PART-WORN TYRES - READ ME BEFORE YOU BUY OR SELL!
Before you buy (or sell) PART-WORN TYRES or fit them to your car, please have a quick read of this guide.
You might drive like a nun, but can you guarantee that the guy you are buying the used tyres off hasn’t hit every pothole and been speed testing on the autobahn? Will you be safe? How do you know what you are getting?
Here is a description of what goes into making a tyre do its job and what to look for in terms of damage so that you can make your own mind up. Your safety, that of your passengers and other road users could be at stake.
What am I looking for?
Firstly, consider why you are considering buying a used tyre. It’s all down to physics in the end – stop yawning! - but the bottom line is, and let’s face it, tyres are your only contact with the road. Without good grip, your brakes and your steering will be seriously compromised…
Sipes / tread
More tread is better. The sipes are designed to clear water from the road surface so that the tyre can make contact with the road. The deeper the tread, the more water can be cleared from the road, meaning the less likely you are to find yourself aquaplaning.
Aquaplaning happens when a layer of water builds up between the tarmac and the tyre and causes your brakes and steering to stop working. If this happens, all the ABS and electronics will be of no help at all – you are simply going in a straight line.
On a part-worn tyre, the tread will not be as deep as on a new tyre, meaning less grip in wet conditions. The legal limit is in fact very low, and should be seen as an absolute minimum rather than the point at which a tyre should be changed. All tyres have wear indicators that are little raised areas between the sipes. If you can see them, then the tyre manufacturer is trying to tell you they are past their sell-by date.
Sometimes, tyres that have been damaged ‘delaminate’ which is where the tread parts company with the carcass of the tyre. This is what caused Top-Gear’s Richard Hammond to crash that jet-powered car, and also caused numerous crashes in Ford Explorers fitted with Firestone tyres.
I personally change my tyres every two years (or 20, 000 miles). Those who try to do a million miles on a set might think this a little excessive…but you might thank me if I manage to stop before I smack into you or if I have enough grip to swerve around your kid when it runs into the road. In one job I was doing 10,000 miles a month, and no I didn’t sell my part-worn tyres on ebay!
The carcass is made up of a weave of steel wires and fabric bonded to a rubber casing. The rubber compound that then goes to make the tread is wound around the carcass before being placed into a mould where pressure and heat imprint the tread.
The carcass is surprisingly easy to damage (potholes, punctures etc.) but that damage is often hard to detect. Look for obvious signs such as areas where the tread is uneven or lifted, bubbles, or a wiggle in the tread that isn’t repeated all the way around the tyre.
You can often see damage better looking from the inside of the tyre – only possible if it is not mounted on the rim of the wheel. Grab the sides of the tyre and pull them apart so that you can see the inside. There should be no rubber powder or granules inside, and the pattern inside should be uniform. Still holding the sidewalls apart, press the tread of the tyre down onto a step or other (not sharp!) corner. Rotate the tyre, looking for any damage evidenced by any changes in pattern or shape or anything out of the ordinary.
The sidewall of a tyre gives compliance of ride. The sidewall adds extra ‘squish’ to the car’s suspension, and the deeper the profile of the sidewall the more compliance will be added to the ride. This is why low-profile tyres (less compliant) give a harder ride. The perception is that low profile tyres give better steering response, which is definitely true on the track or a smooth surface, but the trade off is that low-profile tyres tend to follow the camber of the road and ‘tramline’ (steer off-course) much more than ones with a higher profile. Personally, I much prefer to drive a car with thinner, higher-profile tyres as you can have fun at lower speeds and get more feedback from the road.
Sidewalls also happen to be the part of the tyre that get pinched against kerbs, or even cut, and this is a place to look for damage. Any deformations in the sidewall (inside or out) that are visible show that the tyre is shagged and dangerous and should not be used. Damage to the sidewall cannot be repaired.
Another thing to watch out for is where the writing has been rubbed off the sidewall. This is a sign that the tyre has be ‘rolled’ in corners either due to extreme cornering speeds or due to under-inflation. If a tyre has been used under-inflated, then there is a much greater chance that the internal structure has been compromised and that delamination could occur at speed (see above). It is harder to tell visually whether low-profile tyres are under-inflated.
It goes almost without saying that any cracking or perishing shows you that the tyre is old and therefore not to be used. This is sometimes only obvious when it is fitted to a wheel, inflated and when the car is standing on it. Don’t be afraid to waste a fiver and ask the garage to take it off again if you see that the tyre is knackered.
The bead of the tyre is what holds it onto the rim. It is basically a ring of steel wire embedded into the inner diameter of the sidewall. Removing a tyre from the rim can potentially cause it damage, and you should carefully inspect the bead, running your finger around the inside and outside as well as performing a visual check. Any visible damage at all means that the tyre could pop off the rim causing a rapid deflation or delamination and hence become a full-scale blow-out. Remember always that damage may not be visible! Having suffered both rear and front-wheel blow-outs I have to say that the rear variety is easier to correct as you retain more steering control. Both varieties are exciting in all the wrong ways, and you are most likely to have a blow-out when you are cornering or braking.
This is going a bit beyond the remit of this guide, but is worth a quick mention. Tyres are, simply put, made from rubber compounds that can be harder or softer. Soft ones give more grip, get very hot at speed and wear faster. Hard compound tyres last for ever but give you precious little grip (especially in cold conditions).
As a rule of thumb, tyres made in the Far East are very hard compound but cheap. If you like smoking your tyres at the traffic lights, these are the ones for you. You might just get them hot enough so that they will stop you at the next junction! To be un-scientific, you can test how hard the compound is by feel – softer ones yield more to the touch as well as generally picking up more dust.
A last word
I hope that this little guide has been of interest. I suggest considering spending a little bit more on tyres even if it means not getting the furry dice, upgraded stereo or high-maintenance partner. Check out your local-bloke-works-out-of-a-shed for the best prices and service on new tyres.
Don’t forget that if you buy part worn tyres you still need somebody to fit them for you and to balance the wheel (budget a fiver per wheel) assuming that they are prepared to do so.
PART-WORN TYRES - READ ME BEFORE YOU BUY OR SELL!
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14 February 2007
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