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Modern Tire Sizes
#1
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Keegan Chaput
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I tried to do a search to see if this was covered already. I know the original size of the rims and tires, but I don't know the equivalent in the modern sizing.

tirerack.com says that the 7.60x15 converts to 225/75/15, but it also lists about 4 other sizes. With the narrow rim of 15x5.5 it would be easy to pick a tire too wide. And I'd like the speedo to run as accurate as possible.

Also, what is the bolt pattern on these?

Mine is a 55 Clipper.

Posted on: 2008/2/24 13:59
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Re: Modern Tire Sizes
#2
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BigKev
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I am using the same rims as a '55 Clipper and I am using 215/75/R15 and they work just fine. Remember that the origial ply-bias tires had a narrowered tread that modern radials do. If you go with a tire that is too wide, you may have issues in getting the tires on and off on the rear with out jacking the car up really high.

Posted on: 2008/2/24 14:52
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Re: Modern Tire Sizes
#3
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BH
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About twenty years ago, I was working with a former BF Goodrich engineer, and the topic of reproduction vintage tires came up. I felt that having a tire made from an original mold was no guarantee the carcass that went into the mold met original quality. Also, suppliers didn't always offer the size that I was looking for. (Mis always an issue, too.)

He saw nothing wrong with using modern radial tires on my old cars, but I was concerned about tire circumference - wanting to avoid recalibrating the speedometer or swapping the pencil gear. He then showed me how to do the math on bias-ply vs. metric radial sizes to get the best match.

When it came to my V8 Packards, it looked like a 235/75R15 would replace the 8.00x15 (later, an 8.20x 15) tire on a 15x6" wheel, as used on 1955-56 Senior Packards. It was a close call for the 7.60x15 on a 15x5.5" wheel, as used on 1955-56 Junior Packards (Clippers) and the 1956 Executive, but I prefer the 225/75R15 for those cars/rims.

The use of these radial sizes seems to be supported by Coker Tire's conversion chart:

http://resources.coker.com/tire-tech/ ... ial-conversion-chart.html

I did find, however, that I had to let some air out of the 235/75R15s to get them to fit between the brake drum and the wheel opening of one of the rear fenders (even with skirts removed) on my Caribbean Hardtop.

I don't know the bolt circle off-hand, but they are different on Junior vs. Senior cars.

Posted on: 2008/2/24 20:23
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Re: Modern Tire Sizes
#4
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Owen_Dyneto
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According to Coker's catalog, The 225/75R15 has a slightly smaller diameter than a 7.60-15; if you calculate the circumferences the resultant speedometer error will be small, just over 1.1%.

Posted on: 2008/2/25 9:29
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Re: Modern Tire Sizes
#5
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Keegan Chaput
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Maybe I'll just put a bit more air in the tire to make up the 1% difference

I can live with an error of 1%. Hell, my motorcycle has a speedo error from the factory of almost 10%!

I'll have to get one of those Coker Catalogs, it seems like a good reference if it lists classic and antique tire sizes.

Posted on: 2008/2/27 23:43
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Re: Modern Tire Sizes
#6
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Charles Neuhaus
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Not that anyone asked, but some wide white radials are made from discontinued molds sold to other manufacturers. Accordingly it is hard to be sure of quality. Here in South Carolina is am outfit called Diamond Back Tires that vulcanizes wide white sidewalls on fresh modern radial tires from known manufacturers (Firestone, Michelen etc). I have a set of 235/75/15s on my 56 Patrician and am very satisfied. Their prices are competitive. Their phone number is 888 922-1642 and they are on the web at www.dbtires.com

Posted on: 2008/2/28 12:34
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Re: Modern Tire Sizes
#7
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Keegan Chaput
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Great Link Chuck! You should add it to the Packard Directory under Tire Venders. Do you work for these guys?

http://packardinfo.com/xoops/html/mod ... es/viewcat.php?op=&cid=36

Posted on: 2008/2/28 13:51
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Re: Modern Tire Sizes
#8
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BH
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chuck -

Your report of manufacturers using discontinued molds to make WWW radials mirrors my concerns about the repro bias-ply tires. In all fairness, I must admit that a friend purchased some Coker-branded wide-whitewall (WWW) bias-ply tires for his '50 Pontiac Streamliner and had no poblems.

However, the price of WWW bias-ply tires - even "house-brands" - in the hobby sector is ridiculous for anything other than a show car. Personally, I'm not very interested in having my cars judged anymore, and I know plenty of other old car owners who feel the same way. Yet, the price of WWW radials isn't much better, especially with their quality now in question.

Now, Diamond-Back sounds like a better alternative, but the price is such that I'd still only spend that kind of money for one set for my '56 Carib (but only after I've repainted it). I put a set of white-stripe (WS) tires on it, and I have to admit that the Carib sure looses something (aesthetically) without the wide whites. I'll recycle those WS tires on one of my sedans, as the radials significantly improved the ride and handling of my Carib.

For the price of a good WS radial tire, I can live without the look of a WWW on a cruiser or driver. Haven't shopped tires lately, but I paid only $40 a piece for WS 235/75R15 Generals at Sam's Club about ten years ago.

Posted on: 2008/2/28 13:51
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Re: Modern Tire Sizes
#9
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Charles Neuhaus
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Reply to Keegan. Good suggestion, I've added this firm to the directory. No, I don't work for Diamond Back, but when I had decided to buy from them I was amazed to learn they are only about 20 miles from me.

Posted on: 2008/2/28 19:18
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Re: Modern Tire Sizes
#10
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Owen_Dyneto
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A friend just bought a set of Diamond Back radials for his senior 1941 Packard. The carcass is Chinese-made, though I believe DB backs them with the same warranty they give to their other tires.

Posted on: 2008/2/28 23:26
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