I have been unable to find any manufacturer that makes a winter (snow crystal mark) tyre in size 255/70R18. My vehicle's current tyres are made by Bridgestone and M+S marked.

My vehicle also has a Swiss sticker on the driver's door frame stating only a single size of wheel and a single size of tyre is permitted.

I know I can physically fit a different set of wheels with 17" or 16" diameter without any mechanical issues. This would provide at least a choice of tyre sizes with a similar rolling diameter and load rating. However, what process do I have to go through with paperwork and insurance to legally modify my vehicle for winter use? I don't want to buy new wheels and winter tyres and find that I cannot legally use them.

My vehicle was purchased new in Zug from a main dealer and is Swiss type approved. Incredibly the specific model I have cannot use any type of snow chains, not even 'S' class chains as is. Wheels with another 1/2" of backspacing would provide sufficient clearance for 'S' class snow chains as confirmed by a well known European manufacturer (König).

The main dealer says the original equipment tyres are suitable for all round use. Technically, I also know this is true, and I'm happy to use them in winter running at 5psi lower than in summer. But I would like to know how I get through all the Swiss BS regarding modifications.

What exactly do you have for a make and model car..? It's possible 255/70R18 isn't the dimension of the winter tire it requires.

Just make sure you put your approved summer tires and rims back on when you have to take it in for your testing. Get a set of 16 or 17 inch steel rims and winter tires for the winter months.

The vehicle handbook is quite clear stating only one size for my model, as is the Swiss sticker in the door frame.

I know I can get 265/75R16 winter tyres with roughly the same 32" outside diameter but I will need to run these on rims with more backspacing than the original equipment.

It appears to me that the vehicle got Swiss type approval without any official actually checking that winter tyres of the correct size exist.

But what's the Make and Model of your car..?

Toyo and Continental make tires in that size with an off-road tread that should be aggressive enough for snow.

Thanks for the suggesting these brands. I looked on their European and US websites again tonight just to check that they have a 'snow crystal' marked tyre in my size but still no luck. Toyo do have two tyres listed on their US site in the right size that are M+S rated, but they are probably similar to the Bridgestones I have already. I don't know if the Toyos listed were 'E' marked or just 'DoT', I couldn't find them on a European listing.

In snow here, I prefer a less aggressive tyre that does not have a good self cleaning ability. A tyre that can hold some snow in the voids at slow rotational speeds gives good snow on snow traction. I have found that mud tyres usually only work well in snow that is crunchy or very deep (15" or more). I don't think I'm ever going to see snow that deep on a highway in Switzerland and I would rather have an actual winter tyre for a vehicle that is unlikely to ever be driven on an unpaved road. It's just a shame that nobody makes them in the size I need.

I find it really amusing that my vehicle probably has the largest after market industry in the world for end user modifications than any other vehicle currently in production but living in Switzerland I am not allowed to modify it to suit my needs.

It's a 4-door Jeep Wrangler Sahara.

Am I missing something here? Are you saying that modifications are only illegal while the vehicle is being tested? Is it perfectly legal to use a modified vehicle on Swiss roads at all other times?

And all this time I thought you were talking about some exotic sports car not a 4WD offroader..!!

Did you (or the Dealer) import the Sahara from the States? The Swiss Jeep website only shows a Rubicon or Sport Wrangler, no Sahara mentioned. Looking closer at the USA site the Sahara is the only model which has an 18" rim, all others use a 17" rim. All 4 models have the same engine/transmission/suspension set up which would bring me to the conclusion the Sahara shouldn't have any problem running a 17" set up like the others do. Is it legal..? With the proper papers most certainly, your dealer would supply you with the certificate if there was ever a question raised during an inspection. Being stock wheels it wouldn't come into question anyway but if you went with aftermarket rims then the certification would have (should be) to be with the vehicle at all times.
My VW normally come with 13" wheels but it has stock (with VW insignia cap) 14" aluminum rims for summer and (aftermarket) 13" aluminum rims for winter. Had my inspection in June with the 14"ers and nothing was asked about them.

Modifications such as aftermarket wheels are legal if said wheels carry a certification of approval for your vehicle. Unapproved parts and modifications are always illegal. Sure you can try to get away with something illegal on your vehicle but if there is a road side inspection you could face a hefty fine. Also if you're involved in a traffic accident with your illegally modified vehicle not only will you face a fine your insurance company would most likely refuse payment on any damages caused.

All modifications are illegal unless tested, approved and recorded in the registration documents. Obviously, you would provoke the tester, if you turned up in an unapproved vehicle.

The police sometimes make random roadside checks. Unapproved modifications will result in penalties.

Even worse is if you are involved in an accident. You may be innocent. But the other persons' insurers would accuse you of gross negligence and refuse compensation. That could be very very expensive.

Manufacturers' certificate of approval is necessary but not sufficient. You must take the certificate to the road-transport authority, register it and get a new registration document.

you should go for 16''. there are no offroad-winter-tires in 18'' size.
i prefer cooper discoverer m+s (http://www.offroadreifen.com/program...12&reifentyp=o). this is a real good winter tyre. the Nokian Hakkapeliitta LT is also a good tyre but not available in your size...

anyway, having 18'' rims on a offroader is like having 195/65R15 on a ferrari, go for 16'' or 17'' and stay with it, you'll find plenty of different tires in this size.

2 registration documents? One for winter and one for summer..? I'm not so sure new registration documentation is necessary, especially when it comes to wheels which would only be mounted on the vehicle half a year. When I bought my car new the dealer said I needed to keep the certificate for the aftermarket wheels onboard at all times. The dealer attended to all of the registration and there is nothing on it declaring aftermarket wheels being used during winter months.

The Sahara was in the Swiss 2007 model range, what bugs me is that we wanted a 4-door diesel Rubicon but they were only available in Italy and Belgium at the time. Our Jeep is most certainly a Swiss edition as it is powered by a 2.8CRD that is currently illegal in the USA. It also has Swiss warranty, Swiss Free Servicing and all documentation in German.

Funny how Jeep in Switzerland didn't spot that before offering the vehicle for sale. Even funnier still is that none of the models sold in Switzerland can use snow chains either without ripping off the rear brake pipes.

I am surprised that the Swiss government does not compel vehicle manufacturers to sell new vehicles with both summer and winter wheels and tyres. It would certainly make things a lot simpler for everyone.

Manufacturer of the wheel or manufacturer of the vehicle? What does a certificate look like? Is a letter stating compliance good enough?

I know for a fact that my brakes will fit 16" rims without a problem. Keeping my axle gears as they are, I would need to find a tyre size with an overall diameter of 32". The trouble is that the stock Wrangler 16" or 17" wheels cannot be used with a 32" tyre and provide enough clearance between the tyre sidewall and brake pipes for snow chains. I either have to modify the routing of the rear braking system to make it the same as all other offroad capable Jeeps designed prior to 2001, or fit wheels with 1/2" or more backspacing. I can find suitable aftermarket wheels in the USA no problem. But with a certificate for use in Switzerland?... Hmm.

• When vehicle manufacturer has certified for the specific vehicle type: Then it is original equipment. No problem when vehicle manufacturer has branded the rim. Rim and tyre dimensions must be among those specified in the vehicle's handbook.
• When rim manufacturer certifies: Obviously not original equipment. RTA (Road Transport Authority = StrassenVerkehrsAmt) must approve, register and issue a new registration document. The RTA can accept the rim manufacturer's certificate and waive the test. RTA is however not obliged to do so and can decide to insist on testing.