do tyres most commonly wear out or fail in another way?

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andrew_s
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Re: do tyres most commonly wear out or fail in another way?

Postby andrew_s » 22 Oct 2017, 10:25pm

Brucey wrote:yes it makes sense but the tyre within the contact patch is also strained differently (much more) in the case of the narrower tyre. I think this is perhaps an important and not well-understood effect.

If both tyres are run at pressures that give 15% drop, is not the change in tyre shape at the contact patch the same?

MikeF
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Re: do tyres most commonly wear out or fail in another way?

Postby MikeF » 22 Oct 2017, 11:16pm

andrew_s wrote:
Brucey wrote:yes it makes sense but the tyre within the contact patch is also strained differently (much more) in the case of the narrower tyre. I think this is perhaps an important and not well-understood effect.

If both tyres are run at pressures that give 15% drop, is not the change in tyre shape at the contact patch the same?
Surely the narrower tyre will have a longer contact patch than a wider one? Pressure is force per area. The force is a fixed value.
"It takes a genius to spot the obvious" - my old physics master

Brucey
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Re: do tyres most commonly wear out or fail in another way?

Postby Brucey » 23 Oct 2017, 12:26am

andrew_s wrote:
Brucey wrote:yes it makes sense but the tyre within the contact patch is also strained differently (much more) in the case of the narrower tyre. I think this is perhaps an important and not well-understood effect.

If both tyres are run at pressures that give 15% drop, is not the change in tyre shape at the contact patch the same?


the tyre is squashed flat against the road; if the tyre is a larger section the strain in the deformed part of the tyre carcass is less than if it is a narrower section tyre.

For example if a 25mm tyre is partly squashed flat, the outer surface of a 2.5mm thickness tread must deform by at least 10%. If it started out as a 35mm tyre with a similar tread thickness, then it will deform by more like 7% when it is squashed flat against the road.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

amediasatex
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Location: Sunny Devon! just East of the Moor

Re: do tyres most commonly wear out or fail in another way?

Postby amediasatex » 1 Nov 2017, 8:41pm

An example being Panaracer Pasela skinwall tyres, the pair on my town bike are about 18months old, probably only done ~3000 miles as it's a short trip bike, and there is little in the way of appreciable tread wear but I'm contemplating replacing the rear at least. The sidewall has the tell-tale hatching and is visibly distressed, they have some life in them yet but the carcass is obviously damaged.


^ I said that on page one...seems I was overly optimistic about how long that rear one would last as it started to split on the way home tonight :-( Felt a bit 'lumpy' and when I stopped to check found this:

Image

Brucey
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Re: do tyres most commonly wear out or fail in another way?

Postby Brucey » 1 Nov 2017, 9:47pm

amediasatex wrote: ....^ I said that on page one...seems I was overly optimistic about how long that rear one would last as it started to split on the way home tonight :-( Felt a bit 'lumpy' and when I stopped to check found this:


ooh blimey.... :shock: that is not good...

It almost looks as if the carcass has been subject to a chemical attack/degradation of some kind.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

amediasatex
Posts: 236
Joined: 2 Nov 2015, 12:51pm
Location: Sunny Devon! just East of the Moor

Re: do tyres most commonly wear out or fail in another way?

Postby amediasatex » 1 Nov 2017, 10:18pm

The only thing it's had on it is road spray (I've not ever even cleaned it) so possible it's picked something unpleasant up, it definitely appears to have degraded more in some places, but it has had a hard life in terms of load too. Hey ho, at least I noticed it feeling funny before it went properly :-)