snow chain sizes

A snowHead

hi all - am currently in the french alps and expecting snow before we leave on Saturday, but have no chains. The hire car has 225/55 R18 tyres, and none of the supermarket sizes seem to match (we have tried 5 different shops). We can find bigger and smaller but not identical. Does anyone know if there is some tolerance in the sizes? for instance, would a 235/45 R18 do? Thanks for any advice.

A snowHead

Snow socks usually have a bigger range of sizes... and are Legal in France and just as effective if you drive carefully.
Another option - Leave after skiing on Friday before the snow starts? Or Saturday after it has stopped...

Well, the person's real but it's just a made up name, see?

For chains you wanna have the correct size - if not they can really do serious harm to the car!

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@HandyHomeJames, The circumference of your tyres in mm is...

((Rim diameter in inches * 25.4 for mm)+(tyre width mm * aspect ratio * 2))* pi

((18*25.4)+(225*0.55*2))*3.142= 2,214mm

The 235/45/18 is

((18*25.4)+(235*0.45*2))*3.142 = 2,098mm

Hopefully you can use that maths to find a set that works. Pretty sure it’s correct but I’m not by my PC to check!

Anyway, snowHeads is much more fun if you do.

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First, I'm assuming your car has winter tyres? If it does, then you're much less likely to need chains. Most threads here on the topic are full of people saying "I've had winter tyres since 1848 and I've never needed chains ..." And it's true that with winters on, the probability of needing chains is very significantly reduced. They should cope with 'ordinary' snow conditions, and you're more likely to need them in the village to negotiate an icy car park ramp, or a steep drive out of a chalet etc. If the tyre says 'Winter' on it that's obvious, but the sometimes the product names aren't meaningful and you need to look for the 'Three peaks and a snowflake' symbol on the tyre sidewall (google 'snow tyre symbol'). If you have winter tyres then your' problem is less pressing.

If you don't have winter tyres then it's more urgent.

Second, check that the car can actually take chains. It probably can, but it's worth checking. The Owner's Manual should have a section where it lists the tyre sizes with some notes about which sizes can't carry chains. All is not lost if it can't take conventional chains because there are some designs - albeit expensive - that can overcome this problem*. For example, my manual says "Snow chains may only be used in pairs on the rear wheels with tyres of the following sizes ...". If you car can't take them, then you'll be liable for any damage if you fit chains when they're not certified and cause damage. Many SUV/4x4 and some AWD hire cars don't come with chains precisely because they can't be fitted to the wheel size and with winter tyres, the hire companies assume you'll cope with 98% of most conditions. The other 2% will probably be an icy/snowy steep drive out of where you're parked, or police mandating them, or really heavy snow (once it's too deep, the car's undercarriage won't clear the snow anyway).

If the ones fitted are OK to take chains, then you've been unlucky in not finding suitable chains so far. Doing a quick check on one of the UK chain suppliers websites, they have 13 different products that fit your tyre size. Most products actually do fit a range of sizes - there's a degree of latitude. But the product labelling should show this. As mentioned, if the product label doesn't mention your size, then I wouldn't use it. It may be that the cheaper brands in the supermarkets don't have this latitude and a car shop will be a better bet. This is one reason why an £80 pair of chains might be a better bet than a £30 pair - because they are more adjustable. If there's a manufacturer's garage locally, they may also have the right chains in stock, although you'll probably pay a premium.

So if you decide that you need chains, then you may have to take time out to drive to a valley town or somewhere lower down where there's a French equivalent to Halfords - I'll let others more familiar with France suggest the likely retailers that you can search for.

And if you do find chains that fit a wide range of sizes, then you may need to sit down with them and manually adjust the links to fit your particular combination of wheel+tyre. THis may not be obvioius from the ENglish translation - with my current chains I had to do this and I realised that what in English came across as a suggestion was much more strongly-worded in the original German i.e. unless my car had the smallest size quoted, I had to adjust the size via the links (which took about 20 mins per chain set, in the warmth of a garage with good lighting and on the spare lying flat on the ground).

[*Like the Spike Spider Easy, Thule K-Summit and Maggi Trak Sport - but these are upwards of £250+ !]

Hope this helps ....

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@HandyHomeJames, where in the French Alps are you

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@ski3, The 3.142 gives you the circumference, leave it out and you do have the diameter.

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@ski3, I think that @Matt1959, has got it correct. "otherwise the wheels are over six feet tall" he has calculated the circumference not how tall the tyres are. I guess what it demonstrates is how significant the changes in tyre size are on the ability of chains to fit.

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@ski3, I think that @Matt1959, has got it correct. "otherwise the wheels are over six feet tall" he has calculated the circumference not how tall the tyres are. I guess what it demonstrates is how significant the changes in tyre size are on the ability of chains to fit.

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@Matt1959, oops, yes my mistake you're right.

Suppose it's trying to equate it on the packaging of the chains as although they state the sizes they are principally headed with wheel diameter plus the tire form.

The circumference clearly changes a little but they don't generally reference it, hence the OP problem.

@ski3, tomorrow’s job is to see if I can add some adjustment bolts to my Koenig chains to make them drop a size Happy

You know it makes sense.

