Questionable snow facts

[Dactyl]

These two "facts" have been presented to me over the last couple of days in reference to the recent weather. Can anyone shed any light on their veracity?

1. Due to a puncture on Sunday my front drivers side wheel has a space saving tyre on it. Not ideal for driving in slippery conditions I thought, however, when I went to get the tyre replaced the mechanic said "You'd be better off having four of those on when driving in snow". My own logic tells me "Thicker tyre = better grip", who's right? (I'm assuming he is, but I'd like an explanation why).

2. Someone yesterday said "All the gritters in Stockholm couldn't grit all the bus routes in central London". Is this true, false or true but misleading?

[jw]

Originally Posted by Dactyl

These two "facts" have been presented to me over the last couple of days in reference to the recent weather. Can anyone shed any light on their veracity?

1. Due to a puncture on Sunday my front drivers side wheel has a space saving tyre on it. Not ideal for driving in slippery conditions I thought, however, when I went to get the tyre replaced the mechanic said "You'd be better off having four of those on when driving in snow". My own logic tells me "Thicker tyre = better grip", who's right? (I'm assuming he is, but I'd like an explanation why).

Would it not be just a question of balance? Assuming of course, that this is what he meant. I can't see how four of the smaller tyres would be better for grip than four standard ones.

As for the other question, we could have done with some of those Stockholm gritters yesterday, too!

[Dactyl]

Originally Posted by jw

Would it not be just a question of balance? Assuming of course, that this is what he meant. I can't see how four of the smaller tyres would be better for grip than four standard ones.

He certainly meant it would be easier to drive in snow with four thin tyres rather than four standard tyres. My boss says he's possibly right but can't explain how.

[Jay Tea]

I'd have assumed that a wider tyre 'footprint' would be beneficial in snow. Winter tyres differ from regular tyres in terms of tread pattern and rubber compound - it makes sense that the more of this in contact with the ground, the better.

[Zachary Fizz]

Originally Posted by Dactyl

These two "facts" have been presented to me over the last couple of days in reference to the recent weather. Can anyone shed any light on their veracity?

1. Due to a puncture on Sunday my front drivers side wheel has a space saving tyre on it. Not ideal for driving in slippery conditions I thought, however, when I went to get the tyre replaced the mechanic said "You'd be better off having four of those on when driving in snow". My own logic tells me "Thicker tyre = better grip", who's right? (I'm assuming he is, but I'd like an explanation why).

2. Someone yesterday said "All the gritters in Stockholm couldn't grit all the bus routes in central London". Is this true, false or true but misleading?

I don't know about gritters in Stockholm, Dactyl, but as for point 1, I think your mechanic is right. Driving in snow is about getting as much weight onto the contact patch as possible - one way is to put a sack of spuds in the boot, and another is to reduce the size of the contact patch by using narrower tyres.

Curiously, that's the oppostie of the type of off-road driving that I do - in the desert, you want light weight, spread across as much rubber as possible. So we use wide tyres, with very low pressure.

[BluesScale]

A thinner tyre would put more pressure per square inch on the ground and so be more likely to get to road surface. However, if it didn't then it would have less grip. I think that the answer to this one would be "It depends"

Blues

[A Turtle Named Mack]

Originally Posted by Zachary Fizz

I don't know about gritters in Stockholm, Dactyl, but as for point 1, I think your mechanic is right. Driving in snow is about getting as much weight onto the contact patch as possible - one way is to put a sack of spuds in the boot, and another is to reduce the size of the contact patch by using narrower tyres.

Curiously, that's the oppostie of the type of off-road driving that I do - in the desert, you want light weight, spread across as much rubber as possible. So we use wide tyres, with very low pressure.

Consider a NASCAR racing tire, and probably most other race types other than road rallies where you encounter all forms of weather and road conditions. They are very wide and completely bald. Why? Because when you have an excellent traction surface on the road, you want as much rubber in contact as possible. Now consider a general purpose tire, and how they advertise the ability to handle slick conditions - the point of the patterns is to allow a smaller surface area which can push down through the water (which at higher speeds can be firm enough for you to ride on top of, which is what hydroplaning is - not fun at all, if there are any obstacles). A narrower 'doughnut' tire (as we call them) does much the same thing, but has the drawback that you cannot drive faster than about 50 mph, which limitation is a good idea on snow-covered roads as well.

The counter-consideration is that placing concentrated weight generates heat which can create a thin layer of liquid water on top of ice. This is what makes ice skates so effective - you have a lot of weight on thin blades, which liquefies a bit of ice for you to ride atop. Ice itself would not be nearly so slick.

So I think the answer would be - if you are riding on fluffy or crunchy snow, the thinner the tire the better, but if you are riding on ice, a much broader tire would be preferred. But realistically, if you are going over ice, you had better have studded tires or 'snow chains', or better yet, stay home.

[Hans Off]

My thoughts...

1. He probably means/thinks that the thin tyres will cut though the snow and reach the road surface fininding some magic grip...

Maybe in 1% of road conditions you encounter, but not in nearly every other 99%!

Fat wide tyres are better for deep/packed snow, you want as much surface area and (oddly) rolling resistance under engine load as you can get. Same logic as desert tyres but with a softer compound and different tread.

