Casualties of the snow

[steve_earwig]

*eyes glaze over*

I'll tell you what though, all this slippage is probably not going to be good for the old clutch...

[V6Exec]

Tbh I don't think I need to have someone tell me what acceleration is... What you say is wrong.

I can assure you that what I have said is correct.

When you depress the clutch the wheels go all of a sudden from 0 to 5mph (1st) or to ~double that (2nd gear). Of course you can modulate this by depressing the clutch very slowly, but not too much.

That is not correct - when you dump the clutch the wheels will accelerate, but equally the engine may decelerate depending on its inertia. And that is the key to everything inertia not energy. There will be a limiting friction that gives a maximum accelerating force without wheelspinning. If you exceed that limit the wheels will start to spin, as they spin they will throw up small anounts of the surface they are on (snow or mud for example) the reaction from that will provide a tiny accelerating force. Climbing out of a stream in a 4x4 one technique is to floor it an let is scramble out by digging down to good ground, climbing up a steep incline on good ground and you use the crawler gears and you do not wheelspin.

You just want road speed to match wheel speed (well, I don't agree: in certain situations wheelspin helps you going), since road speed is 0, you want to start the lowest possible. Torque is not a factor here. Of course in lower gear there is more torque: torque is just how much energy is transmitted to the wheel per engine rotation. Nm = Joules not by chance! This energy at stationary speeds is of course dissipated. Since total torque is constant (provided by the engine) lower wheel speed means more torque.

This is the crux of your confusion - accelerating a mass is not a matter of conservation of energy, it is an inertial problem and therefore conservation of momentum.

Have you ever seen F1 racers start in 2nd gear? Or racecars? Those also have so much power that they spin wheels at the slightest blimp of the throttle, even on the tarmac. What's the difference?

Launch control in F1 allows for maximum power transfer to the wheels by preventing them from going into a wheelspin. Sort of like ABS in reverse.

[OdinEidolon]

It gets a bit handwavey, but as well the torque T which causes Fd, there is the additional torque T' = I*d(omega)/dt (moment of inertia - fixed, multiplied by angular acceleration). This additional torque is the reason that, as you say, dumping the clutch in first would cause wheelspin but gently releasing the clutch is less likely to do so.

Now, there is more torque available in first than second (at a given engine power output): P = Tw. This is obvious - it is the reason you pull away in 1st, then move up to 2nd, 3rd, etc. The increased available torque means that rate of change of torque with transmission input speed (dT/dn) is greater, and so small movements of the throttle are likely to cause larger angular accelerations in 1st compared to 2nd. If this exceeds the frictional force Fr, the wheel will slip. The increase in transmission input speed can come either from further engaging the clutch (reducing clutch slippage) or increasing engine speed - they are one and the same as far as this is concerned.

Therefore for less experienced drivers, using 2nd means that their not-so-good clutch/accelerator control has less effect on angular acceleration and is therefore less likely to cause wheel slip. For experienced drivers, 1st gives you more control at the expense of requiring greater skill.

I believe that 3rd and above are not generally recommended since:
1) The output torque is so low that it begins to require good clutch control again in order not to stall the engine.
2) Due to the gear ratios the clutch slip duration would be longer in order that the vehicle can accelerate to above stall speed before the clutch is fully engaged, and that final speed would be too high for the conditions.

You are entirely correct in that some slipping is required, in fact the coefficient of friction of rubber increases slightly as it begins to slip (weird material).

As a side note, I notice you used "\mu". Are you a TeX user by any chance?

Agreed on that one and in general on the above.
Of course I am a Tex user . I graduated in physics in november and for a physicist knowledge of (La)TeX is almost compulsory

[Welly]

@rwb - sorry you hit the curb mate, you can't help it sometimes if that's where your heading that's it - game over.

My Winter tyres have been a dream this weekend; all my neighbours have had to leave their cars at the top of our hill but not me I paid £260.00 second hand (all with 8mm tread and about 12 months old) and they've been worth it. I reckon I will get at least 4 x seasons out of them, and like Bailes said they save you wearing your expensive Summer tyres out.

I've been doing up to 45mph on the snow but the trouble I've found is that I'm getting stuck behind everyone else on their 'summers' I did a couple of overtakes but felt a bit of a knob head so just ended up towing the line

I can also choose untreated roads and get home quicker

The biggest problem by far with winter tyres in the UK is other drivers not having them, you have to drive for them and expect the worst.

[DaiRees]

And as for the "I'll just drive carefully" argument, it's bunk. When there's ice and snow on the road, there is no way you can drive carefully enough that you're able to stop if someone runs out it front of you, even if you go 10mph and cause a traffic jam. Summer tyres are absolutely useless on snow and ice, even on dry roads in cold weather winter tyres fare better. Only if by "driving carefully" you mean "I'll stay home if there's any snow at all" can your decision to forego winter tyres be OK in any way.

