I'm So Tired...

Although there were four circular rubber things mounted on the car, they were only technically tires. The PO had been upfront about their condition... if not the price of replacements. They were of the bias-ply variety, manufactured sometime in the late Cretaceous Period and vulcanized in Pompeii, and had more cracks in them than George Clooney's straight-guy facade. So we decided that new tires would be at the top of our road worthiness list.

There are a few things to consider about new treads before tire shopping, or even car shopping for that matter. The first issue is availability. This is going to be based primarily upon tire size and popularity. If your car requires a fairly common tire size, such as P205/70R14, you will have little difficulty finding tires and can likely pick some up for less than $70 a piece. If, however, your car takes an odd sized passenger tire - such as P205/70R16 - the price could run substantially higher.

But we're getting ahead of ourselves. If your car was manufactured before about 1972, it probably came with tires listing a size like "6.00x16." I know it looks weird but it's just the way tires were measured back before Al Gore invented the metric system. All it means is that the tread of the tire measures 6" shoulder to shoulder and the inside diameter (or bead) is 16" across. Back when bias-ply tires were popular all tires carried an aspect ratio of around 80%. That means sidewall height of the tire was about 80% of the tread width. In our 6.00x16 example it would be about 4.8" tall from ground to rim, or 25.6" overall.

Now, that's all bias-ply tires, which are for purists who still use asbestos for their seat cushions, and their electrical system is based off some odd number like 7.3 volts. For anyone planning on driving their car on a regular basis there really is no choice but to switch to radials. I had made the switch on my first car, a 1966 Mustang. What a difference! Overnight the car went from handling like a freight train to handling like a logging truck. Looking back, I can't believe my parents let me drive that car with those things... for three years. It used to get airborne on Central Expressway in Dallas at any speed over 35 m.p.h. Wonder what my life insurance was like back then?





Wait. Not that picture... this one.





The key to switching to radials is getting a tire that closely approximates the look and size of the original. That means deciphering the jibberish that is modern tire sizing, like P205/70R16. I'm going to kind of gloss over this because you can find detailed info all over the web. The letter designation - in this case 'P' - stands for the type of use the tire is designed for, as in passenger tire. 'LT' - Light Truck - is another common one. Next is the width of the tread in millimeters. This is the same measurement as the "6.00" in our old bias-ply tires, but now it is metric, because metric is so much more accurate. I don't know who in the hell can picture something exactly 205 mm wide, but that's what it is. Easy enough to convert into human numbers, though.

205/10=20.5 cm/2.54=8.0 inches
In case you were wondering that '6.00' from before comes out to 152.4mm

We'll get back to those sizes after we finish with the rest of the numbers. The 70 is our aspect ratio. They didn't have a reciprocal number in the old measuring system because, as I stated earlier, all tires came with a standard 80% aspect ratio (90% for the really old thin tires). In our P-tire example here, the 70 tells us that the sidewall height is 70% of the tread width. Tread width is 205 mm (8.0 in), so the sidewall height is 143.5 mm (5.6 in).

The next designation is the type of tire, in this instance 'R' for radial. You may see a 'D' for diagonal bias or a 'B' for belted bias, but we're really concentrating on radials in this article... because that's what we have and I don't know much about bias-ply car tires. And finally we have that wheel diameter again, which is in inches. I'm not really sure why the wheel sizes haven't been changed to millimeters, too. The result is that our modern tire size designations are a combination of letters, metric measurements, ratios, and standard measurements. Nice and simple. How typically American. (Yes, I know The Frantics were a Canadian comedy group, but Roman Numerals is great! Give it a listen.)

Back to wheel sizes: all of the other variables are... well... variable, but the last digit is not - unless you plan on changing out your wheels for some of those hifalutin ones with the shiny bits and spinny things... but people'll shoot you over those, so I'd just stick with the old steel wheels. You can get all sorts of cool accessories for them.

Okay, so size is a big consideration. About halfway through the 1947 model year Plymouth switched to 15" wheels. That was good timing for anyone restoring a 1947 ½ or later Plymouth... not so much for us. Red is equipped with 16" wheels. Now, 16" wheels themselves aren't especially hard to find these days. With the popularity of low profile tires, wheels of 17, 20, 22, even 28" (or 711 mm!) are available. But all of them are a foot and a half wide! Try finding a 16" tire for a 4.5" wide rim. Yeah, that's right... 4.5 inches.

