Common wear types and their causes
In this guide, you will see some of the different types of tire wear that you can expect to find on track day tires around the circuit paddock. The intention here is to help you learn more about bike tire wear so you are better equipped to deal with a nasty tear if/when it rears its ugly head.
However, like most tire based guides, the nature of the subject is quite complex, so it’s not as easy as saying this causes that, or that causes this (especially when talking about suspension adjustment) so please take this as being a somewhat simplified guide to motorcycle tire wear, not the definitive resource.
Cause – Cold tear is caused by the tire being over inflated. When the tire is over inflated the contact patch on the ground is too small so it cannot generate heat that is widespread enough to bring the carcass of the tire up to operating temperature. Instead what happens is the surface of the tire super heats very quickly while the carcass stays below operating temperature, so the surface of the tire is ripped straight off.
Symptoms – The tears are in fact quite deep into the carcass and are somewhat fingernail shaped. If you can get a fingernail under them and almost peel a sizable chunk of the rubber back off the surface of the tire then this is a sure fire sign of cold tear.
Cause – Hot tear is caused by the tire being under inflated. An under inflated tire causes the contact patch to be too large on the ground which in turn means the tire overheats. When the whole of a tire over heats, the surface gets hot and is melted off very quickly and is pitched away due to the centrifugal force created when the tire spins.
At first glance it’s quite similar to cold tear but because the whole tire is overheating instead of just the surface, the rubber comes off with less effort as opposed to being ripped off a cold carcass like you see with cold tear, this then means hot tearing isn’t as deep.
Symptoms – As said above, it doesn’t take as much for the surface rubber to come off of an under inflated tire because the whole tire is overheating, so the tears on a tire experiencing hot tear are fairly shallow and more spread out and you shouldn’t be able to get a fingernail deep under them like you can with a cold tear.
Also you will notice when looking at the tire that the tears come down and into the center of the tire in an arc shape because of the centrifugal force of the tire.
Suspension Related Tire Wear
When we start talking about suspension and how incorrect settings can affect tire wear, it’s difficult to explain what symptoms mean what because not every form of wear is unique to one particular component of the suspension. However, outlined below, are some points that should help you better determine if your tire problems could possibly be suspension related.
If your rear suspension settings (rebound, compression, sag or spring rate) are incorrectly set to the point where they are then asking the tire to act as a part of the suspension, you are immediately going to see some unusual wear or tearing because the tire simply wasn’t designed to be used in that way.
To the untrained eye, tire wear brought on from incorrect suspension settings could quite easily be palmed off as a pressure related problem (hot or cold tear), but there are some differences and some questions you can ask yourself to get you started on the right path to fixing it.
Do you know you have the right spring? – If your spring is either too hard or too soft for your weight, the carcass of the tire will be put under a lot of strain because it’s being asked to act as a significant part of the suspension (with the spring not doing its job properly.) This means the tire ends up quickly shredding itself to pieces with incorrect loads.
Is the affected area uniform in width? – Have a look at the thickness of the tear. If you notice that the width of the tear is not uniform and changes considerably as you follow it around the tire, then this is a good indicator that something is wrong with the suspension, usually rebound being out of adjustment. The picture to right demonstrates this.
Does the tear go all the way around? – If it does, that may be poor tire pressure or geometry.
However if it doesn’t and you follow the tear around the tire and notice that it is not a continuous tear i.e. there is an affected area, then there’s a sizable area where it’s clean, then there’s some more damage, then it goes clean again, this is another indication that a suspension setting is out, most probably rebound or compression, or even a combination of them both.
Are the edges of the tread raised? – If you have a raised area on either the leading or back edge of the tread, this is a strong sign that rebound damping on the forks or shock is set either too fast or too slow. Usually if it’s on the leading edge rebound is too slow, and if it’s on the back edge it’s too fast.
By answering the above questions, you should be able to determine whether or not you have a suspension related issue.
Not enough weight on the front
Cause – This type of motorcycle tire wear is not quite as common as things like hot or cold tear as it comes from an incorrect geometry set up which usually affects the front tire. What you see in the picture is a result of there not being enough weight on the tire so it cannot get to operating temperature.
This means it cannot get proper grip or traction and as a result the front tire pushes and drags across the ground when the rider gets on the throttle, rather than rolling over it as it should. The surface is then super-heated and subsequently ripped up.
Symptoms – With a geometry tear where there’s not enough weight on the front it will be the edge third of the tire that is showing signs of incorrect wear, so the affected area is quite large.
If your tire is showing bad wear patterns on the edge third, where the start of the wear pattern (the bit closest to the middle of the tire) follows the circumference of the tire uniformly, you can be pretty sure you’re suffering from geometry tear and do not have enough weight on the front.
Too much weight on the front
Cause – As the above heading would suggest, the other type of geometry tear is too much weight on the front. What happens in this instance is that when you start to turn the bike into a corner, because of the excessive weight on the front it will actually plow across the ground (rather than rolling), and it’s only when you have finished turning the bike and get back on the gas that you take the weight away from the front end and the tire is relieved.
As well as having too much weight on the front, this type of tear can often be caused by the front end being too soft in conjunction with too much weight.
Symptoms – What you’ll see is a much smaller band of tearing that looks very similar to hot tear on a rear tire, only the band will be about 5-10 mm thick, usually about half way between the center of the tire and the edge. Again like having not enough weight on the front, if the wear pattern closely follows the circumference of the tire it is most likely geometry related, if not pressure.
You often see the question come up ‘why are my tires blue’ or ‘what’s this blue stuff on my tires’ with people suggesting that when you see it the tires are done. This isn’t completely true.
What makes it blue? – Motorcycle tires actually contain oils that keep the tire soft and the blue/green tint you can see on your tires is just the oils coming to the surface.
Why are they on the surface? – After the tires have been used to the point where they gain significant heat, when they cool down again (this is one heat cycle) the oils in the tire will often come to the surface. When you go back out and ride the bike these surface oils are scrubbed off and it’s only when you come back in and let the tires cool down again that you’ll see more oils coming to the surface.
Each time you take a tire through a heat cycle you are losing the oils that keep the tire soft, so the more heat cycles a tire has been through the less effective the rubber is going to be for you.
As a side note, heat cycles will affect track tires a lot worse than road biased tires, as road tires are expected to go through these cycles.
What we want to see from our tires
So we know what we don’t want to see in terms of tire wear, but what DO we want to see?
Have a look at the picture to the right, this is what you’re looking for. If you have a pattern like the one in the picture which looks like a beach where the tide has gone out, you’ve nailed it.
This doesn’t mean to say it will give you optimum performance (racers often sacrifice tire life for better performance) but it does mean you are highly likely to see great longevity from your tire with enough grip for any track day rider.
Motorcycle tires are very expensive and probably the biggest expense for any track day rider or racer (apart from track time maybe), so making sure we are best equipped to deal with a tire wear problem if it crops up is extremely important for keeping your tires, and your wallet in good condition.
Taking the above advice into account, you will now be able to spot some of the clues and tell-tale signs that show up when we experience unsavory tire wear. As a result, you can get on top of it as soon as possible before it ruins your tires.
It’s also worth noting however that this is a fairly simplified guide to tire wear and tearing as there are a multitude of factors that come into play such as pressures, suspension make up, how the rider rides the bike, and even the nature of the track where the problems occur. So, this is intended to give you some baseline knowledge so you can head in the right direction of getting your tire problems fixed.