Clothoid?

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Horse
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Clothoid?

Postby Horse » Mon Nov 04, 2019 8:46 pm

Your 'standard' is how you drive alone, not how you drive during a test.

TheInsanity1234
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Re: Clothoid?

Postby TheInsanity1234 » Mon Nov 04, 2019 9:31 pm

Whilst not strictly a spiral entry bend (I think, it might be), I do recall a very sharp s-bend on the entry road into Lambourn, here.

Quite early on in my driving career, I noticed these bends seemed to catch a lot of people out, people frequently ran wide into the centre of the road at the midpoint of the s-bend going in either direction, and I realised that the reason is because on both entries, the road actually curves slightly to the left before the actual sharp left bend, thus giving a spiralling transition into the bend, meaning people often entered the sharp bend with too little steering angle and too much speed. This was resolved by looking at the limit point on the centre line, rather than at the kerb, because then you noticed that the actual bend was much sharper and tighter than the inner edge would have you believe.

Quite an important lesson to learn, I gather!

vanman
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Re: Clothoid?

Postby vanman » Tue Nov 05, 2019 9:27 am

One of the first bits of advice I got before I got my first bike Royal oilfield 250 GT "if you feel you are going too fast into a corner open the throttle and lean further" Never once fell off on a corner in 16 years. Black ice, oil, diesel and gravel yes but not corners.

Gareth
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Re: Clothoid?

Postby Gareth » Tue Nov 05, 2019 9:28 am

Is this a bike thing? Although the linked article mentioned cars, it didn't seem to make the case that drivers were having this particular difficulty.
there is only the road, nothing but the road ...

Gareth
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Re: Clothoid?

Postby Gareth » Tue Nov 05, 2019 9:42 am

TheInsanity1234 wrote:I noticed these bends seemed to catch a lot of people out, people frequently ran wide into the centre of the road at the midpoint of the s-bend going in either direction, and I realised that the reason is because on both entries, the road actually curves slightly to the left before the actual sharp left bend

'Locals' knowing there isn't an unsighted entrance? Drivers trying to enter the bend at their highest comfortable speed instead of leaving something in reserve? A combination of too high an entry speed and a slightly tightening radius?

Tightening radius bends are reasonably common, so it's something that drivers ought to expect when they can't see how a bend develops. And, here, the bend is blind in both directions, which makes it impossible to see all the way through on approach.
there is only the road, nothing but the road ...

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Horse
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Re: Clothoid?

Postby Horse » Tue Nov 05, 2019 9:46 am

Gareth wrote:Is this a bike thing? Although the linked article mentioned cars, it didn't seem to make the case that drivers were having this particular difficulty.


It was on a bike-specific site. I doubt that the road geometry knows what vehicle is travelling along ;)

When you say linked article, did you mean the two PDFs linked at the end of the main article?
Your 'standard' is how you drive alone, not how you drive during a test.

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GTR1400MAN
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Re: Clothoid?

Postby GTR1400MAN » Tue Nov 05, 2019 10:19 am

These are the sorts of corners that can conflict with the (awful) 'chase the limit point' soundbite often used. It is paramount when teaching limit point cornering techniques that the fact you may need to ease/feather the throttle mid corner is discussed.

These corners do catch some out but I do know Duncan (and Kevin from SurvivalSkills) have a bee in their bonnets about this aspect of cornering. ;)

(Horse, well done for waking up a quiet forum with this blast from the past! :) )
Mike Roberts - Now riding a Triumph Explorer XRT. My username comes from my 50K miles on a Kawasaki 1400GTR, after many years on Hondas of various shapes and styles. - https://tinyurl.com/mikerobertsonyoutube

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Horse
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Re: Clothoid?

Postby Horse » Tue Nov 05, 2019 11:32 am

:) I have been known to do the same elsewhere, usually by posting a ridiculous 'conspicuity' thread :)
Your 'standard' is how you drive alone, not how you drive during a test.

TheInsanity1234
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Re: Clothoid?

Postby TheInsanity1234 » Tue Nov 05, 2019 5:43 pm

Gareth wrote:
TheInsanity1234 wrote:I noticed these bends seemed to catch a lot of people out, people frequently ran wide into the centre of the road at the midpoint of the s-bend going in either direction, and I realised that the reason is because on both entries, the road actually curves slightly to the left before the actual sharp left bend

'Locals' knowing there isn't an unsighted entrance? Drivers trying to enter the bend at their highest comfortable speed instead of leaving something in reserve? A combination of too high an entry speed and a slightly tightening radius?

Tightening radius bends are reasonably common, so it's something that drivers ought to expect when they can't see how a bend develops. And, here, the bend is blind in both directions, which makes it impossible to see all the way through on approach.

Yes, my point was that the locals seemed to regularly be caught out by it, as well as loads of visitors! People approached these bends and made the same common mistake of carrying too much speed into the bend, and not steering enough.

I'd argue that perhaps each individual person had a different thought/observation process that led to the same mistake, of thinking the bend isn't as sharp as it is, and the one constant is the fact that the bend requires you to start steering to a certain angle, and then surprises you with the sharper bend when most people have settled into a fixed angle and speed they assume is the correct one to get them through the bend!

You would hope people would learn the roads they drive regularly in order to know the safest speeds and how certain bends may differ from the initial impression they give, but then for a lot of average drivers I know, they very rarely recall any journey they've made, even on local roads, and that when they navigate somewhere from memory, they're not actually remembering much, just where they turn at a junction and perhaps the road names/numbers they need to follow, and so it doesn't surprise me that much that locals would get caught out regularly by the same bend, because 99% of the time, nothing happened and thus there's nothing that'll make them think "ooh, I'll take that bend a bit slower next time"!

Triquet
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Re: Clothoid?

Postby Triquet » Tue Nov 05, 2019 7:47 pm

But even the simplest of bends catches people unaware.

https://www.google.co.uk/maps/@51.63553 ... 6656?hl=en

See that nice little fence on the left hand side? This is a most unusual picture as about once a month somebody will visit the bush at close quarters demolishing the fence in the process.


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