Alex Roux wrote:If what you say is true, can one not then extend the argument that ons does not need any spare on a long trip anymore?
I.e., if you don't need 2 spares, then why need 1? You always stop when pressure drops quickly, and patch up - off you go again.
If you need two, do you not need three? or four? Exactly the same argument.
Flying is too dangerous because of the risk that there can be a bomb on board the plane. However, since the risk of two bombs being on board the plane is so low that it I deem it perfectly safe to fly, I now just carry my own bomb along whenever I need to fly.
Now statistically speaking the same principle lies behind both these arguments. The question is can you control, influence or manipulate the propability.
Remember, you DO NOT need a spare wheel. You only need a spare wheel once you have a flat wheel that cannot be repaired. You carry a spare wheel based on the propability that you may get a puncture/damaged tyre. The propability of this happening is defined by various factors (road conditions, speed, load, etc.) and will be specific toe each individual. You can calculate the average interval between tyre incidents by deviding the total distance in km travelled by the number of incidents. You can refine it by further looking into type of road, type of load etc. But this is merely the average interval and not indicative of the propability, which depend on various factors, but is a good departure point. So one need to balance the probability and the outcome of an incident taking place.
The amount of caution applied have a big influence on the propability, even though it can not reduce it to 0%. However, after the first puncture/tyre damaged, more caution will be applied and it can be safely assumed the propabilty of sustaining another puncture will decrease. Then looking at the average interval for the specific conditions it will become clear that, though not impossible, it is highly unlikely. TPMS etc all reduce the propability. But the argument should be, if I sustain a irrepairable puncture, is the next place where I can get it repaired/replaced within a distance that allows a reasonable propability for me to reach it safely? Normally, even in Angola/Botswana/Zambia/Mozambique, that is 1 fuel tank away, but may require to deviate from planned route.
If you really, justifiably, required two spares for each trip, it would be indicative that owning a patrol is very expensive and you spend more on tyres than fuel.
If you do not have a TPMS and you are worried about the effects of losing a tyre, a 150km interval tyre-stop (and then you have to measure the pressure) will allow you to catch the slow punctures in time.
Daily checks of tyre pressure is essential and I do not know a lot of people who do this, or even check wheel nuts regularly.
I will speak for myself, but I believe 1 is enough for my type of use and my requirements.