Spot of insomnia last night.
Found myself wondering how steep the slope on a road would have to be before a car (let's assume an average car with tyres in average condition) would just slide down it.
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I seem to recall that one of the landrover claims was that the defender could climb a 45% angle, so staying stationary should be even higher.
All down to the coefficient of friction the tyres can generate. I never was that good at applied maths.
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I've done a hill start on a 1:3 as part of a driving competition (rolling back was penalised) in a Maxi on 155x13s. It was quite easy thanks to a decent handbrake and the see-saw effect of the suspension.
Some cars seemed incapable of achieving it.
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Steeper than this:
i151.photobucket.com/albums/s138/Cliffordpope/BUS....g
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That looks a lot steeper than 1/3, how about the guiness steepest road in the world?
en.wikipedia.org/wiki/Baldwin_Street,_Dunedin
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That looks a lot steeper than 1/3
"At its maximum, the slope of Baldwin Street is approximately 1:2.86"
Edited by Focus {P} on 26/08/2009 at 13:21
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Sorry, I was refering there to Cliffs picture :)
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Sorry I was refering there to Cliffs picture :)
Sorry, should have worked that out.
I've driven over Wrynose Pass in the Lake District a few times, and that's quite fun - supposed to be 'up to 1 in 3' according to t'internet, but I think that's only on the bends. That one in NZ looks scary - my bike ride home out of Reading involves a bit of a hill, but I can see it could be a lot worse :-)
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The road from Edale and round back of Mam Tor where it leads you out to Blue John Cavern whilst not exceeding 20% is a very good hill to drive up espically with its endulating road surface.
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>>The road from Edale and round back of Mam Tor where it leads you out to Blue John Cavern
Isn't that Winnats Pass?
www.castleton-rocks.com/winnats.html
I have distant memories of setting the front brakes on my (automatic) Triumph Dolomite on fire while making good progress down Winnats, using it as a short-cut across to Sheffield in the late 70's.
www.rural-roads.co.uk/winnats/winnats11.jpg
Edited by Another John H on 28/08/2009 at 18:17
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Apologies if I've missed the irony, but that first picture has been Photoshopped, and the angle the bus has been pasted is exaggerating the slope on the road (although no doubt it is still a bit steep)
Edited by Armstrong Sid on 26/08/2009 at 13:57
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How steep would Lombard Street in San Fransisco be had they need put in all the bends/switch backs?
www.sftravel.com/lomabardcrookedstreet.html
en.wikipedia.org/wiki/Lombard_Street_(San_Francisco)
EDIT: Wiki has the gradient as 27% if it were not for the switch backs.
Edited by rtj70 on 26/08/2009 at 14:01
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It's not photoshopped, the camera was at an angle to accentuate the slope. Rotate the picture clockwise 15 degrees or so to see the real picture.
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On closer examination the bus does appear to have been added to the original landscape (which is rotated - the level running from bottom left towards top-right behind the bend in the road should be near horizontal in reality.)
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If the coefficient of sliding friction between the tyres and the road surface is 1.0 then the minimum slope before the car starts to slide is 45° to the horizontal.
Edited by L'escargot on 26/08/2009 at 16:15
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:-)
I doubt my Missus would allow me to push her wheelchair down that one in New Zealand!
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If the coefficient of sliding friction between the tyres and the road surface is 1.0
...but what is the value for average tyres on an average road?
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I used to be able to do this sort of calc .......
Referring to to OP. Would it depend on whether the vehicle was facing up or down hill?
For example if facing uphill is there a set of conditions that would allow it to tip over before it slips?
I think there are!
FTF
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>> If the coefficient of sliding friction between the tyres and the road surface is 1.0 ...but what is the value for average tyres on an average road?
Probably about 1.0.
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From hyperphysics.phy-astr.gsu.edu/Hbase/Mechanics/fric...l
"Jones and Childers report coefficients of friction of about 0.7 for dry roads and 0.4 for wet roads. The tread design represents an "all weather" compromise. If you were an Indianapolis race driver, you would use "slick" racing tires with no tread. On dry surfaces you might get as high as 0.9 as a coefficient of friction, but driving them on wet roads would be dangerous since the wet road coefficient might be as low as 0.1."
EDIT: I was just looking it up when you posted!
Edited by Focus {P} on 27/08/2009 at 08:51
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So it will probably be 1.0 on a dry road with good modern tyres and on such roads, they are likely to have used a more skid resistance surface than usual.
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So it will probably be 1.0 on a dry road with good modern tyres
Even if they could only get 0.9 with slicks?
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Of course the inside of some tight bends on minor roads or at road junctions sometimes approaches vertical, but only over a very short distance. I remember reversing round a very tight turn into a side road once, and without warning the inside rear wheel suddenly dropped over the edge and the car landed with a crash on its nearby jacking point.
On inspection the moderate slope on the outside had gradually turned into a vertical 9" wall on the inside. The surfaces were tarmacked to hide this.
The inside of the tight bend at the bottom of our lane must be about 1:1 - it's almost impossible to walk up.
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