Prius Plug In

[johalareewi]

I think you are all correct.

For heat, the prius uses the ICE to burn petrol. In winter the temperature difference between the ambient temperature and the operating temperatue is greater. There is also the potential for the heat to be lost more quickly (although grill blocking can minimise this) requiring more topping up.

But air resistance does increase with density so that too is a contributing factor.

Especially at speed (air resistance increases as the square of the speed).

[JSHarris]

Somewhere I have the data I captured from my Gen 2 Prius , when I was doing a commute of around 40 to 45 miles each way for a couple of years. I know for a fact that the graph of fuel consumption very, very closely matched the air density graph, month by month, so close that I find it hard to see that there wasn't a very strong correlation between the two. As a scientist who spent a fair time working on aerodynamics, the relationship seemed pretty clear to me.

Yes, the engine does cycle on and off to run the heater more in winter, but if you stick a scanguage on and look at the fuel usage when it's doing this it is small, as the engine isn't actually producing very much power at all, and the injector on time is tiny. There is a small impact on fuel consumption from this, bigger perhaps for those driving very slowly in very cold weather, but other effects tend to dominate for most people.

The rolling resistance one is interesting, as I measured tyre surface temperatures when I was trying to get to the bottom of the wide winter/summer variation with the Gen 2 Prius, and even in freezing weather they warm up pretty quickly. Bridgestone had some data on the change in hysteresis with temperature, and working back to determine the effect this had on energy return from normal road perturbations (the effect of absorbing energy rising upwards and then returning that energy by tyre rebound going down) wasn't massive, but was enough to account for the fairly rapid tyre warm up in cold weather. Once the tread temp got above about 10 deg C there wasn't any significant difference in tyre energy absorption, and tyres seemed to warm to this temperature is a few minutes at normal speeds.

[IanIanIanIan]

What you say makes sense but as the tyres warm up so quickly why are winter tyres recommend when the temperature drops below seven degrees Celcius?

[JSHarris]

I've never bought the winter tyres, so don't know for sure, but assumed (maybe wrongly) that they had a tread pattern that was more suited to clearing snow and that was less likely to get clogged up.

From the couple of times I've driven on snow in one of the older Priuses I've had, I know that the tread on the standard tyres clogs up with snow very easily, making them, in effect, pretty smooth, whereas the types I used to have on an old 4 x 4 Daihatsu had a tread pattern that was more open, that meant that they stayed pretty clear of snow. Whether this is the case with the winter tyres Toyota recommend I don't know.

[PeteB]

What you say makes sense but as the tyres warm up so quickly why are winter tyres recommend when the temperature drops below seven degrees Celcius?

it's mainly a softer rubber compound that doesn't go so hard as summer/all season tyres below 7C. They will grip better even on a dry road, but also on snow or ice.

[IanIanIanIan]

That is the usual reason given for using winter tyres. But if, as JSHarris says, the tyres get up to 10ºC quickly, where is the advantage on dry roads? which is what we have here for the greater part of winter.

[johalareewi]

In general, winter tyre compounds are more suited to lower temperatures.

While summer tyres will warm up in winter, consider that they only warm up if you are moving.

In slow moving traffic in the cold they will pretty much be at the ambient temperature.

The sipes in winter/snow tyres are designed to trap the snow to improve grip.

Snow is fairly sticky stuff (think of rolling snow to make a snowball) so having some stick to your tyres encourages grip.

[MEP's Yaris GS]

As Alan has said, sipes are designed to hold the snow and snow against snow grips much better than rubber against snow. And the higher silica content in winter tyre as mentioned makes them far superior at road gripping the the dry / wet below 7C, which is where a summer tyres performance deteriorates rapidly.

[kithmo]

On ice, it doesn't matter what tyres you have on they ain't gonna grip unless they are studded.

[MEP's Yaris GS]

On ice, it doesn't matter what tyres you have on they ain't gonna grip unless they are studded.

