Tyre blow out. Cause?

z0mb13e

Esteemed Pedelecer
Jul 28, 2009
578
3
Dorset
Hi All,

I had a rear tyre blow out on my Wisper 905 Se Sport a couple of days ago. This is the original Kenda tyre with a little over 200 miles use from just under 4 weeks riding.

They were at 60psi on Sunday.

On my way to work I noticed the rear wheel felt a little unbalanced but couldn't see any distortion in the tyre or wheel. I thought at the time that maybe the slime had pooled in one spot. On my way home I experienced a sudden change in the rear tyre. I noticed a hard bumping as I was riding followed quickly by a loud pop and a thankfully, rather controlled deflation of the tyre, giving me just enough time to stop.

On inspection the tyre is frayed along a section at the wire bead, with a small hole (in the picture the pen is to show the hole). Anyone know what might have caused this?

Also while I am now looking for a new tyre, I see that most people recommend the Schwalbe Marathon Plus. I take it that replacing a 26 x 1.95 with a 26 x 1.75 tyre is ok? Or should I be looking at 26 x 2? I wasn't sure if this is a significant issue on ebikes. I have never given it much thought on previous bikes - I just fitted what was available or affordable.

 
Last edited:

flecc

Member
Oct 25, 2006
50,464
28,351
I've seen this many times and it's usually the sort of blowout that results from carcase casing damage at the beading following bumping over a kerb, pothole edge or a sudden large object in the road, often entirely accidental. In those circumstances the tyre edge gets pinched between the hard edge of the object and that of the rim. On rare occasions it can be a manufacturing fault in the carcase weave.

Either 1.75" or 2" is ok for the MP tyre, choose on your comfort preference. Because of their thick inner protective layer, the MP tyres are rather stiffer than standard ones so the 1.75" can be felt as less absorbent of bumps than the Kenda to a greater degree than you might expect.
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Mussels

Esteemed Pedelecer
Jun 17, 2008
3,207
8
Crowborough
I've had the exact same thing happen 3 times with Kenda tyres, the last 2 I spotted just before complete failure and I gave them back to Wisper recently to show the problem. I've not had it happen with any other tyres, the Kenda ones just seem rubbish and always fail like that if I have them on the back wheel.
 

z0mb13e

Esteemed Pedelecer
Jul 28, 2009
578
3
Dorset
I hadn't hit anything other than the usual bumps in the road that I ride everyday.

I will admit to having jumped a few kerbs to avoid cars but not recently and I can usually clear the kerb rather than bumping the tyre. The fact that it was ok when I put the bike away and was a bit 'lumpy' the following morning makes me wonder if it was a manufacturing issue. Tough one to call.

If tyre size isn't an issue then I will give the Marathon Plus 26 x 1.75 a go as I can get them locally.

Is there a tyre with a thicker or stronger side wall? I am amazed at how thin bike tyre sidewalls are these days...

Cheers for the advice.
 

Howard

Pedelecer
Jul 8, 2008
73
0
Hi z0mb13e
I've had almost exactly the same problem as you with the Kenda tyres on my Wisper - the following link is for my post at the time:

http://www.pedelecs.co.uk/forum/electric-bicycles/3659-done-first-time-but-2.html#post47922

I was a bit fed up at the time! The bike was 4 months old, and had done 400 miles. I replaced both tyres with 'Continental Contact Security 08' (26x1.75)and have had no punctures at all since then. The cheapest price I found at the time was 15.95 each: (Continental Contact Security

Others recommend the Schwalbe Marathon Plus tyres, but they are a bit more expensive.

Hope that helps - get those tyres changed!

Cheers,

Howard
 

Wisper Bikes

Trade Member
Apr 11, 2007
5,978
1,952
67
Sevenoaks Kent
Kenda

I will be meeting Kenda in October and discussing this problem, it does not seem to happen on the majority of the bikes but we need to sort it out.

I will report back.

Regards David
 

Straylight

Esteemed Pedelecer
Jan 31, 2009
650
2
In the interests of balance (pardon the pun), I've done 1500 miles on the original set of kenda tyres, and had no punctures whatsoever. Wether this makes me lucky, or you guys unlucky, is a subject for conjecture, or maybe David has some hard data about the number of bikes sold vs complaints about the tyres.
 

flecc

Member
Oct 25, 2006
50,464
28,351
I too rode Kenda for well over a year and a couple of thousand miles on two bikes, all without trouble and believe it or not, no punctures!

Maybe they've hit a bad batch. I remember many years ago when Dunlop made an ill advised switch to Egyptian cotton which led to numerous carcase failures, cost them dear in free replacements and lost them their place at the top of the market which they never regained.
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z0mb13e

Esteemed Pedelecer
Jul 28, 2009
578
3
Dorset
I had high hopes for the Kendas as they were the first set of puncture resistant bike tyres I have ever had (except for the solid rubber tyres I had on my first bike in the 70's). However, I don't think the side wall giving out is any refection on their puncture resistance. Just one of those things. There may be a direct cause, there may not. It's hard to say.

Indeed I am sure there are many more happy riders who don't give their puncture free Kendas a second thought and concequently don't post on the forums.

