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?
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.
I don't peddle bikes.
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.
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:
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.... that is not good...
It almost looks as if the carcass has been subject to a chemical attack/degradation of some kind.
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
UPDATE- lost the front to the same thing this week, basically sidewall has given up the ghost, numerous small areas of damage resulting in attempted tube prolapse. Spotted it quicker this time as it was on the front and I noticed the small wobbles appear visually before I felt them.
Anyway, front now replaced as well, so will see if this pair last any longer or suffer the same fate over time. Oddly my smaller Paselas on 700c bikes never die in this way, so I'm pretty sure it's a result of the bigger tyres being run at lower pressures (more deformation), plus the additional loads of carrying weight (even more deformation!) and possibly more UV exposure that's causing this.
It’s rare that I ever get a tyre to wear out ( as in loss of rubber / tread ) before the bead fails, or the carcass gives out, resulting in a bulge that ends in a tube failure. I’ve had particular issues with a particular German brand of tyres.
I've had a tyre split (explosively) from the bead (my fault, I stored them next to the garage roller door which rubbed against the tyre) but mostly I've binned them because they had worn thin and become too susceptible to punctures.