Oh, they make 'em, but not many of them. And that means that you will pay a premium. We wanted wide white walls for that "classic-y" look. Specialty tire manufacturers such as Coker Tire make them and are quite proud of them. Wide white radials in a size approximating the original equipment found on our 1946 Plymouth run about $240... a piece. Before installation or road hazard or valve stems or balancing or air or...



I like the black wall Goodyears we picked out.







Now, the size of our wheels is a problem with our car, although we could just step down to the 15" wheels (after all, they came standard on Model P15's of different years), but we wanted to stick with original equipment. You may not care about doing so, but if you go changing wheel /tire sizes and styles be sure that they will fit on your vehicle. Things to look for are steering clearances, suspension travel, and - as in the case of our rear tires above - clearance behind the fenders while changing tires. Going to an enthusiast site, such as P15-D24.com, is the best way to get information from people who have already tried different sizes. Increasingly the guy at the local tire shop is only good at sounding like he knows what he's talking about. There are just too many variables involved.

Let's look at a real life scenario. As I stated, our car came with 6.00x16 bias-ply tires on 16x4.5 wheels. Remember that that first number is the tread width in inches. Now, by taking the 80% aspect ratio, multiplying it by 2, and adding the diameter of the wheel, we end up with a tire that is 6 inches wide and 25.6" tall.

To get that in a radial tire we are going to have to convert the first number to millimeters:

6 x 2.54 x 10 = 152.4 mm

We'll of course keep the same aspect ratio (80%) and wheel diameter and take these measurements to our local tire store. The salesman will tell us that tires don't come in 152.4 mm widths, so we'll have to settle with a 155/80R16, at which point he will wheel his 10-speed Schwinn around the corner and offer us the front tire. All of that is theory.

For our car I researched the forums, looked at photos, considered the real world, and the fact that the 'power' in our power steering would be coming strictly from my biceps (the wider the tire the tougher to steer manually), and decided to go with a P205/70R16. They had to be ordered. On the theory side these tires should be 8.07" wide and 27.3" tall.
















This is the result of the real world application: 6.5" wide and 26.25" tall., as opposed to the 6" and 25.6" of the originals (I know the width photo is confusing and just generally sucks, but that was way down close to the floor and I'm just not going to squat that long down there. In fact, I pulled off about six shots in rapid succession figuring I'd get at least one good one. Oh well, it's decent anyway. Besides, it's not like you paid to see this photo.) But why are the measurements so different than our calculations? Because the calculations are based upon non-load dimensions. Once you put the tire on your wheel and under the weight of your car everything goes out the window. That's why it's best to get as much information as possible from people with experience before you go ordering new tires.

Overall, I think our choice came out pretty well. While I wanted to maintain a look close to the original, people in the automotive world can be divided into two categories:

1. Matchbox men
2. Hot Wheels heads

Matchbox cars (especially the early ones) had those wheels that left all that space between the tire and fender, and never seemed to extend all the way out to the edge of the wheel wells. They were your bias-ply tires of the toy car sect. The Hot Wheels cars always had much cooler wheels. I was a Hot Wheels kid. Oh, I owned and painted them both with everything from Magic Markers to my mother's unattended fingernail polish, but I always liked the Hot Wheels cars better. So here's how Red turned out with the new radials.

That's Red in front of Campbell's Field Restaurant on the left, and with the 6.00x16's on the day we first saw him to the right. What do you think?

In addition to the sizing information above, tires are also stamped with tread life, speed, load, maximum psi rating, and operating temperature information. Look up this information as applicable for your vehicle. My Goodyear Eagles LS-2's have a 118 mph speed rating. That's a handy piece of information to have should I ever decide to drive the Plymouth at full throttle... down the side of a skyscraper. Do note, however, that the maximum psi rating is just that: the maximum amount of air the tire can handle. Inflate them to a level appropriate for the design of your vehicle. (Be careful that the tire can handle the psi recommendations. Too low and you could lose your bead in hard cornering.)

