Marathon tyre Bulging

[Andy in Germany]

I've just been asked:

have you had issues with Schwalbe Marathon Plus tyre sidewalls bulging. Mines done this from new and the bulge is getting bigger. Its as if there's no threads in the area with the bulge. No visible damage to the tyre to cause the issue.

Anyone have any thoughts?

 

[Racing roadkill]

I've just been asked:



Anyone have any thoughts?

They have very stiff side walls, if you give them too much grief ( take them off road for example ) the side walls can, and do fail. I’ve had one set let go like this, I don’t take them off road now.

 

[I like Skol]

Schwalbe tyres are sh1te! Used to be good, not anymore.

www.cyclechat.net/threads/schwalbe-quality.240874

 

[Yellow Saddle]

Tyres are prevented from expansion upon inflation by a weft of non-stretch cords that criss-cross the tyre from side to side, at a bias. The angle of the cords w.r.t. the plane of the wheel is very precisely set at 35 degrees. At this angle, the tyre cannot expand when more air is pumped into it. Instead, it slightly constricts the tyre on the rim, tightening it on the rim. In other words, these cords scissor-jack in such a way that the tyre's radius decreases with inflation. The angle is not 45 degrees as one would assume on casual expansion, because hoop stress is twice longitudinal stress in a pressurised tube. A tyre is just an endless tube.

Now, if one or two of the cords are broken, which happens easily if the tyre bottoms out on a rock, the hoop stress causes an outward bulge that does not extend longitudinally. In other words, bulges are always round, seldom oblong.

Bottom line, your tyre suffered some internal damage akin to breaking a rib.

Spare a thought for the way in which cords can be severed without rupturing the rubber. This is the same mechanism whereby a bull is castrated.

 

[I like Skol]

Good explanation from YS above, except the tyre in the OP was bulging from new and is getting worse. This points to faulty manufacturing, like the tyre i rejected because it was 3-4mm thicker in cross section at one point once inflated on the rim. The fact that it was exchanged without quibble does not make up for the fact that schwalbe now seem to be shipping substandard tyres with little in the way of QC.

 

[Yellow Saddle]

Good explanation from YS above, except the tyre in the OP was bulging from new and is getting worse. This points to faulty manufacturing, like the tyre i rejected because it was 3-4mm thicker in cross section at one point once inflated on the rim. The fact that it was exchanged without quibble does not make up for the fact that schwalbe now seem to be shipping substandard tyres with little in the way of QC.

Yes, new tyres can also have cord defects. It sort of makes sense, considering that these cords are fed from spools which must run out at some stage. Good QC would eliminate much of that, I suppose. Ironically, the more "puncture proof" the tyre is made, the bigger the effect of a broken cord has. This is because on puncture proof tyres the cords are thicker and there are fewer of them. One breaks and the effect is large. On tyres designed for low rolling resistance rather than puncture resistance, the cords are thinner and there are more of them. The TPI is higher. When one breaks, the bulge is smaller and the damage tolerable.

 

[Nigelnightmare]

The fact that it was exchanged without quibble does not make up for the fact that schwalbe now seem to be shipping substandard tyres with little in the way of QC.

Probably because it's working out cheaper to replace the faulty ones rather than doing the QC.
It's the same with Car manufacturers, if a fault is projected to cost more to "recall" they will just fix the ones that get reported.
I blame the "bean counters" (accountants). Either way it's the end user that loses out.

 

[Racing roadkill]

Probably because it's working out cheaper to replace the faulty ones rather than doing the QC.
It's the same with Car manufacturers, if a fault is projected to cost more to "recall" they will just fix the ones that get reported.
I blame the "bean counters" (accountants). Either way it's the end user that loses out.

Not quite. The tyres are batch controlled. Modern Q.A. systems are set up to optimise turn over, whilst still maintaining standards. Essentially, in a given batch size, there’s a requisite number of tyres that need to be checked. There are criteria set for ‘pass’ ‘alarm’ and ‘fail’ numbers. If the dodgy tyre comes from a ‘passed’ batch, they will use discretion, if it’s from an ‘alarm’ batch, they will probably replace without argument. ‘Fail’ batches shouldn’t make it out of the factory.

 

[Nigelnightmare]

I'm sure your right.
My point is that more of the FAIL batches are being relegated to ALARM status because the criteria has been altered.
For Example:
>1 in 100 failure = Fail. This batch of 1000 had 13 fail so should be "Fail", now put into "Alarm" because it's cheaper to replace the odd failure than it is to scrap the whole batch.
As a retired QC I was often pressured into changing the result category (it didn't work with me because I didn't want the job anyway).

 

[User6179]

Don't know how the marathons are made but the racier Schwalbe tyres are glued between sidewall and puncture protection band, they come apart here when the glue fails but the outer tread holds them together and you get a bulge, had this happen on about 6 tyres before I ditched them.

 

[Racing roadkill]

I'm sure your right.
My point is that more of the FAIL batches are being relegated to ALARM status because the criteria has been altered.
For Example:
>1 in 100 failure = Fail. This batch of 1000 had 13 fail so should be "Fail", now put into "Alarm" because it's cheaper to replace the odd failure than it is to scrap the whole batch.
As a retired QC I was often pressured into changing the result category (it didn't work with me because I didn't want the job anyway).

Quite right.