Why does a snakebite flat produces only 2 cuts in the tire?

DDRider62

I know the question may sound silly, but please do not post nonsense or bad humor responses. The question is serious.

When a pinch flat happens, the tire compresses so much, that the rim cuts the tube, producing the snakebite. This happens, if I understand it correctly by the tremendous pressure of the rim against the tire. The pressure is so high that the tube is cut through the tire (the tube is never in direct contact with the edge of the rim, or else the tire would pop off the rim on a pinch flat. At the time when the pinch flat happens, the layers of tire parts are like this:



---V^^^^^^^V--- RIM EDGES (Edges marked as V's)
===== ======= TIRE (closest to rim)

---

Tube (surface closest to rim)
+++++++++++++++ AIR

---

Tube (surface closest to road)
============== Tire (closest to road)
RRRRRRRRRRRR ROAD

When I hit the pothole or obstacle with my bike, all these layers collapse in a very high pressure sandwich in such way that the AIR layer dissappears due to displacement, and the 2 rim edges exercise brutal pressure on the tube (through a layer of tire as I understand it), that it will cut the tube it in 2 places (The 2 V's I drew for the rim will cut the tube even though the rim is rounded in reality, not sharp), producing the commonly known snakebite.

Analyzing my rudimentary diagram it's apparent that the pressure is exercised in 4 places in the tube: 2 on the left side, and 2 on the right side. The outer part (closest to the road) and the inner part (closest to the rim). So, comes my question: Why is the snakebite only 2 cuts instead of 4? And also: Why does the snakebite cut happens on the tube section closest to the road and not the one closest to the rim, where you would expect the highest pressure to happen?

Please correct me if my diagram is not right. If you know of slow motion movies showing the anatomy of the pinch flat, I would love to see it.

I had an accident due to a pinch flat last August that sent me 5 days to the hospital, left me 3 months out of work and bad concussions. I am obssessed with understanding perfectly the nature of the pinch flat.

Thanks for your answers in advance, and again, please, don't post silly jokes as responses.

DDRider62

meanredspider

I don't know but my guess is that, given the extreme pressure, this is only likely to take place in one point unless your wheel was perfectly aligned to a perfectly square edge so that two points apply extreme pressure at exactly the same time. I can't see this happening very often.

cougie

Just focus on not hitting potholes or objects in the road would be my advice.

You dont need to understand the damage. You just need to avoid it.

lesfirth

meanredspider wrote:

I don't know but my guess is that, given the extreme pressure, this is only likely to take place in one point unless your wheel was perfectly aligned to a perfectly square edge so that two points apply extreme pressure at exactly the same time. I can't see this happening very often.

I think that just about sums it up.

I know you do not need to know but like DDrider62 I like to know why things happen and how things work.

sungod

if the sandwiched tube is cut across the 'edges', it will result in only two holes even though two layers of rubber have been penetrated at each cut

DDRider62

meanredspider wrote:

I don't know but my guess is that, given the extreme pressure, this is only likely to take place in one point unless your wheel was perfectly aligned to a perfectly square edge so that two points apply extreme pressure at exactly the same time. I can't see this happening very often.

But if you have seen a snake bite cut tube (and all the pictures I have seen online), the cuts are one on the left, and one on the right in the surface closest to the road (never the inner part of the tube closest to the rim). So the 2 cuts are (for what I can tell) really 2 cuts, and not the same cut through 2 layers of tube. What you say sounds logical but does not match the evidence shown in a snake bitten tube. Anyway, thanks for the response. I do appreciate the time and effort. Hopefully multiple contributions to the topic (like yours) will bring light to the issue.

butcher of bakersfield

Is the tube cut on the wire bead of the tyre? In my experience a pinch flat happens when the pressure is so low, and force so strong, that the tyre itself touches the rim, sandwiching the tube in between.

The exact physics of why you nearly always have two symmetrical holes I don't entirely understand, but in my mind they must be punctured by the wire bead on a clincher tyre, or by the rim. And I think I read somewhere that pinch flats do not happen on tubular tyres...

DDRider62 wrote:

But if you have seen a snake bite cut tube (and all the pictures I have seen online), the cuts are one on the left, and one on the right in the surface closest to the road (never the inner part of the tube closest to the rim).

In my experience they are always closest to the rim.