In addition to size, there are several other considerations you should make concerning your wheels. Older vehicles used bias-ply tires with inner tubes. Because of this not all steel wheels were designed to be air tight. Mine were not, but they are holding air just fine (although the front right has a small dent in the edge that needs to be straightened). This is where that enthusiasts forums can really help: see what kinds of experiences others have had. You may end up having to run tubes or switch to metal valve stems.

My wheels are designed to use 10" moon hubcaps. This means each one has five clips riveted to it for holding the hubcap. It is important to note whether all of the clips are present: no clips, no caps. It also makes the wheel that much more specific to our vehicle. I had to order a spare wheel from North Dakota. And those hubcaps? They can get pretty difficult to find. My car is also equipped with beauty rings. On the open market? About $30 a piece. You can see why some people switch to aftermarket wheels just because of the cost of hubcaps and beauty rings. So carefully consider the rolling accoutrements when shopping for an old car to work on and/or restore.

No tire purchase would be complete without installation. Back in the day when we did things ourselves we'd just put the tires on at home. Do you know how to do it? Would you know where or how to begin? Instructions are in my owners manual, so I guess we are supposed to do it ourselves. Don't worry about your manhood - I'm not going to say I mounted these tires on my Plymouth. I have the tools and I used to change tires back in college, but not anymore. So I found a place I trust. This is very important. Find a place you trust and then watch the guy mounting the tires.

You know how scary the guys at the tire shop are: long, unwashed mullet; one green and one yellow eye - slightly crossed; lunch stains on the shirt; lunch in the corner of the mouth; a chaw of tobacco in the cheek; no less than six earring holes scattered from the right ear down to the left nipple. And that's just the salesmen... you should see the guys actually changing your tire. These guys would have to dress up just to get into a methadone clinic. And having worked there I can assure you that they aren't always the brightest bulbs in the drawer... or even sober. That really doesn't matter one way or the other if they are mounting tires on your '04 Hyundai, but handling a 70-year old wheel you had shipped from a junkyard in Tibet might affect your nerves.

Be prepared. Approach the tire shop the right way. Try to get them interested in the car and point out that you are bringing it to them because it's going to be very delicate work and you just don't trust anyone else in town to do it. Politely ask if they have a guy who has experience with old cars. You might even say your cousin who has a shop in Arizona suggested asking. They may not have an old car guy on staff, but you're more likely to get the guy who's been out on parole the longest. Hang around and watch what they do. Don't look angry while doing it - just interested. They may not like it but they're not going to loosen the cam and let your wheel grind off the balancer before it's done turning while you're watching. And be very hesitant about letting them actually mount the wheels back on the car.

Dodge/Chrysler has long liked to play with safety features. One of those on my car is that the lug bolts (yes, bolts instead of nuts) tighten accordingly with the directional spin of the wheel. That means that on the passenger side of the car the lug bolts follow the "Lefty: Loosey; Righty: Tighty" Rule, but on the driver's side it's just the opposite - "Righty: Loosey; Lefty: you just broke my lug bolt." If your car is equipped with something like this you need to let the tire shop guys know. They will put that air ratchet on there and go to town trying to get your lug bolt loosened... BWAT-tah, BWAT-tah, BWAT-tah, BWAT-tah... even after the head pops off.

The most common violation perpetrated by tire jockeys is not using specified torques. Every car comes out of the factory with a recommended torque for the wheels. Too much toque can cause damage to lugs and even warp disk brake rotors. Tire shops are equipped with torque sticks - extensions that go on the air gun to prevent going over various torques. These are color coded to match a graph. All of these things can be found above the tire mounting machine and under at least six months of dust and cobwebs. Know your torque specs and make sure they follow them. Or better yet, do like I did and take the wheels in, have the tires mounted, and bring the wheels back home to mount yourself with a torque wrench. It's much more convenient than searching for 64-year old lug bolts.

Finally, save those old tires and tubes! There's really nothing more convenient around the cheap man's shop than a nice old inner tube. Good for a million uses. Insulating electrical components, makeshift gaskets in a pinch, securing small parcels or unruly kids, or sealing the speedometer cable fitting on your transmission while you're waiting for your new cable and housing to come in from Tennessee. And those old bias-ply tires? Well, I hear they make great photo props.