Any tyre experts?

That is not wrong or ilegal, but not a good idea. if you have a spare tyre for each size, you are OK. but if you have to change your tyre and have the wrong size then you are dangeous and illegal to drive, some cars have smaller size spare tyres but that is only in width. some 165's and 175's can be bigger in height, so there fore dangous to drive mixed even at a low speed. I would recomend to have them all the same size. As for winter tyres becareful what you buy. as was proved this week by a leading car organisation in Germany and Austria. Not all winter Tyres are good,even the expensive trusted makes! I drive my own medium sized van, which is rear wheel drive in heavy snow and ice, since I live in Austria, I use Austrian Tyres ( Semperit) which are reasonable in price. But came 2nd in the snow and ice tests. (braking and handeling) The new Firestone snow and ice tyres just by a few points beat them. I have to go up high mountain roads, to look after a friends house near a skiing resort. the van is performing as good as some of the 4x4's with chains and these good tyres, last year in 2meters of snow better than the VW golf automatic4x4 nealy as good as the Jeep.

My advice get yourself a Haynes manual for your car, it tells you all you would ever want to know about the car, inc. tyres and pressures, and maintance. I always find my tyre pressures wrong after the so called experts have fitted them. last year one was 70 lbs the other on the same axel was 30. and that was on snow, the correct pressure 52lbs. so check like I do, I even carry an electric pump with gauge as well as a hand gauge. and check before you drive, since when tyres are driven they warm up, so the correct temp. is when cold. and correct pressure is so important, don't listern to anyone who says lower your pressure in the snow, since you lose the grip in the middle of the tyre. look after yourself, your car is only as good as the tyres you drive on:

Its important to understand what the measurements mean - for example: 175/55 R15 means "tyre width/tyre height/wheel diameter.

If the tyre width is different, that shouldn't matter as long as:

1) Both fronts and both backs are the same

2) Both front and backs have the same "rolling radius" - that is tyre height and wheel diameter in combination

3) The different widths fit within your wheel arch.

So if your width is different, this may not be an issue - if any of the other measurements are different, then you will have incorrect speedometer readings and a possible safety concern.

As above, tyres on the same axle should be the same size. Front and rear can be different sizes, (some cars are made with larger wheels and tyres on the rear). Your astra was made with all tyres the same size, and if you're changing them it's an idea to go back to that, (what if you need to fit the spare?) but it's not illegal or dangerous as described. The tyre fitters will know what size to fit to return to standard.

Wont cause too much trouble if the insignificant differences are on the same axle. Just don't want your differential to be turning all the time if they are on the same axle, with slightly different rolling radius. Your are not too different. I jus read the answer above me who claimed it would be dangerous if they were paired up. They would not be dangerous if your spare would be put on in case of a flat. The differential wear out increase is the only problem. There is too little of a difference to be unsafe even on the same axle.

the /65 or /70 refers to the ratio of the depth of the tyre to its width. /65 is 65% of the 175mm width, /70 70% etc.

You need to take advice as to the correct size for your car. That nice Mr Kwikfit will help.

Yes it wrong, and you shouldn't be driving like that

first of all thoes number represent the wheel wall, so one ot hem is bigger than the other one inwhich will lead your car to instabiliy, shock worn out, tire trend bald faster.

Its better to match your tire size with your stock or recommend size so check your car(i think van) and with Chevy(i think) for your recommend tire size and get fix.

Yes Tires Cost a lot espcially WINTER tires!

Its fine!

As long as the axle pair are the same it does not matter.

in fact, having larger tyres on the back makes good sense. It gives more grip on the road and so more controll and less likely hood of the back sliding round corners.

You can either find the proper tire size from your manual or from the dealer. It's ok to drive like that but they should be the same size for your cars sake. you can also try to find info about your car on-line

As long as they are all the same type (Radial), the back are a tad wider, thats all, you're fine, change all to the same size if you want, or keep it the same way it is now, no problem !

its sounds wrong... there are too much imbalancing between the two tyre.... u should bring it to the mechanic and ask them what is happening.... ask them is it suitable as i knoe such tyre in winter is quite slippery