Correct, luckily 99.9% of the time we're not driving on sheet ice, what winter tyres will do though is enable you to grip a lot better and retain control should you be fortunate enough to come off of the sheet ice before binning it. I've only once nearly lost it on sheet ice with winter rubber, and would say that with my normal summer rubber on there was at least a 75% chance that I'd have still bounced off the roadside (on a bend) after coming off of the ice based upon previous summer tyre performance coming on and off of sheet ice. But who knows.

[Sagitar]

On ice, it doesn't matter what tyres you have on they ain't gonna grip unless they are studded.

I would have agreed with this until recent years but there are now a number of independent tests that appear to show stud-less tyres outperforming studded tyres on sheet ice.

Here is a summary video from Tirerack http://www.tirerack.com/videos/index.jsp?video=7&tab=winter but it was made in 2008. It makes the point that stud-less tyres had undergone more development of tread patterns and of the elastomers from which the tyres are made, while studded tyres continued to depend upon the studs and there was less carcass development.

Of course it may be that studded tyres have caught up in the years since 2008 but my quick search found no indication of this.

I have no experience of driving on studded tyres, but must say that my Continental winter tyres perform incredibly on icy surfaces.

[kithmo]

I'm afraid I can't put much faith in a video made by someone who sells tyres, give us a link to the independent tests.

[Sagitar]

I'm afraid I can't put much faith in a video made by someone who sells tyres, give us a link to the independent tests.

But you expect me to believe your completely unsubstantiated statement that only studded tyres will give a grip on ice.

As far as I am aware, Tirerack has no connection to any tyre manufacturer. Have a look at this link https://ie.linkedin.com/company/the-tire-rack

What reason do you think they would have for bias in their tests. They are in the U.S. market of course so likely to miss tyres from other parts of the world but I believe their material shows clearly that modern un-studded winter tyres give a good grip on sheet ice.

Perhaps you would prefer this summary statement from the Teknikan Maailma organisation in Finland. It comes from their 2013 comparative tests of studded and un-studded tyres winter tyres.

More or fewer studs

THE NEW regulations concerning studded tyres allow manufacturers to use any type of stud on their tyres, and even their number is not limited, as long as the tyre does not exceed the road wear limits. Another option is to adhere to the maximum number of studs and certain other limitations; a road wear test is not required in this case. Some manufacturers have been happy to take up the opportunity to add studs and improve grip. The winner of our winter tyre comparison test that starts on page 14 has 190 studs, whereas tyres from another large manufacturer only have half of this number. Non-studded tyres are also developing rapidly. We are at a point where the difference in grip between the best non-studded tyres and the weakest studded tyres is more or less non-existent, even on an icy road. Even the most die-hard fans of studs should try them out – the results may be surprising. The authorities also need to account for the development of tyres when con- templating usage limitations and other controls. Non-studded tyres are now an even better alternative. On the other hand, the best studded tyres have improved their safety characteristics while reducing their road wear. Both the consumers and the authorities need to consider the situation, and old attitudes deserve to be changed.

JUKKA ANTILA

[kithmo]

My unsubstantiated statement is based on simple physics, the only thing that will grip on ice (and I'm not talking about packed snow or icy patches here) is something that will dig into it, and plain rubber, regardless of its temperature range, will not dig in to the ice, it will simply slide over it.

Regarding tirerack's bias, I never said they had any connection to any tyre manufacturer, but they are a tyre sales company and the only reason for all the tests they do is to make people buy tyres.

Jukka Antila's statement sounds interesting, but he's says the best unstudded and worst studded are close on an icy road, which is a bit vague, an icy road could be patches of ice and it still says to me that for grip on ice, best is best studded going down to worst studded then down to best unstudded, which still makes studded better than not.

[JSHarris]

The big problem with studded tyres in the UK is that it is very rare in most parts to have completely snow or ice covered roads for any significant period. Driving studded tyres on tarmac is seriously dodgy, in terms of safety, damage to the tyres and damage to the road surface. It's fine in places like the northern parts of Scandinavia, where the roads can stay covered with packed snow and ice for weeks or months on end, but, IMHO, they aren't best suited as winter tyres for most of the UK.

