Stumped by my five year old.
I was buying new tires for my car last week and my daughter started running her hands over the display tires. She noticed the tiny little “fingers” that protrude from the surface of the tire and asked me what they were for.
The best I could come up with was that they were there to let buyers know that the tires really were new and not used. Anyone in the know on this burning question?
I always thought it was the left over rubber from where the molten rubber is injected into a mould. I’m not an expert on tyres, however, and I have no real idea how they are made.
I always thought the same as +MDI said.
You are both right. Injection molding.
Since the OP may not know why injection molding leaves the little hairs:
When pouring something into a mold, the air has to go somewhere. In this case, you put a lot of tiny little holes in the mold for the air to escape. When the rubber is forced into the mold, the rubber forces the air out thru the holes and then a little rubber then follows into the holes. The rubber in the holes are the hairs.
For some things made with injection molding, there is a followup step of removing the extra bits and smoothing the product. For tires, no one cares so it isn’t done.
I bought a couple new tires a few months ago and noticed the cillia. I figured, like the above posts, that they were the injection molding gates, but I had never seen them before. Are tire makers not bothering to buff them off any more, or has there been a change in the way tires are molded?
DD
My father working a tire factory when he was goign to school in late 60’s early 70’s. They use to shave the cillia off of the tire as the last step in production. Now I belive they are now just left on the tire to prove its new as others have suggested.
Fans of Sniglets may recall that the term for these is “tire quills.” Although, “rubber cillia” is pretty cool in its own right.
[ nitpick ]
Unless injection molding is significantly different than casting, the cilia are vents, not gates. The gate is the point at which the material to be formed enters the mold. The vents are the more numerous and tinier locations where the trapped air escapes.
[ /nitpick ]
Thanks for the replies. I had figured that the “cilia” were some byproduct of the manufacturing process, but wondered why they weren’t shaved off before the tires reached the customer. It looks like my WAG was correct.
I can once again look my daughter in the eye and claim that “Daddy knows everything”.
Not that it’s true, mind you. But she doesn’t know that. 
I agree that they are byproducts of manufacture, but I think we’re not giving the OP enough credit. Those quills or cilia would be trivial to remove, and would be removed, like the “flash” from all but the cheapest plastic injection-molded products, if the public didn’t like them.
I think there’s real truth in the OPs quick guess. I think the public associates them with new (vs. used) tires, and likes/expects them. This may be the real reason they exist for more than the 60 seconds it’d take to trim them. After all, other production byproducts/ marks are removed at the factory. Tires aren’t shipped straight from the mold; there’s an appreciable amount of post-production prep, including the much more tedious trimming of flash from the lettering. I wouldn’t be surprised if the quills were deliberately preserved by the factory.
As a teenager in the 80s, I noted that the pricer retreads had them, along with more careful flash and surface treatemnt than the low end tires from the same manufacturer (my experience was limited, though; it could have been just that one manufacturer] Certainly gluing them onto used, tires would be prohibitive
Good work tomndeb! Keep fighting munchkin consumerist ignorance! Maybe the next generation won’t suffer $4 take-out coffee. (Until, of course, inflation leads to pinball machines that take $5 coins)
:smack: You’re right. Been years since I’ve exercised the synapses associated with casting/molding and I got them backwards. Those cillia would be awfully tiny for injecting a tire’s worth of rubber into the mold.
DD