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

[hamster]

SIdewall damage or really big cuts seem to kill all mine before they are worn out - but I live in an area with flint being the main geology. Ligh racing tyres seem to last less than 2000 miles before a fatal cut. By fatal I mean completely through the tyre and more than around 6mm - enough to distort the tyre's outline.

[Brucey]

so is the provisional conclusion that -with variations in local conditions, rider tolerance of defects and randomness skewing the results- it is more likely that lightweight tyres are going to be cut badly enough to limit their life, but heavier duty tyres are (somewhat paradoxically, bearing in mind that they will usually have a longer wear life) more likely to wear out instead of being damaged?

If so, it seems reasonable to me.

I've mentioned this before but I carried out an experiment over the last few years in which I ran ostensibly 'the same tyre' in 25mm (front) and 36mm (32mm actual, rear) sizes on the same bike. The tyre pressures were set to be about the same, which resulted in about the same relative 'drop' because the loads were not the same. The net result was that the front tyre suffered flint damage and the rear didn't, the front suffered punctures and the rear didn't, the front suffered a large gash from a piece of glass, and the rear didn't, the front wore fairly quickly, and the rear didn't.

I can't say that this was exactly what I expected! -it is at odds with my prior experience of width-matched sets. It is possible that the rubber compound and/or the carcass wasn't really 'the same' after all, but even so to flip the usual pattern of behaviour almost on its head is quite a surprise.

cheers

[hamster]

Wow, that is an interesting finding. Usually it's rears that live nasty, brutish and short lives.

[LuckyLuke]

Hi, just wondering re the above. Have read that wider tyres are less likely to puncture than narrower ones, due to differences in tyre pressure. (Think it was in Bicycle Quarterly, or maybe on this forum?) The explanation being that a narrower tyre is typically pumped up to higher pressures to avoid pinch punctures, & these higher pressures push / force the glass / thorn / flint etc. into the tyre.
Brucey, do you think any tyre pressure differences could explain it? Or it's something else?
Best wishes, Luke

[Brucey]

well, in anticipation of exactly that conversation, I'd set the pressures in the tyres about the same. Admittedly they may have gone soft at slightly different rates, but pressures alone don't provide me with a convincing explanation.

One thing that I note is that the carcass in a narrow tyre strains more to flatten against the road, and I think this does make a difference to what happens to flints that start their way into the tyre tread.

cheers

[esuhl]

I use good quality Kenda tyres on my mountain bike. However, my riding style is very tame!

I've probably got through about 10 tyres, two sustaining damage to the side-wall. The other eight just "wore out". I've never noticed any inner threads... I replace them when I notice a loss of traction, and the knobbles in the centre of the tyre are (almost) completely worn down.

[gloomyandy]

I may have got this wrong but my understanding is that with the same pressure the contact patch will be roughly the same size for narrow and wide tyres. However they will be different shapes (long on the narrow, wide on the wide). Now in my mind this means that on the narrow tyre you will be "reusing" more of the tyre to provide the contact patch as the tyre rolls forward, while with the wider contact patch you will be using a different part of the tyre as the wheel rolls. This I think would account for why you wore the narrow one faster? This may in turn be why it was also more likely to puncture? Basically with a wider tyre you are spreading the wear rate over a larger area?

Does that make any sense?

[Brucey]

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.

cheers

[gloomyandy]

One thing I'm not really sure about is the construction of a wide v narrow tyre even of the same make/type. Are they actually the same in terms of depth of rubber on the contact area, or do wider tyres tends to have more rubber?

I've also wondered about tyre pressure variation and tyre width. I suspect that most people do not check pressures every time they ride, so a tyre will be ridden with a range of pressures over time. I wonder if riding a narrow tyre at a slightly "low" pressure has more impact on wear rate etc. than the corresponding impact on a wider tyre? I wonder what the typical pressure drop is over say a week on two different widths of tyre?

[PH]

I may have got this wrong but my understanding is that with the same pressure the contact patch will be roughly the same size for narrow and wide tyres.

I've read this several times too, but no one has explained why you'd run different widths at the same pressure?
I have 90psi in the rear 28mm on one bike, I can't imagine what that's be like (Nor do I want to) on the 38mm on another which has 60psi.

[Brucey]

I may have got this wrong but my understanding is that with the same pressure the contact patch will be roughly the same size for narrow and wide tyres.

I've read this several times too, but no one has explained why you'd run different widths at the same pressure?
.

because the loads are different.

cheers

[gloomyandy]

Well upthread Brucey described a situation in which he did just that. Basically a narrow front tyre and a wide rear, with more weight on the rear such that the "correct" pressure for both is actually the same. I can imagine that a touring bike with only rear load might be an example of that?

[PH]

I may have got this wrong but my understanding is that with the same pressure the contact patch will be roughly the same size for narrow and wide tyres.

I've read this several times too, but no one has explained why you'd run different widths at the same pressure?
.

because the loads are different.

cheers

But isn't the idea that different widths at the same pressure having the same contact patch dependant on the loads being the same?
Maybe what I should have asked was why would anyone run different widths at the same pressure in the same situation?

[Brucey]

Gloomyandy's point about contact patch shape kind of makes sense still in that the contact patches won't be the same shape even at the same pressure and different loads. Looking at the tyres and the width of the tracks they leave as they go through puddles on otherwise dry roads etc, it seems likely that the contact patches were similar widths, within a mm or two.

BTW almost every unladen bike has a rearwards weight bias. Unladen bikes usually pan out at somewhere between 30:70 and 40:60 weight distribution, F : R.

cheers

[meic]

I've read this several times too, but no one has explained why you'd run different widths at the same pressure?

The common claim for wider tyres is that they give lower rolling resistance at the same pressure.
Which is then restated as they give lower rolling resistance, if you want to take advantage of that lower rolling resistance you would run them at the same pressure (if your rims could stand it ).