Avoiding a slow speed skid on ice.

[redbeard]

Hi,
I'd appreciate any advice I can get on this one. During the particularly icy conditions which lasted a few days last year my car skidded off line at the same point twice as I was trying to get down my street.
To give some background. At the time each of the streets I had to choose from were pretty carved up with potholes and at this particular point there was packed ice over a quite nasty pothole. Cars parked on the road meant I had no real option to steer around it.
The car is an A4 Quattro and was admittedly on it's normal Continental summer tyres, 35 profile on 19" rims.
The first time I was caught out I was in 1st gear, so I can accept that it may not have been the best choice because of the high torque. Also I possibly underestimated the effect this pothole would have.
So next time, I was, I thought, prepared. Crossing the hazard in 2nd at the slowest speed I could achieve without the engine labouring. No joy, it caught me again.
I'm likely to fit winter tyres this year, but can anyone advise me on the technique I should have adopted which might have helped?

[Horse]

Snowsocks?

No idea if they'll make a difference - but you've already suggested winter tyres

Otherwise, walk up there with a spade and clear the ice - seriously!

[redbeard]

Thanks,

I'd be busy though. The area's littered with untreated potholes. I was looking at the snow socks, but they seem to me like a bit of a pain. Use them to get to the main road, then you have to remove them. Having said that, winter tyres are a very expensive option, especially on these 19" wheels.

[Gareth]

Does your car have aftermarket wheels or were they a factory option? I had a quick look and it appears the standard size may have been 225/50R17, and there is a choice of winter or all season tyre in that size.

I'm not sure there are any techniques that can be quickly and easily learned that would enable you to work around the problem of the wrong tyres for the situation.

[redbeard]

They were a factory option. I think the 3.0 TDis get 18" wheels by default.
There are Winter tyres available, but it took a good bit of digging to find them in that size.
I'll check with Audi tomorrow as they have a winter tyre offer.
I suppose the way to rationalize it is that, yes they're pricey but it's offset by the fact that you're not putting wear on your summer tyres.
I must admit to being quite shocked by how much of a handful the car was off the main roads. I expected the Quattro would be an improvement over a 2wd car but in fact the only cars I've had that were worse in those conditions were RWD Beemers, and I really was tip toeing around.

[michael769]

I was also very surprised by how poor a Quattro A3 was in snow and ice. Much worse that any other car 2wd I have driven in snow and ice. My problem was that getting out of my estate involved turning right onto a very steep hill. The power needed to get up the hill from virtually a standing start was sometimes greater than the amount of available grip, and the traction control turned out to be more of an impediment than anything else.

I too found that in rutted snow the car became very jittery sliding from side to side a little in the ruts even at walking pace. I do feel that the standard fit tyres were possibly the worst I ever encountered in snow and ice.

Snow socks were very effective getting the car up the slope to the (gritted) main road. The take about 10 minutes to put on and 2 to get off (that's for 4 wheels) so by no means troublesome compared to 5-10 minutes to nurse the car up the slope.

This winter I have a new (proper 4x4) car, all weather tyres, but I have also got a new set of snow socks as a back stop just in case!

I was in two minds about the all weathers.Out council is very good at keeping the roads clear, the only real problem is the 250m up to the main road for the 24-48 hours it takes for them to get a JCB in to clear out the estate. For that to be honest the snow socks seem to be enough!

[redbeard]

How do you find the all weathers in normal (can we call Summer normal?) usage Michael?
Do they feel like a compromise or are handling, traction and stopping distances good?

[michael769]

How do you find the all weathers in normal (can we call Summer normal?) usage Michael?
Do they feel like a compromise or are handling, traction and stopping distances good?

I don't really push hard enough in driving to get a good idea as to the full impact of on stopping distances. The data I have seen says that stopping distances in the wet are better all year round than either summer or winter tyres. On dry conditions the summers do perform better in warm weather, but in cold conditions they outperform both summer and winter tyres in the dry. It's only really in deep snow that they perform less well than winters.

For my driving style I can say that I detected no reduction in stopping distances or cornering ability over the summer. In typical winter conditions I did not find any noticeable improvement (but was not expecting to) but in ice and snow conditions the handling of the car was significantly improved over the summer tyres, and I found the need to take other measures to get up the hill was much less than before.

It is hard (on the Audi) to judge how well they wore as the Audi tended to wear even the summer tyres very quickly compared to my experience on other cars, and I am not clear if it was the car or the tyre. but they did not wear appreciably faster than the originals.

Here in the Central belt of Scotland the local and trunk authorities are very good at keeping the roads clear and the only time you experience issues is during or immediately after very heavy snowfall and in the 200m or so out of housing estates. So I found it very hard to justify the cost and hassle of keeping two sets of wheels. I found the combination of using tyres that would perform acceptably in winter conditions, with the backstop of something like Snow Chains/ Snowsocks was an acceptable compromise for our climate. With wet weather being more prevalent that either snow or ice the extra wet weather grip all year round is potentially welcome.

If I lived in a remote rural area I'd probably want full snow tyres - but I don't.

BTW: I am talking about the "mountain" type of all-weathers such as the Bridgestone A001. I know that some manufacturers sell their summer spec as "all weather" - that's not the same thing.

