Advanced Braking Techniques

Practise this and try to stay fashionable!

Many motorcycle instructors, from CBT up to Police Advanced, still quote the following old chestnut :- "you brake 75% front and 25% rear on a dry road; and 50%:50% in the wet".

This advice is also enshrined in "Motorcycle Roadcraft" and the " IAM Group Handbook". So it's a pity that, nowadays it’s totally wrong. Progress changes things.

The 75 %:25 % rule made its first appearance a LONG time ago. The early diagrams explaining it, show drum braked Triumph Speed Twins; so it's not unfair to assume that the 75%:25% rule has been around at least 25 or 30 years!

The old Speed Twins (and their ilk) had little in common with today's motorcycles. They had one twin leading shoe front brake of about 7 inch diameter (I can't find anyone who's old enough to be certain), operated by a Bowden cable from a hand -brake lever. The rear brake was single leading shoe, about 6 inch diameter BUT operated by a sturdy 10 inch long foot -brake lever; pushed by a leg honed to muscular perfection by kick-starting the damn bike in the first place!

And the tyres? They were no wider than the widest mountain bike tyres of the 1990's and poorly designed even compared to the car tyres of the day (many cars already had tubeless tyres but all Motorcycle tyres were high aspect ratio, tubed crossply's). The usual tread pattern was ribbed front and block rear. The all-important contact patch was long and thin, not least because the wheels were 20 inches or more in diameter.

But above everything else, it's the design of motorcycle frames that has changed. The old Speed Twin and its like were TALL. The vertical engine, surmounted by a spine tube frame (with enough gap to allow daily tappet adjustment) meant a high riding position. The centre of gravity of a bike (with rider aboard), in the 60's was probably a foot or more higher than it is on most sports bikes of today.

And there were two sorts of front forks: - "Rock hard" (race bikes and those carrying heavy Rickman fairings) and "Spongy soft"; prone to dive to the fork bottoms under the lightest braking. The net result of either type was that, under braking the front went almost rigid; like a pushbike's forks.

If you've got locked forks, a narrow (low grip) front tyre and a centre of gravity that small planes have to detour around; it’s not surprising that you're cautious of using your front brake. If that brake is a grabby drum brake (they "self-servo-ed", so the braking effort was not proportional to how hard your hand squeezed the lever) you did as much as you could with the "controllable" rear brake. Anyway, a locked rear was controllable, even on a Speed Twin.

"New Tricks Motorcycle Design" has moved on since the old dogs of the 1960's. In fact, it had already moved on far enough to make the 75%:25% rule questionable by the 1980's

The BIG sign that 75%:25% is wrong, is that most bikes these days (since the RD350 at least) can do "stoppies'' and not crash immediately after. In a stoppie you push the front brake to its limits, you brake so hard that the rear leaves the ground. This is neither big nor clever; but it does prove to the most hide-bound among us that the bike, at that instant, was stopping using 100% Front brake and 0% Rear !

I'd now like you to think about proddy racing because in Production Racing (apart from Owen's missing alternator, sorry Mr. Scrutineer) the bikes used should be the same as those you meet on the road. Now, I understand that, in a race, most competitors are trying to ride as fast as they can. They’re not there to put on a show of stunt riding to impress the crowd.

Yet, horror of horrors; they do NOT brake 75%:25%! Stand at the braking point at the end of the straight (do not stand on the bend at the end of the straight: it's where Reg Ford usually smashes into the crowd). You will see many of the riders lift their rear tyre clear of the deck under maximum braking. They’re doing stoppies, yes they’re braking 100% Front and 0% Rear!

And they’re not doing this deliberately to show off (apart from Jamie Whitham at the end of a race!). They’re doing it because nowadays, it's the natural, instinctive way to brake as hard as the bike can possibly brake.

So What's New Pussycat?

Modern motorcycles (as above, this includes most road bikes designed since the RD350) are radically different from that old Speed Twin. The few that aren't, retros like the Zephyr and trail bikes, probably still have to brake 75%:25%.

(Apparently, one of the first things Geraint Jones teaches at his Moto-X school is how to brake. You do this by learning to stop a Motocrosser from 50mph on mud , using only the front brake. So, even on the dirt, there's scope for more front brake use - if you have the cojones!)