2. Most probably Not sure what the road mileage in London is, but it is enormous. I would put a lot of money on "true"

[Hans Off]

Originally Posted by A Turtle Named Mack

The counter-consideration is that placing concentrated weight generates heat which can create a thin layer of liquid water on top of ice. This is what makes ice skates so effective - you have a lot of weight on thin blades, which liquefies a bit of ice for you to ride atop. Ice itself would not be nearly so slick.

That's what I thought, but apparently it doesn't entirely explain what is going on...

http://www.bbc.co.uk/blogs/theonesho...ce-slippy.html

[RichardM]

Look at the tires used by competitors in rallies where it is snowing. Generally those tires are much narrower than the normal gravel tires and certainly narrower than tires used for tarmac rallies. That said, a space saver tire probably would not work too well in snow due to the tread pattern and rubber compound of the tire.

As to tread, the purpose of tread is to let water or snow or mud or whatever have a place to go when the bottom of the tire is on the ground or pavement. It is not to amplify the pressure to the ground.

[Troberg]

1. You do not want a too wide tire in the winter, you want one that cuts through the snow instead of skidding on top of it. I've tried driving on 12" wide tires, and the car was almost completely uncontrollable.

If nothing else, there's a reason that UK gets chaos for 5-15 cm snow (I saw BBC describe it as "disaster" and "mayhem") while such an event is not even noteworthy in Sweden (here, snow chaos begins when the undercarriage of the car isn't high enough to clear the snow). If we wake up in the morning and find 20-30 cm of snow, we don't even consider staying home from work/school, we just swear about having to brush the snow off the car and get on with it. This is, of course, partly due to being used to driving in snow, but it's mostly due to taking it seriously and having the car properly equipped.

Look in any tire catalog. Winter tires are not available in wide models, simply because it will not work.

2. Now, this is something I know. I'll assume that they mean all the gritters that are active in the Stockholm area, not just the ones employed by Stockholm city (the national road administration takes care of the main roads, and the surrounding suburbs have their own as well).

They are able to do the entire road network of Stockholm, including sidewalks and bicycle roads (there's a lot of them, so don't underestimate them), in less than 24 hours. All important roads, bicycle roads, and most minor roads, as well as more trafficked sidewalks are done in 12 hours.

I don't know how much bus network London has, but it's fair to assume that it's less.

A thinner tyre would put more pressure per square inch on the ground and so be more likely to get to road surface. However, if it didn't then it would have less grip. I think that the answer to this one would be "It depends"

Now, the wider one would still have less grip,as it would skid on top of the snow, while the thinner one would cut down a bit, acting a bit like a ski, giving some control. The only time wider tires are better are when they are on tractors or wheel loaders and such, which already has the needed grip and don't want to sink too deep.

Fat wide tyres are better for deep/packed snow, you want as much surface area and (oddly) rolling resistance under engine load as you can get. Same logic as desert tyres but with a softer compound and different tread.

Nope, it just doesn't work like that. In a desert, you don't want to sink, in snow, even if you don't reach all the way through, you want to sink, as long as the undercarriage does not rest on the snow.

Even if the snow is packed, you want increased pressure to get a grip, especially with studded tires.

If you go offroad, things might be a bit different, but then you have a completely different vehicle.

[Floater]

Originally Posted by Dactyl

2. Someone yesterday said "All the gritters in Stockholm couldn't grit all the bus routes in central London". Is this true, false or true but misleading?

I have no idea about this but considering the difference in sizes it seems like comparing pears and apples.

[Troberg]

I have no idea about this but considering the difference in sizes it seems like comparing pears and apples.

Stockholm has a system designed to handle an arctic climate. They are also very serious about sanding the sidewalks and bicycle roads, as quite a few injuries happens there if they are slippery. The sidewalks and bicycle road network is several times longer than the road network, and, for practical reasons, slower to cover, so that's an important factor to remember. They have several big snow falls every year, and icy roads are a problem throughout the winter. They need to have the capacity to plough snow and spread sand/salt quickly and often.

London, on the other hand, can't really have that level of readiness, it would not be economically justifiable. One can't build a system capable of handling some oddball occurance that happens once every five years, it costs more than the costs of a few days of badly working traffic.

I think the main problem would be that they would have to go so far to refill. Stockholm is quite far from London...

[lord_feldon]

Originally Posted by Troberg

They are able to do the entire road network of Stockholm, including sidewalks and bicycle roads (there's a lot of them, so don't underestimate them), in less than 24 hours. All important roads, bicycle roads, and most minor roads, as well as more trafficked sidewalks are done in 12 hours.

That's how my town is (it's fairly unusual here). All of the streets, including minor residential streets which in some places take a week or more (if they're done at all), are usually totally clear within 12-24 hours depending on how much snow and what type it is. It was always so much fun going to school when every other district in the area got the day off. I hated it then but I certainly appreciate it now! I wish clearing sidewalks was a civic responsibility, though...

[Troberg]

I'd like to revise my earlier statement about the snow handling capabilities of Stockholm, after a discussion with one of the people responsible for it. Within 12 hours, the entire road network, including sidewalks and bicycle roads, should be done (snow removed, and if needed, gritted or salted).

[Debunker]

According to the Tire Rack:

"A wide, low profile or large tire has to "plow" a wide path through snow which causes more resistance. The narrower the tire, the easier you can get through snow."

So there.