I've just driven 15 miles to work, I drove down my street which is pretty bad with compacted snow (although it's much better since I personally cleared the turn around area at the top and gritted the whole street yesterday), maybe 100 metres to the next road, which is clear, then a main road, then a dual carriageway, then another main road, then an access road (which has been cleared) then the works car park which has a bit of snow but is dead flat. So I was actually on snow & ice for about 110 metres out of the 15 miles, the rest is just wet roads. I'll do the reverse trip this afternoon and that's my lot, tomorrow it'll be better, in a couple of days there'll be nothing.

Temperatures are dropping to about -3 overnight and are reaching +3 during the day this week, any frequently used roads are gritted so they aren't icy, they're just wet. I appreciate that the performance of my Pirelli PZero tyres may be reduced due to the temperature, but I'm aware of this and am driving carefully to compensate for it. This is still considerably less dangerous than the millions of people driving around on shyte quality or poorly maintained tyres .

2 weeks ago it was 10 degrees and raining, the long range forecast for a week today says 6 degrees and raining, and that's winter finished! So, the upshot is that if I had winter tyres they'd only really be useful for 2-3 weeks, and would actually have done less than a mile on snow and ice. And they want £1000 for a decent set of winter tyres on rims for my car??! IN MY CASE it simply isn't worth it.

Last year it didn't snow at all where I live and the year before that we had one downfall similar to the one we've just had.

That's still not to say that I won't get a set, if I luck into a good used set (like Welly ya jammy bastud ) and/or if I can afford it (which I can't at the moment) I may get a set for next year, but having said that for a grand I could buy a fairly decent 4X4 and keep it in my garage in case of snow

There's also the potenial that a set of winters might make me take more risks, rather than spending the weekend taking my kids sleighing and playing in the snow, sitting in the house watching telly, drinking wine and generally talking bollocks on the internet, I'd have probably gone out for spin "just 'cos I can", potential for disaster there!

[Welly]

I have to say I was dead lucky to get my tyres, they were advertised late one night on the Volvo forum and I sent a PM to the seller at 07:00am the next morning. If it wasn't for this I wouldn't have bothered with them. I needed two fronts anyway so it all kinda fell into place.

Dai's right though it's only the side roads that get bad in the UK. The councils do a good job gritting and clearing the main roads, and of course there's that much traffic the poor little snow flakes don't stand a chance.

[KozmoNaut]

Temperatures are dropping to about -3 overnight and are reaching +3 during the day this week, any frequently used roads are gritted so they aren't icy, they're just wet. I appreciate that the performance of my Pirelli PZero tyres may be reduced due to the temperature, but I'm aware of this and am driving carefully to compensate for it. This is still considerably less dangerous than the millions of people driving around on shyte quality or poorly maintained tyres .

2 weeks ago it was 10 degrees and raining, the long range forecast for a week today says 6 degrees and raining, and that's winter finished! So, the upshot is that if I had winter tyres they'd only really be useful for 2-3 weeks, and would actually have done less than a mile on snow and ice. And they want £1000 for a decent set of winter tyres on rims for my car??! IN MY CASE it simply isn't worth it.

I don't know which kind of tyres you're used to, but Pirelli PZeros are absolutely rubbish on cold wet roads. If you've tried driving around on average winter roads on a good pair of winter tyres, you'd know that there is absolutely no comparison. "Driving carefully" is all well and good, but are you absolutely certain of how long your braking distance is on a near freezing cold wet road driving on performance summer tyres?

As long as temperatures are below 10 degrees, winter tyres fare better than summer tires. They have softer rubber compounds to deal with lower temperatures as well as aggressive tread patterns to deal with snow (and mud). So they are in fact tyres for general winter conditions, including slush and wet roads. Dedicated snow/ice tyres are something else altogether, they usually have studs in them or look like gnarly offroad tyres (because that's what they are).

I live in Denmark, we have pretty much the same climate as the UK. Some snow, but mostly slush and temperatures hovering right around the freezing point. Winter tyres are not strictly necessary 60-80% of the time, but when they're needed, they're really NEEDED to make any sort of safe progress. I have mine on generally from November till March, which is when the average temperature climbs above 10 degrees.

[DaiRees]

I don't know which kind of tyres you're used to, but Pirelli PZeros are absolutely rubbish on cold wet roads. If you've tried driving around on average winter roads on a good pair of winter tyres, you'd know that there is absolutely no comparison. "Driving carefully" is all well and good, but are you absolutely certain of how long your braking distance is on a near freezing cold wet road driving on performance summer tyres?

