Potholes, kerbs, emergency stops, drag races, fast cornering, max-speed on the autobahn...you know what you have put the tyres on your car through. But do you know what the bloke who you are buying tyres off drives like? Can you tell a good one from a bad one? Sorry to sound like your auntie, BUT...read this before you bid on part-worn tyres; understand the construction of a tyre, then make your own mind up!
Consider why you are buying a used tyre in the first place. The tyre is your only contact with the road surface, and without good ones, your brakes and steering will be seriously compromised. To be 'boring', roadholding all comes down to physics. If you are trying to save money, then please don't save money on this part of your car - get a cheaper stereo and a lower-maintenance partner, ditch those bling wheels and the furry dice to find the pennies before you try and save money on tyres.
I have tried to summarise the main points to look out for:
When you buy a part-worn tyre, you are obviously buying a tyre with less tread than a new one. The grooves in the tyres are calles 'sipes' and their function is to clear water from the road surface so that the tyre can grip the road. The deeper the sipes, the more water can be cleared and the less likely the car is to 'aquaplane' when a layer of water builds up between the road surface and the tyre. This can lead to loss of control, especially if you try to brake or steer when this happens. In the dry, a brand new tyre will also grip better than a part-worn one. The legal limit should be considered an absolute minimum!
The 'bead' is what holds a tyre onto the rim of a wheel. This consists of a load of steel wires formed into a belt which is encased in a fabric and rubber ring. Every time a tyre is put onto a rim, there is the possibility that it will be damaged by careless handling. You will not be able to see this unless damage is severe.
This is the bit that adds compliance to the ride of your car over and above what the suspension can offer. The sidewall is supported by the air pressure in your tyre. The larger the sidewall's section, the better the ride will be, which is why low-profile tyres mean a less comfortable ride. During cornering, the sidewall 'bends' (a lower profile tyre has less give, so gives sharper cornering response). Corner too fast, espescially on an under-inflated tyre, and you will 'roll' the tyre, meaning that you are running on the sidewall instead of the tread. This causes wear in the wrong areas and can be evidenced by the writing on the tyre sidewall being rubbed off. Often, on a low-profile tyre, it is hard to tell by a visual inspection whether the tyre needs air (much easier to spot on a tyre with a taller section). Sidewalls also get damaged by 'kerbing' from parking the car. If a tyre is severely pinched, then lasting damage can occur that might not be visible. Higher-speed impacts cause bubbles and 'wobbles' in the sidewall.
Casing and remoulds
The casing of the tyre is the bit where damage can often be present without being seen. The casing is basically a web of steel wires in a canvass and rubber sandwich. My dad ran Star Tyres (based in Durham) in the '80s. They remoulded worn tyres, and to be honest weren't too bad for what they were, but the point of this is that I have seen all sorts of horrors as we sorted tyres that are only apparent upon very close inspection of the internal body of the tyre - bubbles that show that the tyre has been kerbed, for example, and which might lead to delamination of the tyre (which is what happened to the tyre on the jet car that Top Gear's Richard Hammond had a near fatal crash in). The remoulded tyes that failed were the ones where the casing was damaged but where the visual inspection did not pick this up or where the tread was not properly moulded onto the donor casing and delamination occurred. It is worth noting that remoulded tyres might have as their donor casing all sorts of different tyres (and therefore constructions) so my best advice is to steer (!) clear.
Apart from anything else, you will need to pay somebody to fit your 'new' tyre for you, and to balance your wheel. Don't forget to check how much this might cost you before you go ahead (if you must) and buy your part-worn tyre. You might be shocked at the price! Please don't try and do it at home - you could really do your self some damage!
This is a bit beyond this guide, but is worth a mention. Basically, the softer the rubber compound of a tyre, the better grip you will get, particularly in cold conditions. The other side of this is that a soft compound tyre will wear faster, and will heat up faster at speed. A hard compound tyre will last longer, but provide less grip, so your cornering, braking and acceleration performance will be reduced. Most road tyres are a compromise, but as a rule, far-eastern tyres (often the cheapest) are generally the hardest compound and therefore offer the least grip. You can feel a tyre and see this for yourself - the 'stickier' and softer it feels, the softer the compound. If it is shiny and unyealding then the compound is probably too hard.
I've already bought my tyres!
Well, all is not lost - but carefully inspect them...First, look at the tread and sidewalls. If there are any areas of uneven wear or if there are cuts or 'wiggles' in the sidewall or casing then you must not use the tyre. These are sure signs that it has been damaged and could endanger your life, or perhaps worse, your passenger's lives or other road users.Second, run your finger around the bead. It should be smooth and unbroken inside and out. Next, pull the sidewalls apart as you press the tread down on a step or similar. Look inside the tyre for any damage, which will be more apparent as you do this. Again, if you see even small imperfections then discard the tyre. Other signs to watch out for are worn writing on the sidewall, powdered rubber inside the tyre or evidence of over- or under-inflation which will be evidenced by changes in depth of tread as you go across the tyre (use a coin etc. to check).
Hilda's last word
By the way, I never let the tyres on my car stay there for more than 20,000 miles or two years. Old tyres are, in my view, very bad news even if they have lots of tread. You might think that a bit extreme (especially if you take pride in doing a million miles on a set) but you might just thank me if I am able to stop before I run into you, or to steer around your kid when it runs into the road. I pay no more than £60 (each) fitted for 205 60/15 Pirelli P6000s or Conti EcoContacts. Email me and I'll tell you where (if you live south-west of London), but I suggest that you try your local guy-who-works-form-a-shed independent garage if you want the prices and the service.
Happy motoring, and thanks for reading - hope it was useful.
Are PART WORN TYRES a good idea? - beware remoulds too!
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5 February 2007
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