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BMW on Motorway??

Tend to agree. You might as well just have an overheat light.

But I'm sure it suits those who ain't got a clue how an engine works and would be worried by knowing the truth. ;-)

Reply to
Dave Plowman (News)
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No spare of any sort on one of them.

But it's perfectly possible to have a space saver with the same rolling radius as a full sized wheel.

Oh - sorry. Forgot it was you. Get someone to explain rolling radius to you.

Reply to
Dave Plowman (News)

Of course it is, but then it wouldn?t save as much space. Manufactures are supplying space savers with a smaller radius.

Maybe you ought to fact check space saver sizes rather than assuming that they must be the same diameter.

Tim

Reply to
Tim+

Sounds improbable. Maybe a limited slip diff wouldn?t like it but I can?t see a regular diff being seriously stressed by a small difference in rolling radius. Many space savers *are* smaller in terms of overall diameter/rolling radius.

Tim

Reply to
Tim+

Dave Plowman (News) expressed precisely :

The speedo's are usually optimistic, but not the odometers. They are usually very accurate.

Reply to
Harry Bloomfield

As a matter of interest, how much smaller diameter are we talking about?

You may well be right. I'm intrigued. I'll do some measurements. I always assumed that the diameter was identical and that all the saving was in the

*width* of the tyre, on the maybe naive assumption that if you put a smaller tyre on one axle, the car will want to go round in circles - irrespective of whether the wheels are joined by a differential (front wheel) or are totally independent of each other (rear wheel) - and will dip down at that corner, putting less weight (and so less traction if the opposite wheel is a driving wheel) on the diagonally opposite wheel.
Reply to
NY

I've never had a car with a space saver. My brother has had two - a BMW and now an Audi. On both, (estates) there is space for a full sized wheel in the well. And that's what he does - buy a used full sized wheel as those cars are used for towing.

Reply to
Dave Plowman (News)

I'm talking about normal use over a period of time. Which only an idiot would do with a space saver. The gears and bearings in the differential part ain't rated for continuous use. If you've actually ever stripped one down, many have plain bearings for the planet wheels. While everything else has ball bearings.

Reply to
Dave Plowman (News)

Then maybe you?re not best qualified to tell others about their dimensions? Just a thought...

Tim

Reply to
Tim+

The common recommendation is a maximum of 50 miles.

Tim

Reply to
Tim+

What has a variable speed limit got do do with people driving at 70MPH?

Reply to
ARW

Does it matter whether or not the space-saver tyre is on a driven axle with a differential, for the handling of the car?

If you put a smaller tyre on the same "virtual axle" as one with the normal size wheel, won't mean that the car will be lopsided and the car will try to go round in circles instead of going straight ahead with no steering input? How much does the suspension of a car adjust to different sized tyres to keep the car level and hence the same load on both of the driving wheels - assuming it's not clever suspension like Citroen's hydropneumatic.

By "virtual axle" I mean two tyres that are side by side (two front or two rear), whether they are connected by axles and a differential or are completely independent (in the latter case, the front wheels of a RWD car or the rear wheels of a FWD car).

Reply to
NY

And another thought. You've never seem one in use and judged for yourself?

But it could be you think it must have a different rolling radius because it simply looks different?

Reply to
Dave Plowman (News)

And so was I. Merely pointing out that using a differential long term for something it wasn't designed to do can have consequences.

Reply to
Dave Plowman (News)

Dunno. I was merely pointing out the possibility of differential damage if different sized tyres are used long term.

Reply to
Dave Plowman (News)

Some of the gantries carrying the lane based VSL signs and per lane cameras also have good old double flash speed cameras set at 70(ish) sticking out the side. Saw a couple of the double flashes when the VSL wasn't active...

Reply to
Dave Liquorice

There you go, making assumptions again

Maybe I?ve actually bothered to do an Internet search? Seems it?s common for them to be a bit smaller.

If you can?t be bothered to to a few seconds of research why are you contributing to this thread when you also lack any first-hand experience?

Tim

Reply to
Tim+

And who suggested that anyone intended using mismatched wheels for long term? Oh yes, it was you.

Tim

Reply to
Tim+

12 miles in 11 minutes with my foot down to the floor and the speedo up against the stop at 92. Several pretty burnt out valves when he sold it when I went to college but I had had some fun.
Reply to
F

Yep, 65mph in an Anglia will do that. ;-) (12 miles in 11 minutes is nowhere *near* 92 mph).

Tim

Reply to
Tim+

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