How to Handle Decreasing Radius Corners

[Pirate Ridaaargh]

Heya,

Wrote this up on my blog but wanted to share it with you all.

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Nothing gets a rider’s heart jumping into their mouth and their eyes opening out like saucers, then finding themselves in a decreasing radius corner going too fast. It can set off instincts like nothing else on a bike, with riders chopping the throttle and standing the bike up, causing more trouble than it fixes.

A decreasing radius corner is essentially a corner that tightens up. That means that if you take a normal mid apex line into the corner as you might on a constant radius turn, you’re going to find yourself running wide unless you have enough in ‘reserve’ to really lean the bike over. That’s not a good place to be if you have oncoming traffic (or other things to crash into).

So, how can you spot a decreasing radius corner? And what’s the best way to approach them? Well, read on (or watch on) to find out.

Spotting a Decreasing Radius Corner

It should go without saying that if you’re riding on unfamiliar roads, you should be going at 6/10ths of your limits to begin with. That way, if you do find yourself in a tightening corner, you’ll have the ability to keep rolling on the throttle and lean the bike over to exit the corner smoothly.

That said, you can, with some practice learn to spot a decreasing radius corner on the road.

In a decreasing radius corner, you’ll find that the further you go into the corner, the vanishing point will appear to be coming towards you. This effect is quite subtle compared to how a vanishing point moves away in an increasing radius corner, but with enough practice, you’ll begin to spot a tightening turn, allowing you to position the bike correctly for a later apex.

Taking a Decreasing Radius Corner

A decreasing radius corner requires two things – late turn in and late apex. Have a look at the diagram below.

By turning in late, you cut down the lean angle required to make the turn. Same with the late apex. But putting theory into practice isn't always easy, so let’s break it down. We’ll cut the corner into three sections to help make it easier.

https://therideadvice.com/wp-content/uploads/2014/06/Decreasing-Radius-Corner-Image-Smaller.jpg

The first part of the turn involves staying as wide as possible until you turn in. Some riders may find this difficult, as you’re well into the turn before you actually turn in and commit. The natural inclination is to look towards the inside of the corner straight away – but in this situation, it would mean you hit the apex around the midpoint, and as the corner tightens, it would throw you wide.

The best way to overcome this is simple – look where you want to go. As you enter the corner, spot your turn in point and look towards it.

Remember throttle control too. Again, a rider may be apprehensive about being wide so far into the corner and reduce throttle. That will lower speed and therefore the bike will move towards the inside of the corner. You’ll need neutral to slightly open throttle to maintain the wide line.

Upon hitting the turn in point, you’re in the second part of the corner. Flick the bike over quickly and head for your apex. Immediately roll on the throttle (don’t chop it whatever you do) and put in enough lean so you don’t run wide. Rolling on at this point will unload the front end and put as much grip as possible into the rear tire. Because of taking such a late turn in, you won’t need to lean in nearly as much and that allows you plenty of reserve should you need it.

Third, upon hitting the apex, continue to open the throttle and make a nice smooth exit.

See https://www.youtube.com/watch?v=c838GmSBomM for the video.

Following these steps will probably take some practice, as the approach to a decreasing radius corner can feel counter intuitive. If you have access at a local track that features such a corner, keep practicing by taking later and later turn-in points until you feel you've got it right. Alternatively, do the same on a quiet piece of road at lower speeds until you feel confident.[/url]

[fatjames]

tl;dr - countersteering?

[map]

[Rogerborg]

[Northern Monkey]

I followed a 'ped rider round one recently.From his lead, the response of 'sit up, pull the front brake, then fall off' has room for improvement
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[talkToTheHat]

scarier than taking a decreasing radius corner faster than one's comfort zone is watching the cage in front of you stand on the brakes mid corner...

Roads that were designed with elevated vehicle speeds in mind will usually employ an easement curve, historically a third order parabola, particularly if the corner is banked, to allow for a smooth transition of cornering forces and smooth transition into any banking the corner might have. Our DfT continues to specify such transition curves.