I have a pair of Continental Contacts on my old bike and loved them as they roll easy on the road and are pretty grippy in the wet, but I did get a few punctures even with slime. Might be worth trying again what with the 'Security 08' bit bringing puncture resistance.

Hmm choices choices...

Right - popped to local bike shop - am picking up a Marathon Plus on my way home. Will get a spare when pay day rolls around and may even get a pair of the Continentals to keep as spares (shop didn't have any of the Travel Contact Security 08's).
 

z0mb13e

Esteemed Pedelecer
Jul 28, 2009
578
3
Dorset
On a reasonably related note, what do people reccomend for inner tubes?
 

Mussels

Esteemed Pedelecer
Jun 17, 2008
3,207
8
Crowborough
In the interests of balance (pardon the pun), I've done 1500 miles on the original set of kenda tyres, and had no punctures whatsoever. Wether this makes me lucky, or you guys unlucky, is a subject for conjecture, or maybe David has some hard data about the number of bikes sold vs complaints about the tyres.
I doubt he hears about many of the failures, mine would never have come to light as the retailer just brushed off the premature (1 week) failure saying tyres are not covered by the warranty.
 

z0mb13e

Esteemed Pedelecer
Jul 28, 2009
578
3
Dorset
Right Maraton Plus fitted - surprisingly easy to do considering the extra bits and bobs that make the magic happen.

Was paying attention to my route to work this am and there are plenty of lumps, bumps and cracks in the roads, drain covers that have sunk etc all of which may have taken their toll.

The thickness of the sidewall on the Marathon Plus gives me confidence that this will last a bit longer.

I wasn't aware of the need for long stem valves when I purchased an inner tube but it doesn't seem to have been a problem. Will be interesting to see if the rim cuts into the valve. Will get a couple of the Continentals for spares.
 

Mussels

Esteemed Pedelecer
Jun 17, 2008
3,207
8
Crowborough
The thickness of the sidewall on the Marathon Plus gives me confidence that this will last a bit longer.
It's not the thickness that's the problem, if you look closely at your tyre you'll see what looks like stitching holding the tyre to the bead and this is the bit that failed causing the rubber to split.
 

z0mb13e

Esteemed Pedelecer
Jul 28, 2009
578
3
Dorset
The material substrate was exposed along a section on the Kenda (but not all the way round - about 12" long on one side and showing signs of wear on the other). Having had a chance to give it some more thought, it looks like it was wearing where the sidewall contacts or wraps around the rim as a natural function of the tyres deformation under load.

The sidewall on the Marathon Plus is thicker than on the Kenda. In this situation I would expect the thicker sidewall could take more wear before it weakens to the point of failure.
 

Extra Cold

Finding my (electric) wheels
May 20, 2009
19
0
I had a strange thing happen last night. I checked the pressures in the morning and they were bang on 65 front and rear. I rode for 25 miles and put the bike to bed. About an hour later there was a loud bang and the bike fell over. There was nothing visibly wrong with the tyre, but the actual inntertube had a hole in it, large enough to stick my thumb through. I was just glad it didn't happen on the ride home!:(

Obviously I need to be more careful of pressures in future, but I'm sure someone on here said they regularly inflated there Wisper 905 Sport tyres to 65psi?
 

z0mb13e

Esteemed Pedelecer
Jul 28, 2009
578
3
Dorset
That is weird - mind you given the stress the tyres and tubes must be under with 60psi+ it shouldn't be a surprise when they occasionally do give out.

I'm sure I read that as well (running the Whisper tyres to 65psi). The Marathon plus says 75psi max, so am running it at 65psi for now...
 

Fecn

Esteemed Pedelecer
Sep 28, 2008
491
2
Warlingham, Surrey
I had a strange thing happen last night. I checked the pressures in the morning and they were bang on 65 front and rear. I rode for 25 miles and put the bike to bed. About an hour later there was a loud bang and the bike fell over. There was nothing visibly wrong with the tyre, but the actual inntertube had a hole in it, large enough to stick my thumb through. I was just glad it didn't happen on the ride home!:(
That sounds like the inner tube got pinched between the tire wall and the rim. I've blown up an inner tube that way before after repairing a puncture. Tire was reinflated and back on the bike for about 5 mins, and just before we were about to set off... Bang... Hole the size of my thumb in the inner tube.
 

flecc

Member
Oct 25, 2006
50,464
28,351
I had a strange thing happen last night. I checked the pressures in the morning and they were bang on 65 front and rear. I rode for 25 miles and put the bike to bed. About an hour later there was a loud bang and the bike fell over. There was nothing visibly wrong with the tyre, but the actual inntertube had a hole in it, large enough to stick my thumb through.
That's not completely unknown. It happens when a part of the innertube is pinched under the tyre bead so that a small part of it is outside the tyre wall and between it and the rim wall. After the tyres are pumped, the pressurised air can slowly seep under the beading into the outer small portion, and as that swells like a bubble beyond the rim wall, it will eventually burst as it's unsupported by the tyre carcase.
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Mussels

Esteemed Pedelecer
Jun 17, 2008
3,207
8
Crowborough
The same type of puncture can happen if the rim tape is badly seated or weak but this time the hole appears on the inside of the tube where air escaped through a spoke hole.