Blowout!!

[MikewsMITH2]

My wife and I set off for a short trip to the beach this evening for a firework display. I pumped up the tyres of our trusty vintage tandem as usual to the recommended 100PSI. At the end of the road the front tyre blew off the rim with a loud bang and put a 6 inch tear in the tube. We walked back home fitted a new tube, inflated it to 80 psi and set off again. This time we got just a little bit further and again the tyre came off the rim. This time I was quick enough to open the valve and avoid bursting another tube. I refitted the tyre and inflated it to 60 psi, using the mini pump we carry and it has been OK for the trip.

The tyre is a Marathon 700x32C steel beaded and the rim is the original steel Rigida. The tyre and tube have been on and undistrubed for a year and have done a few hundred miles. What went wrong? Do modern tyres need modern hooked rims to withstand the pressure? Should we run at low pressures and risk pinch punctures? Should I change the rim? We have a Super Champion at the rear and this has been OK so far at 100PSI. I have tried unsuccesfully to find another Super Champion. What would be a good look-alike to fit?

[Velorum]

As you will see in the fist part of this thread a very similar thing happened to me last night.

viewtopic.php?f=15&t=27856

The Scwalbe Swift fitted to the front states max 65 psi. I had inflated to 90 psi.

When fitting another tube this afternoon I first double checked the rim for problems and all looked well. As I inflated past 65 psi I noticed that an area of tyre was beginning to bulge upwards away from the rim. Further inflation to 75psi caused the area of the tyre bead to pop off the rim. Thinking that the tube might be trapped under the edge of the tyre rim I deflated and jiggled things about to ensure that everything was OK. Upon inflation the same thing started to happen at about 80 psi. In the end inlfation to 65 psi seemed OK and I covered 14 miles this evening at this pressure without problem.

One thing I noticed is that the rim appears to have a slight flat spot in the region that the tyre popped off - perhaps damage from an earlier mishap prior to my ownership.

I have inflated tyres well above the max quoted in the tyre sidewall for over 30 years without a problem up until now. Indeed, the rear wheel of the same bike is running at 90 psi without a problem despite the max being stated as 65 psi. It is a new rim however........

[MikewsMITH2]

Has anyone else experienced this problem?

As an engineer, I'm not a great believer in co-incidence, so maybe there is an underlying problem with Schwalbe tyres and old rims. I always thought that the higher the pressure the tighter the tyre was held onto the rim and the first thing to go would be the rim! This tyre/rim combination had completed a 100K Audax in October plus several training rides beforehand and 3 or 4 rides of 20 miles since. However, I hadn't used my new Joe Blow track pump previously on this tyre (my Lidl one won't attain such high pressures).

So at least until I can find a new rim, I'll stick to 65PSI

I'm also not convinced of the quality of of some of this far eastern manufactured stuff. I fitted new tyres and tubes to my wife's bike last week Panaracer tyres and Nutrak tubes. On the front tyre the tube split at 80 psi. I examined it and it had split along a "seam" or moulding line. I took it back to the shop and they changed it without question. I fitted the new one and inflated it very slowly. This one let rip at 60PSI. This time I took the whole wheel to the shop and the mechanic examined the wheel and thought on area of the rim was "a bit rough". He sanded it down and fitted a different tube - no problems. This rim is 20 years old and had never punctured before, so I'm not convinced of his diagnosis. From now on I'm sticking to Continemtal "hand made in Germany" tubes (buy 2 get one free at Halfords).

[rjb]

I have had exactly the same thing happen to me. Again it was on a Tandem and the front tyre a Schwalbe Marathon suddenly popped off the rim for no apparent reason. The hooked rim had no obvious defect. This tyre had been on the front wheel for about 2 months and had covered approx 1000 miles without any problem. After this event I could never get it to stay on the rim again. No matter what I tried to do even building the seat up with tape it would not stay on the rim. Eventually I binned it. I will not be useing Schwalbe tyres again on the tandem and will stick to Conti's.

[gsdavies]

I had exactly this problem - Schwalbe Stelvio on an old steel Rigida Rim. I think the problem is that old style rims don't hold the tyres on as well. In the old days when I only had an ordinary handpump I could never get enough pressure for the tyre to pop off the rim. After getting a proper track pump, a Michelin World Tour blew off the rim at 60 psi and a brand new Stelvio did the same at about 70, ruining the tyre and tube into the bargain.

I've since got some modern rims and haven't looked back.

[reohn2]

I've been using Schwalbe Marathon tyres for a number of years (6 or 7) in 28mm, 32mm and 26inx40mm on solos and tandems,I've never had the problem you describe.Though my use has always been on modern rims.

[andrew_s]

What went wrong? Do modern tyres need modern hooked rims to withstand the pressure? Should we run at low pressures and risk pinch punctures? Should I change the rim?

Yes, modern tyres do require hooked rims, at least at pressures much above 60psi. It generally says so on the side.
Old non-hooked rims generally had a deeper well than modern box-section rims. This meant that you could make the tyres a tighter fit and still be able to fit them without too much difficulty.

[Velorum]

Ive returned to this thread following a most frutsrating couple of hours in the garage this afternoon.

A while back a family member wanted some advice regarding tyres for their 70's Raleigh. They were running Michelin 27x11/4 tyres but wanted something more puncture resistant. Seeing the Schwalbes on my Dawes they asked if I would fit a pair for them. They brought the bike round today along with a new set of 27" Marathons and Schwalbe inner tubes with presta valves.

