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Am curious about something in tire sizes. Several have chosen the Diamondback II series 235/75/15 for their senior post 50 Packards. That size is supposed to be the equivalent to the original 800/15 as per the Diamondback comparison chart. The section width is about 9" with a diameter of 29". Tread width is just over 6", load 2028.

I notice Diamondback has a special size 700R15 which they say will replace 3 sizes including the 700-15 on the Clipper and the 800-15 on the 51 on senior cars. Section width and tread width is about 1" less than the larger 235 size, load capacity is slightly more and the diameter is closer to original bias size - but there is a confusion. Just wondering what I am missing since the diameter is different on the 3 sizes that it replaces. Seems like there would be a speedo error to contend with on the smaller size end -- or is the size close enough it wouldn't be significant.

Since tires are needed for the 47 am seriously considering that 700R15 in spite of the larger diameter but it also looks like a candidate for the 235's since the section width is less. Tread width is less too but is it less than the original bias tire? Many have complained those 235's are a bit tight for the wheel well so just curious if the additional tread width is enough to justify the fit and problem of having to deflate the tire to remove it. Anyone using the 700R15's?

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One thing to keep in mind about the 700R 15 - they are truck tires (6 ply I think) so you should run 40 -50 psi and that will make the ride a bit harsher.

I'm not sure you can compare a bias to a radial for exact fit because of the stance/sidewall. The new numbers are metric so 8" is 8 x 25.4 = 203 mm(tread width), so a 235 would be >1" wider tread. 205 would be right. I'm pretty sure "75's" are about the same radius as a bias, so the speedo should be OK, close enough. If you drop to a 70 or 65 maybe a bigger issue. Call Coker, for exact match to the factory size. They make radials to match and look like bias plus bias are still around...

The whole radial vs bias is a controversy. Each gets kudos and bricks so it boils down to what is most reliable and economical on the long term.

The specs I mentioned are what Diamondback posts in their catalog so the conversions are theirs. The main reason Diamondbacks are getting my attention is because they are available thru one of the PAC regions and so many have had nothing but good to report with the tires and with their conversion. Not so the Cokers or some of the other "classic" brands.

I don't have experience with radials on anything but modern cars driven regularly. Don't know if they have the same problem with sitting as bias does -- namely the fact bias tires become square if stationary for long periods. I've heard radials also deform but are much easier and quicker to revert back when driven. Bias tends to permanently acquire a flat surface -- at least that is my experience. Anyone have experience with long term stationary radials?

On a car destined to sit a lot, bias would be the economical choice and is available locally -- as are the Cokers if I want to take a chance my set would be one of the good ones. Luck being what it is, the set I bought would be one where tread separates or the tire goes flat without cause so they are not under much consideration.

If radials get the nod, still contemplating the 700R15 vs the regular 215/75 radial equivalent to the original size. The diameter is an issue to consider but one nice thing on the 700's is if specs are correct, they should also fit the 56. As to the inflation pressure, Diamondback also recommends fairly high pressure on the regular radials so not sure how much extra harshness is to be expected.

"Flat spotting" of bias ply was much more of an issue in the era of Rayon cord tires, nowhere nearly so much of an issue with modern Nylon cord construction. The 7:00x17 bias ply Lesters on my 34 have never given an indications of flat spotting after winter storage but I do give them a few extra PSI when going into storage, 40 PSI for storage as opposed to the normal 35.

If you go with radials, based on experiences of quite a few friends, I'd avoid the Coker-brand though I do hear that their quality problems have been behind them for a while now. IMO absolutely nothing looks correct or right compared to the 7:00 x 15, especially from the Firestone mold with the raised lettering on the whitewall and I have a friend with a 47 Super Clipper with them that tours quite extensively and likes their driving quality. I personally wouldn't have radials on a collector car of that era even with a steady diet of touring, but if I did, I'd give serious consideration to the Hankooks (Diamondback).

Agree, the polyester cords in bias and the bias lay-up design leads to more "flat spots". The rubber compound was also very different and that contributed. They used to have to "heat up" to get pliable. I never did like the bias tires living north then.
"Modern" radial tires have many advanced materials in them and each manufacturer has different strategies on compound. Loosely, wet grip is softer and high mileage is harder (durometer) Used to supply polymers to them for various functionality.
The technology outstrips the science. When I was in graduate school my math proof, for his PhD dissertation, derived and solved the bias ply tire stress equations, ten years after radials were on the market...

Agree, the polyester cords in bias and the bias lay-up design leads to more "flat spots". The rubber compound was also very different and that contributed. They used to have to "heat up" to get pliable. I never did like the bias tires living north then.
"Modern" radial tires have many advanced materials in them and each manufacturer has different strategies on compound. Loosely, wet grip is softer and high mileage is harder (durometer) Used to supply polymers to them for various functionality.
The technology outstrips the science. When I was in graduate school my math proof, for his PhD dissertation, derived and solved the bias ply tire stress equations, ten years after radials were on the market...

