radial tires

[Robert D.]

Hi ALL,
After much thought I have decided to put radials on my '62. I was originally
going to purchase michelin but, if I ever decide to have the car judged I think the tires would score zero points as opposed to a brand like goodyear which I think would score 40% of the total. Is this a correct assumption on my part ?
Also is 205-75-15 the correct size for a C1 ? Thanks in advance for all your help.

Bob

[Dennis C.]

Re: radial tires

Bob, I use P215 - 75R15 Firestone blackwalls... And yes, if the car is judged, you will fair MUCH better with an OEM supplier and should receive no deduction on condition points. Best, Dennis

[Robert D.]

Re: radial tires

Thanks Dennis. Is 205-75-15 or 215-75-15 the direct replacement for 670-15 ?

Bob

[Rick A.]

Re: radial tires

Bob, when I queried this "august" group about radial tires for my 1963, I was told the closest replacement for the 6.70-15's were the 205/75-15's

[Rick A.]

Re: radial tires

Bob, forgot to mention that I shod my 1963 with Goodyear Regatta II's - Duke would say I should have went with a performance tire, but I don't plan on driving my 1963 as aggressively as Duke drives his car

[Jack Layton]

Re: radial tires

A radial replacement tire for the old bias tires is a collection of compromises. Mathematically the 6.70 is an inch measurement for the cross section of the original tire.
Convert 6.70 inch to metric millimeters by multiplying 25.4 mm/inch. Answer is 170 mm.
Problem is that radial tire construction always produces a slightly wider cross section measurement. Plus the original tire's aspect ratio was probably an 80 series. Can't buy 80 series tires. However, 75 series tires are the closest available today. The general rule of thumb is that everytime the aspect ratio value drops by a factor you add a jump in the cross section value. Now, remember that 170 mm cross section on the bias ply 6.70? Well a rough comparison would be 175 mm but the radial design causes that 175 to be better represented by the 185 radial tire. Then the drop from an 80 series to a 75 series has us jump to the 195 radial tire. So mathematically the 195x15 radial shoud be very close. Then there is the issue about the rolling circumference of the tire. A radial will be a little different than the bias tire. This issue is evaluated as revolutions per mile. Do you know what that value is for a 6.70 tire from 1963? Compare it to the tires available today. Then there is the issue of how close to the original in exterior appearance would you like? A 215x65x15 might have a closer match in revs per mile but you might not like the low profile look. or you might want a narrow white wall instead of raised white letters. or some folks might want a high performance tire as opposed to an all weather tire. Then there is the issue of availabilty. Can you actually locate a 195x75x15 narrow white wall
tire for sale today? It actually might be easier to find a 205x75x15 narrow white wall radial all season tire. I used Michelins for my 1965 since the math on a 7.75 tire from 1965 left me at the 205mm size and the appearance of the 75 series tire more closely approximated the look of my originals. Keep in mind that the performance of an all season radial tire made today far exceeds the performance of a 7.75 and 6.70 tire from the mid 1960's. A lot of quality issues for you to crank into your thoughts before buying a set of tires. The one word of caution is to beware buying a tire that is tall and wide. Like a 225x75x15 which came on C3's. Those tires may very well knock out the lip of the front wheel well.

[Dennis C.]

Re: radial tires

Bob, I had an old non-DOT 6.70-15 laying around and measured O.D. The F/Stones I bought came very close to matching that O.D. The one catch: Seems there is no uniform agreement among tire manufactures about what size is what size. I tend not to trust any of their listings unless I've got my eyeballs and tape measure on their tire. And, I must admit the "look" of the tire is usually part of the equation. Best

[Robert D.]

Re: radial tires

Rick and Jack,
Thank you for the information. I will probably settle on 205-75-15. Now I just have to decide on a brand based on some hopeful points in the judging system.

Bob

[Duke W.]

Re: radial tires

Tire and Rim Association standards allow an 8 percent range for actual specifcations and production dimensions, but most tires are fairly close to the nominal middle of the acceptable range.

Duke

[Mike McKown]

Excellent, Excellent Excellent, Excellent! *NM*

[Dennis C.]

Re: radial tires

Wow, Think I'll try to impose on Jack Layton should I have any future tire questions. I am sincerely impressed with his grip on the subject. Thanks

[Duke W.]

Re: radial tires

C3 OEM size beginning in '73 was 225/70R-15, not 225/75; 225/70R-15s are the same nominal OD and revs per mile (760) as the 6.70-15, but they need at least a 6" wide wheel (sevens are much better), and will not fit C2s without fender clearance problems with the possible exception of drum brake models because they have slightly less track than disk brake models.

In any event, a 225/70R-15 on a '67 six inch rally wheel (0.60" offset) on a drum brake C2 would come down to the individual car and would probably require a touch of negative camber at the front to preclude fender interference.

Duke

[Robert D.]

Re: Excellent, Excellent Excellent, Excellent!

To All,
Thanks for the wealth of information.
Bob