As long as temperatures are below 10 degrees, winter tyres fare better than summer tires. They have softer rubber compounds to deal with lower temperatures as well as aggressive tread patterns to deal with snow (and mud). So they are in fact tyres for general winter conditions, including slush and wet roads. Dedicated snow/ice tyres are something else altogether, they usually have studs in them or look like gnarly offroad tyres (because that's what they are).

I live in Denmark, we have pretty much the same climate as the UK. Some snow, but mostly slush and temperatures hovering right around the freezing point. Winter tyres are not strictly necessary 60-80% of the time, but when they're needed, they're really NEEDED to make any sort of safe progress. I have mine on generally from November till March, which is when the average temperature climbs above 10 degrees.

Are you purposely going out of your way to miss my point?

Firstly, there are very very few people on the roads of the UK with winter tyres, estimated at around 3%, the vast majority of drivers don't use them. I've already stated that I know that the performance of my tyres is going to be affected by cold temperatures, but to say that they are "absolutely rubbish" is plainly rubbish, you have to compare them like for like and in any conditions they're going to behave as well, if not better, than most equivalent tyres. Of course, winter tyres will perform better in cold / snow / ice conditions, I'm not arguing with that, my argument is that we don't get enough of those conditions to justify the outlay of £1000, it's a simple cost / benefit calculation.

So far this winter we've had one snow-fall that caused a bit of disruption (the first snow in 2 years). Other than that we've handful of nights where the the temperatures have dropped below zero, but all the major roads have been treated so, while driving to work the following mornings there has been NO ICE on the roads near me. Even on the rare occasions when there is ice, it's usually all gone by lunch time, so a little extra care is needed in the mornings. So I'm driving on cold, wet roads, not snow, not ice! I am more than capable of adjusting my driving to take account of these conditions. I don't have problems stopping because I drive safely and allow plenty of space, when I need to do an emergency stop I invariably end up looking in the mirror to moderate my braking in order to avoid a rear end shunt.

Strange that the companies advertising winter tyres market them as "Improved performance in temperatures less than 7 degrees", yet you've now chosen to up this to 10. Fair enough, I still maintain that we only really spend a few weeks a year with those kind of temperatures, mostly our winters in the Welsh Valleys are mild, gray and drizzly!! A quick google tells me that your average winter temperatures in Denmark are considerably colder than ours, and that you get significantly more snowfall, so while our climates might be "similar", you clearly get harsher winters than us.

The upshot of my argument is that, FOR MY PERSONAL SITUATION, winter tyres are not financially viable and, while I don't argue for a second that they would be beneficial for a few weeks each year, they simply are not needed. Someone living in Scotland or the North of England, or someone in a rural area may feel differently.

To be honest, should 50% of the British population suddenly decide to start using winter tyres, that would be a far more dangerous situation. Imagine driving along in a traffic queue where half of the cars could stop 20% better than the other half, there'd be carnage!

Once again I'll state that, should I suddenly come into money, I'd happily get a set of spare wheels and winter tyres for my Volvo, but then I'd be very aware that I'd still need to drive carefully to account for all those around me who didn't have them! Or again, for the same kind of money I may opt to get an old 4X4 and leave my lovely car safely at home.

[trem1]

so you dont think winter tyres are any good then Dai............................

[DaiRees]

so you dont think winter tyres are any good then Dai............................

Fek arf Trem.....

[trem1]

found this interesting

http://www.youtube.com/watch?feature=pl ... Ov2g5qTpvA

[OdinEidolon]

Or again, for the same kind of money I may opt to get an old 4X4 and leave my lovely car safely at home.

Do not fall in the common error... a 4x4 without winter tyres is not much safer than a standard vehicle without winter tyres. You have more traction but the overall handling and grip on snow lower due to the higher body and high weight. small 4x4 + 4 good winter tyres is the best

[trem1]

Or again, for the same kind of money I may opt to get an old 4X4 and leave my lovely car safely at home.

Do not fall in the common error... a 4x4 without winter tyres is not much safer than a standard vehicle without winter tyres. You have more traction but the overall handling and grip on snow lower due to the higher body and high weight. small 4x4 + 4 good winter tyres is the best

oh i think Dai of all of us is aware of the handling of 4x4's, did you ever see any pic's of his Suzuki out in the wild ???

[OdinEidolon]

Or again, for the same kind of money I may opt to get an old 4X4 and leave my lovely car safely at home.

Do not fall in the common error... a 4x4 without winter tyres is not much safer than a standard vehicle without winter tyres. You have more traction but the overall handling and grip on snow lower due to the higher body and high weight. small 4x4 + 4 good winter tyres is the best

oh i think Dai of all of us is aware of the handling of 4x4's, did you ever see any pic's of his Suzuki out in the wild ???

Unfortunately not, but must be good stuff . Suzuki makes some great small offroaders.

[trem1]

im sure Dai will oblige with a few photo's