Advice: Tyre cleaning

Slip-slop-slap

Scrubbing in tyres is yet another one of those 'black arts' that riders seem to struggle with. Let's get down to basics. A tyre is made in a process known as injection moulding. Meaning a mould or mirror image of the tyre is formed by a tool called a 'die.'

This die is usually in two halves (left and right) and is put together to form the shape the tyre will attain. The rubber is then injected into the die under pressure, causing the rubber to expand and form the shape of the tyre. When the rubber has cooled sufficiently, the mould separates and the newly manufactured tyre is removed.

In order for the tyre to be taken from the mould and not stick to the surface of the die, a mould release agent is used. This agent is the shiny/slippery stuff on your tyre when it's brand new. It's this stuff we need to get rid of as quickly as possible, so we can actually get to the compound of the rubber which enables the tyre to grip to the road.

Racers often use a product called 'tyre buff' (a form of acetone) that when rubbed over the surface of the tyre, takes off the bulk of the mould release agent. This, combined with tyre warmers, makes scrubbing in a tyre a process that takes all of about a lap or so.

On the track, you simply build up the lean angles and the amount of force used progressively until you've used all of the tyre surface and it's up to optimum temperature. Once you've done that, the job is done.

For the road rider, it's a little harder to scrub a tyre in as you have all of the uncontrolled stuff in the environment to deal with as well as your new questionable traction situation. What often happens is the rider decides to 'take it easy' for a period of kilometres in the belief that this will handle it, which is not always true.

What this means to most riders is that they don't lean the bike over much and they are really gentle with the controls. Whilst there's no problem with this initially, if your use of lean angle and force doesn't progressively increase, then the only part of the tyre being scrubbed is the middle. This leaves the edges still with the slippery surface intact. Then, one day, you get into a corner a little too hot and have to lean it over further than you have before. Now you're on the part of the tyre that's not been touched to the road before and there is no grip. Next thing you know you're watching your bike and body parts disappear up the road in a shower of sparks and skin.

The key is in the progressive use of the tyre. When the tyre is new, you have to be very careful and gentle with the controls and how much force you put into it. What you will find is that once a particular part of the tyre has contacted the road, it loses its slippery feel.

If you can imagine the contact patch of your tyre as being an oval shape, then when the bike is upright and on the scrubbed part of the tyre that has been used, the total area has useable traction. When you lean it over just a few degrees for the first time, you will reach the edge of the scrubbed part of the tyre, and a small amount of 'new' tyre will contact the road. You'll no doubt find that this feels a little slippery and your survival instincts spark up, getting your attention a little bit or a lot (depending on just how slippery it felt).

Once that particular part of the tyre has contacted the road, you can go back to that lean angle and you will find that it no longer feels slippery. This is because the mould-release agent has been worn off and it is in essence, scrubbed. You can now lean it a little further so that once again you just contact the edge of the 'new' tyre, which is now further around it.

By doing this, the bulk of your contact patch is always scrubbed tyre that will give you grip. If on the other hand you decide to 'take it easy,' and then find you have to lean the bike over dramatically more than it has been leant before, the bulk of your new contact patch is now a part of the tyre that has never contacted the road before. Chances are, it will suddenly slide away from you.

This can be confusing to riders because they may have done several hundred kilometres of 'taking it easy' and believed that the tyre should be scrubbed in. The truth though, is that you will only wear off the mould-release agent when that part of the tyre contacts the road, and not before.

To scrub a tyre successfully, progressively build up the lean angle and force you place on the tyre until you have used what is available to you. Once you've done that, the tyre will grip well through the remainder of its life on the bike regardless (to a point) of lean angle and force.

Good luck with your scrubbing...

Steve Brouggy is the owner of the

Contact:
2 / 76 Rushdale St
Knoxfield, VIC 3180
Australia

Phone: 1300 793 423
+613 9763 3338