Another Tire question for Duke

[Michael H.]

I purchased a set of Pirelli PS 4000 215/70 ZR 15's . My car is a 66 327/300 roadster. I've owned the cars since 1977 . When I bought the car I put a set of 67 rally wheels on car . I ran those for years. I liked the look but I went back to original wheel covers on rally wheel. I bought the pirelli tires in 2006. The tires are unused 0 miles. Stored on car in garage under car cover. Garage does have windows but direct sunlight doesn't hit the tires . Question #1 Do you think they are still usable do to age. question #2 using this tire and rally wheels will I have any clearance issues.
The car has been out of use for some time going to be road ready soon

[Gary B.]

Re: Another Tire question for Duke

Michael,

Is your garage temperature controlled? If not, the annual max and min temperatures would affect the answer to your tire aging question in my opinion.

Gary

[Michael H.]

Re: Another Tire question for Duke

Hey Gary garage not temp controlled I live in Phila .Pa. I've read a lot of the archives plenty of opinions. It sounds as if the worst damage would be sitting in sunlight all day. and running improperly inflated. Hate to toss good tires. Sounds to me they're so well constructed should they fail wouldn't be a total blowout. I'll probably use them till I decide on which to choose next considering these type of high speed rated are harder to come by.
Mike

[Wes S.]

Re: Another Tire question for Duke

Tires are 17 years old. They begin degrading the day they are made. There are some schools of thought that after six years they should be replaced.
I have had several tire failures based on age, so I won't use a tire older than six years. Had a Uniroyal tire fail after four years that did $6800 in damage to my truck, fortunately Michelin paid the entire bill. Catastrophic failure of a tire in a Corvette will result in body damage that will be very expensive to repair.

[Chris H.]

Re: Another Tire question for Duke

Just replaced my 23 year old Eagle GT2s with 3 year old Goodyear Assurances of the same size. The ride and handling improvement is shocking.

[Duke W.]

Re: Another Tire question for Duke

I purchased a set of Pirelli PS 4000 215/70 ZR 15's . My car is a 66 327/300 roadster. I've owned the cars since 1977 . When I bought the car I put a set of 67 rally wheels on car . I ran those for years. I liked the look but I went back to original wheel covers on rally wheel. I bought the pirelli tires in 2006. The tires are unused 0 miles. Stored on car in garage under car cover. Garage does have windows but direct sunlight doesn't hit the tires . Question #1 Do you think they are still usable do to age. question #2 using this tire and rally wheels will I have any clearance issues.
The car has been out of use for some time going to be road ready soon

The Pirelli P4000 has a W speed rating - 168 MPH - that is part of the "service description" (load index and speed rating) that follows the size. They have this high speed rating because of the high quality of the design, materials, and construction processes, which includes a spiral wound nylon cap belt that is nearly always present on tires rated H or above. The basic construction, side walls and tread, is placarded right on the side of the tire. There's a TON of good information about tire molded right into the sidewall, but I doubt many people read or understand it.

I've lost track of how many times I've made essentially this same post, but most guys don't seem to understand that all tires are NOT created equally or lead the same life after they are manufactured.

So I'll say it again for the umpteenth time: The CHEAP, low speed rated tires that most install on their vintage Corvettes lack the safety of that spiral wound nylon cap belt that will usually keep the tire from disintegrating in the event of an internal structural failure.

It seems most are only concerned with sidewall cosmetics and give no thought to safety or performance; and regarding cosmetics, how many vintage Porches and Ferraris do you see with anything other than plain black sidewall tires?

I've experienced three tread separations on well used H and V rated radial tires - ALL while hot-lapping the Riverside and Willow Springs race tracks - and they all stayed in one piece and held air allowing me to safely return to the paddock. The tell-tale warning was a big vibration and upon inspection each had a big bulge in the tread area. One I even drove the 75 miles home from Riverside because I didn't have a suitable spare and made the trip without incident.

I have stashes of H and V- speed rated tires for all my vintage cars, some up to 30 years old that are stored in a dark, cool downstairs closet of my house, and I will mount them without hesitation when they are needed. So I would have no hesitation mounting those P4000s since they have been properly stored as long as a visual inspection reveals no flaws, which is likely the case.

