the autocross if I don't get the seatbelt really tight. After 22 years and over 200 autocrosses in my 911 I can tell you with no hesitation, the tire difference change was a big improvement is traction.

The 15s were a lot smaller and lighter and the speedometer error before was off by several MPH. The new 17s are almost dead on for the speedometer.

My acceleration is almost certainly a bit slower, but a 200 HP 85 Carrera has not been a drag racer ever. I can certainly stop a ton faster now.

[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.

[RWebb]

the contact patch changes shape with wider tires...

R&T or C&D had a diagram of this back in the ancient past

[911boost]

I have always been curious how much $ Jack has into that 911. I have zero doubts he could get around the track in a similar time in my RS.

Notice I said he could, not me.

[Deschodt]

Same idea with a wheel in it, in my garage, last year... 991 vs 72 911. no prize for guessing which ones I prefer handling...

[island911]

Originally Posted by GH85Carrera

What? So all the people putting bigger tiers on cars are just wasting their money? ...

I never said that.

Wider tires allow a softer compound to be used and not overheat. But make no mistake, the width is for thermal management of the rubber, which can then improve grip via consistent temp on a softer compound.

Haven't we all gone over this before?

[JackDidley]

Would this car get traction on a little skinny tire of the same compound ? I dont think so.

[Bob Kontak]

Originally Posted by island911

Haven't we all gone over this before?

Relative to Glen's original post picture your argument is thermal management?

[herr_oberst]

Originally Posted by island911

Wider tires do not provide more traction.

What do they provide? Serious question.

[island911]

Originally Posted by GH85Carrera

What a difference.

It would be interesting to figure out just how much more traction that giant tire with modern compounds has compared to the little skinny Michelin "state of the art" street tire of 1970.

So some of you believe that if you took that skinny old tire and made a wide version with the same rubber... it would have more traction because it's wider?

Sticker rubber gives more traction

Make that tough old compound wider and you will have a cold rolling tire (hard rubber - not all that sticky)