French Halfords = Feu Vert

Otherwise you'll just go on seeing the one name:

A snowHead

@HandyHomeJames,

French equivalent to Halfrauds is https://www.norauto.fr and they are usually next to a carrefour / auchan or whatever hypermarket in most big towns, they probably won't be cheap there though.
If it was me I would do this :-
Get some from a supermarket that are the right diameter and as near as possible in the other dimensions as possible. Without going into the calcs described before I would tend to go for correct diam, followed by correct profile and then as close as possible upwards in width. That should hopefully mean that the stiff ring at the back of the wheel does not touch the ground.
In the same supermarket, or in a DIY shop, builders merchant or whatever get a bag of chunky cable ties and a pair of cutters.
When you put the chains on and link the rear ring up you will find you have lots of baggy chain hanging around, hopefully mostly on the outside of the wheel. Tighten it all up as best you can with the actual chain tensioner then add the cable ties to pull the slack bits together.
You should be able to tighten it all up in some fashion. Try and keep the cable ties so that they do not contact the road.
Bits flapping about on the outside of the wheel might give you a bill for scratched alloys / bodywork but getting them wrapped around a driveshaft / brake pipe on the inside is pretty disastrous so try to keep all the slack on the outside without bunching it up that big it hits the arches.
The usual caveats apply about stopping after a few yards and tightening etc. Obviously go as slow as techcnically / socially possible Toofy Grin

I did this once when given a hire car with wrong chains. And yes I did check, the box, but not the actual chains........

A snowHead

Oh and be aware that if you buy them from a supermarket they will not take them back if have opened the plastic case, there is usually a cable tie or something on the handle.

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@endoman, I still think that @Matt1959, is correct. In his worked example 55 is the aspect ratio, that is the sidewall height expressed as a percentage of the width. So in his calcs it's 225x.55=123.75 which he has correctly doubled for each side of the tyre. 18 is the diameter of the hub, in this case (and always it seems) measured in inches, so he has converted it to mm, but not doubled it. The formula for the circumference of a circle is 2*pi*r or pi*d where r is radius and d is diameter. I think it's reasonable to assume most tyres are round as Dave Brailsford famously once told the French!

Ref:
https://www.parkers.co.uk/what-is/tyre-sizes/

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let me ruin your young mathematicians club party. You only look at wheel diameter, completely ignoring tire width. If the tire is wider, to cover it's thread you need more chain, thus compensating from radius surplus.

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@kosmoz, killjoy! Of course you are right and I am sure that is what @endoman, was saying too. Basically you need to find chains that the manufacturer says will fit your tyre size. There is probably little lee-way to be safe and avoid damage to the car.

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Understood. Always thought aspect ratio was height of sidewalk in mm’s. agree the original calcs are correct but it still won’t make a supermarket or feu verte open up in resort before Friday!

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Length of rope and a sharp knife:

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@HandyHomeJames, what time do you have to leave the resort? If not too early I wouldn't sweat it.

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Winter tyres are better than snow socks, so if you have winter tyres on already, there'd be little point in fitting socks. It'd actually be retrograde. So, as mentioned, check to see if you already have winter tyres on the car and if you have, the whole situation is less problematic.

Also as mentioned, whether a particular chain will fit a particular wheel+tyre is a three-dimensional question that involves the tread width as well as the tyre circumference. You can't really determine the fit-ability solely on the basis of the xxx/yy-zz numbers. Also, some chains have an adjustment mechanism that tightens the chain after you have driven on it for a short distance. Sometimes this is automatic, some you have to tighten the adjuster manually. Thus a very cheap chain is likely to have very little leeway in fitting, whilst a more expensive one will have more, and so that's why I'd not recommend fitting a chain that is not listed as your tyre size, especially if it's at the cheaper end of the scale. Basically, if it says it fits you tyre size, then it'll fit. Otherwise assume it won't.

This is before the problem that just because a chain will fit a tyre size and is certified to do so, it doesn't mean that there's enough space behind the wheel for the (conventional) chain components to rotate, without their fouling the suspension, brake pipes and if FWD, steering mechanism. Only the Owner's Manual (or the garage) can tell you if the wheel and tyre fitted to your model has the necessary space. Look at the space on my car's wheelarch (the small blue part is the brake pipe connection):

and you'll appreciate why the manufacturer doesn't certify any chains to be fitted on this wheel size - the gap is too small to comfortably allow possibly (probably) slightly loose chains to rotate at speed. I have to either fit narrower (although not necessarily smaller-diameter) wheels. Or get the expensive front-fitting chains which dont' have any gubbins on the inside of the tyre.

@endoman The aspect ratio is the ratio of the sidewall height in relation to the tread width, expressed as a percentage. Thus my summer 245/35 tyres are 245mm wide and 35% of 245mm high = 73.5mm sidewall height. Because the wheel diameter is expressed in inches, you have to convert, and so the rolling radius of these 245/35-18 is 18 inches + 73.5mm (2.9") = 20.9" - which you can then use to calculate the circumference.

