How hard can I brake?
Riding skills: How hard can I brake?(And what stops me braking harder?)
14 June 2011 10:59
Trying to answer this question on a real road, with a real bike, is bloody good fun. It’s also something almost anyone can get good at with enough practice – and it’s not quite as lethally dangerous as it sounds. More of which later.
So how hard, then? Roughly speaking, a good rider on a good bike on a dry road can get from 100mph down to 40 in three seconds, using maybe 85 metres of road. And despite what you might think, that’s been the case for at least 15 years. I know, because I’ve got a set of datalogged figures from 1992, recorded by the UK technical journalist John Robinson on a ZZ-R600 Kawasaki, and they more or less match the last time I datalogged a bike over this speed range – a GSX-R1000 K7.
Hang on – haven’t tyres become super sticky in recent years, and brakes got more powerful? Yes they have, but they aren’t the main factor affecting how quickly today’s bikes can stop. That honour belongs to the centre of gravity.
If you think about jamming on the front brake on a chopper, it’ll tend to lock up the front wheel and push it along the road. That’s because the centre of gravity is too low and far back. When the bike’s weight gets thrown forward temporarily under braking, it hardly presses down on the front tyre at all.
On the other hand, if you raise the centre of gravity too high and forward – for example by braking whilst sat on a sportsbike’s tank, like a stunt rider – the weight transfer becomes too efficient, and the bike stands on its nose. Chassis engineers figured these two extremes out a long while ago, and since then they’ve been nudging the c of g around, trying to get the best balance between braking, accelerating and cornering for each particular model. A typical height for modern c of g would be about 550mm above the asphalt, with the rider moving it up another 200-250mm when he or she gets on.
So braking power isn’t that relevant. What counts is ease of control – and that’s what the new technology should be giving you. For a given level of braking, a 2010 non-ABS Fireblade will reassure a panic-stricken rider more than, say, a 2000 model. But only a bit – and the differences will come from the tiniest things: radial mountings (which reduce flex, and thus make designed-in flex easier to control); an improved tyre construction; lighter weight; better quality forks; and so on.
Even with all that, a mediocre rider could easily take take five or six seconds to shed the 100mph above 30mph, and a beginner ten seconds or more. You might have the best brakes on the planet, but you still need the skill to use them. And that’s a lot trickier than standing on the pedal in a car: somehow you have to create the maximum weight shift forward without doing an endo, whilst simultaneously holding the tyre at just above locking – all the way from whatever speed you were doing when you grabbed the lever.
Fortunately, almost anyone can get really good at this. All it takes is practice. Even if you’re scared to use the front brake hard, just sit up, keep your elbows bent, grip the tank with your knees and squeeze the lever – gently at first, then harder and harder as more weight piles onto the front tyre. As the bike slows, try and expand your awareness of what’s going on. How near is the tyre to where you reckon the limit is? (If it chirps when you hit a bump, the answer is: pretty near! If the bike fishtails, try more compression damping in the forks). Amazingly, nearly everyone who accidentally locks the wheel in a straight line doesn’t crash. Instead, your hand lets go of the lever in a reflex action. I’ve seen 100 guys try to lock the front this way on a course at the Nürburgring in Germany, and they all survived.
There’s no harm in trying one of these crash stops every time you ride (but check behind you first, obviously...).That way it becomes muscle memory, rather than a conscious effort. In the end you’ll be able to decelerate most bikes at 0.8-0.9g – which is considerably better than the rate at which a Hayabusa can accelerate.
If you go to top level racing, it starts to get truly amazing. A 2006 data trace of Nicky Hayden going from 174mph to 121mph shows an average deceleration of 1.35g. How does he do it? Skill, electronics and the finest chassis and tyres the human brain can devise – probably in that order. There’s also a big air-brake effect at that speed. Just sitting up on a bike at 130mph pulls about 0.5g.
Back on the street, we are likely to be the last generation of riders who have to learn to brake in the old-fashioned way. Anti-lock for all bikes is only a matter of time. It’s just a case of when we, the macho bike-buying public, can bear to accept it. And when it happens, even the biggest numpty should be able to get right on the limit, rain or shine, baking heat or winter chill. Which ain’t a bad thing.
Rupert Paul's new book, "Pass the Bike Test (and be a great rider too)" is out in mid July, available from www.uit.co.uk