I'm not at all convinced that winter tyres are needed here. I used to keep a set of snowchains in the car many years ago, but only used them once or twice in around 20 years, so threw them out. I do have long lengths of synthetic woven strap, rather like luggage tie downs, that can be threaded through the wheels and around the front tyres as an emergency aid in snow, but they've stayed in their plastic bag in the boot for the last four cars I've owned.

[steverally]

In reply to JSHarris, and sorry this is off the original topic, like him I was sceptical about the benefits of winter tyres, having survived without them for 50+ years. Like JSH I'd carried a set of snow chains for years, but only used them once in 2010.

But three years ago saw a set on eBay near to me, and having just had a problem getting home in a light covering of snow, the Prius traction control, removing all drive on a slight hill, though I'd bite the bullet and try them.

Now three years on I can't emphasise the difference in feel when they're fitted in the winter. The car feels that more sure footed and has coped well in minor snow falls, there's even a more positive feel on the few frosty mornings we've had.

So for me Winter tyres are a Plus and will be fitted in just over a month through to end March/April. Yes I do inform my insurance company when I've swapped wheels and then receive a 5% discount which has already paid for the set of wheels and tyres.

[Grumpy Cabbie]

Winter tyres are the best thing ever.

I remember years ago fitting a pair when I lived in the sticks. Driving up Sutton Bank in a snow storm in a 2wd Datsun and passing a brand new Shogun which was stuck with all their wheels spinning.

They gave the car fabulous traction and the only thing that stopped it was build up of snow at the front like a snow plough.

Don't have them now as I live in the town and barely go anywhere, but if I lived in the sticks again I'd have a pair for sure.

[Sagitar]

My unsubstantiated statement is based on simple physics, the only thing that will grip on ice (and I'm not talking about packed snow or icy patches here) is something that will dig into it, and plain rubber, regardless of its temperature range, will not dig in to the ice, it will simply slide over it.

Regarding tirerack's bias, I never said they had any connection to any tyre manufacturer, but they are a tyre sales company and the only reason for all the tests they do is to make people buy tyres.

Jukka Antila's statement sounds interesting, but he's says the best unstudded and worst studded are close on an icy road, which is a bit vague, an icy road could be patches of ice and it still says to me that for grip on ice, best is best studded going down to worst studded then down to best unstudded, which still makes studded better than not.

The physics (and chemistry?) of the tribology of elastomers in moving contact with ice - simple - mmmmmm - I don't think so.

Jukka Antila's statement includes non-technical statements that I find telling, especially in view of the fact that he comes from Finland, a country where winter temperatures can get down below - 30C. So when he says "old attitudes need to be changed" I am prepared to take him seriously.

I doubt if you and I are going to find consensus on this matter so I'm content to note the very significant difference between your original statement - "On ice, it doesn't matter what tyres you have on they ain't gonna grip unless they are studded" and your final statement above "for grip on ice, best is best studded going down to worst studded then down to best unstudded, which still makes studded better than not".

[Sagitar]

The big problem with studded tyres in the UK is that it is very rare in most parts to have completely snow or ice covered roads for any significant period. Driving studded tyres on tarmac is seriously dodgy, in terms of safety, damage to the tyres and damage to the road surface. It's fine in places like the northern parts of Scandinavia, where the roads can stay covered with packed snow and ice for weeks or months on end, but, IMHO, they aren't best suited as winter tyres for most of the UK.

I'm not at all convinced that winter tyres are needed here. I used to keep a set of snowchains in the car many years ago, but only used them once or twice in around 20 years, so threw them out. I do have long lengths of synthetic woven strap, rather like luggage tie downs, that can be threaded through the wheels and around the front tyres as an emergency aid in snow, but they've stayed in their plastic bag in the boot for the last four cars I've owned.

