Cycling UK Forum

Just suffered the second of these on tour, both rear wheel. Sudden BANG with no apparent immediate cause, tyre still on rim but bead detached from tyre.

First was on the old gatorskins the bike came with, second on a new (~500 miles) vittoria randonneur.

Photo of the second attached.

Never experienced anything like it before, the second suggests more than mere bad luck.

Ask advice and suggestions welcome.

It's a laden tandem.

If the bicycle has rim brakes then that is the classic result of brake blocks running too high and rubbing against the tyre. Check and adjust.

wjhall wrote: ↑1 May 2024, 4:28pm If the bicycle has rim brakes then that is the classic result of brake blocks running too high and rubbing against the tyre. Check and adjust.

Thanks, should have added, disc brakes. Though there is a residual Canti used as a parking brake, which is worth checking...

The tandem does not have rim brakes. See photographs in this thread - https://www.cyclechat.net/threads/the-b ... 943/page-2 and also note the OP's similar new thread in CycleChat - https://www.cyclechat.net/threads/tyre- ... st-7191443.

OP, front or rear, or both? The rims look different (deeper section front rim?). It might help to provide information and/or photographs of the rim in question.

What is the rim internal width, and what tyres and widths were they? (Were the tyres wider than recommended for the width, esp. given higher pressures for the extra weight of a tandem?)

I would check visually and by feel the interior surface of the rim where it touches the tyre sidewall.

you may have a wee bleb or plookie on the edge of the wheel rim; this will 'nibble' that part of any heavily laden tyre, unless it is smoothed off.

slowster wrote: ↑1 May 2024, 4:43pm The tandem does not have rim brakes. See photographs in this thread - https://www.cyclechat.net/threads/the-b ... 943/page-2 and also note the OP's similar new thread in CycleChat - https://www.cyclechat.net/threads/tyre- ... st-7191443.

OP, front or rear, or both? The rims look different (deeper section front rim?). It might help to provide information and/or photographs of the rim in question.

What is the rim internal width, and what tyres and widths were they? (Were the tyres wider than recommended for the width, esp. given higher pressures for the extra weight of a tandem?)

I would check visually and by feel the interior surface of the rim where it touches the tyre sidewall.

Thanks the rims front and rear are Ambrosio P20 V shape. 20mm internal I think.

The first tyre to blow was a gatorskin 32mm, the second a vittoria randonneur 28mm.

I believe 28mm is slightly narrower than recommended.

Both tyres were at, or very close to, recommended max pressure (I have a proper pressure gauge with me).

I am not familiar with tandems and what they require in terms of tyres and pressures, but:

- Vittoria max pressure for the Randonneur tyre is 75psi per this article - https://road.cc/content/review/vittoria ... yre-292225, which I would have thought made it unsuitable for the sort of weight expected on a loaded touring tandem,

- Recommended ranges of tyre widths for given rim widths here - https://www.schwalbe.com/en/technology- ... imensions/. For 20mm internal width, 28mm is close to the minimum recommended. For a tandem I would have thought it would be best to choose a tyre in the middle of the range or a bit wider, i.e. 40mm wide or more.

Brucey wrote: ↑1 May 2024, 4:53pm you may have a wee bleb or plookie on the edge of the wheel rim; this will 'nibble' that part of any heavily laden tyre, unless it is smoothed off.

Yes. I think I've seen one blowout in 40+ years riding nearly daily and it wasn't my bike. After two in quick succession, I'd be suspecting the bike and checking things like the rim very very closely.

slowster wrote: ↑1 May 2024, 5:45pm I am not familiar with tandems and what they require in terms of tyres and pressures, but:

- Vittoria max pressure for the Randonneur tyre is 75psi per this article - https://road.cc/content/review/vittoria ... yre-292225, which I would have thought made it unsuitable for the sort of weight expected on a loaded touring tandem,

- Recommended ranges of tyre widths for given rim widths here - https://www.schwalbe.com/en/technology- ... imensions/. For 20mm internal width, 28mm is close to the minimum recommended. For a tandem I would have thought it would be best to choose a tyre in the middle of the range or a bit wider, i.e. 40mm wide or more.

Thanks. The absolute max possible is 32 for clearance, and they're tight. Of course we've blown one of those too, so I'm not convinced wider would help.

Recent rim?

Jezrant wrote: ↑1 May 2024, 8:41pmRecent rim?

New to us but not recent, original build 2018.

Have you carefully checked the rim for a burr or some irregularity that might be causing this as Brucey suggested?

both same place on the rear wheel? (yes ,as above, a sharp protrusion on the inner of the rim.)

Looking at the photograph, it appears to me that the failure originated *within* the sidewall. There is a fairly continuous crack line on the outside of the sidewall, which extends a few cm either side of the tear (and runs a few mm above the tear). It looks to me as though the threads were progressively failing inside the sidewall, and without the strengthening reinforcement of the threads the tyre was then expanding and deforming outwards, which caused the cracking in the outside surface.

As per my post above, it appears that the tyre has a rather low maximum PSI (and a threadcount of 30 TPI), and I think that might mean that it would not be suitable for a fully laden tandem.

Touring bike with panniers?

It took several sidewall failures for me to track the issue down to riding with a solo pannier on the driveside which is where the sidewalls would fail. Took one tyre back to the shop and they diagnosed block rub as the cause but had to eat humble pie when I said I was running discs.