If the car is going to sit it really should be put on jack stands under the frame so the springs don't sag. The wheels don't have to be off the floor, only unloaded.

Unfortunately I don't see any quick jacks on the market and that is something I am always running around in my head.

The old Martins where notorious for needing warm up, but they were also the absolute best bias ply tire ever.

There are more variables that go into tire failure than sitting and, given how many cars sit in inventory, if sitting was a danger there would be a DOT regulation.

One variable not in the bias ply equation is belt separation, so I would feel safer with bias ply for long idle periods.

Tim, I agree, those Martins were very fine tires for their time, perhaps the very best and followed somewhat closely IMO by the Kelly Springfield tires. In fact, were not the Lesters or at least some of them made in the old Martin plant until quite recently? I seem to recall that the DOT plant code on my last set of Lesters corresponded to the Martin Tire & Rubber Co.

Have replied to this topic before. I'm running Bridgestone R230 radials on '47 Super Clipper. Like the identical spec Yokohama LT radials Diamond Back charges extra to vulcanize a slightly too narrow "wide" whitewall, they are in the correct bias size of 7.00 x 15 for our cars, and many other 1941-on domestic automobiles. Google tread design and specs.

The first ride with them i was amazed not just at the
handling improvement, but the stopping ability. It's all
about wee performance tweaks of these fine road cars for me,
so i carry a couple extra pounds cold psi than what you'd
probably like or need: 46 psi. You can play around with
this.

The only drawback with such radials is that you'll be
tempted to take corners faster than you should, to "outdrive" your car.

Do NOT buy the metric sized tires you mention above.
They're for S(tupid) U(seless) V(ehicles) and will look
dorky. In fact, the 235s can rub the fender on hard
opposite lock. Again, they don't look right. The 205s
will be too small. Go with Bridgestone or Yokohama 7.00 x 15 LTs. Until the early aughts, Michelin also offered these with the same specs, but figured the market didn't justify continued production.

Bridgestone is a Japanese brand now. Yokohama Canadian.
Ironies abound. The raised black letters are impossible to read unless some car nerd crouches by your car to scrutinize the writing, and who cares what such losers think? If you don't pay Diamond Back to vulcanize a too narrow whitewall over this, you can always touch the characters with a die grinder.

Additionally, i like blackwalls because NO new cars in 1946-47 at any price range were delivered with whitewalls,
tho' a very few during the last month or so of the '47 model year may have. So with blackwall 7.00 x 15 you've got historical correctness on your side in the win-win bargain.

1941-47 Clippers are sleek, sophisticated automobiles,
which is why it's so sad seeing whitewalls, ostentatious hood ornaments that are a hangover from the dated box office poison prewar traditional bodies and already pretentious on those junior-based 1939-on cars (other than the leftover '38 Twelves).

Skip the gargoyle hood ornaments, curb feelers, go with
Bridgestone or Yokohama 7.00 x 15 LT radials. If you feel
compelled to do the suburban concours d' nonelegance conga
line, then order a set with too narrow whitewalls from
Diamond Back at a hefty premium for historical incorrectness.

Most wealthy folk in the day thought whitewalls, etc.
gauche, tacky. Leave that crapola to the '41 Chevy and Cadillac-ack-ack-ack-ack-ack-ack monkey see, monkey do crowd.
With blackwalls and less junk, you really "see" the car.

In the day, Packard retrofit windshield
washers, R-11 overdrives into earlier models. As motor oil
and lubricants improved, you'd use these. If you took
your '41-'47 Clipper into a Packard dealer for a new engine
after 1948 or in the early '50s, they'd install a 288 or 327.

Don't use tubes. Just make sure your wheels are smooth, the rivets tight.

These are a u t o m o b i l e s. Good road cars. And you're not butchering anything. Michelin offered radial tires beginning in 1946. Packards were worldclass automobiles.

I know '40s Packard and Cadillac owners running radials, several 1936-37 Cord drivers, a coupla S-Type Bentley Continentals, the latter with the same GM-type IFS and curb weight as our Clippers and 15-inch wheels, reported nothing but success. Yokohama and Bridgestone (and until a decade ago, Michelin) also offer 7.50 x 16 LT radials and i've talked with various delighted 1930s Cadillac and Packard owners so equipped.

Let the whining and yeah, buts begin.

A merry sixth day of Christmas, for those who also enjoy tradition, and an East Grand 2014 to all visiting this splendid site, tho' we remain puzzled why a simple
question on a recent post "356 finetuning" regarding timing
returned but one (1) response, and a question as to 1941-47 Clipper rear vent window removal not even that, while endless fairy castle and unicorn what ifs, radial rehash, extra carb titillation abound.