I wouldn't want to argue with anything that you say. I believe it's actually illegal in this country to damage the road surface by the inappropriate use of studded tyres, but the phrase that prompted my response was a general one, not limited to the UK.

I think the need for winter tyres is one that has to be decided by individuals and is dependent upon a range of issues that will vary considerably. We have debated it at length previously and we are off topic so I don't want to pursue it except to say that for me, personally, they have proved very worthwhile.

[kithmo]

My unsubstantiated statement is based on simple physics, the only thing that will grip on ice (and I'm not talking about packed snow or icy patches here) is something that will dig into it, and plain rubber, regardless of its temperature range, will not dig in to the ice, it will simply slide over it.

Regarding tirerack's bias, I never said they had any connection to any tyre manufacturer, but they are a tyre sales company and the only reason for all the tests they do is to make people buy tyres.

Jukka Antila's statement sounds interesting, but he's says the best unstudded and worst studded are close on an icy road, which is a bit vague, an icy road could be patches of ice and it still says to me that for grip on ice, best is best studded going down to worst studded then down to best unstudded, which still makes studded better than not.

The physics (and chemistry?) of the tribology of elastomers in moving contact with ice - simple - mmmmmm - I don't think so.

Jukka Antila's statement includes non-technical statements that I find telling, especially in view of the fact that he comes from Finland, a country where winter temperatures can get down below - 30C. So when he says "old attitudes need to be changed" I am prepared to take him seriously.

I doubt if you and I are going to find consensus on this matter so I'm content to note the very significant difference between your original statement - "On ice, it doesn't matter what tyres you have on they ain't gonna grip unless they are studded" and your final statement above "for grip on ice, best is best studded going down to worst studded then down to best unstudded, which still makes studded better than not".

The final statement you quote was not my opinion but a summary of Jukka Antila's comments, which still shows studded as better than non studded on ice, even if, as he claims, there is very little difference, there is still a difference.

(FYI. Tribiology is applied to finding better lubrication and less wear between surfaces not better grip.)

[Sagitar]

Tribology - http://www.uktribology.net/tribology-benefits

[MEP's Yaris GS]

An interesting review on the Outlander PHEV here

[Grumpy Cabbie]

The gen4 Prius and gen 2 Prius plug in had better be GOOD to compete with this car. I like it. It ticks all the boxes. Sure it may be a bit more thirsty if run in hybrid mode only, but a 15 minute fast charge when needed for another 25-35 miles with ideal. Makes the 9-14 miles of the expensive PIP look positively out dated.

Mitsubishi have a cracker and I think they know it. I posted the above link on the US forum and they are really interested in the car as it hasn't been released there yet.

[MEP's Yaris GS]

Makes the 9-14 miles of the expensive PIP look positively out dated.

See I still disagree, and you've hit the nail on the head, it's very thirsty as a hybrid (some claims of only 30mpg, which doesn't sound untrue), and has bigger car running costs (massive tyres etc). It's also a different class of car, not everyone wants a tank sized vehicle.

I agree, if used mainly as an EV, then yes it'll be a great vehicle, but for those doing any reasonable mileage then it'll start to make a hole in the pocket with fuel costs, which although most Chelsea tractor drivers are not bothered with, if looking at overall running costs I think the PiP still wins hands down.

It'll be Interesting to see if the fast charge functions kills the Battery off prematurely or not. I know it's not recommended for regular use on the nissan leaf from memory.

[Grumpy Cabbie]

It has been proved incorrect that fast charging damages the Battery, at least in the UK. In the heat of Arizona on a hot day with a hot Battery is where you get problems. The UK even on a hot 34c day is nowhere near the 45c of Arizona or Australia.

And Bobby Llewellyn said he got good 60's to the gallon out of the Mitsubishi and was surprised by it. I'd take the 30 mpg figures with a pinch of salt, the same pinch where people say the Prius only gets 35 mpg.

But time will tell.