Steel Rims and Tire Pressure

With a vintage road bike, sometimes things don’t work as well as they would on a modern bike. Either modern parts don’t work right or don’t match at all. One example is the steel rim.

Tires are probably one of the biggest issues the Pinnacle has. If you’ve kept updated on my Pinnacle series (which has primarily taken over my blog recently), most updates include something about the tires.

Tires themselves aren’t complicated. Although they come in many different shapes and sizes, they’re all fairly simple. When you think of it, a tire is constructed like a sports ball: a rubber balloon (“bladder”) inside, a structure, and rubber on the outside that actually makes contact with the ground.

But with older bikes, it can be a challenge to get tires to work properly. Many older bikes – including the Pinnacle – have the so-called “steel rim.” This type of rim is loathed by everyone, and lacks a hook that most modern tires require to stay mounted on the rim.

“Blowout After Blowout”

For the first couple years of owning the Pinnacle, I had very few problems with the tires. They did what they were supposed to do – hold air and provide a smooth ride and some traction.

The tires that came with the Pinnacle when I bought it were the original “Golden Boy” pair from 1981 – which is what it would’ve came with from the factory. They even had the original tubes. The front tire didn’t even last a week before being replaced due to a puncture, but the rear casing held on much longer (although with a new tube.) The original tires required 70 PSI on the front, and 75 PSI on the rear.

It wasn’t until after the rear original Golden Boy tire wore down that I started having problem after problem with the bike. The bike shop owner installed a Cheng Shin Tire on the rear that was rated for 90 PSI, but there was a problem.

When I pumped up the tire to the recommended 90 PSI, I wouldn’t get far before an ear-piercing “BANG!” came from the tire. The first time I thought it was a gunshot, before the bike wasn’t able to move. I was going up a hill when it blew, and a kid riding a scooter below me on the hill stared at me with a worried look.

We replaced the tire casing multiple times. But each time, the same result: tire pops off rim, and tube ruptures with a “BANG!”

It wasn’t until I dug into the internet that I found the culprit. The rims on the old bike weren’t “compatible” with modern tires that require a “hook bead.” In essence, modern tires have a molded hook to “lock” the tire casing into the rim.

My bike doesn’t have a rim for the tire to lock into. Therefore, the tire isn’t secured to anything and eventually pushes itself off the rim before BANG!

Sheldon Brown has a great quote on his 27 inch page:


Traditional 630 mm (27 inch) rims were straight side design, but in the late ’70s they evolved to a “hook edge” design which would permit the use of higher pressures.These days, many 630 mm (27 inch) tires are marked “For hook edge rims only” (some companies use the term “crochet type” instead of “hook edge”…this is the result of poor translation.)


The fact is that modern 630 mm (27 inch) tires will work on older straight-side rims, but they won’t handle as much pressure as they are capable of with hook edge rims.


Generally, the “rule of thumb” for traditional 630 mm (27 inch) tires is that they should be inflated to 70-75 psi. This shouldn’t be a problem with any tire, despite whatever disclaimer the manufacturer puts on the sidewall. However, if you’re restricted to this pressure range, you probably shouldn’t be running tires narrower than 1 1/8, or preferably 1 1/4, unless you’re a very lightweight rider.

Sheldon Brown

Solutions?

There are some work around’s that I’ve discovered in making it work.

  • Inflate to lower pressure
  • Get a tire with lower recommended pressure
  • Replace the rim with new rims
  • Ride on the original tires and hope they last forever
  • Replace the entire bike

I chose option A. But lowering your tire pressure can come with some other nasty consequences that can equally blow tubes, damage tires, damage rims, or trash your bike. (See the next heading.)

Option B isn’t always an option. After finding the culprit, I scoured the internet trying to find a suitable tire that had a reasonable tire pressure. It can be hit and miss. Both of the tires that I currently run on the Pinnacle are actually suitable. The front, a Bell Kevlar which you can pick up from your local Walmart, has a large pressure range that goes as low as 40 PSI and as high as 90. The rear tire, a Vittoria Zaffiro, has a smaller range but ends at 70 PSI on the high end. But the CST tires that the bike shop originally installed had a recommended range from 70-90. (Being a heavier rider, I need to go at the higher end of the scale.)

