How To Negotiate Decreasing-Radius Corners

Helping you to prepare for the unexpected

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Perhaps no corners strike greater fear in the hearts of motorcyclists than decreasing radius corners. However, the corners themselves aren’t really the cause for the concern. It’s the surprise of entering an unfamiliar corner, setting your speed and your line, only to suddenly have the rules change midway.

Remember that, despite the surprise, if your bike isn’t dragging hard parts, you have the ground clearance to lean the bike over even more — probably more than you think.

Before we discuss the challenge of decreasing radius corners, we should quickly review an easy one. This will make sure we have the same techniques in mind. In an idealized constant-radius corner, the rider can see from entry to exit. So, the bike’s approach would be wide at the entrance, and setting the appropriate speed before the turn-in point.

A rider should look through the corner, initiate the turn, and begin rolling on the throttle. Rolling on the throttle settles the suspension and keeps the bike from falling into the corner as the bike heads towards the apex. After the apex, acceleration can increase as the bike begins to stand up, putting a larger footprint on the pavement and following its line to the outside of its lane at the exit of the corner.

Constant Radius Curve

The ideal line through a constant radius curve starts wide at the entrance, tightens to the apex, and then exits wide. Photo courtesy of the Motorcycle Safety Foundation.

If the entire corner could be seen at the entry, the tightening of a radius could be planned for from the beginning — just like with our idealized corner. So, in order to address the fear of the decreasing radius, we should look at the proper way through the corner and then backtrack to see how we can apply this knowledge to corner entry — even when we don’t know a decreasing radius lies ahead.

Motorcycle Cornering Clearance – What To Do When It Runs Out

If you’re taking the classic line through a corner and the radius tightens — even just a little — it will have the same effect as early apexing a corner: The bike will run wide at the exit. So, when approaching a decreasing-radius corner, the best tactic for a street rider would be to set the entry speed for the tighter portion of the curve, hold a wide line at the entrance of the corner, and dial in more lean until the line heads towards the apex of the tightened radius.

Decreasing-Radius Corner Graphic

If we treat a decreasing-radius corner like a constant-radius one, the line takes us off the road as the curve tightens. Holding a wide line gives us maximum flexibility to modify our line as the corner’s radius tightens.

Newer riders will want to set a slower speed at the actual corner entry. For more advanced riders, trail braking through the initial corner to the tighter section can be utilized as long as you’re cognizant that traction for braking is reduced by cornering forces. Smooth application of the brakes is paramount, as an abrupt spike in brake pressure — or abruptly chopping the throttle — can cause traction loss and send you tumbling.

While traction for braking in a corner is limited, entering the corner trailing the brakes and having the bike’s weight shifted on to the front end actually helps with steering input. The fork’s rake angle decreases as it compresses, making the bike respond more quickly to steering input. You have also compressed the tire, giving it a larger contact patch and more traction.

However, the harder you’re cornering, the thinner the line is between having enough grip to brake while leaned over and a low-side crash. Once initiating your line in the tighter section of the corner, begin accelerating for the exit as you normally would.

In the example above, we assumed we could see the entire corner and, therefore, could plan accordingly. However, on the street, you will frequently enter corners where you can’t see the exit. While you can draw clues for where the corner goes from trees or telephone poles or fence lines, these can be misleading. (Have you ever been following a row of telephone poles for miles only to see them go straight off into a field while the road makes a turn?)

Proper Motorcycle Lane Positioning

So, when riding on an unfamiliar road, you should always hold at least 20 percent of your skill set, traction, and ground clearance in reserve for the unexpected — which could come in the form of a tightening radius, an obstacle, liquid, a bicyclist, or any other of the myriad of things you might encounter in the real world.

Decreasing Radius Corners Action

The rider’s wide initial line gives him the time to detect a decreasing-radius turn and begin tightening his line.

