PSI: why?

January 20, 2012

Imagine the scene. You’re 90 miles into a 100-mile ride. Your stomach feels like it’s trying to tear through its fleshy confines in a bid to find sustenance. Then you see a fellow peddler in the distance. Slowly, you reach him and explain your plight. “Please, I’m desperate. Do you have something, anything I could eat?”

The stranger smiles. “Yes, my friend. Yes, I do have food to spare. In fact, I have 130 grams of energy bar, of which you may have half. So rejoice, for you shall now be fed.”

This, of course, would never happen. Not even the most number-obsessed cyclist would ever use grams to convey the amount of food they are carrying in their back pocket. Our fictional food supplier would say he had two bars, not 130g, even if he somehow knew the person he was talking to was also aware that energy bars typically weigh 65g.

So why, then, do we use PSI? Like sticky, packaged clumps of carbohydrate-based fuel, the pressure inside your tyres can also be measured in bars: six bar for wet weather, eight for dry or fast conditions, seven for hedging your bets. Yet typically, you’re more likely to hear fellow cyclepeople talk about PSI, the overly-precise alternative to bar.

PSI is more exact, but uselessly so: looking at the pressure gauge on my pump, I can see that the difference for 80, 100 and 120 PSI (the equivalent of six, seven and eight bar) is no less than six PSI and no greater than two. You would never notice the difference.

And as well as sounding more dweeby, “120 PSI” takes longer to say than “eight bar”. It is, quite literally, a waste of time.

Maybe the nature of the task it relates to has something to do with PSI being the more popular unit of measurement. Inflating tyres is a dull, mechanical process, and bar is a dull, mechanical-sounding word. PSI sounds clever and scientific, as if your tyres are another fancy gadget to play with, like a powermeter or GPS device. You’re pumping your tyres when you’re using bar, but with PSI you’re, er, uploading air. That’s the least dumb theory I can come up with, anyway.

One incident has given me hope that bar can make a resurgence. Somewhat behind schedule, I punctured on the way to the Hillingdon winter series a couple of weeks ago and was frantically removing the inner tube on my rear wheel when a red Mini pulled up. The door opens, and out comes a fellow Dynamo brandishing a track pump. He has one question: “Eight bar?” A short time later I’m riding again, and I make it to the signing-in desk with minutes to spare. So thank you, bar-loving ‘Mo: unlike the gram-obsessed cyclist I used for illustrative purposes, you actually exist.

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