Modern bikes are lower - by about a foot (compare even a "modern" GPZ500 with an old 750 Triumph - the GPZ is more powerful, too). Modern bikes tend to be shorter, by around 5 inches. And have smaller wheels, these days fronts are 16 inch to 18 inches they used to be 18 inch to 21 inches. And wheel widths (hence the contact patches) are at least twice as wide as they used to be. The modern tyres are stickier - even in the wet and they’re radials (or bias belted), so they deform to grip the road far better. Added to that, the low sidewalls help the bike's centre of gravity stay low.

And front suspension, even if you don't have upside down fork legs, is ten times better at absorbing ripples that might upset a tyre under braking.

Brakes

You'll notice I haven't mentioned the brakes. I think the grabbiness of 1960's brakes and the need to stand on that big footbrake lever, is one of the root causes of the 75%:25% rule. That was how people found they had to brake, so they assumed it was the best way to brake.

Since then, Triumph have died, been reborn; died again and been reborn as a far better bike. Rules for braking written to suit the 1990s SpeedTriple would differ a lot from those written for the Speed Twin of the '60s.

But the masters of motorcycle design are the Japanese. Now, believe it or not, they tend to design things to do their job. Very occasionally they screw up, but most things they get right. Mudguards keep the mud off. Footpegs don't bend under your weight. You can reach the levers and the switches at the same time. (The old Triumphs, sad to relate, didn't manage any of these things.)

So we'd expect modern Japanese bikes to have brakes suited to their function - stopping the bike as quickly as possible. So, how do they set up their brakes?

Front Two 320mm disks, each gripped by 4 or 6-piston callipers.

Rear One 220mm disk, gripped by a 1 or 2-piston calliper.

At a conservative estimate, the front brakes are 5 times as powerful as the rear (remember the diameter of the disk has a big effect). And I'd bet that the foot lever is now as short as the handbrake lever.

So why have the Japanese fitted brakes so out of line with the 75%:25% rule? Are they foolish? Is it some sort of "look at the size of my brakes, darling" fashion accessory? Or is the 75%:25% rule just plain wrong these days?

Answer: the 75%:25% rule really is "just plain wrong" these days (for most modern bikes on most dry roads).

What's the truth? The truth is, there is NO truth. Any fixed apportionment of braking effort, front to rear is wrong. In cars, they teach taper braking - you bring the pressure up gently, to avoid a skid until the weight transfers forwards; at which point you can brake hard; and you let it off gently as you roll to a halt, to avoid a jerk when you stop.

Bikers, too, need to learn taper braking. But as we have separate front and rear brakes, we also need to learn to taper the force from rear to front and back to rear again as we slow.

(Owners of Moto Guzzi and Honda linked brake systems can leave now - but remember, as you depart, that racing Guzzis always removed the linked brakes - they aren't quite as good as separate systems, right at the limit.)

An ideal stop goes something like this:

You apply both brakes gradually and with almost equal force for the first phase of your braking.

The weight will transfer forwards as the front suspension compresses, and your arms bend.

There's now more weight on the front (up to 100% if you're braking at 1g - and modern road bikes can brake at up to 1.2g).

You now let off most - or all - of the rear brake and increase pressure on the front, which now has most or all of the grip. This middle phase of braking can be 100%:0% - if it is less than 85% front, you probably aren't braking anywhere near your bike's limits.

The bike slows and the forces you are exerting through the brakes and tyres diminish (the energy in the bike is proportional to the square of your speed).

The front begins to rise back up on its suspension.

(If it's an emergency, you now breathe a sigh of relief and a small prayer of thanks).

You taper off on the front brake - to prevent a slow speed lock up - and increase the rear brake pressure once more.

Even stopping from 100 mph, the last 5mph are slow riding, and you should only use the rear brake for slow riding. So you do the final phase of stopping 0% front and 100% rear.

If you MUST quote a fixed apportionment of effort - I'd say it is 85%:15% - which is in line with the way Japanese bike designers set up the brakes.

But the truth is, situations will vary which is why we should forget 75%:25%. Motorcyclists need to learn to taper brake; to balance front and rear brakes in a sensitive, reactive fashion - not to follow an outdated mathematical tenet.

And, to slip in two quick plugs - you can learn how at the Nurburgring Perfektion Training courses or on London Advanced Motorcyclist's Machine Control Days.
Back to top