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(Concours) JCNA tire size rules


JCNA tire size rules

I would appreciate comments from JCNA Judges on this list or from anyone else who might have supporting information. Apologies to those who aren't this deeply into it but I'm about to face this problem at our upcoming concours and need a few "second opinions".

JCNA Rule Book: There are several sections of the book which address tire size: ChV, p5-6, para 10a. "...comparable or superior equipment of proper size and compatibility..."; "Size must be consistent with the original profile."

ChVI, p6-2, para B4d. "Tires are considered expendable and may be replaced only with comparable or superior equipment of original size and compatibility with the Jaguar. The standard industry tire sizes, which are moulded into the tire sidewalls, are acceptable proof of correct size without further measurement,......Size must be consistent with the original profile."

ChVI, p6-7, para F7. "Size must be consistent with original profile."

Appendix B, p3. "Tires are considered expendable and may be replaced only with comparable or superior equipment of original size and compatibility with the Jaguar. Every consideration should be paid to selecting a replacement tire with the same side aspect ratio as the OEM tire. This ensures that the car will maintain the proper stance and appearance as designed."

Appendix B, p5, Notes,(The May/Jun 1997 issue of Jaguar Journal p13, amended this section allowing both 6.40x15 and 185x15 tires on all Series 1 E-types and further allowing Series 2 E-types to use 185/70x15 tires provided the tires were purchased prior to 1997.)

Glossary Page 14. "Wrong Size for Jaguar" "It is a JCNA rule that the tires on an entry may be of a different make than the original equipment, but must be of the original size. If the entrant has installed tires of a size different from the originals a deduction must be made (see Chapter.... etc)

Fact: Coker tires U.S. says that their current radial-tire size P195/75R15 is the DIMENSIONAL equivalent of the 640-15 tires orginally supplied by Jaguar for their 1950s-60s small saloons and E-types. Coker also says that the optional 185HR15 tires, supplied by Jaguar for some of the same cars, were about 1" smaller in diameter. In Coker's opinion, the 185HR15 was actually too small for the application.

Comment: The foregoing establishes that Jaguars with 640-15 bias-ply tires stood/stand approximately 1" higher than those with 185HR15 radial tires. Two different stances OK.

The QUESTION!!! Under the preceding rules, are replacement tires acceptable as authentic if they: a. Accurately matche the diameter and aspect ratio of the original equipment tires, b. Provide the proper vehicle stance, c. Look like the original tires, BUT d. Have a different size molded in the sidewall.

Does size mean the physical dimensions of a tire, or the numbers molded in the sidewall?

Is the Coker P195/75R15, which is a precise dimensional equivalent of the original 640x15, an acceptable replacement tire? Yes, one is a radial and one a bias-ply but JCNA has allowed there to be that choice?

Thanks for your input.

Dick Cavicke Ch. Judge San Diego Jaguar Club

I've hated this question ever since I went through the trouble to track down old Dunlop technical personnel in England just to seek the truth and then found 185-15s to be listed as acceptable for virtually any series 1 e-type according to the new concours rules. I can understand that many people invested in tires before us judges became so concerned with tire size, but truth be known, 185-15s WERE NOT original tires on every stinkin' E-type made. The FACT is that they were introduced in Europe first, then DOT certified and introduced to the US later (around late 1967). You can verify this reading old motoring publications. Besides, anyone who was mounting tires back then (me included) knows that America was sold on bias ply tires and as a consequence, dealers equipped new cars with them for quite some time. Could they be purchased by the owner after the vehicle was purchased? Sure. But that then isn't what the factory was peddling at the time.

Thanks for the soapbox time, but the answer to your question is the following:

Original size and configuration is just that. 185-15 or 640-15. No judge should be spending the time to measure the tire for aspect ratio and therefore must rely on the rules as written (which only stipulate those two sizes). I interpret original configuration to mean "H" rated as well (or better).

This said, the 185-15 Michelins I had on my last E-type were actually much larger than the 640-15s they replaced. So, the only reason I assume Coker is saying this is because the 185-15s I've seen from Avon are actually more stout than the Michelins or 640-15s, possible looking smaller. But since I never measured any of these, maybe they're right.

Steve Kemp 62 OTS

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