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Tire size for judging-GR 70 15


philip roitman
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I have entered my 73 Stage 1 Sun Coupe for the Virginia Beach Spring Meet. I have a question as this will be my 1st AACA Meet. I cannot find GR 70 15 tires anywhere. (Coker, Tire Rack, etc.) I can find G 70 15 tires. My car came from the factory with the radial tires (GR 70 15) either black wall or white wall. What is the correct tire size that I can use for my car? 215-R70 or 225 R70 or? I would like to put on Radials as that is how it was ordered/optioned from the factory and not put on Bias Ply. Thank you for any answers in advance.

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  • 1 month later...

After speaking to AACA VP Judging (Thank You) a 225/70/15 would be a correct replacement for the GR/70/15 in whitewall or blackwall without the P prefix though. These tires are also currently not available without the P. I am downgrading to 14 inch rims w/G70/14 RWL Wide Oval tires that were also an option on my car to be 100% correct for AACA.

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B.F. Goodrich makes a P225/70R15 with a red line. Isnt that what yoy need? Universal Tire Co .has them for 233.oo each

No I cant use them #1 is they are redlines #2 as I stated 225-70-15's would be a proper replacement for the GR 70 15, NOT P225-70-15's. Something about the P (Metric) and not available till 1979? I was told by numerous tire Companies that the P means passenger tire and isn't a metric classification. Oh well, just to let you know I think BFG also makes P225-70 15's in a whitewall. (SilverTown)

Edited by philip roitman (see edit history)
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You could try this from the Judges Guidelines:

Tire Documentation

Owners not able to find a correct

replacement tire should send a letter to

the VP Judging indicating the specific

size of the correct tire and that at

least two tire manufacturers have

been contacted and the correct tire is

not available. Tires one size larger or

smaller are acceptable. A letter from

the VP Judging is the ONLY AACA

ACCEPTED documentation regarding

a vehicles’ substitute tires. Any letter

issued by the VP Judging should be

shown to the Team Captain at the time

of vehicle judging.

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You could try this from the Judges Guidelines:

Tire Documentation

Owners not able to find a correct

replacement tire should send a letter to

the VP Judging indicating the specific

size of the correct tire and that at

least two tire manufacturers have

been contacted and the correct tire is

not available. Tires one size larger or

smaller are acceptable. A letter from

the VP Judging is the ONLY AACA

ACCEPTED documentation regarding

a vehicles’ substitute tires. Any letter

issued by the VP Judging should be

shown to the Team Captain at the time

of vehicle judging.

I have done that and have had numerous discussions via email and phone with Eric Marsh VP of judging. The 14 in wheel with G 70 14's RWL or G 78 14 WW tires or H 78 14 oversize (from my option list) WW tires seems to be my only option at this moment. I am hoping in the future some Co. will repop the GR 70 15's in WW or BW instead of only RWL. It also seems I was told that the VP of judging no longer writes these letters for judges and you must recieve said letters from tire dealers/Companies. I am a little sad I cannot find correct Radials as that is how my car was ordered from the factory. Either way it is all good. I was lucky to have a set of 14 in. Rallye rims on one of my other cars as they are super hard to find. All part of the pleasure of owning old cars. :-) P.S. I will use the Bias Ply 14's with rims only for AACA shows.

Edited by philip roitman (see edit history)
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I think I'm confused, from your last post I'm understanding that the tire size that you need is available but with a red line and you need either a black wall or a whitewall. If that is the case why not buy the tires, mount the Redwall turned to the inside and paint the Redwall black

BTW...Rick March specializes in tires and teaches a CJE class on tires but Herb Oakes is the VP of Class Judging

Edited by real61ss (see edit history)
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OOPS Sorry Herb Oakes was indeed who I spoke to. I recieved his name and info from Mr Marsh and I thank them both for their time, kindness and understanding of my situation. I look forward to meeting them at the Va. Beach meet. The AACA will not allow tires to be reversed or I would have used the GR 70 15 available with RWL. I asked and it is NOT approved as it would not be as delivered from the factory. The statement is a dealer would probably not do that at delivery either and on top of that you are not allowed to tamper/change a tire. (ie; Shave a P off a P225 Radial or to paint over/alter the tires). The Red line tire in the above post is a P225 Radial therefore not allowed as are the white and black wall P225's available. Catch 22. At least there was a partial solution.

Edited by philip roitman (see edit history)
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As a matter of clarifying metric tire sizes . . . which is "historic", possibly a little farther back than some might realize . . . the original metric sizes were in millimeters rather than inches (as we used in the USA, for section width designations). These were what I'd consider "true dimensions" rather than otherwise. An 8.25x14 tire size (in the pre-section width designation-use times) would have been a 205x14 tire size. When the USA "feds" mandated tire sizes (physical for each tire size, allowing for a 7% variation from their specs) and also then designated the "letter designation" (for better alleged consumer understanding and shopping results), that's when the section width was added to the mix. The "old metric" 205x14 became a 205R78x14 size and then "GR78x14".

