Viewing 25 posts - 41 through 65 (of 65 total)
  • 4×4 or 2wd with snow tyres?
  • molgrips
    Free Member

    The section of road is the A6 between Buxton and Bakewell:

    Blimey, I thought you meant some farm track or country lane somewhere.. just get winter tyres!

    coffeeking
    Free Member

    4wd with snow tyres, of course.

    The section of road is the A6 between Buxton and Bakewell:

    Lol, just get a half decent modern car with snow tyres.

    For the record I have ploughed around all over scottish snow-covered roads in both a normal fwd diesel and a 4wd sports car with 125mm ground clearance (permanent 4wd with LSDs) and I’ve never got stuck once – it’s largely about how you drive it and sticking within sensible limits. That said I’d rather go out with the 4wd over the fwd, but snow tyres on the fwd make a world of difference. That said, I would rather have a nice tall 4wd with M&S tyres over any of them for those times when it gets really nuts, but it’s not common enough to bother the rest of the year with.

    BearBack
    Free Member

    4wd is NOT a replacement for winter tyres. 4wd will help you go but won’t do anything to help you stop!
    Whilst 4×4 would be better than 2wd without winter tyres, the false confidence that 4wd gives you is far more concerning to road safety that the actual increased safety that 2wd on 4 matched winters gives you.
    Mikewsmith… Knowing how to get unstuck isn’t really the point. Being able provide stop/go/steering input in order to react to other road users to keep yourself safe is far more significant.
    Something along the lines of an imprezza/xdrive/quattro probably doesn’t give up too much mpg over 2wd alternatives.

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    coffeeking
    Free Member

    4wd is NOT a replacement for winter tyres. 4wd will help you go but won’t do anything to help you stop!

    Strictly, 4wd helps you go as well as you stop in snow (by bringing 2 more contact patches into the mix). You just normally stop better than you go with a 2wd 🙂

    By far the biggest risk I see people taking is not getting stuck, it’s ploughing around at stupendous speeds in snow and ice. I spend half my time driving in snow adjusting my own direction and speed to predict where morons will go sailing across junctions and potentially take me out.

    Northwind
    Full Member

    My crappy Focus with Icebears on pulled a stuck freeloader out of pitmedden once 😆 That was mud rather than snow but same rules apply I think.

    With the mondeo and snowproxes I always suspect it’s a little bit too good at getting going, it’d be relatively easy to get in trouble if you don’t keep your head engaged. So many people obsess about getting started and don’t think so much about the other end of the equation.

    But as far as making progress in fresh snow, on the flat the limiting factor is when it’s ploughing so much snow in front of it that it comes over the windscreen (er, and crushes the front splitter, ah well)

    mattzzzzzz
    Free Member

    Have had a 4×4 for the last ten years up til last spring, bought snow/ winter tyres for the mundano this winter and we haven’t **** had any snow!!!!

    coffeeking
    Free Member

    Have had a 4×4 for the last ten years up til last spring, bought snow/ winter tyres for the mundano this winter and we haven’t **** had any snow!!!!

    This actually happened with my other half’s car. We had an epic winter (-17, gelled my diesel!) and she decided to invest. Sod all snow ever since.

    retro83
    Free Member

    ^^ Can you two buy wet weather tyres next year please?

    coffeeking
    Free Member

    Sure, I made sure she got rain tyres with her new car but it doesn’t seem to have helped. Maybe it’s because the snow tyres are still sat on the old car in the drive rotting. I’ll palm them off on someone.

    BearBack
    Free Member

    (by bringing 2 more contact patches into the mix)

    I would argue that a 2wd car has the same number of wheels as a 4wd car. 😉

    trail_rat
    Free Member

    And i would argue that having 4 driven wheels you can use engine braking to provide controled 4 wheel braking and even hill decent if you have a low box. Soon as you touch the brakes going downhill youll slide and 1st gear isnt low enough, ive watched it happen many times while i sit at the top and watch them before engaging low box and letting the engine braking guide me down slowly and safely with no sliding.

    coffeeking
    Free Member

    I would argue that a 2wd car has the same number of wheels as a 4wd car.

    But not active in “going” as they are with a 4wd 🙂

    molgrips
    Free Member

    And i would argue that having 4 driven wheels you can use engine braking to provide controled 4 wheel braking

    Don’t get this. Why is 4wd engine braking any different to the same retarding force applied through the brakes?

    trail_rat
    Free Member

    Dont do much off roading then,

    Going down hill and apply the brakes – youll get weight shift to the front and your bias vslve will send more power to the front brakes and youll lock up once you lock up on ice you will speed up!