More recently there has been enough evidence to convince lawmakers in some US states that easement curves cause accidents because of their psychological effects on drivers, appearing first as a gentle curve before suddenly tightening. California has led the way and curves are required to be constant radius.

For British riders, most bends in our roadways are likely to include easement curves. As the offset and length of the easement curve varies with the sixth power of speed, roads where the the vehicle speed is expected to be at the NSL (or above) will exhibit the greatest effect, and this will be more obvious on narrower roads. The Cat and Fiddle run is probably the most notable example in the country, with long easement curves into small radius corners.

A popular engineering anecdote (although I have likely sold the books that could back this up, and am regretting it as I want to go back and read them) is that when the M1 was first built, easement curves and banking were specified for a vehicle speed of 120 mph, which when discovered by the moral majority was seen as preposterous given the maximum comfortable cruising speed of your average family car at the time was significantly lower. Of course the M1 at the time had no speed limit, and the engineers had planned ahead for a time when having cars easily capable of that speed might be commonplace. Use of the M1 for testing endurance racers before LeMans in showed that sustained runs of over 160mph were possible, with vehicles reaching over 180mph. (I cannot help but wonder if the 186mph agreement is a reflection of this.)

I would suspect that forward-thinking engineers have made similar future proofing decisions on selecting easement curves on the majority of other trunk roads, creating a network of roads where the corners have long easement curves that deceive motorists.

I further note that the easement curve is usually the braking zone into the corner for cage drivers, causing the opposite effect where back roads that don't have such hints to be massively treacherous.

I find that it's much easier to observe the easement curve on the way out of a corner than on the way in as more of the road can be seen, which is helpful for understanding road design but not useful for judging entry speed.

It is therefore a relatively safe assumption that any bend in front of you is going to take a pattern of easement, constant radius, easement, so if you can't see the road out of the corner it's going to tighten and you can guess at how much by how much you can't see. If you control your speed such that you are able to stop in the road ahead of you that you can see to be clear, you shouldn't end up in a situation where you need to do something drastic.

Of course if you are using the road as your racetrack then I recommend knowing the track and having flag marshals at the entry to corners to warn you of unseen dangers on the way out...


I am not sure what the shift light demo has to do with any of this.

[Slacker24seve...]

TLDR:

1. Slow in, fast out
2. Turn in late.
3. Look for the vanishing point
4. Gas it?
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[Val]

that is all good, however the most common scenario is when you have decreasing angle and you do NOT expect it.

Means you get a little hot in and you do not turn late and you just see ooops we have decreasing angle here.

The only way so far I am able to handle this is - relax on the handlebars, lean more and some times very light clutch but not throttle off I try to keep it smooth. And I try not to use all of the road means to leave some reserve left, so if it is a left turn I try not to get too close to oncoming vehicles if right I try not to get at the end of the road where we have sand and stuff.

If you guys have some tips for the unexpected decreasing angle let me know?
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[Slacker24seve...]

[talkToTheHat]

A dab of clutch might tighten the line if the engine is pushing the bike, or it might send you wide by removing the engine braking that was already tightening your line, and you risk breaking traction at the rear when you let the clutch out if rpm or road speed changes whilst clutch in or at least having the opposite effect. I suspect if one has already fucked up a corner, pulling the clutch in a panic will cause much hurt.

[Wafer_Thin_Ham]

In 99% of situations if you think you're going wide, just lean it more. In the 1% of situations that you've got the bike at it's max lean on the road, you've just overestimated your talent somewhat and you're probably going in.
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[Rogerborg]

[dydey90]

I use the incredibly boring strategy of not hammering it into bends on roads that I don't know, when I can only see the first five yards of road.

Of course, this does often result in disappointment when the corner turns out to be a lot less severe than it could have been.

It did save me yesterday however, when I ended up riding through a random village and the road suddenly went into a hair-pin bend because some inconsiderate idiot had shoved a house down right where the road wanted to be.
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[Matt B]

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[talkToTheHat]

[barrkel]

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