Mar 5, 2020 update to the Porsche 911 Carrera project car

Project Porsche 911: Testing the New Yokohama A-008P–And, Yes, Tires Do Stop the Car

Brakes don’t stop the car. Tires do. And the tires on our 1984 Porsche 911 Carrera, we admit, had gotten way too old.

How old? Too old to admit.

Tire Rack, as detailed in two articles here and here, says that six to 10 years is the lifespan for a tire. 

In fact, our own testing said that we had committed a major faux pas. For those who didn’t click the link, here’s the takeaway: A set of never-used yet 33-year-old Michelins required more than 160 feet to stop from 60 mph, while a brand-new set of Vredestein Sprint Classics only needed 140 feet. And, at the same time, the new tires were quieter while exhibiting much better handling.

Before they aged out, our Porsche’s Pirelli PZero System tires had served us well over the past decade. They were perfect for the task at hand.

First, they delivered sporty performance: a soft 140 treadwear rating along with A ratings for treadwear and traction. Tire Rack places them in the Max Performance Summer tire class—perfect for a sports car that doesn’t see any inclement weather.

Second, they just look the part: retro looks along with a tread pattern appropriate for an ’80s icon. 

One more thing to love: Porsche N-specification approval. What does that mean? 

Here, we’ll crib from Tire Rack:

Porsche designs and manufacturers some of the highest performance vehicles in the world. Because of the integral role that tires play in vehicle performance, Porsche has integrated tire development throughout their process of vehicle development. To be an Original Equipment tire provider on a Porsche vehicle or be approved by Porsche for the replacement market requires the joint product development efforts of the tire engineers working alongside the Porsche vehicle engineers.”

Despite the soft compound, the Pirellis wore well, too. They come sporting 10/32 inch of tread. Our fronts showed 7/32 with the rears at 6/32. (Okay, maybe we need to drive this one more.)

The Pirellis still looked good, too: no cracks, no issues. 

And then we spied the build dates: 2007 for the fronts and 2009 for the rears. Yeah, these tires should have been removed from service a while ago. (Do as we say, not as we do, okay?)

So, back to our Porsche: Step 1 was research. 

Tire Rack no longer shows our rear PZeros in stock and, to be honest, we figured it was time for a change. We still had the same goals all these years later, though: sporty performance, appropriate looks and Porsche’s N-rating. 

While we were elbow deep in our research, Yokohama dropped a bit of engaging news: Its A-008P, an ’80s performance icon, was heading stateside in Porsche-specific sizes. They’d carry a UTQG rating of 240 A A.

Game, set, match. 

One thing about the A008P’s N-rating, though: Its N0 rating may not seem to match the latest spec. Woody Rogers, knower of all tire things at Tire Rack, provides more information on that subject:

The N# homologation marking system used on the A-008P is an older, less specific version of the new, going-forward system of NA#, NB#, etc., that ties the homologation to a particular chassis. Porsche realized some years ago that with a growing number of platforms that have some tire size commonality, they needed a more precise designation system to help keep things separate. Their tires are so highly tuned to the platform they felt it was a disservice to go only by the presence of an N-Spec number and assume it is the best option for a vehicle. 

For the A-008P N0 tires, they could never get a NA# type rating, because it isn’t available in the correct sizes for the new platforms that benefit from the new system. The sort of potential for inter-platform crossover has expanded with the Carrera GT, all the 911 vintages, Boxster/Cayman generations, Cayenne, Macan, and Taycan. Porsche rolled out the clarified rating starting with the 992 (911) platform last year and will use it for all new homologations going forward.”

We also had to consider the available sizes for the A-008P. We had been running the OE sizes for our Porsche, meaning 205/55ZR16 fronts along with 225/50ZR16 rears. Yokohama only offers the A-008P in two sizes: 205/55ZR16 and 245/45ZR16. Would the wider rears be an issue?

We did the numbers.

The 225/50ZR16 Pirellis have a 25.1-inch outside diameter along with a 9.3-inch section width. The 245/45ZR16 Yokohama sport a 24.6-inch outside diameter and a 9.6-inch tread width. We figured that the slight reduction in overall diameter would, if anything, quicken acceleration a tad, while there’s plenty of room inside those rear fenders to accommodate the increased width.