The prudent street rider will set road speed based on the radius of the corner at its entry (while keeping that 20 percent reserve) but will maintain a wide line. Once the corner’s exit is spotted, the final line, which clips the apex, can be selected. A wide line gives the maximum view of the road ahead, increasing the time to react to the unexpected. Even while holding the wide line, you can accelerate through the corner to settle the suspension as you normally would. If a corner begins to tighten up, you have that reserved cornering clearance to dip in to.

If you suspect the changing radius will ask for more ground clearance than you have, you can modify your speed — or prevent it from increasing — by lightly applying the rear brake and maintaining a neutral throttle. If the corner requires that you slow even more, roll off the throttle — do not chop it — and smoothly apply the brakes. When practicing this technique, notice how, when you decelerate while leaned over, your line will naturally tighten, aiding in achieving your desired path through the corner. After you’ve set your new line, treat the corner’s exit just like every other corner.

Decreasing Radius Corners Action Rear

The rider has chosen his line through the tighter section of the curve and is already looking ahead to the next corner.

One other tactic for solving the decreasing-radius corner dilemma should be mentioned, although it applies more to the track or roads with which you are familiar. When you know a corner has a decreasing radius before you enter it, double apexing a turn essentially turns the corner in two with each being dealt with separately. However, we’ll discuss this technique in a future article.

Motorcycle Downshifting Techniques

Decreasing-radius corners are just another part of the enjoyable challenge of riding motorcycles. If you practice these techniques, you’ll have them to draw on in an instant when a blind curve becomes more challenging than it initially looked.

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  • fastfreddie

    Lean it on more baby!

  • Justin

    if you need this you dont ride. If you ride youve attended a course….this is like getting a a black belt in Karate online

    • Z223

      I’ve taken a course and I found this a helpful refresher…

    • http://www.gtgmobile.com/ Patrick Shaughnessy

      Hi Justin, I felt the paragraph about

      “While traction for braking in a corner is limited, entering the corner
      trailing the brakes and having the bike’s weight shifted on to the front
      end actually helps with steering input. The fork’s rake angle decreases
      as it compresses, making the bike respond more quickly to steering
      input. You have also compressed the tire, giving it a larger contact
      patch and more traction.”

      was really helpful. While we all, I think, understand in concept, few would be able to articulate as eloquently, especially in writing where brevity counts.

  • Brian Stevens

    The Great Ocean Road In NSW Australia had many of these turns, with a bit of loose gravel just to make it exciting and a narrow road. (oh and riding on the left!) made for an exciting ride! This information helps even if you take a course as a good reminder.

  • georgeR

    there really is no such thing as an apex with street riding; stay on the wide radius till you see the exit straighten out. then you’ll see the full turn and will be able to react as needed…

    • Kevin Duke

      The word apex has roots in Latin meaning “point.” In terms of corners, it refers to the tightest section of a corner or at whatever point the bike is leaned over the most. Hence, all corners have an apex.

  • Doug Just Doug

    On the 90-degree corner shown in the first diagram, it’s best to delay the turn-in much longer than shown, and take a much later apex. That way, the rider can see much farther around the corner for cars, other obstacles or road hazards before committing to a line. And the Triumph rider in the photo appears to be weighting the wrong peg and leaning his upper body the wrong way, particularly as he’s in a bank with a lot of positive camber.

  • Ken Condon

    Good information here. Decreasing radius turns appear all the time. It’s having the tools at your disposal through experience, knowledge and skill that will get you through. Trailbraking is a technique that is ideally a planned technique used to stabilize the traction load, but can be used to slow mid-corner if you muck it up. Here is some information on trailbraking: http://www.ridinginthezone.com/10-things-you-need-to-know-about-trailbraking/

  • harleygwr

    Dont forget to be prepared for a stopped vehicle as your rounding that turn.Had that happen many a time on my riding adventure. They put speed limits on sharp turn for a reason .Ride safe project ahead by at least 6 seconds ,dont freak your bike can lean a lot more than you think..Speed kills your not eivel kinieval.

