Wheel fitment 940.

[Laird Scooby]

Originally Posted by Stephen Edwin

All I can say re size is, decide the size you consider best and get that size. Unless you are confident that a different size will fully serve your fundamental purpose re .... safety.

Tall and skinny. I think I might have heard that years ago. Thank you David.

I'm about to fit in a little while some 195 65 15 winter tyres. Almost exactly correct diameter for my car's speedo. Not tall, not skinny. Perhaps the winter tyre qualities are more important than being tall and skinny?

I haven't heard before about regional variations. Is it road surfaces, or local prejudices? What do you think David?

I looked up winter tyre reviews. The opinion seems to be that they do grip better at or below 7 deg C. And a proper M&S winter tyre will perform well even if one encounters snow. So I am treating myself to a set of winter tyres, on a spare set of wheels. A personal decision. Right or wrong.


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Like i said above, regional variations in road surfaces. Tall and skinny works better as it is easier to push a skinny tyre through snow and actually reach the road underneath than short and wide which just compresses the snow into a packed block which soon refreezes into ice - usually black ice too!

Go back 30+ years and i had a 144 DL auto running the original fit 165/15 tyres - standard profile which i believe is 78. About 10mm smaller in diameter than your 195/65s (which will almost certainly help your speedo accuracy) and that winter was quite harsh with snow everywhere.
I picked a colleague up on my way to work each day, she lived on an estate down in a dip with only two roads out, both steep hills. One morning after witnessing a Land-Rover spinning all 4 wheels and slithering backwards into the kerb, i had a go and just drove straight up - a little sideways action halfway up where the Landy had warmed the snow and turned it to ice but other than that, as if the weather wasn't bad. His tyres were much wider so had simply crushed the snow and flattened it.

Use some butter to see the different effect. Use the blade of a knife as if cutting it to represent the skinny tyre, turn it 90 degrees to represent the wide, low profile tyre and push each different way into the butter with the knife. Which gets to the butter dish easier?

Get the tyres to the butter dish/road easier with whatever width tyres and you get more grip - simples.

Squash the butter/snow with extra wide tyres and you don't get to the butter dish/road.

[Laird Scooby]

Originally Posted by XCR

Like I said David, the speedo error is fractional. Have a look at the site I linked.

"If you're able to find 175/70/16 they'd probably be about the best compromise between what you need for snow/ice and fitting on the 16" wheels. I'm not even sure it's a "real" size as in one that is manufactured though."

I must remember that one !!!!!
As for 'Reading 70 when I'm actually doing 55 ?" I wonder what tyres would actually need to be fitted in order to produce that reading ! I'll pop back and let you know.........................

ETA....
205 55 21 - 70 mph
225 60 13 - 55.3 mph

Like i said, download that "SPeedy" app, take your car out for a drive and compare what that reas on a flat road with your speedo. On the 185/60/15 tyres that Volvo originally fitted to mine, at an indicated 70mph i was doing about 61mph in the real world. I now have 195/65/15 and at an indicated 70mph, i'm really doing about 66mph.
To get the speedo more or less accurate (+/- 1mph of the indicated speed) i would need to fit 205/70/15 tyres. Like i said, Volvo speedos are notoriously over-optimistic.

Your "fractional error" is the error based on the assumption your speedo is accurate to start with. Factor in a speedo that reads a good 10% over in the first place and it will be a lot more!

The app is free, try it and you'll be surprised! Even on 205/55/16 which are about 2mm bigger diameter than 195/65/15 if memory serves (without checking - might be 2mm under) you'll almost certainly find about a 6% over-read on the speedo now.

[Stephen Edwin]

Well. I wonder about regional variations. Interesting.

30+ years. About 1990? There was some brief heavy snow about then. On the Thursday I walked some miles home. On the Friday I was one of few who got to work, walking some miles. On Saturday because I had snow chains I was driving happily about almost deserted roads. Very handy because my aged parents needed a vist and shopping. Otherwise goodness know, Dad would probably have gone shopping, fallen over, EEK.

My second hand experience of tall skinny tyres is a chap who in the really serious snows of the 1960s made excellent progress with his sit up and beg Ford Pop.

I would guess his experience and yours were with "ordinary" tyres? Modern winter tyre reviews show seriously impressive results for modern winter tyres including in snow. And they don't mention tall and skinny. So far as I know, countries that require M&S tyres in winter don't make exceptions for tall and skinny tyres.

I don't know.

[XCR]

I've never had a speedo read 10% over in any car I've owned David. And there have been more than a few !
This speedo (when it behaves itself) is almost bang on....
I dunno where you're getting these figures. I'm beginning to form the impression that they're not from an entirely scientific source....see my previous post....

[XCR]

Tall and skinny you say ? Time to get the motorbike out as its so useful in the snow....like a knife through butter !

Speaking of butter, in order to replicate your butter test, do I use salted or unsalted ?

[classicswede]

Most 240 speedos read 5-10% fast

For snow a narrow is best as explained about but for all other conditions a wider tyre is better

[Laird Scooby]

Originally Posted by Stephen Edwin

Well. I wonder about regional variations. Interesting.

30+ years. About 1990? There was some brief heavy snow about then. On the Thursday I walked some miles home. On the Friday I was one of few who got to work, walking some miles. On Saturday because I had snow chains I was driving happily about almost deserted roads. Very handy because my aged parents needed a vist and shopping. Otherwise goodness know, Dad would probably have gone shopping, fallen over, EEK.

My second hand experience of tall skinny tyres is a chap who in the really serious snows of the 1960s made excellent progress with his sit up and beg Ford Pop.

I would guess his experience and yours were with "ordinary" tyres? Modern winter tyre reviews show seriously impressive results for modern winter tyres including in snow. And they don't mention tall and skinny. So far as I know, countries that require M&S tyres in winter don't make exceptions for tall and skinny tyres.

I don't know.

Thirty years ago would be 1988 (same as my 760) so 30+ years ago would be before that! Try 1985!

[XCR]

But, but, what about the butter ?

[Laird Scooby]

Originally Posted by XCR

I've never had a speedo read 10% over in any car I've owned David. And there have been more than a few !
This speedo (when it behaves itself) is almost bang on....
I dunno where you're getting these figures. I'm beginning to form the impression that they're not from an entirely scientific source....see my previous post....

What are you measuring it against? Have you measured any of your other cars? I've only ever had one that has been accurate to within 1mph through the rev range and that is my 827 Sterling - last count i had owned 235 cars and i've owned a few more since then, i'm not even going to bother trying to remember them all.

Out of those, i've only checked the speedos on a few of them against either sat-navs or GPS mobile speedo apps.

If you think they're from anunscientific source, download the app and do your own checks, i don't talk cowshed confetti, i've been an engineer all my life so there is no need, if it doesn't work then it doesn't work - simples. No need to dress up the facts as something they're not, enhance, embellish or otherwise.

I had already advised you of the app i had used and invited you to download it and do your own checks, you then proceed to extract the urine. Get your facts right first!

[Stephen Edwin]

1985? Oh yes there was heavy snow about then one night lasting in to the next day. I had a broken windscreen in the beginning of that flurry. Most cars seemed to get around OK. Where I was.

Anyways. Thank you for reminding me about tall and skinny. (Sounds like a modern coffee.) That could tip a decision between different tyre sizes.

My guess is. If a car maker specifies tall and skinny, that's a bonus in snow. Most makers specify a tad wider which as Dai says is better when there is no snow. Work out what is best for oneself.



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