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Re: Winter tyres

Posted: 8 Feb 2017, 4:39pm
by Samuel D
Threevok wrote:Compound makes no difference on ice …

If the ice is anything but perfectly smooth, this is not true.

Tyres have two sources of grip: molecular adhesion and hysteresis grip. Molecular adhesion requires direct contact between tyre and road, so is vastly reduced in wet conditions (and ice at British temperatures usually includes a thin layer of water, even if only momentarily under the pressure at the contact patch).

Hysteresis grip comes from the rubber not rebounding with as much energy as was absorbed when it distorted around surface asperities (road roughness). This is the main source of traction in wet or icy conditions (or on diesel spills for that matter), but it depends on the surface having appreciable roughness. Wet manhole covers can be deadly because they are smooth, robbing the tyre of most of its only significant source of traction in the wet. However, even manhole covers usually have moulded features to offer some hysteresis grip, so tyres make a difference even there. That manhole covers don’t have many more, much smaller features is a failure of design.

Traditionally, tyre compounds used carbon black as a filler. This greatly improved hysteresis grip (i.e. wet grip) along with other desirable characteristics. However, increased hysteresis came with increased rolling resistance, which we obviously didn’t want on bicycles.

To alleviate this unhappy compromise, tyre makers have recently (popularly in the last decade or so) replaced carbon black with silica. Silica compounds have the fascinating property of variable hysteresis with stress frequency. They can be made to have low hysteresis at low frequencies (corresponding to rolling deformation) and high hysteresis at high frequencies (corresponding to the tyre sliding over small asperities). This makes possible low rolling resistance and high wet grip in the same tyre.

But it is still not magic. The hardness of the tyre also matters insomuch that optimum hysteresis occurs around the so-called glass transition temperature (at which the rubber changes nature from brittle to flexible). If the compound is used in temperatures far below or above the glass transition temperature, hysteresis grip is dramatically reduced. Therefore you need to choose a tyre for the prevailing temperature of operation.

Winter tyres therefore need to have high hysteresis (preferably only in the high-frequency domain) and a low-temperature compound.

For narrow tyres, three seem outstanding in these regards:

  • Michelin Pro4 Grip (only available in 23 mm)
  • Vredestein Fortezza Senso Xtreme Weather
  • Continental Grand Prix 4-Season
Any of these will significantly reduce the risk of winter falls compared to something like a Continental Gatorskin (carbon black compound designed for summer temperatures).

There may be other suitable tyres too, but manufacturers hide their tyre properties beneath reams of useless marketing terms (e.g. that “4-Season” moniker above), so getting good information is hard.

Re: Winter tyres

Posted: 8 Feb 2017, 4:55pm
by Threevok
The point is mute now - mainly because, by the time it took me to read that, summer came

Re: Winter tyres

Posted: 8 Feb 2017, 5:48pm
by Samuel D
Maybe someone else is interested in how tyres work rather than hearsay. There are plenty of people here.

You meant moot.

Re: Winter tyres

Posted: 8 Feb 2017, 6:45pm
by Threevok
Yeah sorry moot

and not hearsay - fact

Re: Winter tyres

Posted: 9 Feb 2017, 2:06pm
by fausto copy
I've still got two pairs of studded tyres for sale on this forum of anyone's interested. :)
They're made by Nokia(n) in Finland. I expect they know a thing or two about proper winters. :wink:
fausto.

Re: Winter tyres

Posted: 9 Feb 2017, 2:20pm
by foxyrider
Threevok wrote:Yeah sorry moot

and not hearsay - fact


Summer certainly isn't here - it was below freezing and snowing here when I was out earlier today!

Re: Winter tyres

Posted: 9 Feb 2017, 3:04pm
by Threevok
foxyrider wrote:
Summer certainly isn't here - it was below freezing and snowing here when I was out earlier today!


That IS a Welsh summer :twisted:

Re: Winter tyres

Posted: 9 Feb 2017, 4:29pm
by horizon
Samuel D wrote:There may be other suitable tyres too, but manufacturers hide their tyre properties beneath reams of useless marketing terms (e.g. that “4-Season” moniker above), so getting good information is hard.


Many, many thanks Samuel D for giving us the information that manufacturers don't (as with many products).

Re: Winter tyres

Posted: 9 Feb 2017, 4:39pm
by mjr
Garry Booth wrote:OK so the Conti tyre seems to be made of the right stuff, but doesn't come in a 25 size. I guess the sensible thing to do is stay off the road when it's icy!

You don't say where in East Anglia you are, but Norfolk does not grit cycle tracks, so the sensible thing to do is stay on the road when it's icy, unless you've studded tyres!