A couple of other members have experience with the P4000. Mark Hedberg's are at least 15 years old on his '64 with a recently dyno tested Special 300 HP engine configuration, and George Jerome ran a set on his '65 FI Coupe for at least a decade, but I believe he recently replaced them.

Let the guys who run the cheap, low speed rated, no nylon cap belt tires fret about replacing them every six years or whatever. If you have H or above speed rated tires with the nylon cap belt that spend most of their life inside, away from harmful things like UV light and ozone, they should be good for decades of low annual mileage service.

Of course, frequent inspections, at least annually, or before a road trip are highly recommended, to include not just tires, but most of the critical systems to ensure a safe and trouble free trip.

Post #5 in this thread mentions that a new set of tires improved ride and handling. This is common. Of course, it somewhat depends on the characteristics of both the old, aged, and new tires, but for sure the following happens to tires with age, which is really not a safety issue. When new new typical tires have at least 10/32" of tread depth and the rubber is fairly soft and resilient. With miles and time the tread depth decreases and the rubber hardens resulting in increased high frequency ride harshness and reduced grip. This process happens so slowly that we don't notice it until a new set of tires is installed and suddenly the high frequency ride harshness disappears and grip improves.

A couple of other tips: Pay attention to load rating and wear rating. Mot guys think that a wider tire will provide more grip. That's a myth! Width is a factor, but load capacity and wear rating are more important. The less load a tire carries relative to its maximum load capacity the better the grip. Likewise, the lower the wear rating, the softer the compound and the better the grip. Typical cheap tires have wear ratings of 500-800. They might last for 50K miles or more in moderate service, but how long will it take to accumulate that many miles on a vintage Corvette. The 205/70R-15 96V Avon CR6ZZ has a mere 6" wide tread with a wear rating of 80, and it will run circles around the widest rock hard compound BFG Radial T/A you can stuff under your radiused wheel wells.

As far as clearance is concerned, you didn't say which Rally wheels you are using, but if they are the '67 Corvette 15 x 6", .030" offset type clearance is usually not an issue with 215/70R-15 tires (Note that KO wheels, including adapter and '67 bolt-on aluminum wheels have the same offset.). Of course, clearance be checked on each car due to OE body tolerances and possible beyond tolerance dimensions due to body damage repair.

If clearance is an issue, adjust camber as required to obtain adequate clearance. Moving camber one-half inch in the negative direction will provide approximately 1/8" more fender clearance with a nominal 27" OD tire. Nominal "touring" camber settings are zero front and negative one-half rear. Nominal "sport" settings are up to negative one degree camber, front and rear.

Duke

[Michael H.]

Re: Another Tire question for Duke

Hey Duke thanks for the response. I know its an old subject. It makes sense to me buy a higher speed rated tire even if not doing those high speeds . The quality and design with the nylon caps you speak of sounds much safer. I bought these tires in 2006 actually it was from you recommending them since the were about to stop production . I knew the would sit for awhile. They have been mounted since purchase . I don't know if that matters in relationship to if they are stored properly.
I just checked the rims they have an AG code . From what I've been searching they would be 68 rally wheels . I've used them for years with a set of radials just don't remember if they were 205 or 215's
Also I checked my old receipt from Vulcan tires $88.00 a piece. I've been pricing your other recommendations. Dunlap and vredestiens . Prices have changed I guess we could wear that subject out too. Inflation outsourcing etc....
Well anyways I'm gonna use them If any problems I will go with another high speed rated tire . I know everyone has there own opinion on whitewalls,Redlines, goldlines. Me personally I always liked the plain black
wall. ( just looks faster LOL) thanks again Duke and others who responded.
Mike

[Duke W.]

Re: Another Tire question for Duke

The '68 7" Corvette Rally wheels are unique to that year and Corvette. A later 7" version with zero or near zero offset was used in later years on G an maybe A-bodies.

The negative offset for Corvette was to provide adequate clearance to the rear spring ends. There are reports of the zero offset version being used without harm, but I don't recommend them. There was a REASON why Chevrolet built the unique negative offset 7" Rally wheels for Corvette.

Those Pirellis on the 7" Corvette Rally wheels will likely NOT provide adequate fender lip clearance without a lot of negative camber.

It's easy to measure offset with or without a tire mounted.