Option C is simple, or at least you think. Just replace the old rims with new rims. Easy as pie! But not as cheap as a piece of pie. New rims are costly – and, in the case of the Pinnacle, can cost more than the bike itself or the cost of a replacement. If you have a strong sentimental attachment to the bike and insist on keeping it on the road forever, I guess this is the best option.

Option D isn’t likely. The rear Golden Boy tire lasted a couple years of regular riding before it finally disintegrated into almost nothing but parts of the sidewall and the nylon cords. I’m lucky there weren’t “goose eggs” on the tire.

Option E is actually probably the most cost effective in the long run. Just replace the bike. If you’re like me, this can be hard to do. These vintage road bikes have a special character to them and stand out, while new bikes look like every other one. Plus their drive trains are more reliable, and even the low end models like the Pinnacle were well put together. If you’re attached to the bike but was able to replace it, you can still use it as “decoration” and a backup. That’s my plan, at least for the Pinnacle after it gets replaced.

Option F wasn’t listed – but you could keep blowing tubes. You could drain your paychecks on tubes, and make the tire manufacturers and rubber companies in China very happy.

The Right Pressure

I’m a pretty heavy rider, weighing in at 330 pounds. While inflating my tires to 60-65 PSI worked well, it didn’t provide very good cushioning, and the rear tire was still underinflated. And with fall coming on, the tire pressure can drop quickly over just a couple of hours. Time to experiment.

I took a considerable risk and actually slightly overinflated my rear tire today. The Zaffiro has a rated maximum at 70 PSI, but I decided to try 75 PSI in it. So it’s overinflated by 7%. In the past it was inflated to 65 PSI, and then I tried 70 PSI and found it had just a marginal improvement.

The rear tire inflated to 75 PSI…

After inflating it to 75 PSI, there was no bang. Even after riding it a short distance, the tire stayed on and didn’t show signs of wanting to pop off and ruin my day by leaving me out of a bike, and leave my ears ringing for the next week.

Then the front tire. Bell must’ve thrown their hands in the air when coming up with the recommended pressure range on my tire, as it has quite a wide range from 40 all the way to 90 PSI. 70 PSI is in the middle, so I inflated it from 60 to 70 PSI. As with the rear, no surprise explosions of bulges.

Front at 70 PSI…

Beyond just adding 10 PSI to each tire, the tires are actually inflated to what the original Golden Boys recommended. 70 in the front, 75 in the rear. It worked quite well on the GBs. Plus, Sheldon Brown recommends the 70/75 mix, and he’s not alone if my memory is working right.

Another nice thing about the pressure increase is it no longer looks as if the tires are underinflated when I hop on.

Concerns

In my bike tires 101 page, I addressed both the pros and cons of running tires that are underinflated and overinflated.

In essence, underinflated tires leave you at a risk of getting all kinds of fun types of flats. Snakebite flats, pinch flats, valve separation flats, just to name a few. Plus, underinflated tires can royally mess up your rim by causing impact spots, broken spokes, or can straight up taco your rim.

On the other side of the spectrum, overinflated tires are just as risky. Have you ever heard a close gunshot or explosion and had your ears ring for a week afterwards? If so, overinflating a tire is a good way to recreate that. Like a balloon, the tire can only take so much before something gives up. Usually that results in a loud BANG! that ruins your tube, sometimes your tire, your day, and your hearing for the next week.

Overinflated tires carry other caveats. There’s little cushioning – you can feel every bump in the road. Overinflated tires offer less puncture resistance, and typically tend to fail more catastrophically than an underinflated tire.

By inflating the tires to 70/75 PSI, I’m not worried about whether or not the rims can handle it. Because with the original 1981 tires, the rims did their job great. But my concern lies on whether or not the rear Zaffiro tire can handle it, especially with the original 70 PSI limit and the concerning “MOUNT ONLY ON HOOKED RIM” notice.

The Zaffiro’s “MOUNT ONLY ON HOOKED RIM” notice.

Time will tell if the Zaffiro and the Pinnacle can handle it. So far, things are good. But tomorrow will be a true test, complete with bumps, potholes, and other objects that the Pinnacle has handled fine so far.

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