Ah, but what is the rolling radius? That's the distance from the tread surface on one side of the wheel to the tread surface on the opposite side, using a line drawn through the centre of the wheel. Generally, this has to remain consistent as you fit wheels and tyres of different sizes. Otherwise (a) the tachometer won't record the right distance travelled (b) the speedometer won't show the right speed and (c) the handling dynamics will change. Thus, when I swap to my narrower winter 225/45 tyres, I have to fit a 17" wheel so that the overall rolling-radius stays the same. And this also changes the aspect ratio up to 45% from the summer 35%.

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You know it makes sense.

@Charliegolf, I've used them with great success on a couple of hire cars - (but I'm quite use to driving on snow and ice) They are deffo legal look for the certificate to show the Gendarmes.
Like this. http://www.autosock.co.uk/pdfs/AutoSock_B26_France.pdf

FAQ's about socks answered here http://www.autosock.co.uk/faqs/

Otherwise you'll just go on seeing the one name:

@Charliegolf OK, I've resisted so far, but I can't hold back any longer - here's my Winter Tyres and Chains chart, which I hope helps provide a framework for these discussions:

and which partly answers your question. Really, the aim for any driver is to defer having to fit chains for as long as possible (as conditions worsen). Socks help someone with summer tyres defer having to use chains. But not to the same extent as if they had all-season tyres on. Similarly, all-season tyres don't go as far as winter tyres. And as conditions get worse, even someone with winter tyres has to fit chains eventually. Although as I said, 'worse' may mean a lovely bright sunny day with clear skies but a steep drive out of where I'm parked that's a complete ice sheet.

The 'Gap' rubric was inserted as part of another discussion about how all-seasons and winters are still beneficial in winter conditions, even without snow. I'm also aware the diagram is deficient - it tries to represent a lot of variables in just 2 dimensions. And it's trying to represent a wide range of vehicles and differences between individual tyre brands as well.

Traction Settings Oh, and your hire car may have traction settings specifically for snow that will help a lot. So it's always worth trying to determine what the snow setting should be, at leisure, before you drive off. I know, this can be a problem if the hire car Owners Manual is only in German or French.

A snowHead

@LaForet, If you have winters on and NEED to put chains on you probably may be shouldn't be out there snowHead

A snowHead

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@LaForet, Yep! I noticed our village snowplough/blower tractor has had its chains put on today. I guess because tomorrows snow will be falling on top some quite hard compacted areas in the car parks.

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Initiating moving from standstill on an incline might be a problem with fwd/rwd car/van even with winter tires. Remember in 2017 march there was a heavy snowfall in Les Arcs/La plagne and everywhere around, Saturday included, due to heavy traffic Waze offered me to go over Belle plagne to Champagny, over the mountain. So going uphill I was holding gas pedal all the way down all the time, except 180 degree turns on serpantines, ESP light was flashing all the time, if I stopped - I would need to put snow chains on to start moving again. VW Transporter, 6 persons, loaded, new winter tires. Going downhill was easy.

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In the heavy snow fall just before Christmas this year I went out to help a british guy who'd got his FWD Audi A5 stuck on the slope outside of our apartment (incidentally not too far from@LaForet,). He was on the main route in to the village but it kicks up to about 12% just in front of our place and he just couldn't get up it. Most others drivers were sailing by including the post bus without chains. When I went to help he asked to borrow some chains but my chains would not fit, despite us also having an Audi but not an A5. He told me that the car had winter tyres and sure enough it did but not a brand that I recognised. The biggest problem was that the tread was right down to a level that I would suggest was barely legal. Unfortunately I couldn't help him and he left the car overnight. He came back a day or so later with a better fitting set of chains.
Moral of the story: not all snow tyres are created equal and if you let the tread wear down they are pretty much the same as summers when it comes to grip in the snow.

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@Rareperk Definitely re minimum tread depth for winters - which is 4mm, at which point you need to change. Unless perhaps you're running them into the Spring to get the most out of them before switching to summers.

Tyres don't degrade linearly either. Here's the chart for one brand of summer tyre showing braking distance vs tread depth:

As you can see, even on this summer tyre, the braking performance drops off sharply after the 4mm mark, and you'd want to replace it a long way before it gets to the 1.6mm legal minimum, and that's on hot tarmac. It's probably a performance car tyre - where the assumption is the driver wants to sustain shortest braking distance as long as possible and isn't too concerned about replacing the tyres before the legal minimum.

And yes, brands differ a lot: the average quality tyre has about 600 separate components which all gets vulcanised into a single homogeneous-looking black carcass. You can have a cheap brand that looks completely the same (better perhaps, with a funky, but meaningless tread pattern) with half the components and terrible handling characteristics, or abysmal wear, or hopeless water dispersal etc.

The need for chains also varies depending on the car, even with Winter tyres.

For example, and as you would expect, my current Land Rover Disco Sport copes very well in the snow without chains (although I still carry them in the winter and they are a special type due to wheel clearance so don`t go round the back), but my previous Jaguar XF saloon was awful in the snow and would have zero traction even on the flat, let alone getting up a hill, so chains were an absolute necessity.

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Where can you get summer tyres from? I've never seen them for sale.

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