When the need for lower rolling resistance tires (and higher inflation pressures, up to 35psi for normal passenger vehicle tires, "standard load"), this newer design orientation led to the "P-metric" sizing, circa 1979. This new change caused MUCH confusion of what older size equated to the newer P-metric sizing. Initially, as the newer P-metrics used higher total inflation pressures and slightly increase load carrying capacity, one prevalent orientation was to use equivalent weight capacities for such cross-over sizes. Unfortunately, such an orientation usually resulted in tires being used which were physically smaller in outside diameter (and the resultant "revs/mile" spec). This was not good, appearance-wise or for speedometer accuracy.

The "P" in "P-metric" meant it was for passenger vehicle use, plus containing other letter and designations we hadn't seen previously. In the case of Corvettes, Z/28s, and TransAms, they used the GR70x15 size in 1978, then the P225/70R-15 size in 1979. Both of those tire sizes were direct equivalents in revs/mile specs and other size aspects. GM used the same speedometer gears for both sizes, too.

In 1973, due to the performance orientations of the G70 sizes (14" and 15"), almost ALL of them were "white letter" tires, not blackwall, although there were also some in that size that were whitewalls, from the factory or otherwise. If you had a performance tire, you wanted others to know about it! Buick termed them "Billboard White Letter" tires, or similar, in their sales literature of the time. Such "white letter" tires were just as much of a status symbol, back then, as whitewall tires were an upscale or luxury orientation from the basic, standard level (in many cases) blackwall tires. It was not until the 1980s that we started to view "blackwall" tires as more or a "Euro-influence" situation and whitewall tires seemed to totally disappear from vehicle option lists.

In the past several years, I've noticed that some are now using "205/75R-15" tire sizes to really mean "P205/75R-15" tires. The "P-metric" is a federal US tire sizing system. I suspect that the sidewall will still reflect the "P-metric" sizing although the sales literature might not, for some reason, especially as those listed without the "P" are of the same exact size specs as those same tire sizes with the "P" in the sales literature listings.

At the factory equipment level, and related replacement tire level, the GR70x15 tires were either white letter or whitewall. Same for the earlier bias ply sizes, as I recall, especially in OEM brands, although some other non-OEM brands might have also had them in blackwall sizes.

One reason why "reversed" tires don't work is that the inside sidewall was where lots of additional things happened. For example, the tire serial number is stamped, there, plus other production-related things which are NOT on the outer sidewall's surface. IF they were the same inside or outside, that would be different, but they are not and never have been that way. In this case, "cosmetics count".

In the case of your Buick, I strongly suspect the OEM tire brand would have been UniRoyal, or possibly Goodyear.

The GR70x15 size was not only used on Corvettes, Z/28s, and TransAms, but also on Monte Carlos and Grand Prix, back then. It's on these other cars that they were available from the factory with "white stripe" whitewalls other than white letters, due to both the performance and luxury orientations of those two cars.

Also, in the 1973 orientation, I strongly suspect your Buick probably had bias-belted tires (not reflected in the G70x15 tire size, as that was a build-orientation rather than a size designation issue) rather than the prior "bias ply" tires. Getting that type of tire can be even more problematic, especially in a blackwall tire. Therefore, although I haven't looked at the AACA Judging manual, I feel that your best alternative for modern, currently-available tire is the P225/70R-15 size. That tire has appeared on many Corvettes, Z/28s, TransAms and such with good performance and cosmetic results AND was what the factories used to replace the earlier GR70x15 tire size. The sizing is correct, too. IF you might prefer a whitewall tire, they are available in some brands, too, as you can find on TireRack.com. For a GS, though, the white letter tire would most probably have been the tire that came on it as a part of the GS package.

Just some thoughts and clarifications . . .

NTX5467

Edited by NTX5467 (see edit history)
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Thanks for the reply NTX5467. It was very interesting to read and learn. I have been told over and over P225's are not acceptable. If you ordered Radial tires for a 73 Century Gran Sport the options were either GR-70-15 Whitewall or blackwall tires and came with specific suspension and Styled steel wheels. The other tire options were; Whitewall Tires- G-78-14, Wide Oval White Billboard Lettered Tires-G-70-14, or Oversize Whitewall Tires-G78-14. This info is directly from the Sloan museum and is from the copy of the 1973 Buick Gran Sport Wholesale Car Order Form. Believe me if allowed I would be using my P225-70R-15's with RWL if I had that option which I do not. I would certainly be using P225-15's in White or Blackwall if allowed. As stated above I am looking forward to the meet in Va. and seeing nice cars and meeting new friends.

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so what do we do for judging when the correct tires is no longer made.???

My only option was to go out and use 14" wheels from one of my other cars (thank G-d I had a set) and purchase new G70 14 tires. I was told many people have

1 set of wheels just for AACA shows only and 1 set for everything else and I needed to do the same. I will now use the 14" combo on the SunCoupe in Va. and also use them on my 73 GS S1 4 speed when it is finally done with its frame off restoration as that car came with 14" RWL Bias ply tires from the factory.

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so what do we do for judging when the correct tires is no longer made.???

From the Judging Guidelines...

Tire Documentation

Owners not able to find a correctreplacement tire should send a letter tothe VP Judging indicating the specificsize of the correct tire and that atleast two tire manufacturers havebeen contacted and the correct tire isnot available. Tires one size larger orsmaller are acceptable. A letter fromthe VP Judging is the ONLY AACAACCEPTED documentation regardinga vehicles’ substitute tires. Any letterissued by the VP Judging should beshown to the Team Captain at the timeof vehicle judging.

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