Overinflated my inner tube - exploded. Presta help!

[Custom24]

My first time with a Presta valve, new bike. Used to a Schrader on my MTB.
Don't know how I managed to do this. Bike shop said they'd set the pressures, but the front felt softer than the rear, so decided to check.
Tapped the valve to let out a little bit of air, put Presta side of my track pump on there. No pressure reading - zero. Didn't get enough sleep last night, so started pumping like an idiot. I must have put 100psi on top of whatever was already in there, and it was getting very hard to pump. A few minutes later, it exploded.

Beading was kinda scarred looking in two places where it had come off the rim, but the tyre (a Marathon Plus 28mm 700) went back on OK with the new inner tube and seems to be fine - haven't ridden it since then.

1. Do I need to worry about the tyre?
2. Both my pumps were misbehaving in terms of measuring the pressure already in the tyre, and using a Presta to Schrader converter with a pressure meter for Schrader was just hissing when I tried to measure it (although it did give a reading) Is there some trick to Presta that I'm missing?

In the end, my Topeak Mini Morph, with the head converted to Presta, sort of agreed with the pressure meter using the Schrader converter, so I left the pressure 10psi lower than I'd like to be on the safe side. The track pump, with the dedicated Presta head, was saying the pressure was 20psi lower than the Topeak, so I didn't trust that.

 

[snorri]

If my experience is typical,acceptance of Presta is a three stage process.
Presta are a pain in the neck when you first come across them. Then there is the period of doubt, as you try out different pumps, frequently losing much air in the process. Eventually you realise Presta are just fine and you just cannot understand why you ever had any problem in the first place with the Presta system.
Perseverance is the word!

 

[jhawk]

Thanks for sharing your story, Custom.

I've got Presta valves on my touring bike and will no doubt be pumping the tyres (Schwalbe Marathon Pluses), and inner-tubes, up many times over the next years!

 

[jack smith]

i always have this issue of it not reading the pressure the best thing to do is firmly push the pump air but agianst the valve straight and it usually gives you the pressure reading. i always loose air on the gauge as i pump though but it never actually comes out the inner tube its just coming out the seal of the pump so the needle shoots up to the pressure then falls back down quickly i just pump it until the needle hits 120 then falls down then leave it, you can tell by feeling it when you get used to tyre pressures

 

[ColinJ]

The pump will not tell you the pressure in the tube because the valve is designed to stop the air coming that way!

The way to tell the pressure is to press down carefully on the pump handle while watching the reading on the pressure gauge. When the pressure in the pump just exceeds that in the tube, you will hear the valve make a slight 'click' as it opens. The reading on the dial at that moment is what the pressure has just gone to.

If the tyre bead is only scuffed up a bit, carry on using it. If you think there is a chance of it tearing, scrap the tyre or you risk it exploding in use!

 

[Shut Up Legs]

My Serfas FMP-500 floor pump can tell me the pressure in my Presta tubes fairly accurately. Although, Presta valves can be a bit tricky that way: put the pump head on just the wrong way, and you can't pump any air in and the pressure reading is wrong.

 

[Custom24]

The pump will not tell you the pressure in the tube because the valve is designed to stop the air coming that way!

The way to tell the pressure is to press down carefully on the pump handle while watching the reading on the pressure gauge. When the pressure in the pump just exceeds that in the tube, you will hear the valve make a slight 'click' as it opens. The reading on the dial at that moment is what the pressure has just gone to.

If the tyre bead is only scuffed up a bit, carry on using it. If you think there is a chance of it tearing, scrap the tyre or you risk it exploding in use!

Thanks. I assumed once the screw was loosened that the valve would behave like Schrader.
The bead has a wire in there, I think, which is intact. Or did you mean a risk of the bead tearing the tube?

 

[John the Canuck]

.............. I assumed once the screw was loosened that the valve would behave like Schrader.
..................?

I'm soon to take delivery of a road bike with Presta valves... never had them before

? do you have to loosen the screw before pumping up..?
why..?

have a medical prob with left shoulder and right hand and need to use a CO2 inflator
anything to be carefully of..?......cheers

 

[ColinJ]

I'm soon to take delivery of a road bike with Presta valves... never had them before

? do you have to loosen the screw before pumping up..?
why..?

have a medical prob with left shoulder and right hand and need to use a CO2 inflator
anything to be carefully of..?......cheers

The bit you screw up locks the valve shut to stop air leaking out. That also stops air going in!

The other thing you need to do before inflating the tube is what Custom24 said he did - 'Tapped the valve to let out a little bit of air'. That is because the valves often stick even after unscrewing the ends. Once you have let out some air, you know the valve has been freed. You don't need to let out much.

If you are using CO2, be very careful that your tube is not trapped anywhere by the tyre bead, and that the tyre bead itself is properly seated. It is easy to explode tubes if you get this wrong, as I have witnessed other people doing in the past!

Obviously you need to carry enough CO2 cyclinders to cover expected needs. I'd want to carry at least 3, but I am the kind of person who carries 2 or 3 tubes and a puncture repair kit!

One other solution for pumping with a bad shoulder is to buy a pump like a Topeak Mini-morph. They are like small track pumps, with a fold-down foot
pad at the end. This allows you to use body weight to operate the pump rather than arm strength.

 

[John the Canuck]

^^^^ thanks Colin

i thought the OP was referring to the nut at the 'bottom' of the stem where it goes through the rim...doh.!

'''Tapped the valve'' thanks for the tip

i'll repair tubes at home - so as you say, 2 spares + 3 or more CO2

 

[Custom24]

One other solution for pumping with a bad shoulder is to buy a pump like a Topeak Mini-morph. They are like small track pumps, with a fold-down foot pad at the end. This allows you to use body weight to operate the pump rather than arm strength.

Just to note that although these are labelled as MTB specific (and come set up for Schrader), you can fiddle with the bits inside the pump head and they work on Presta fine, as I discovered last night.

Great pump. They do come with a mount for the frame, but you might struggle with space to get it on. I just keep mine in my backpack.