1. Lay the wheel or wheel tire assembly on a flat surface, outside face down.

2. Lay a straight edge that overlaps the OD across the top. A length of 2x4 works fine.

3. Measure the distance from the bottom of the 2x4 to the ground, and call this dimension A.

4. Measure the distance from the bottom of the 2x4 to the plane of the wheel/disk interface, and call this dimension B

Offset = B - A/2

I don't think it makes any difference if tires are stored mounted or unmounted. If mounted I would just fill with enough pressure so you can easily roll the tire around, like no more than about 10 psi.

Speaking of tire sidewall data, if you saw last week's Republican presidential candidate debate you undoubtedly saw the Boeing 707-320B-based Air Force One that was in service for 29 years serving seven presidents including Reagan. It's mounted on concrete pedestals and the main gear tires are at eye level so I could read the placarded data on the sidewall. I recall the tires have something like 13-15 plies (bias type I assume) with a speed rating of 250 MPH and a max psi pressure pretty near the speed rating. I don't they they'll have to replace them very often.

If you're ever near Simi Valley, CA the Reagan Museum is a real treat and that concours condition 707 facing the "glass wall" is an incredible space.

Duke

[Michael H.]

[Duke W.]

Re: Another Tire question for Duke

You transposed A and B and got the wrong algebraic sign. The equation is B - A/2, so:
Offset = 4.124 - 4.40625 = -0.28125 (NEGATIVE zero point 28 inches)

So the wheels appear to be the real deal '68 Corvette Rally wheels.

I can't say for sure if the 215/70R-15 P6000s will fit or not without fender modification, but can can tell you my own experience.

Back in 1968 I installed a new set of 205HR-15 Pirelli CN-72 radials to replace the Michelin X 6.70-15 radials that had been on my SWC since 1964. Initially installed on the OE 5.5" steel wheels I was not happy with their performance. The Pirelli was actually a 70-series tire with the same OD as the OE 6.70-15 bias ply tires and Pirelli's technical literature clearly stated that the new, wide tire designs needed to be installed on suitably wide wheels.

Knowing that the OE wheels were likely too narrow I bought a set of the new '68 Corvette Rally wheels, but with the tires mounted there was clearly inadequate clearance. I thought about if for a day or so and decided to shave off the horizontal fender lips including the bonding strip flange inside the front fenders.

Looking at the car from the side there is no change in contour, You have to slip your fingers inside the top of the wheel wells to detect the modification. The first drive proved it was a wise decision as the big Pirellis on the wider wheels were clearly superior in every way compared to the Michelins on OE wheels, and the OE wheel covers fit fine. With the tires pushed out to the very edge of the fenders and the "Ben Hur" wheel cover spinners sticking out beyond the edge of the body, the car took on a very aggressive stance that I really liked in addition to the near race car-like handling

In the seventies I replaced the CN-72s with a set of 225/70VR-15 CN-73s, which are a bit wider, but there was still adequate clearance. A friend with a '67 installed the same wheel/tire combo on his car. Clearance was tighter, but still adequate due to the the slightly wider track of disk brake cars relative to drum brake C2s.

So you're going to have to do some experimenting and measuring. If clearance is inadequate and you don't want to shave the fender lips, the P6000s should fit with adequate fender clearance on a set of 15x6", +0.030 offset '67 Corvette Rally wheels.

A shorter tire like a 225/60-15 will likely fit okay but they are nearly two inches shorter, look silly, and cause your speedometer to read about 7 percent high.

Duke

[Michael H.]

Re: Another Tire question for Duke

Hey Duke thanks for the heads up on my calculation error. I appreciate your correction. Well anyway I know I ran these rally Wheels rims with a radial tire. Probably a smaller size than the 215/70/15 . I'm gonna do some fitment trials. However I'm not going to cut fender lip. I think my best bet is to find a set of 67 15x6 +0.030 rally wheels . I will be running a stock 66 hubcap
Over them . I was wondering what you think of the aftermarket wheels. Correct dates obviously not an issue. Just wondering about quality aftermarket vs original.
Hey Duke I like your discription of the stock
Wheel covers "Ben Hur" . I always looked at them as " James Bond " now I have a new name to use. Well thanks for your help and everyone else on the board.
Mike

[Michael H.]

Re: Another Tire question for Duke

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[Mark E.]

Re: Another Tire question for Duke

I'm with Wes: I wouldn't risk riding on 17 year old tires, no matter their quality or speed rating. Why take such a large risk? Get new tires.