revtothelimit - motorbike forum

The recent 'rear brake' thread moved into cornering in general.

One thing I thought worth illustrating is how different ways of determining the maximum stopping distance (and so that limiting your speed) can appear.

At this point it's worth noting:
- if the bend radius decreases and you haven't allowed any margin for error, then you're over-riding the stopping distance that will be available
- stopping a bike while leant over is likely to need a longer distance than when upright and straight
- you ought to plan to stop within 'your' lane which, if you're riding out in a 'view' position, will be even more difficult as ideally as the bike slowed you would bring it straight and upright. The only way you could achieve that would be by initially turning tighter.

Roadcraft covers that with the 'stop on your side of the road ... between you and the limit point'. [2005 edition, I'm very happy to edit this if there's an improvement now]

It also says:
- 'It gives the point at which to start accelerating'

This referring to 'as the bend straightens your view begins to extend'.

New readers: the Limit Point (or limit of vision, or of visibility, or vanishing point) is:
- 'the furthest point ... uninterrupted view of the road surface'
Or:
- 'where the right hand side of the road appears to intersect with the left'

Think of the road ahead as an arrow head:



Fascinating trivia: on a level surface, that will always be at your eye height!

If the road curves away to the horizon, it will look like this:



The more acute the angle that the road edge is to the horizon, the tighter the bend.

As the point moves back towards a straight (running, to use one term), the bend is starting to open.

But can using the limit point lull you into a false sense of, well, not 'security', but 'comfort'? Especially if you're using it to determine stopping distance (and so your speed) and when to increase speed?

Regular readers will have heard the 'surprise horizon' mentioned. A term coined by Stephen Halley in his book Mind Driving, it's the closest point at which you can be surprised, ie you don't have a clear view.

Here's a bend, with a few gaudy lines added:



Bright red, intersecting with the hedge on the left, is the limit point.
Orange is how Roadcraft defines your stopping distance
Yellow is the surprise horizon
Dark red is your stopping distance to where something emerging could get you

Have a look at this pair of photos, from either side of the same bend:





The side turning - and, potentially, the Caterham - is invisible from even an extreme offside view. Which means you would be invisible to the driver.

NB photos taken on a closed road!

Here's another interesting road:



In traditional terms, see earlier quotes, the limit point is the crest of the bridge - but look how many blind side turnings there are (look for the wheelie bins).

SH info (book contents):
http://www.skilldriver.org/index.asp?pa ... .0.Welcome

Final thought:

You answer your last question somewhere near the start. If you can't remember what you've written, you old duffer, let me remind you:

"New readers: the Limit Point (or limit of vision, or of visibility, or vanishing point) is:
- 'the furthest point ... uninterrupted view of the road surface' "

slowsider wrote: Tue Nov 24, 2020 8:21 pm You answer your last question somewhere near the start. If you can't remember what you've written, you old duffer, let me remind you:

"New readers: the Limit Point (or limit of vision, or of visibility, or vanishing point) is:
- 'the furthest point ... uninterrupted view of the road surface' "

If that's your biggest criticism, it can't be far wrong

Hope there's a buffer stop behind that coach

I find the Limit Point to be incredibly useful, and it's one of the cornering tools I use most frequently. But I don't think there's any single tool on its own for judging bend severity.

Regarding @Horse's Surprise Horizon, my biggest issue with the Limit Point is close encounters of the animal kind. On rural roads locally, I've lost count of the number of animals that have emerged from the foliage on the nearside. It's been good practice for my emergency stops! Horse is right: sometimes, the Surprise Horizon can be much closer than the Limit Point.

While I've found Motorcycle Roadcraft has lots of useful tips, it's short on advice about animal hazards. And what does Roadcraft advise about a zebra crossing?

Is that some sort of Horse pisstake? :|

Hot_Air wrote: Wed Nov 25, 2020 9:42 am I find the Limit Point to be incredibly useful, and it's one of the cornering tools I use most frequently. But I don't think there's any single tool on its own for judging bend severity.

Don't get me wrong, it's incredibly useful. But not the only limit.

Where's the limit point when the edges don't meet? Specsavers?

Trinity765 wrote: Wed Nov 25, 2020 11:13 am Where's the limit point when the edges don't meet? Specsavers?

In the pic there are side turnings, a parked bus, a long high wall (may not show, but it has gateways, etc.

Trinity765 wrote: Wed Nov 25, 2020 11:13 am Where's the limit point when the edges don't meet? Specsavers?

Google shows that they are surprisingly popular:

https://www.google.com/search?q=specsavers+crash

Hot_Air wrote: Wed Nov 25, 2020 9:42 am Horse is right: sometimes, the Surprise Horizon can be much closer than the Limit Point.

Horse?

The Surprise Horizon - and the Vision Blockers that conceal them - are ALWAYS closer than the Limit Point. And that's why we should be focused on spotting them first!

If... and ONLY if... you can't see any Vision Blockers should we be setting our speed to the Limit Point.