[redbeard]

Thanks Michael. That's really helpful. Sounds like you're driving style and mine are quite similar.

[Renny]

It sounds like you should look at the winter tyres option to see what size of wheels and tyres will be appropriate. The limiting factor on wheel size is usually clearance around the brakes, but you should be able to drop to a smaller diameter wheel with higher profile tyres. For example my BMW is on 205/45R17 as standard, but the winters are 195/60R16.
The fashion/trend of wide low-profile tyres means poor winter performance as well as reduced ride comfort due to the shallow non-compliant sidewalls (run-flats are even worse). Also the power delivery of a large turbo diesel, which delivers large amounts of (rapidly increasing) torque at low speed put a premium on traction that summer tyres cannot cope with, even with four wheel drive.
Another factor is the traction control systems which work by cutting power and applying the brakes to the spinning wheel. This stops the tyre tread self cleaning (by spinning the snow out of the tread) and causing fulctuating torque levels. If possible turn the traction control off, or partially disabled to stop this.

[redbeard]

Thanks Renny. I do have the option of deselecting traction control. Might experiment with that in a clear area some time.

[YorkshireJumbo]

The turning onto our communal drive is a sharp right-angle from an un-ploughed, uphill minor road to a steeper hill. Our auto Honda on normal tyres wouldn't get up it in the snow despite tinker with tyre pressures and left-foot braking unless I cleared 2 long ruts of snow. In fact, it was so bad that I couldn't get going again on the road and had to go back down to the ploughed junction before I could get back up the hill to the bottom of the drive!

After 3 days of clearing snow for over 90 minutes each, I fitted some winter tyres, and never had a problem again. I sailed up in fresh snow, ploughing several inches of snow off with my front spoiler. Our next door neighbour with a quattro S3 on normal tyres struggled up it behind me. Another neighbour crawling past in her Range Rover tried to stop to chat to me when I was clearing snow, and didn't stop till the bottom of the hill, some 30m past me. Winter tyres make a huge difference, at least in snow. Mind you, the wife's Yaris on 175/65R14 tyres only failed to get up once. ISTR that taller tyres are better in snow and ice, but don't ask me why...

[Astraist]

I agree that snow tires should be used. They can increase the coefficient of friction from 0.2 (or less on proper ice) to 0.35 or 0.4. They are also necessary in cold winter conditions even if the snow is cleared off of the road, since "summer" tires will simply be out of the effective temperature range. It's also important to ensure that the tire is carefully inflated and that it's unworn and unaged. Four years of service at most (plus up to one year in storage), are likely to cause dryness and crazing that can reduce tire grip levels very sharply and require replacement.

ISTR that taller tyres are better in snow and ice, but don't ask me why...

Since the grip levels are reduced, the tires' ability of building up strong forces is reduced and the sidewall will not deform nearly as much as it would in dry conditions, so the inherent advantage of a low-profile tire is much reduced. On the other hand, low-profiel tires are typically performance-intended, and therefore their issues when operating in low temperatures is aggrevated. Wider tires also build up less heat, particularly when the rolling ressistance is reduced on hard-packed snow or on ice, or on none-abrasive tarmac.

Also, low-profile tires are meant to operate in conditions of quality. Bumpy roads (not as common in the UK, as I recall) makes the low sidewalls unable of dealing with the bumps and puts a toll on the suspension, so overall the grip level will be reduced. Also, once the grip levels of such a tire are exceeded, they will break-away much more sharply. The tire is also supposed to offer more control (even when the grip levels are exceeded) but on snow and ice this advantage is much reduced by the lower ressistance and acceleration values (and subsequentally the reduced cramming of the sidewall).

[YorkshireJumbo]

Since the grip levels are reduced, the tires' ability of building up strong forces is reduced and the sidewall will not deform nearly as much as it would in dry conditions, so the inherent advantage of a low-profile tire is much reduced. On the other hand, low-profiel tires are typically performance-intended, and therefore their issues when operating in low temperatures is aggrevated. Wider tires also build up less heat, particularly when the rolling ressistance is reduced on hard-packed snow or on ice, or on none-abrasive tarmac.

It also has something to do with contact pressure: same weight and narrower tyre means greater pressure. Many years BC (before children), we went on a cycling holiday across Bhutan around Christmas. The North-facing sides of mountain passes were sheet ice, and to get over them we had to over-inflate our tyres. People asked why we dildn't lower the pressure to increase the surface area, but would you rather go downhill over a length of ice on smooth or spiked shoes? I guess it is the same with car tyres - on Rally Sweden the cars certainly used very narrow, spiked tyres on snow and ice. It is also probably the reason the RR slid past me on it's infeasibly wide tyres - great for dry tarmac, but obviously useless on ice...

[Astraist]

Yes. On snow and other kinds of terrain (not on ice!) narrow tires "bite" into the surface, as do more grooves, angled tread patterns, tread blocks and little sipes in the tread help specifically in snow. Indeed, on the road and in a car (to differ from off-roading or bikes) over-inflation is preferable to under-inflation in almost any sense and way, Amongst other things, it keeps the tire rigid and increases it's ability to penetrate the snow or even the film of water on the road, as well as keep the tread pattern from deforming. One must keep in mind that in modern, steel-belted radials, the shape of the tread is not so dramatically changed by tire pressure.