OT Sat Nav

[The Natural Philosopher]

No, its the circumference that matters

That's the bit that's connected to the road.

[Robin]

Yes but to be precise the dynamic rolling circumference which does change with load.

In passing, I've also been reminded that at least one of the systems for monitoring tyre pressure claims to work by monitoring the effect of lower pressure on dynamic rolling radius:

[Roger Chapman]

As far as the geometry is concerned it is the rolling radius that determines the ratio between road speed and rpm of the wheel. There is always going to be a flat area (the footprint) where the tyre sits on the road. Any circumference changes as circumstances change are going to be extremely limited compared with the changes in the rolling radius as tyre pressure changes.

[Ret.]

For a short while, (during the period that Brunstrom was in charge), North Wales introduced a stricter policy - although they offered 'Speed Awareness Courses' for anyone 'booked' at less than the ACPO recommendations. I am not aware of any forces that are currently not complying with ACPOs recommendations. Are you?

[Ret.]

My previous car, a Rover 75 estate, had exactly the same pressures for all conditions - including towing. That's the only car I've had like that however.

-- Kev

[Ret.]

My comment was, actually, an attempt to be amusing... !

[Dave Plowman (News)]

Probably a mistake when they printed the handbook.

[tony sayer]

SWMBO just went on one of these .. all of Four hours duration and in the end was told to drive in Third gear in 30 MPH zones;!...

[dennis]

That's a bit silly, I can drive in fifth unless its up hill or i want to accelerate (to stop geof from getting past without him hitting the milk float coming the other way).

[Tim Lamb]

In message , tony sayer writes

Yes.

We have a common rail Fiesta diesel and find 3rd the best gear for 30mph zones.

Engine braking seems less pronounced than on a conventional diesel.

regards

[tony sayer]

In article , Tim Lamb scribeth thus

U seriously telling me you stay in Third in 30 zones then?..

[Ret.]

My auto box decides what gear to be in - not me - but it's rarely less than

5th when cruising on a flat road at 30 (it does have 7 gears though...)

[charles]

It's what I do. It saves constantly looking at the speedo. But it will depend on the gear ratios on your car.

[Tim Lamb]

In message , tony sayer writes

Generally. Particularly where there are cameras. 4th. is OK where traffic flow is 35 or so.

regards

[dennis]

Why do you need to constantly look at the speedo? I drive with a data logger on me and I hardly ever look at the speedo in 30 zones and I am usually at ~30 when I think I am at 30. I can't imagine its a skill that's unique to me. Its suggests that you need more practice.

[charles]

I don't look at the speedo, I stay in 3rd.

[tony sayer]

In article , charles scribeth thus

Trouble is what the car that she was using if you just pushed the go pedal a slight bit it would well whip past the 30 mark. 6 Fwd gears on this one..

[tony sayer]

I'd Just like to ask why?. Surely you can set the throttle to maintain the required speed?..

[Bob Eager]

Same here. When i got the current car I found myself speeding a lot. It was the diesel version of the previous car, and of course behaved quite differently. I discovered that 3rd gear nicely limited me to 30 (revved too much above that). Pretty well the same for 4th and 5th/40 and 50, and then 6th for 60 and above.

[Andy Champ]

Yes, and it only increases the fuel consumption by a third (and that is not what they say on the course - where they lie, and say it makes no difference!)

Andy