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Keeping the Rubber Rolling


The modern mountain bike is an amazing machine, capable of bewildering feats. In the right hands it will scale tricky climbs with the prowess of a mountain goat, tear down the side of a cliff with the agility of an ibex, and soar through the air with the grace of an eagle. But to have a hope of accomplishing any of this, there is one thing that all mountain bikes need - rubber that grips and rolls.


Now, I know what you're thinking... well duh! Obviously mountain bikes need to have tyres. But when it comes to keeping your tyres rolling while you're out on the trails, just having them on your bike with some air doesn't mean they're ready to handle everything that you might come across while you're out on a ride. And when you think about the fact that two rubber contact points bouncing over undulating terrain are all that keep you in control of where you're riding, it's actually a really important consideration.

I was reminded of this while I was out for a ride recently, which in truth was my inspiration for writing this particular post. On one of my favourite local trails, a number of sections had become somewhat rutted out, revealing, as often happens in Nerang, numerous roots and rocks. Admittedly there were also smoother sections beside the bumpy parts of the trail that I could have taken - but where's the fun in that?


So down I went through every rock and root filled rut at a moderate speed (the photo above belies the steepness of the terrain) when all of a sudden I realised that I was rapidly approaching two trees without the ability to steer away from them... because my bike had disappeared from beneath me. So, I did the only thing I could do. Raised my forearm to protect my fact and relaxed as best I could to lessen the consequence of the impact. Reviewing Strava after the ride revealed that I'd gone from 27.4 km/h to 0 instantaneously.


As it turned out, I was fortunate enough to initially fly into a thinner tree (the one immediately behind my back wheel in the photo below) before colliding with the larger tree after it. It just so happened that the foot and of space between the trees was just enough to slow my flight through the air to avoid any serious injury. The question remained though - why did I suddenly soar through the air without my bike?


After dusting myself off and returning to my bike I discovered that my front tyre was complete, totally and uterly devoid of any air. But upon closer inspection, there was certainly no evidence of any punctures or tears in what is a relatively new tyre.


So what happened? Well, it looked like the tyre "burped", letting the air out to the point where the tyre no longer clung to the rim. This was confirmed when I managed to inflate the tyre back up without any issue (and for those of you that were wondering if it is possible to seat a tubeless tyre back onto the rim with a portable pump - the answer is yes!).

Now, if you're wondering what a "tyre burp" is as opposed to a normal one, it's simply an event where a tubeless tyre makes contact with something on the ground (or even the ground itself) that creates a compression force so strong that the seal of the tyre breaks from the rim. If you're lucky, it will be a small burp and you'll continue riding along just fine, possibly without even noticing. I had the unlucky kind, the sort where all of the air magically escapes completely from the tyre and disappears into the surrounding environment in the blink of an eye.


And in case you hadn't realised it just yet, mountain bike tyres without air on undulating terrain don't roll very well - if at all. I will say though, that the feeling of flying through the air like Superman (actually, the Greatest American Hero is a better comparison, for those of you old enough to remember) felt really cool, if only for the briefest of moments.

But I digress... because for those of you who are yet experience a burp, you are probably wondering what causes it. The simple answer is not having enough air pressure in your tyre for the terrain you're riding over or for the activity that you're doing. Jumping, rolling down drops, or riding over rough terrain (along with any combination of these) can push the air into your tyre away from the ground which causes the tyre to deform to a point where it can no longer maintain the seal to the rim. And when that happens, the smallest gap can cause a fair amount of air to escape.


The simple way to avoid this problem is to run your tyres with a higher tyre pressure, along with diligently checking your air pressures before you go out on each ride. Of course, you need to balance this out with maintaining maximum grip as well - as having your pressures too high will have a fairly major impact to the ability of a tyre to hug the ground. As always, figuring out the balance is key - and this can change due to a number of factors, including what you're doing, the terrain you're rolling over and how aggressively you're riding. It turns out in this particular case, I just happened to be riding a bit faster on rougher terrain than the pressure in my front tyre would allow. Front tyre stops rolling, bike transforms into an instant catapult...

While I'm on the subject of tyres, I thought I might as well delve into the subject of when to replace them. And let's face it, tyres, like everything in mountain bike riding, are not cheap. So if you're anything like me, you want to get as much life out of your tyre as you can. And while they're on your bike it can be hard to discern if they're really wearing out to the point of needing replacing - until you happen to be riding somewhere entertaining and you realise you really don't have much grip at all!


The easiest way of demonstrating tyre wear is to compare a worn out tyre to a brand new one. The photo on the right shows a front tyre that I had on my bike for about a year. I had been thinking about replacing it for a few months but in general riding it seemed fine. It wasn't until I was riding down steeper trails without being able to slow down that I realised how bad my tyre had become. In a side by side comparison with a new tyre, the wear is easy to see.


Beyond the obvious wear and tear on the outside of the tyre, tyres themselves weaken over time. Tyre tread is not the only part of the tyre that wears away, but so to does the rubber casing. Over time, the thickness of the the tyre construction decreases along the centre and sidewalls of the tyre. This makes them more susceptible to punctures and tears, while the support the tyre sidewalls provide is also weakened. And generally speaking, from the outside, other than perhaps the wearing away of brand logos this internal tyre degradation is generally imperceptible.


Taking a closer look at an older tyre when it's off the rim will often reveal the wear and tear that is often missed at a cursory glance. Cuts, scratches and tears along the side wall and on the inside surface, a worn out tyre bead that is responsible for maintaining the seal along the rim and even clumped up sealant on the inside of the tyre serve to demonstrate this particular tyre was well past its life expectancy. You might also have noticed that the sealant is pretty low as well, which would have meant that any future punctures might not seal.

At the end of the day, tyres are what keep you rolling out on the trails and maintaining them in good order is essential to keeping you on your bike while riding. Checking your tyre pressures, making sure you have sufficient sealant in place and ultimately replacing your tyres before they're too worn out will all not only help to enhance your riding experience, but ultimately will work to keep you safe on the trails.

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