  • http://www.cix.co.uk/~kwh kwh

    I’m really not happy with the advice in this article…

    Firstly the line in the picture, as georgeR says, is inappropriate for the street. If you want to take a racetrack style apex at all, do it when you can see out of the exit of the corner already. But better still, don’t bother; the wider line through the corner maximises your opportunities to see & be seen, and the further you can see, the faster you can safely ride and still be able to stop for a hazard that is currently hidden round the corner. Being able to see a long way ahead also gives you the best chance of spotting a decreasing radius before the corner is already vanishing off to your right and you are running wide…

    Secondly, trail braking into corners is not a smart street riding strategy. Slow in, fast out, do your braking early and in a straight line. Then you are a master of your own destiny, and a slick spot isn’t going to plant you hard on your face in the wrong lane halfway round a blind corner; ‘Trail braking to the apex’ is great on a track in a race where it’s 5 hundredths of a second faster on the limit than the other way, but it’s also much more likely to tuck your front end mid corner, and that’s absolutely no fun at all on the street, Likely to get you killed, in fact.

    I think this entire article needs a good hard beating with the clue stick!!

    • Joshua Barker

      Though valid point that riders shouldn’t use ‘race’ lines while on the street, The line depicted is still more than safe enough for a street. And trail braking when used for advanced riders only adds another level of control to the corner, and lets the bike lean in better with the suspension still stable. Not trail braking correctly, or simply not keeping the bike’s suspension level throughout the corner doesn’t mean the technique itself is wrong, just the execution, and the rider should practice on his/her control and the lines before attempting something advanced.

      In fact, I just ran a mentorship course yesterday and watched as each rider that tried to hug the inside line on our cone track decreasing radius S came out way wide and had to readjust themselves before setting up for the next corner. This was training geared to help these riders better negotiate the streets of Japan, and no one was out of 1st gear the whole track to increase the importance of throttle control and suspension stability at low speeds that we often encounter in the mountains here. Blind decreasing radius corners are the norm, and I promise you the advice in the article is sound.

      • http://www.cix.co.uk/~kwh kwh

        I’d suggest the opposite – you want to be on a positive throttle if you can help it, because loading the front while turning has a much less benign failure mode than loading the rear. I hope it’s common ground that falling off on the street should be avoided at all costs, because of road furniture & traffic etc, all of which can turn what would be an embarrassing but mostly innocuous tip off & slide on a race track into a fatality, and losing the front on the brakes while cornering is pretty much a guaranteed crash, or certainly a likely one. By contrast you won’t lose the front on a positive throttle [h/t Keith Code], and provided you aren’t giving it big licks, losing the rear will probably just have it step out a couple of inches & then grip again. Of course you probably won’t have either happen, but of the two I’d rather risk a rear slide than a front tuck!

        As for cornering lines, funnily enough I made a video about that… sorry about the excessive length!

        https://www.youtube.com/watch?v=qaBtGqHiEyM

      • http://www.cix.co.uk/~kwh kwh

        Oh, I should point out that the line I was criticising was the ‘ ideal line through a constant radius curve’ (their caption) as shown in the thumbnail above. It’s not ideal at all! And the green line they show would also involve a too early second turn in if the tighter part of the corner is blind… and of course if you find half way round that a corner is decreasing in radius then you need to shed speed mid corner to continue to be able to stop in the distance you can see to be clear, but the advice given is to trail brake on initial corner entry, where the ‘decreasing radius’ part isn’t even relevant yet, hence my comments…

      • Joshua Barker

        Just because you’re braking, doesn’t mean you’re loading just one wheel. Trail braking involves both brakes and keeping the suspension and balance of the bike sorted. The positive throttle is something we teach novice riders because it’s an easy skill. Trail braking is more advanced and requires practice. And the ‘blind’ part isn’t blind by the time you turn in and doesn’t so much matter as you should never be taking a corner at the kind of speed you can’t sit up from while on a real street. This is a skill we’re taught in our Military Sport Bike class. We actually practice being at a lean in a constant corner then suddenly having to avoid an obstacle, and I promise I can reliably do this from a knee dragging lean in 1st gear, and so could everyone else in the class. So, simply put, you don’t have to run on techniques they teach during the BRC when you’ve advanced several years beyond the extremely basic skills.