Another tyre failure; caused by dirty bike?

[Brucey]

I've been happily using the same species of rear tyre (on my hack bike) for about the last twenty years on my hack bike. I had a small stash of nicely matured tyres, and yesterday I quite unexpectedly needed to use the last one I had left.

The previous rear tyre lasted (I think) at least 20000 miles; the rubber in it went hard so the tread stopped wearing/cutting up and because the carcass was nylon there was no rotting even though the rubber was terribly cracked. Eventually the tyre died because there was a tiny burr on the rim lip that eventually 'nibbled' its way through enough of the carcass that the tyre went out of shape.

Its replacement had done about eight or 10000 miles (I think) and ought to have a lot of life left in it yet (by my standards...). So imagine my surprise when I felt the familiar sensation (a little jiggle as the wheel goes round on a smooth road) of the tyre going out of shape yesterday.

Sure enough the tyre was starting to fail like the previous one had. I kicked myself; I thought I'd deburred the rim, but maybe I hadn't done the job well enough after all. Sure enough the rim lips felt rough where the tyre was failing. D'oh! Then I felt the rest of the rim and it was all like that.

I can only surmise that there had been enough dirt on the edge of the rim that it had been repeatedly squeezed between the rim and the tyre and that this had roughened the rim edge. I cleaned the rim with scotchbrite and this made it smooth again; the damage wasn't great.

However I am concerned that it will happen again; has anyone else had similar failures? FWIW the rear rim had a fair amount of road dirt on it, but not a huge amount. This bike gets left outside so it gets rinsed in the rain, but maybe there is enough chain lube mixed in with the dirt to make it slightly sticky?

cheers

[531colin]

Long ago I had something similar, rightly or wrongly I attributed it to salt corrosion making the rim edge like a file. Mine looked like an impression of the fabric of the tyre sidewall, it would have been a low thread count cheapie for the winter ride to work.

[mercalia]

Brucey clearly needs some inventory control system to replace the tyres as they are used, so he never gets to the point of only having none left? which year is the best vintage I wonder?

[foxyrider]

As someone who does far less bike cleaning and maintenance than ideal (ie none if i can get away with it), i have to say that i've never seen this phenomena. Could it be something specific to nylon cased tyres? After a few grip 'issues' i won't use them anymore but with those sorts of mileages mayhap they are worth another look!

[Jamesh]

Could it be that the tyre pressure was too low and the tyre wall is in contact with the rim edge.

At 80psi/25c I cannot see it happening?

Cheers James

[francovendee]

Never thought of it causing a failure but it's difficult to get all the grit out from inside the tyre before putting a repaired tube back in. I end up shaking the tyre in an attempt to get rid of the grit.
I've worried more about the damage to the tube and not the tyre. Interestingly I've never worn out a set of tyres, lots of tread left but the sidewalls split.

[hamster]

I've had it happen with MTB tyres - failure at the rim contact point. I initially put it down to brake pad contact but rechecked the pad run and realised that the side had worn through.

[Brucey]

Could it be that the tyre pressure was too low and the tyre wall is in contact with the rim edge.

At 80psi/25c I cannot see it happening?

To an extent it doesn't matter what pressure you are running your tyres at, there will always be some change in the angle between the tyre sidewall and the rim edge when the tyre is loaded. Differences arise in the extent of the angle change and the loading at that point. The tyre was nominally 35mm wide ( 32mm wide on my rim) and was normally pumped up to about 70 or 75psi, usually reinflated when it got noticeably soft (i.e. about 55psi in this case).

There is a chafer ply in most tyres to prevent such damage (sometimes exposed and sometimes not), and this can come out of place or fray away (contis used to do this) and I'd have to say that in both cases this may have been a factor; the rubber covering the chafer ply had weathered away and the chafer ply itself wasn't in great shape. I'll post photos of the tyre(s) when I get a chance. 'Bontrager select K' BTW, purchased about 20 years ago. Closest thing I had to this (overall) in my stash might have been a Zaffiro pro or the next model up (Rubino Pro?), but they are folding tyres and the select K are not.

I've seen the kind of marks Colin describes a few times and it seems much more likely to occur with a coarse carcass fabrics. In my case the rims edges were just rough, almost like they had been shot-blasted. I don't recall riding in unusual soil conditions recently, but the muck on the rims looks sandier than normal, so it is perhaps possible that the winter road grit they are using locally now contains something like sharp sand and this may be helping to cause the damage.

The annoying thing is that I bought these tyres cheap in a sale (with low expectations) and they have been the most reliable tyres I have ever used; I have had precisely zero punctures through the tread in any of them to date. However when I've tried other Select K tyres subsequently I have had punctures in them, even when running them as front tyres. Weird!

cheers

[Brucey]

BTW my theory is that in most tyres, the rubber perishes and then the carcass fabric can rot and the sidewall will split, if you don't wear them out first. If I buy tyres with softer rubber, I just wear them out, and I feel that they usually pick up flints very easily too, such that they will have a pretty good chance of defeating any puncture protection layer (that I'm likely to use, that is).

However if the carcass fabric is made of nylon then it seems to be pretty rot-resistant. I first decided to 'see what would happen' with cracked (nylon carcass) tyres on the rear of my town bike, on the basis that I'd not have far to walk if it did let go. No problems. Since then I've become almost blasé about such cracks in such tyres. However it does not, it seems, confer immunity to other tyres of damage!

cheers

[Jamesh]

Before I had a track pump I used to pump to "that's enough" which was about 50psi and so I got a line of wear around the rim as brucy describes.

Not sure if it's on the latest tyres but then they did do lejog without a track pump.

Cheers James

[Brucey]

the plot thickens; inspection of the tyre shows that the chafer ply was intact and doing its job, but the carcass had started to fail behind the chafer. There was a little dirt (not much) between the chafer ply and the rest of the tyre, but there had clearly been some action between the chafer and the rim itself, judging from the roughening of the rim and the mark on the chafer where the rim had borne against it. I've seen much worse marks on tyres than this though.

All rather mysterious; not sure quite what to make of it.

cheers