    First thing i was told when i started off rosding was – if your using your brakes on the course your in the wrong gear. ( trials not comp safari)

    Obviously if you have abs and other such driver aids then you may well be ok – although our transit – the only we we could get it to move on snow even on winters was to pull the traction control and abs fuses.

    coffeeking
    Free Member

    Don’t get this. Why is 4wd engine braking any different to the same retarding force applied through the brakes?

    As Trail_rat says, if you go for the brakes MOST cars will put 80%+ of the retarding torque through the front wheels. Also, it’s usually quite sharply applied as modern cars are generally over-servo’d. Engine braking with a true 4wd it’s pretty spectacular what you can maintain control on. Naturally it won’t help in an emergency brake situation where you’d not get enough braking from engine braking anyway, but in a “driving around the streets slowly” situation, engine braking is really light years better than just braking. My car has EBD control and that’s pretty good but still nothing compared to 4wd engine braking for smooth slow control. MAybe some of the modern ones that just vary pressure rather than applying slip/grip/slip to wheels might be better – not tried them. 4 wheel engine braking is what the hill descent control gadgetry tries to emulate using brakes on modern 4wd’s, assuming the driver has no skills.

    mattrgee
    Free Member

    2WD with snow tyres it is then! Cheers.

    molgrips
    Free Member

    The Passat applies the rear brakes in preference, to minimise dive apparently.

    If one wheel slips under engine braking, would the other one on that axle not slip if you didn’t have diff lock?

    What’s the difference between hill descent and ABS?

    trail_rat
    Free Member

    The whole idea behind using engine breaking is to slow in such a way that you dont lose traction.

    Ive driven up and down this several times ( i lived at the bottom with no other way in and out) in my land rover on toyo open country m + s road biased ats

    trail_rat
    Free Member

    Abs is like repetitive stabbing of the brakes – the hill descent in my parents rr is like dragging the brakes on your push bike.

    Woody
    Free Member

    The Passat applies the rear brakes in preference, to minimise dive apparently.

    Seriously? Have you any more info on that as I would doubt that any car would employ a rear wheel braking preference. Are you getting this confused with ‘hill descent control’ which some vehicles have?

    coffeeking
    Free Member

    Applying rear brakes instead of front first wouldn’t reduce dive, dive is caused by the longitudinal weight transfer set up when the car is decelerated, regardless of which wheels trigger it. Its a suspension design outcome. The only way to reduce dive on an existing car with any particular brake setup is brake less harshly!

    coffeeking
    Free Member

    If one wheel slips under engine braking, would the other one on that axle not slip if you didn’t have diff lock?

    Quite the contrary in some respects but with the same net result yes. Open diffs provide equal torque at the wheel outputs. In a powered situation, the wheel that slips sets the torque that the other wheel sees (basically zero) which is why they are not great. In engine braking the same applies, whichever slips first will cause the other to provide very little retarding torque. But the wheels will still tend to be turning at speeds similar to the passing snow/ice so they are more likely to regain traction quickly again. However the point is not to break traction at all, as this is often unrecoverable. Much like when walking down a snowwy slope in slippy shoes, if you stomp down trying to get maximal impact braking from your feet quickly you will tend to slip, if you try to smoothly maximise braking over 10 steps you probably won’t slip. Of course you still may run into a tree if it was too close 🙂

    ABS waits for traction to be lost, or be about to be lost, then stabs the brakes repeatedly. Hill descent is a much more controlled method and is done different ways by different manufacturers but its aim is to maintain controllable slow descent without ever breaking traction and without large braking inputs.

    coffeeking
    Free Member

    The big issue is that descent control usually only features on off roaders, whereas gears and engines feature on all cars with similar effect. Of course engine braking is vastly improved if you have 2 axles braking instead of 1, and is even better with snow tyres instead of all season.

    molgrips
    Free Member

    Seriously? Have you any more info on that as I would doubt that any car would employ a rear wheel braking preference. Are you getting this confused with ‘hill descent control’ which some vehicles have?

    I read it on a forum, cos usually the rear pads wear more than the fronts apparently. Not entirely sure if it’s true but here’s some more info/mis-info.

    The whole idea behind using engine breaking is to slow in such a way that you dont lose traction.

    Exactly the same aim as ABS, hence my question. From what you’ve said, if ABS was quick and/or clever enough it would be the same.

    coffeeking
    Free Member

    No it’s not the same as ABS. ABS provides on-off modulation, engine braking provides smooth constant torque. ABS working its bits off is effectively descent control (super fast actuation of each wheel independentl) and is still not as good as proper engine braking on a locked 4wd, but is a close approximation for most uses. However the key difference is that ABS is designed to allow some slip, as that is where best braking lies on tarmac. In snow you absolutely cannot have slip, it’s a subtle difference that requires slightly different control algos which is why it needs to be specifically engaged on cars that use it. Incidentally cars that use hdc and have low range available usually combine both for best effectiveness.

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