dknowles67

The (rallye) wheels that originally came on my 1967 were 15" diameter, and 6" wide. The tires were bias ply 7.75"x15".
After doing some research, I found that most 1967 tires had about an 82% aspect ratio.
7.75" = 197mm.
82% of that is 6.355"
So a modern day equivalent would be something like P197/82 R15.
Of course they don't make those.
NCRS approves of P205/75, and P215/70, but both of these have a smaller diameter, and therefore smaller circumference (~2" smaller).
Seems like this would throw off the speedometer ever so slightly.

A P215/75 would have pretty close to the same diameter (within 1/32").
Why isn't that size approved of?

Since I want to drive it around sometimes, I don't want vintage bias ply tires on it.

Also any ideas which tires are made in USA?
According to http://www.usstuff.com/cartires.htm Cooper, Kelly, Goodyear are, but Michelin, Dunlop, Firestone, Bridgestone, BF Goodrich, General, Pirelli are not.

Tire Kingdom sells Sigma tires which are made by Cooper (?)
Discount Tire sells Arizonian which are made by Kelly (?)
Walmart sells Goodyear.

It's been 10 years since I last changed tires, so I'm not sure I need to spend extra money on long lasting tires. They will dry-rot before I wear the tread off. I don't go to the drag strip. But since it's not something I buy all the time, I can afford to spend extra on better handling tires.
I've read all the other theads about tire sizes, but still didn't see a good answer to these questions.

Nowhere Man

most people use dimand back tires, or Cooker tires.

wmf62

i have Cooper 215x75x15's on my 62 and i'm happy with them
Bill

TIMBERWOLF427

We run Uniroyal Tiger Paw 215/75/15's on our 64. We always thought the 205's looked a little short.

dknowles67

I did a quick search for Diamondback Tires, and Coker Tires.
These are reproduction tires made to look like 1967 tires.
They are all over $125 each. (as I suspected)

I don't necessarily want my tires to look like 1967 tires. I don't feel a need to spend that much.

Still wondering why NCRS doesn't approve of P215/75 size, as according to my math, it seems the closest to the original tire size.
Thanks to those who replied with success stories in that tire size.

Still wondering which brands of tires are made in USA.
Coker is in Tennessee, and Diamondback is in South Carolina.
Maybe they make there tires where the company is located?

TopLess62

I run 215-65's on the front and 275-60's on the back. I like the gas mileage afforded by always going downhill!

66since71

Anyone with better history chime in.. but I recall that early C-2's had 670x15's, which (using the 82%) works out to 27" diameter. I also recall that the 775x15 was also a 27" tall tire, inspite of the diameter implied if you apply today's "aspect ratio" sizing. Hence the 205/75 and 215/70 sizes (they area also 27" tall tires).

Harry

sweet66

according to recent posts Coker have their tires made in mexico. with some quality problems according to other forum members
Diamondbacks uses Cooper or for a bit more $ Firestones . They then shave the markings off one side , apply a red or gold line to the tire
for corvette types white walls in various configurations for cadillac , imperial and lincoln drivers who need ' period correct' whitewalls .

I got the Diamondback goldlines on cooper casings .. they perform well but I don't autocross or drive the car much over 65mph , with 3:73 rear gears the engine gets too busy above that speed .. and I'm never in that much of a rush to get anywhere. if high speed performance is a issue forget the correctness issue and get some pirellis that are speed rated

66since71

I run P-4000's and love them. A lot of the other guys here like them as well. The most common size purchased is 215/70. If you want a little wider tire, they also come in 225/65 (I'm running those and really like 'em, 26.7" diameter)

mdz06vetter

not sure what you mean by this statement: "NCRS approves of P205/75, and P215/70", but both of these have a smaller diameter, and therefore smaller circumference (~2" smaller). Seems like this would throw off the speedometer ever so slightly.

what judging manuals stipulate, if you are going to have your car judged you should use the appropriate sized bias ply tire, by the appropriate OEM, etc. for your year of car.

The tire sizes you mention are current day sizes and NCRS could really care less what size CURRENT tire you want to put on. If you plan on driving the car and are not having it judged put the size radial tire you want to put on.

BTW - I run P215x65x15 Michelins on my 1963 Z06 for driving - not a correct size for 1963 and not a tire OEM for Corvette

JohnZ

Coker tires are low-volume reproduction tires, and their radials ("Coker Classic" sidewall name) are made in Mexico.

Diamond Back doesn't "make" tires - they "customize" the sidewalls of many different brands of current high-volume radial tires made in modern high-volume tire plants.

The NCRS judging standard defines the 205/75-15 and 215/70-15 current radial replacement sizes as acceptable for radials in terms of size and appearance that approximates the original 6.70-15 and 7.75-15 bias-ply tires, and any radials get a substantial standard deduction depending on whether or not they're branded as one of the original OEM suppliers and the sidewall and tread pattern configuration.

dknowles67

Thanks - this was the clue I needed to solve the mystery.
Actually the aspect ratio on '67 tires was 78% which is what the F78/15 designation means.
7.75" with 78% works out to 27" diameter.
The early C2's did have 6.70x15" tires, but I wasn't able to figure out the aspect ratio. Just that the 670x15 and the 775x15s are supposed to be the same modern day tire.
A P205/75 has nearly the same diameter, and a P215/70 is slightly smaller.
So the P205/75 is the closest readily available radial tire to the original physical dimensions.
The P215/75 is actually about 2 inches longer in circumference, which might amount to a 1-2mph error on the speedometer.

Tire Kingdom has the Sigmas for ~$40.
Walmart has Goodyears for ~$60.
They are speed rating S (112mph)

66since71

David, If you want a little wider tire, as well as a higher (W) speed rated one (168 mph - better handling) the 215/70 is 27" tall also.

Harry

soppeng

There was a reference above to using 215-75's on a midyear. I had one mounted a few years ago and tried it on my 65coupe. It rubbed quite a bit. 215-70's work without rubbing.

dknowles67

I can't help being an engineer.
Here's the math behind the figures:

7.75" (tire width) x 78% = 6.045" (sidewall height)
15" (wheel) + 6.045" + 6.045" = 27.09" tire height.
7.75" = 196.85mm (multiply by 25.4)
6.045" = 153.543mm

205mm (tire width) x 75% = 153.75mm (sidewall height) = 27.106" tire height.
215mm (tire width) x 70% = 150.5mm (sidewall height) = 26.85" tire height.
215mm (tire width) x 75% = 161.25mm (sidewall height) = 27.7" tire height.

66since71

I'm an engineer too and ran the numbers the same way. Sorry I missed your typo in the last post. If I'd read a little closer.....I will next time!

Anyway that range from 26.85 to 27.1 is for all intents 27". Remember that typical new tire tread depth is on the order of 10/32's. So tire wear becomes a bigger factor than those small differences in diameter.

Have you decided yet on a tire?