original tire size for 66gt350 and.....

[Edward66GT350]

What is the original tire size for a 66gt350 for both 14 and 15 inch rims?
Are there any modern tires in the proper size w/ raised white letters?
Thank you

[The Commissioner]

6.95 x 14 Goodyear Blue Streak tires were the original size. In a 70 series Radial, think that would be around a 180/ 70 R14, but don't quote me. The 15" wheels, 7.75 x 15 Goodyear Blue Dots would be the tires size, loosely converted to radial, that would be 195 70R 15. We have 225 60R15's on an original 66 GT350 that is fitted with Torque Thrust D's, the tire is slightly oversized, but still looks nice. I run the same size on a 67 GT350, looks good on that, too. Both those cars are blackwall BFG's, but we're running a raised white letter BFG 225 60R14 on a 66 Hertz clone that we're building, can send photo if needed, other cars can be found in the photo section under my name. BFG works good, have a raised letter set on the 10 spokes, as well.

[Edward66GT350]

Thanks for the reply. I'm currently running 225/ 60 series. However, the overall tire diameter is much smaller than the originals, so I would like to run on original size(70 series?). On 60 series, the engine is revving pretty hi at freeway speeds. Any advice?

[The Commissioner]

It'd be nice if you could trial a set of tires/wheels in a varying array of sizes between 190-205/70R15. Think that would be the only true way to see how it rides, any rubbing, speedometer accuracy, etc. I run the 60's on the 67 and on the 66 without any real difficulties, I find the speedo is spot on, and the looks are very nice. What sort of wheels are you using, stock or aftermarket?

[Edward66GT350]

I'm running the original magnum 500's. 14 inch.
Do you know the overall tire diameter of the original tires?
Thanks

[TJinSA]

I have an old tire reference chart. There-in, 6.95 x 14 gave 817 rev/mile and manufacturers varied from that plus/minus 5%. A D78-14 tire is the closest letter size with 820 rev/mile!

7.75 x 15 tires gave 760 rev/mile, also with +/- 5%. At 765 rev/mile, an F78-15 is the closest fit in letter nominclature.

This information roughly corresponds to some early Firestone Radial sizing information-- 6.95x14s to D70-14 on a 5.5 inch rim resulting in 822 rev/mi as compared to E70-14 at 804 rev/mi (25.10" and 25.70" diameter, respectively, tire line SSWO SR. 7.75x15s to F70-15 on a 6 inch rim resulting in 755 rev/mi , 26.80" diameter in thier Sports line. Interestingly, F70-15s in Firestone's SSWO SRB line rolled along with 773 rev/mile; quite a variance for the same size tire.

From the same Firestone sheet: 6.95x14 (@817 rev/mi) equated to 185R14 and the 7.75x14 (@765 rev/mi) equated to 205R15. I'm assuming that's in a 70 aspect ratio tire.

The reason I'm using rev/mi information is because bias-ply and radials resulted in quite varying roll distances relative to their over-all diameter due to their differences in sidewall strength and tread progression on pavement.

Geeze... what packrating will provide