tyre sizes

the two you mention at the end would be very similar in rolling radius. I doubt you could tell any difference, but you could always check with a GPS

The scribbles on the back of a handy envelope say they're all within 3% of the same rolling radius. Legally, your speedo only has to read within

Try this:-

So realistically it could put you over or under the legal requirements

Most likely just upsets the stability of the car if you want to use a bigger balloon tyre. ie using a 65% profile vs a 55% profile. You have to use the correct width rims to suit the width of the tyre.

Most seem to fall within the same radius size except that 195/65-15

Most speedos are out of wack nowdays none of mine read accurately 4kph slow one checked with the GPS And its a bugger calculating mph to kph,

To be *totally* certain, load the vehicle to its normal weight, with the tyres you will be using on it, and take it to your local tachograph centre, where they can check your speedo to within 0.5% on their rolling road, then go to a main dealer who can apply the appropriate correction to the car's computer. Or put your new tyres on, go to a measured mile, (Handily located on a number of major roads near you, and used by the police to calibrate their VASCAR type equipment), travel along it at an indicated 60mph, time it, and divide 3600 by the number of seconds it take to travel the mile to get your actual speed in mph. Have you checked your particular case using the calculator I gave a link to?

I plugged your two desired tyre sizes into the calculator that I linked to, and they say that the error from one tyre to the other is less than

Unless you are a driver who routinely drives at the speed limit plus

In message , John Williamson writes

LOL! Or use a GPS. Preferably held by someone other than the driver, of course. They are much more accurate than a vehicle speedometer and will give a direct comparison.

In message , Rob writes

My GPS(s) can all be set in either Imperial or metric units.

Have you ever had sex?

with a woman i mean.

Yes, thanks. Not only that, I didn't pay. Have you?

More to the point, have either of you ever snipped?

Chris

Thanks for your replies. I found them very useful. There were two Steve/Stephens, I think you got us mixed-up.

I never knew that. So are cars always more stable with lower profile tyres?

it would make little difference in road use, esp. in bad conditions.

Side walls flex more.

Does the cost of the 15" rims offset the difference in tyre price?

Do you have a model of car that has bigger discs and calipers (ie a faster model) than those with 15" wheels - will they physically fit on the car?

IMO you should just use the tyres and sizes that were specced for my model of car when it was designed..

Yes lower the profiles - higher the price.

Have a look at the difference of the tyres mentioned as to the specs and compare the prices (of the same manufacturer of course)

I am planning on buying new rims anyway, so that I can have a summer set of tyres and a winter set on their own rims. I am only going to get steel rims, possibly second hand ones, so I hope the cost of either 15 or 16" will not be too excessive.

It's just a standard 1.4 Astra as far as I know. Nothing sporty.

But all of those tyre sizes were spec'd by the manufacturer and all are listed in the handbook!

Thanks, Stephen.

So pick the cheapest combination of M&S tyre tread and rim you can find on that list for the cold and wet season, and the highest grip/ acceptable wear combination for your current rims for Summer fun. Low profile tyres grip better, but are less comfortable. As to grip, with a decent make, on a 1.4 Astra, you'll probably only really notice the difference if you're going stupidly fast.

Having said all that, if you live in most of the UK, there's no real reason (IMHO, etc...) to have Winter and Summer tyres. If you live where they do make a difference, you should possibly be considering something with four wheel drive.

Enjoy!