Snow tyres - cornering slip angle

To recap from another thread. With winter looming I fitted Michelin snow tyres just to the rear of the Focus to replace the shagged original tyres and am not having a happy driving experience. Even in the bone dry the back end feels like it's about to step out all the time, and often in fact does so if I push it a bit too hard.

I'm finally getting a handle on it all. It's partly about lower absolute grip from the snow tyres but more about cornering slip angle I believe. The snow tyres appear (feel) to be operating at a much higher slip angle than the front summer tyres causing oversteer which then leads to unbalance and in extremis to the back stepping out. In essence it's a similar thing to using radials on the front and crossplies on the rear which is stated to be a big no-no. I can now see why.

This explains why the feel improves when the rears are heavily over-inflated as this reduces slip angle but nothing like enough to fully mask the problem. Until I either get two more matching snow tyres for the front or some spare summer ones for the rear until winter really sets in I'll stick the existing snows on the front and the front summers on the rear. At least then all it should do is understeer like a pig but hopefully not visit any shrubberies backwards which it keeps threatening to do. Happily the dashboard "bendy thing sorter out" light comes on when this happens and tends to keep everything under control.

I can find very little online about the slip angle of snow tyres vs summer ones. Any links would be appreciated. It might also serve as a warning to anyone contemplating doing the same.

Reply to
Dave Baker
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My opinion of someone who fits winters on one axle only would cause paper to blacken and telecoms wires to burst into flames.

Reply to
Steve Firth

Update:

Swapped the tyres round this afternoon - snows on the front and Toyo CF1s on the back now and took it out for a good thrash. What a feckin difference :)

It now actually feels like a proper car again. Yes there's a fair bit of understeer but at least the rear end now feels like it's on rails and everything is progressive and safe. I can exploit the full grip of the fronts knowing the back will still have loads of grip in reserve and never snap out on me. I can actually feel the front snow tyres loading up properly and progressively as cornering speed increases whereas when they were on the back it just felt like two marshmallows back there squirming about and trying to turn the back end more than the front even at modest cornering speed.

Absolute dry grip is probably only about 80% of the best summer tyres like my previous Michelin Pilot Primacies so it's no longer a sports car in terms of cornering G force but I'd say it's at least as good as an average family saloon on skinnier and higher profile rubber than my 205/50/16s.

The other strange thing is wet and dry grip seem almost the same. I'm used to about a 20% differential on summer tyres but the snow tyres don't really seem to care how wet it is. They just seem to have a grip limit of X and you get that whatever the tarmac surface is like. The very soft rubber designed to stay pliable at low temperature plus the high void ratio tread blocks really clear water and bite down to the tarmac but then probably shuffle about so much in the dry that grip doesn't go up much.

What I did immediately notice though was how much more traction they have on the muddy loose surface gravel farm tracks I have to use to get to and from the new house. Instead of just sliding around on those you can really feel them dig in and bite. Now I'm really looking forward to some proper snow up here in Scotlandshire this winter so I can test them out properly.

Reply to
Dave Baker

Well if you read the original thread I intended to have all four tyres swapped over but after doing the back ones we found the other two snow tyres had cracked sidewalls and we had to leave the original summer front tyres in place for the time being.

Reply to
Dave Baker

I did read the thread. Doesn't excuse what you did.

Reply to
Steve Firth

Um, once the snow comes (unless you put winter tyres on the back before then), won't you be back in the same situation you've just left, i.e., grippy tyres on the front and slippery ones on the back?

Tim

Reply to
Tim+

do fwd cars actually need winter tyres on the back? most of the difficulty in snow comes from a lack of steering, acceleration or stopping power, all of which are almost entirely on the front wheels.

Reply to
Mrcheerful

Given the difference in grip summers vs winters, I'd not want to drive a mix. I'd expect if you had summers on the back, winters on the front, going downhill might get interesting as the back overtakes the front.

Reply to
Chris Bartram

I don't know about downhill,but driving AWDsin the snow was fine for starting & uphill but you couldgo a long way sideways in the snow with very little warning.

Reply to
Duncan Wood

There are two possible schools of thought on that. If it does snow really hard I don't actually have to go out if I don't want to because I don't have to commute to work. I'll make sure there's a few weeks worth of food in the freezers and I can stay in the house with the central heating on snug as a bug in a rug until conditions improve. If I do want to go out the main challenge will be slithering my way up the steep farm track and then I'm on gritted and snow ploughed main roads. I only need the fronts to grip to get up the farm track. The back end is irrelevant.

However if I want to go and play really hard on snowy and icy back roads I can fit the spare two snow tyres with cracked sidewalls on the rear. They don't lose any air pressure because it's only surface cracks and the loadings on the back end are minimal compared to the front end so they'll manage ok.

In the past I've always coped perfectly well on normal tyres in heavy snow so proper snow tyres will actually be a luxury rather than a necessity. I'm just dying to see how they improve grip though. I'm told it's pretty dramatic.

Even the farm track is unlikely to stay snowed in for long. Davey the farmer will plough it clear every day for those of us who live further down the track and pull out anyone who gets stuck with a tractor. Sod's law says it probably won't even snow hard but I'm hoping it does. A proper winter would be really nice after the occasional few days of thin mucky slush which is all we've had down south in recent years.

Reply to
Dave Baker

your problem is more likely to be extended power outages

Reply to
Mrcheerful

When it comes to stopping all cars are equal. They all have 4 wheel brakes.

FWD and 4wd gives them the means to get to a speed where they stand no chance of stopping. While with Right Wheel Drive they would never have got it out of the car park. Fishtailing is how it says that's enough and no more.

Reply to
Peter Hill

Captain Redbeard Rum lives!

There's no doubt one school that shares your opinion (consisting of you) and "Everyone else".

Reply to
Steve Firth

Did I run over your cat or something or are you just naturally grumpy? Time of the month maybe?

Reply to
Dave Baker

Coming back home last night down the fairly steep farm track I got to the last corner before my house and the builders who are converting a steading further down the track were coming up on the way back home. One boy in a hatchback in front and a van behind him. I pulled over as far as I could and waited but to get past me the car in the lead had to put its nearside wheels off the track and into the muddy, grassy verge which after the rain we've had up here is basically 4 inch deep mud with some grass on top. At this point with a reasonable gradient working against him he stopped dead with wheels spinning madly so I reversed up out of the way and let them both get past me on a wider part of the track.

On the way out today I tried a little eggsperiment to see if the M part of the M&S designation on the tyre sidewalls actually means anything. I drove up to the same spot he got stuck in and put both nearside wheels into the same bit of mud and stopped the car. Then I tried to drive out uphill from a standing start with two wheels in mud and two on solid track. A fair bit of wheelspin sure enough but she hauled herself out with no trouble at all. I was suitably impressed. If this gives any indication of what these tyres can do in snow I'll be in good shape if it snows hard this winter.

Reply to
Dave Baker

The difference is remarkable IME. At first, the winters feel a bit vague on dry roads before it gets really cold, but below 2 deg or on snow/slush they're great.

Reply to
Chris Bartram

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