General Cycling Discussion - Why Are Some Bike Tires Unidirectional

I noticed while riding with someone today that his skewer was secured on the rightside of the wheel - I had never seen one anywhere but the left side. I mentioned to him that many (perhaps all - not sure - certainly the ones I use) bicycle tires are unidirectional, and if the wheel was mistakenly installed that way (it was that way when he picked it up from the LBS after a tuneup), perhaps he was running his tire in the wrong direction. I suggested that we stop and look.

I looked at my tire first to demonstrate the arrow indicating proper direction of rotation only to discover that when I had fixed a flat last week, apparently in my haste, I had installed my tire backwards. That brought up the interesting question as to why bicycle tires are unidirectional. I can understand many car tires being that way, because the tread is very specifically designed for that.

However, my Specialized Mondo S-Works tires are slicks - they don't even have cornering tread on the sides. Why would slick tires be unidirectional?

maybe they just use the same widewall moldings/printings across tire lines.

Slicks by nature cannot by unidirectional.

But for some traded tires, they can be, since the tread was made to perform a certain way in a certain direction. On the cheap end of tires, Kenda Klaws are like that...if the rear is backwards, it doesn't bite as well....if the front is backwards, you lose cornering grip. Given with the Klaw, as crappy as it is (I still have a pair in my closet), the difference isn't huge, but it is there.

I understand - that's why I am so puzzled by the directional arrows imprinted on the side of my slicks.

Maybe the weave in the casing has more fibers running one direction?
Does rubber have a grain?..I doubt, but the fibres will act like a grain when overlapped.

I think it's just them being asinine.

Look at audio cables on home stereo equipment, you often see direction arrows there as well. Often that has to do with shielding. However, you still see those blasted arrows on cables that don't use a foil shield, so the arrows are completely irrelevant. Note that I'm talking about the good cables, not the freebie ones that came with the CD player or $3 a pair types you find at kmart...I'm talking one with shielding and actually built around a proper design.

Follow the arrows and mount your tyres correctly otherwise when you pedal, you will end up going backwards! :D

Follow the arrows and mount your tyres correctly otherwise when you pedal, you will end up going backwards! :D

lol

Um, there's no direction to shielding on cables...... someone was sleeping through electromagnetics lectures.....

Some bike tires are unidirectional because bike companies think it looks cool, just like why they put a small amount of cosmetic tread on slicks. It serves no purpose except for the ultra knob tires.

I just noticed this yesterday, my City Slickers have a unidirection arrow while the knob tires they replaced have arrows pointing both ways.