I noted that their rims were alloy 'Birmalux' and they tyres were running at 85psi on the back and 65psi on the front.

I took the old stuff off, checked that the inside of the rims were smooth, fitted new rim tape and then the tubes and tyres.

Then the fun started.

At 80psi the front tube exploded! When I looked at it there was a split about 1/4 of the way round. On the premis that the tube may have been faulty I tried again - this time it blew out at 75psi.

As I was standing there scratching my head the rear tyre that I had inflated to 95psi suddenly exploded! Upon removal it was in the same condition as the front. My relative did not seem at all amused by this.

Now out of Schwalbes I retrieved some cheapo Halfords emergency tubes from the cupboard 700c/27" 38's. At least these didnt explode! However what they did do was force the tyres off the rim at 40psi!

Anyway, imagine my relatives joy at having to cycle away on her new tyres at 30psi.

I just cant figure this out.............

[MikewsMITH2]

What I found had happened is that the explosive blowout had deformed the rims over a 6 inch portion of the circumference, by pushing them outwards i.e. making them wider. This meant that the tyres would never stay on again. You can check this with vernier calipers. I corrected this by squeezing the rim back together with a large G cramp and 2 x 3" lengths of hardwood. This worked satisfactorily provided I kept pressure below 60 psi. I have since replaced the rim as I could no longer achieve smooth braking with the damaged rim.

[Velorum]

I am even more preplexed by this today.

She brought the bike round just after teatime saying that it was like riding through treacle due to the low pressures. I slowly added more pressure to both and got them up to 50 psi without mishap - I called it a day there though. The bike was then left standing for 30 minutes and nothing happened. Then a 3 mile ride and they were OK - holding pressure and staying on the rim.

I cant inderstand why they wouldnt stay on the rims yesterday at 40 psi but will do so today at 50. Perhaps I should try for 60 tomorrow...........

Any ideas on this folks?

[DaveP]

Well it is only a thought rather than anything based on years of experience -
During the 70's, the period when I first started cycling, I always found it rather tedious to have to centre the tyre on the rim so that it was equally deeply seated all way round. I eventually realised that simply pumping the tyre up would, like as not, result in a wheel that wavered from side to side when in motion.I ended up pumping to a lowish pressure at which I could move the tyre around by thumb pressure, then eased it down into the rim as far as I could, working all round the tyre. Pumping it up hard then (generally) resulted in an evenly seated tyre.
This sort of performance doesnt seem to be necessary with modern tyres and rims. I wonder if your friends tyres blowing off at 40psi resulted from fitting a modern tyre, which could conceivably be a loose fit by 70's standards, to an old rim without spending time to check the seating.
Not blowing off at 50 could be because the slower pumping allowed things to even themselves out, or more convincingly perhaps, you just achived better all round seating on your last attempt.

[Velorum]

An interesting point. My 80's vintage Weinman rims run high pressure 27" Marathons no bother - Im not familiar with the offending rims - perhaps they are poorer quality?

[MikewsMITH2]

I cant inderstand why they wouldnt stay on the rims yesterday at 40 psi but will do so today at 50

Yes once they are on they are on! They will probably be OK at 60PSI now, provided the rims haven't been damaged. I wouldn't go more than 60 on an old rim though.

I ended up pumping to a lowish pressure at which I could move the tyre around by thumb pressure, then eased it down into the rim as far as I could, working all round the tyre. Pumping it up hard then (generally) resulted in an evenly seated tyre.

I now have a procedure I follow.

1. Fit one edge of the tyre
2. put a couple of pumpfulls of air in the tube, lay the wheel flat and insert the tube evenly around the rim so the tube doesn't poke out anywhere
3. Fit the other edge of the tyre WITHOUT using levers. Wear gloves use your feet toestraps etc if necessary
4. Pump the tyre up a few more strokes of the pump and check that the tube isn't pinched anywhere between the rim and the tyre.
5. Inflate to 20 psi and check the tyre is centred on the rim. At this presuure you can manipulate the tyre so it is centred.
6. Inflate to 30 psi and check again
7. ride the bike up and down the street
8. Inflate to 60 psi and test again
9. Leave overnight
10. ride again and inflate to full working pressure.

You may think this is a bit of trouble, but I have found (3 times) that tyres come off a nd rims blow out 100 yards down the road and once overnight in my garage. Also a friend had a p***ture just before the tea shop, fixed it, spent an hour in the shop and the tyre went bang as he pushed his bike across the car park!

As well as old rims/new tyres, this blowout problems also seems to manifest itself with modern rims and "folding tyres" (this was my tea shop mate's problem). It is essential to make sure they are centred and the tube isn't pinched before going to full pressure. You should hear a satisfyijng "snap" as they seat

[Velorum]

Well, just back indoors from a few fun hours in the garage.

Determined to get to the bottom of this I asked her to bring the bike round again this evening.

I took the Marathons off her bike and fitted some Michelin World Tours from the spares cupboard. They held 90 psi no problem!

In order to be thorough I fitted both of the Marathons on a set of early 80's vintage Weinman rimed wheels. They were a bugger to get on but once in place held 100 psi no problem. No explosions, no lifting off the rims.

I think that the original Birmalux rims just arent compatable with modern high pressure tyres.

Anyway she is mobile again with decent pressure tyres as I have left the Michelins on her wheels.

[MikewsMITH2]

I think that the original Birmalux rims just arent compatable with modern high pressure tyres.

Yes this is the conclusion I reached too with steel Rigida rims, which is why |I have changed them.