I'm not sure if the long topic title will be fully readable on forum users devices so I'll repeat it here...

Which is better in snow, a random hatchback with 4x4 on summer tyres or the 2wd version of the same car on winter tyres?

This always comes up on Elgrand forum whenever there's a bit of snow. I have the 4x4 version(s) and reckon they're better in snow on random tyres than the 2wd version on winter tyres but others disagree.

Yes.

th.

;-)

Depends if the 2wd version is front or rear wheel drive. I've driven my father in laws FWD Audi A2 on winter tyres in far more snow than we are ever likely to get in the UK and it was reasonable. Not as good as my 4WD Range Rover on All Season (but 3 peaks marked) tyres though.

Obviously the best case is to have 4x4 with diff locks and snow tyres...

I mostly mean which is most likely to have push traction to go up a slippery snowy hill rather than preventing the driven end going sideways. Push traction if the driven end doesn't go sideways.

If only 2wd much might also depend on the front/rear axle weight balance, front wheel drives generally better for traction than rear wheel drive because the front end is usually heavier? But some vehicles have equal front/rear balance so would have equal (or arguably more uphill traction) if rwd compared to fwd?

I said summer versus winter tyres but could also include cheap tyres that tend to have big gaps in tread patterns, I suppose the manufacturers use less rubber if there are big gaps in the tread.

Edit - I mentioned quite a lot of things but assuming all other things such as LSD or no LSD being the same. Some vehicles have pseudo LSD (brakes a spinning driven wheel so acts like an LSD). If we're comparing a 2wd vehicle that has that kind of equipment it should be against an equivalent 4x4 that has that kind of equipment.

If going uphill, even with 50/50 weight distribution, the centre of balance will move rearwards so the rear wheels will have a better chance of getting some traction than the fronts. However, as the weight of the vehicle will be trying to push it back, there's a greater chance of it going sideways, whereas if FWD, if a wheel loses traction it will just spin.

Diff locks are over-rated and not needed and as this is primarily a P38 forum, you should be aware of what they can do. What astounded me just over a year ago when I was in Latvia, was just how good the P38 is in snow. Admittedly proper snow, none of this wet, slushy stuff we get here that unnecessarily causes the whole country to grind to a halt because nobody knows how to drive, but around a foot and a half on roads that hadn't been cleared and 2-3 inches of hard packed snow on the roads that had (all they do is run a snowplough down the road so you can see where it is and let the traffic eventually clear it down to tarmac). As mine is pre-99, it only has 2 wheel traction control on the rear (what you call pseudo LSD) but even then I had to try really hard, gearbox in Sport mode and floor the throttle, to get it to kick in. Father in Laws Audi on winter tyres went where you pointed it but could spin a wheel if I tried hard. In both cases, ABS would kick in if I hit the brakes hard but not under normal braking. But, I suspect if I had been on summer tyres, the little Audi would run rings around me.

Big gaps in tread are there to shift water to prevent aquaplaning and a lot of performance tyres have big gaps. It seems counter-intuitive that less rubber on the road will give better grip but it will under anything other than smooth, dry tarmac (when you want slicks) making them better suited to UK weather. Winter tyres have multiple tiny grooves (sipes) so you have more sharp edges to give better grip and are made of a rubber compound that remains flexible at low temperatures. Standard tyres don't really like anything below around 7 degrees C as the rubber compound loses flexibility.

So the number of driven wheels and where on the vehicle they are is less important than the bit that is between the car and the surface, the tyres. In fact, a few years ago I had a set of Goodyear Wranglers on my car and we had the standard UK winter one inch of snow and it slid around all over the place. Fitting All Season tyres then made it quieter in the dry, a lot more stable in the wet and actually went where I pointed it on snow.

Yes, when I was talking weight distribution and fwd/rwd I did realise that centre of gravity moves a little further to the rear if facing uphill so if we had a car with 50front/50rear balance it might become 52/48 facing uphill (or during acceleration). I don't think that's quite the full picture regards shifting axle weights, at least not if we were talking about cornering and moments of inertia etc, but it probably makes the difference we both thought for axle weights and traction on the hill.

Spinning a wheel on the Audi implies it probably doesn't have pseudo or real LSD, or does it? I suppose being an Audi it will be front end heavy...

4wd has another advantage when its patchy because one axle might be on a slippery patch while the other axle still has good traction.

The Audi A2 uses the same engine and transmission as a VW Polo, so no LSD, just plain old front wheel drive. It's the tyres that make the difference on snow. However, the snow we get occasionally in the UK isn't real snow but wet slush so rain tyres would be almost as good as winter tyres. The problem comes when that turns to ice and you aren't going to get much grip on that unless you use studded tyres. The salt they put on the roads also has an effect. It causes the snow to melt but if there isn't enough, the melted snow then freezes on the road surface. In countries that get a lot of snow, they often don't use salt. They plough the road and then the traffic clears it.

I would think the weight transfer is greater than you suggest. I did police driver training many years ago (the normal blue light training not the full pursuit training unfortunately) and was taught to lift of the throttle as you come into a bend at speed then go back on the throttle. You don't lose any speed but the weight transfer moves the weight further forward over the front wheels to give better grip in the corner.