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Unread 03-21-2016, 04:44 PM   #1
Join Date: Aug 2015
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Default Preventative tyre maintainence

I have been in two minds about writing this, but seeing as tyres are a recurring theme in this forum, I set to give them, as well as dampers, a punt from my point of view, which is a point of view of driver safety rather than car mechanics.

If the essay is in any way succesfull (and any remarks, questions, inquiries and discussions are of course welcome in the thread) than more of it's ilk might follow, on mechanical elements as well as driver development from my expertise.

It's important for me to disclaim (again) that I am doing this strictly from a driver's perspective, not a mechanic's. So there's no commercial element involved. If anything, tyre manufacturers push for longer periods of using tyres than I do, and anyhow I'm NOT going to name brands anywhere.

The regulations and common practice of changing and fitting tyres are generally that tyres are usable until they are not. So tyres essentially get replaced just before they disintigrate or aquaplane.

For me as a driver (and I am talking normal road driving here), it's important however that the tyres also perform within reason, providing enough grip for cornering and especially for braking so that when the moment comes, the braking distance in an emergency will be reasonable and hopefully allow to handle the hazard.

This requires being much more strict with tyres and with dampers than regulations suggest, because it's an entirely different parameter of the tyre that we are trying to preserve.

As for tyre brands, as long as it is a respectable brand than generally speaking it's all okay. It's the unknown brands you need to watch out for. Braking distances, especially in the wet (due to neglecting the effort to be put into fluid simulations by the esoteric manufacturers), could be 30-40% longer.

In the appended picture (from an test independent of any brand), tyres from an unknown brand on a similar car in perfectly similar road conditions (which are dry) take about 25 more feet to stop from 60mph!

Tyre age and milleage are important, too. A three to four year old tyre could be perfectly "usable" but could just as well enlogate stopping distances up to 30%, especially in the wet.

Tyres can "last" for many tens of thousands of miles, but at a top of 50,000 they'd again lose out on performance dramatically. Rubber heats up and cools down repeatedly which degrades it, so you lose in friction, stiction, hysteresis and internal ridigity and damping of the rubber.

The tread doesn't wear down all that quickly in modern radials, but experiments had proved that to be anywhere near safe you need 3-4 millimeters of tread depth. Not 2mm requires by law in most countries.

Tire inflation pressure is important, too. Use a personal gauage. Even the cheapest "pen" is likely to be more accurate and reliable than the guage at the filling station so use one to recheck at least two tyres after you inflate.

En route to the station, tyres may heat up so more pressure needs to be pumped beyond the manufacturer's recommendations for cold pressure. In doubt, overinflation is tenfold better than underinflation. Do check pressure every two weeks. TPMS is also a very usefull aid.

Filling tyres with nitrogen does very little to improve tyre performance and longevity, but if you decide on it, be my guest. Rotating tyres is also not too crucial, as long as you at least shift them between the axles at some intreval of miles or another.

As for where the better set of tyres go, I am in the camp of it being on all wheels. If the differences between the two (or more) tyre pairs are small from the outset, than it doesn't matter where you put them. If they are substantial, than putting them in the rear will improve stability, but you'd still pay in braking capability.

The same convention of replacing tyres can be applied to dampers. Manufacturers have in fact realised that and started recommending that dampers be replaced in intrevals of 60,000 miles.

There is a truth in it, because damper fluid degrades, permeates, stiction increases and even shims can bend and low-speed damping tends to go awry without the driver's realising it. However, the actual milleage before the performance envelope suffers ranges here, and at the high end can reach 80,000 miles even.
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File Type: jpg braking distances.jpg (15.0 KB, 218 views)

Last edited by Drivemaster; 03-21-2016 at 05:13 PM.

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