The science of going round corners
Rule the bends
IN THE LIST of things the Romans have done for us, corners isn’t one of them. We still use their fundamentals of road construction today but they preferred straight lines – and a ride on the Fosse Way shows how quickly it stops being fun. Humans evolved to be good at going round corners. Most animals, including us, have a cornering lean-angle limit of 20-25° from vertical — more, and we’d run out of grip and fall over (a few exceed this, but not by much). But, unlike almost all creatures, hundreds of thousands of years walking upright on soft, sensitive feet (not hooves or claws) has given us an instinctive perception of friction – we’re good at detecting traction and countering slip.
We’re also pre-adapted to riding bikes. Anatomically, humans have a high centre of gravity (over half our height) relative to a short wheelbase (our footprint) and naturally make constant tiny adjustments required to maintain a precarious walking balance. Motorbikes also have a high COG, short wheelbase and need tiny adjustments to balance — which is why we have a seemingly innate ability to control the complex dynamics of what is, on paper, a ridiculous idea for a vehicle.
The fact is, most of us are born to ride a bike round corners, with a pre-existing, naturally acquired (ie not learned) predisposition to balance a motorcycle.
And we enjoy it because bikes take a natural human ability — balance and grip — and, with the help of rubber, tarmac and an engine, move it way beyond what nature would normally permit, expanding an already natural inclination (sorry) to new, supernatural limits.
And let’s face it; who doesn’t enjoy feeling superhuman?
1 Lean-angle comfort zones
We all have a lean-angle comfort zone (distinct from the physical limit of grip); the first time we ever ride a bike, the zone is around 20° from vertical. Leaning further requires overcoming fear of losing grip; usually as a series of small increments to build confidence by experience. It’s a learning process; leaning a bike beyond our base comfort zone is an acquired skill. No-one is ‘born’ with it.
With each micro-success, the ‘boundary’ of our lean-angle comfort zone expands. On modern tyres and suspension, it’s rare we get anywhere close to the physical limit of lean-angle grip unless surface conditions or technique intervene. So, with experience, we establish a new lean comfort zone and greater confidence in when and where we can achieve it.
But it’s flexible. A year spent racing expands our comfort zone, even on the road, because we’re acclimatised to greater lean angles. But it isn’t permanent; if we stop racing, after a year or so our lean comfort drifts back to a lower level. It works the other way too; if we scare ourselves, we lose confidence and our lean comfort is lowered. So without practice, our lean-angle comfort zone drops.
Which is fine: only lean a bike as far as we feel comfortable. The problem comes when we get into a corner too fast, or something about the road surface suddenly convinces us we can’t get round it without exceeding our lean comfort zone. Life gets uncomfortable very quickly.
This is a critical moment because we instinctively avoid the loss of grip we think will happen, instead chopping the throttle, changing line and maybe even braking in preference to leaning beyond our comfort zone. The fact is we could lean further without crashing and the accident we have by not leaning — sitting up and crossing the road or riding off the road into a wall —
‘We enjoy cornering as it uses a natural human ability’
‘We never have to consciously think about it again’
may actually be worse than if we did.
This is why successful road riders have a well-developed lean-angle comfort zone, then ride well within a safety margin so even a mistake or mishap never takes us out of it (remember, we’re talking about our personal perception of where it is).
Try this It’s important to realise the goal is to expand our personal lean-angle comfort zone by fractional increments. Big increases in lean are leaps of faith; we want tiny steps. The best way to advance a lean comfort zone is to go on a trackday; you can spend all day in relative safety on a good surface with the same corners. It doesn’t mean transferring that lean angle to the road; just the knowledge it’s possible.
2 Countersteering
Countersteering isn’t a technique, and won’t change the way we ride because we already do it perfectly. It’s in the same area of motorbike skills as putting feet down at standstill – if we hadn’t figured it out, we’d fall over.
In fact, we do, on a pushbike – those first, wobbly moments as a child when we can’t figure out why, at walking pace, if we want to go left we turn the bars left but try it a bit faster and we crash. Then, within a few scary moments of flapping the front wheel left and right, it turns out if we actually turn the bars to the right, we steer to the left. And we never have to consciously think about it again.
The physics of countersteering are fairly simple; by minutely steering in the opposite direction we want to go, we displace the bike’s centre of gravity — literally, we make it topple over. It’s the same principle as making a broom balanced in the palm of our hand fall to the left by moving our hand to the right. We then ‘catch’ the toppling broom/bike by moving our hand/steering to the left to balance the topple. And to straighten it, we counter slightly in the opposite direction.
Understanding countersteering to improve cornering is moot; it might help top-level racers find a fraction of a second but it won’t help daily road riders. It’s not even essential to be holding the bars to countersteer; sitting upright with no hands, if we grip the tank between our knees we can mimic the effect by ‘shaking’ the bike, nudging the steering to the right so the bike leans to the left. We don’t even need a front wheel — snow bikes with a single front ski also use countersteering to initiate a turn. Try this Or rather, don’t try this! To get a feel for how intuitive countersteering is — and if you’re feeling brave — find an empty, straight, wide piece of road and try crossing your arms, putting your right hand on the left bar and vice versa. At first it’s difficult to control the bike — you keep steering the wrong way, and it takes some effort to mentally ‘uncross’ your hands.
3 The right line
The right cornering line depends who we ask. Some say holding a fixed line in the centre of the lane for the entire corner; some say a classic sweeping line with a wide entry, tight apex, and wide exit; and most say something in between.
Instead of trying to prescribe a right or wrong way, it’s better to think about what we’re trying to achieve: optimum line of sight and optimum grip for a given speed.
On modern tyres at sane speeds, grip shouldn’t be an issue for a given surface (depending on our lean comfort zone). The best line of sight is staying out wide to give the best view through a corner — but riding upright following the kerb isn’t much fun and is dangerous if we add any kind of pace — we risk riding off the road.
The best line for grip and sight is mostly the same, but there are compromises (for example, entering a right-hander we want to be riding close to the kerb, but on many country roads it’s too bumpy or pot-holed; we’re better off keeping a foot away from the ideal line). Safety can also be a compromise; in a right-hander, the ideal line in terms of exit space and grip would be to apex close to the crown of the road, but some say that’s too close to oncoming traffic and argue for a more centre-lane apex — where there’s less room for error
‘Smoothness is more important than speed’
on the exit and the potential punishment for peeling in too early is greater.
Using the opposite side of the road on entry to a bend is contentious; some experts advocate it, some don’t. The idea is it gives us even greater vision around the corner and it does, used appropriately. But we don’t want to be caught braking on the wrong side of the road (it’s hard to steer on the brakes if we have to move), or being so committed and carrying so much speed into the apex we need the same amount of room on the exit; that’s bad. But letting the bike drift onto the wrong side of the road, if it’s clear, on the exit is generally considered acceptable too.
Try this If our cornering feels rushed, hasty, forced or uncomfortable, we need to slow our speed and our actions, relax, and pay more attention to being in the right place on the road. Smoothness is more important than speed, so think about making progress through a corner flowing and graceful rather than spiky and aggressive. It’s about, literally, rounding your edges into corners.
The 80% Rule
Finally, try to ride to an 80% rule: position ourselves with 20% margin from kerb to apex; ride with 20% pace left in our pockets; lean with 20% margin into our comfort zones, have 20% left on the throttle and brake with 20% more force left in case we need it.
It’s not as dull as it sounds — not everyone’s 80% will be the same, depending on confidence, experience and practice routine. But the ultimate aim is to turn that 80% into an automated routine — which is when the 20% left can be spent admiring the scenery.