Our car is also running 16x7-inch front wheels and 16x8-inch rears. Yokohama shows those sizes to be well within the range for the A-008P. 

So we ordered a set of the new retro Yokohamas.

While you may not find them listed on Yokohama’s American website, Tire Rack can hook you up. A set of four retail for $860.64. Our Pirellis retailed for $640 when we installed them. 

Initial impressions of the new Yokohamas? First, yeah, the ride is much better on the new, fresh tires as they don’t seem to crash from bump to bump. Steering feels responsive. Yet, at the same time, these tires don’t seem to overpower the chassis. They feel like an appropriate fit for an ’80s sports car that has roots back in the ’60s.

And then there are the looks. Perfect. We’re back to the glory days of IMSA GTP, "Miami Vice" and big hair. 

But we didn’t simply install the new tires and drive around. We wanted to show how they compared to the old ones. While we realize this isn’t a strict apples-to-apples comparison, it does show the difference between new tires and ones that look good but have simply aged out. 

Our testing was simple: 60-to-zero braking. Data was captured via an ApexPro. Testing was done on two separate days, but the weather conditions were nearly identical: sunny with ambient temperatures in the 60s. All testing was done on the same stretch of pavement. Before testing the Yokohamas, we put about 60 miles on them in order to remove any mold release compound.

Driving was by our own J.G. Pasterjak, and here we’ll let him take over the rest of the narrative.

First, I’d like to stress that while the data trace is fairly obvious, it doesn’t convey the full feel of the difference in these two tires. While the old Pirellis felt reasonably grippy when driven under the limit, their at-limit and over-limit performance was very poor and—possibly even worse—very unrecoverable. 

Once you lock a Pirelli, you have to come quite far out of the brakes to get it to start rotating again. I think this bears mention for anyone who feels like their tires may be old but still feel fairly grippy: They may feel decent up to about 90% of their capacity, but that last 10% is what makes the real difference between an insurance claim and merely soiled pants. 


So, let’s look at these stops on the data traces. The red trace shows the data for the old tires, while the blue trace shows the new Yokohamas. Each trace shows one representative stop, and they have been slightly offset to make them easier to read. While the full stop on the old tires looks like it went some 15 feet longer, when you line up the initial brake application points, it’s actually more like an 8-foot difference: 60 feet for the old Pirellis versus 52 feet for the new Yokohamas. 

The first thing we notice is how much steeper and more aggressive the initial application of the braking force is with the Yokomahas. The Pirellis must be loaded more gradually, as can be seen by the rounder and shallower initial part of the speed curve. Those first few miles per hour needed to come off slowly while we found the ideal pedal pressure to avoid terminal lockup.

We also see the main part of the speed trace for the Yokohamas dropping more steeply than the Pirelli trace. This shows us losing speed at a faster rate with the newer tires. 

At around 35 mph, we see the Pirelli trace flatten out completely for a moment as the right front locked up and we had to get out of the brakes, then back in to continue the braking exercise. 

Conversely, while the Yokohama trace has many tiny changes in deceleration rate due to threshold braking, we never see a point on the curve where the car stops decelerating at an aggressive rate.

Toward the bottom of the curve, we were doing some serious modulation with the Pirellis to keep from terminal lockup. That’s the sawtooth part of the trace toward the bottom. 

Except for one small hiccup at the bottom of the Yokohama trace, which was not a lockup but more likely just road undulation, the Yokohama curve just continues downward to a stop.

Even the stop itself is different. The Yokohamas came to a full and complete stop in one motion, while we had to “chauffer stop” the Pirellis at the last second by bleeding off some braking force to keep them from sliding to a stop.

And while we’ve offset these curves from each other slightly for reading clarification, we can still see a distance advantage in the newer tires. The Yokohamas came to a full stop in almost 10 feet shorter than the old tires. And while the distance is great—you can fit a lot of kids on bikes in 10 feet—the even bigger story is the lack of drama the new Yokohamas displayed while they did their job. 

Join Free Join our community to easily find more project updates.
Comments
View comments on the CMS forums
Sponsored by

ebay

Our Preferred Partners
oo3zWNv1MuYDJmsgRmexv5EOF2ni2pDEqfYXsLVSOO80F9DCkPy9HkuFmBqsvemZ