Take the 2-minute tour ×
Bicycles Stack Exchange is a question and answer site for people who build and repair bicycles, people who train cycling, or commute on bicycles. It's 100% free, no registration required.

On the tires of a bike, there is a label which shows the maximum allowed pressure for it. However, I am wondering if there are any other factors that affect the maximum allowed pressure in a tire?

  • Does the innertube also has a "maximum allowed pressure"?
  • I need a rim tape to cover the spoke holes in my rim. Does this lower the allowed pressure?
  • Any other factors?

Background: In the last week, two innertubes on two different bikes exploded. They were both under the maximum allowed pressure. I suppose one was old and the other had a manufacturing error. One was exploding during cycling, the other one during inflating the tire. I am now quite afraid of inflating tires, so I want to make sure that this will not happen again.

share|improve this question

3 Answers 3

up vote 4 down vote accepted

The usual cause of inner tubes exploding while being inflated is that part of the tube is pinched under the rim, or was damaged by a tyre lever while you were fitting the tyre (but manufacturing flaws can happen - I once had a puncture in a tube next the stem where it was difficult to patch, and my spare tube failed at the same place as soon as I inflated it (and there wasn't a sharp edge on the hole in the rim)).

But apart from that, if the tube and tyre are properly seated, and the tube is the right size, the tube shouldn't limit the pressure.

Rim tape can make a difference if the wrong sort is used, but shouldn't otherwise, see http://www.schwalbe.co.uk/_webedit/uploaded-files/All%20Files/Technical%20Info.pdf and search for "Which rim tape should I use".

Tyre sizes and rim sizes vary slightly, and a combination that is a slightly loose fit will let the tyre blow off at a lower pressure. The label allows for that, at least to a certain extent (see http://sheldonbrown.com/tires.html#pressure and scroll down to "Pressure Recommendations").

Using a tyre on a rim much narrower than it is intended for can make the rim fail and let a tyre blow off: http://www.sheldonbrown.com/tire-sizing.html#width. So can using a badly worn rim, of course.

share|improve this answer
1  
Also see bicycles.stackexchange.com/questions/10843/… –  armb Apr 15 '13 at 8:51
    
re "tube is pinched under the rim" - or sticking through a damaged tyre: guardian.co.uk/environment/ethicallivingblog/2009/aug/06/… "I eventually tracked down the cause: a large gash in my rear tyre; the legacy of a large chunk of glass the previous summer. With my tyres down at around 40psi, the tear wasn't even noticeable but at 80psi, the inner tube was forcing its way through the gap and getting pinched, causing my punctures." –  armb Apr 15 '13 at 9:06

The limiting factor for tire pressure is the tire . The manufacturer designs the tire with a maximun pressure the tire case will be able to safely control. Exceeding the reccomended pressure can result in the bead being forced of the rim or the the tire case itself could fail.

share|improve this answer
    
Rims also have a maximum allowed pressure (can be as low as 120, typically 160 psi for road bike rims), however it most common for common sense and the tyre to be limiting factor - not many people like the feel of 160psi...... –  mattnz Apr 15 '13 at 22:21

Innertube failure can be caused by a variety of factors, and it is usually possible to determine the cause by examining the failed innertube.

You mentioned: "In the last week, two innertubes on two different bikes exploded". If it literally exploded into many small pieces, then you were probably the target of a saboteur. :) More likely, the innertube has a single tear or puncture, and its size and location will help you track down the problem:

  • A small puncture along the outer side is usually caused by road debris. Since you ask about tire pressure, it's worth mentioning that high pressure can increase the chance of puncture.

  • A tear at the valve can be caused by the age of the innertube or by poor inflating technique--using a hand pump without holding the valve steady can easily tear an innertube. This problem is not directly affected by tire pressure (but trying to reach a really high pressure with a hand pump could increase the risk).

  • A tear on the inner side of the tube can be caused by spokes and may indicate a problem with rim tape or low-quality rims. Note that low-quality rims can limit the maximum tire pressure. I had a mountain bike (used for city riding) which had high-quality tires with a maximum pressure around 90 psi. However, the rim left the spokes very exposed, and inflating above about 45 psi would cause the innertube to stretch near each spoke and eventually lead to a tear. There's only so much rim tape can do.

  • Two small holes in the tube are usually pinch flats, which are caused by tire pressure being too low.

The main factor limiting tire pressure is the tire itself, but some problems can be caused or exacerbated by tire pressure.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.