Post by anon on Feb 1, 2007 20:07:34 GMT
From: rowlf Sent: 10/09/2002
This article is a mixture of years of riding as a despatch rider and as a full time motorcyclist London plus more scientific data which follows in the next two messages. There is always some debate but remember that the Diversion is a touring/commuter bike and as such is set up with quite soft front suspension and will often carry pillions or at least a topbox.
Theories confined to fulltime skilled solo riders on a race track do NOT apply. They use differnt lightweight bikes, carefully set-up with suspension set up specifically for them (often for each individual race track) they use very grippy tyres and have the knowledge that if they fall off (as they often do) they have run-off areas, smooth tarmac and top quality protective clothing. Not to mention medical care immediately on hand.
--------------------------------------------------------------------------------
It is quite good braking practice to apply the rear brake fractionally first, this will 'lengthen' the track as the rear of the bike 'dips' and reduce the centre of gravity a bit. However, applying both front and rear together is just as good and probably easier to acheive in practice.
As soon as the rear brake is applied the weight of the bike will lower, the geometry of the rear has been designed that way (if not for that reason). Obviously, what then happens is, as the bike further deccelerates the weight transfer will move foreward. as the bike 'rotates' (the torque) around it's centre of gravity (or mass) this loads or weights the front tyre more. As this happens and the weight transfer comes off the rear wheel this can cause the rear wheel to lose traction, unless the pressure on the rear brake is lessened.
As the weight of the bike transfers forward you should progressively apply the front brake harder and release the pressure on the rear pedal. You will use almost exclusively the front brake until you are down to about 20mph or so when you can start to progressively apply the rear brake harder whilst progressively releasing the front brake. By the time you have stopped only the rear should be applied !
Remember that is is a very good idea to lean forward too. By lowering your centre of gravity the weight suddenly applied to the front wheel will be less and improve ultimate stopping power. This might seem the opposite as you are moving foreward but it is not the case. It takes some of your weight off the front handlebars (which are directly connect to the front wheel) and moves it to the centre of the bike where you are sitting, thus further back. The centre of gravity of a bike with rider, pillion and topbox is also very high and under braking applies a lot of rotating force to try and twist (or rotate) the bike forewards around it's centre. The rear tyre will lose traction much more easily the more weight you have on the top half of the bike i.e. with a pillion.
If you are carrying a pillion try and train them to keep upright and lean back when braking. What you do not want is for them to transfer their weight forward. This will further load the front and lead to the back wheel quickly losing grip. Even worse, the extra pressure they may apply to your arms will further increase load on the front wheel. For this reason, try and pack heavier things in side panniers and light things on the topbox.
--------------------------------------------------------------------------------
In the wet * (see note below)
Gently does it. Snatching in any way by grabbing the brakes or suddenly taking your hand off the throttle (much less likely) can cause a breakaway of traction. Use considerably less pressure on the rear brake or none (depending on you skill level). The last thing you really want is to lock the rear in the wet. Remember that the rear wheel will already have some engine 'braking' so it is easy to overdo it. I know some say it better to use more rear pressure in the wet but this overlooks the 'real world' physcoligical factor. It is also rather dated.
Most people these days ride a bike and drive a car, that is why I would recommend that you don't touch the rear brake at all in the wet or do so very lightly unless you frequently practice braking first. Car drivers are so used to applying much more pressure with the right foot that it is hard to learn to be gentle enough to control a bikes rear wheel traction when the weight shifts forward.
It is almost impossible for any rider (including race track riders) to concentrate on controlling both wheels at the braking 'limit' at once so better to concentrate on just the front as that is the one with most (or all) stopping effect That is why many bikes pull 'stoppies' the rider is simply putting all his concentration on the front wheel as it has the most effect. A rear wheel skid is actually not that serious, if controlled, but the bike starts to lose gyroscopic force (rotation of the wheel) and the bike will fishtail. The average rider does not have the experience to cope and will tend to panic.
That is what causes many accidents. Using both brakes will improve stopping power but it is something you need to practice, especially in the wet and if you use a car too it is hard not to overreact in 'panic mode'. The rear wheel skidding unsettles the bike and the rider badly so you lose concentration on what really matters, stopping the bike my maximum traction on the front. If the rear wheel is still spinning the front wheel sliding will not throw you off as long as you don't let the wheel 'tuck under' the bike. Again due to concentration and again hard to do if the back of the bike is fishtailing violently. I always adjust the rear brake so that it is possible to have my foor straight on the footpeg (which is much more comfortable) it also reduces the amount of pressure I can physically apply to the rear brake.
Modern tyres grip very well, even in the wet. Obviously if you hit gravel or oil there is not so much you can do. Although even then a skid is not quite so bad as you think, as long as you control it and have enough space to stop in. Being so afraid of a front wheel skid seems to be a big panic factor for riders. If the rear wheel is still spinning the front wheel sliding will not immediately throw you off.
--------------------------------------------------------------------------------
If you regularly carry a pillion it is a good idea to practice with them on too and explain what is happening and what they should do, i.e. lean back ! Practice in the wet and in the dry !
--------------------------------------------------------------------------------
* Please note much of this is personal experience. If you can practice enough and devolop your own technique fine. The ideal is to be able to 'taper-brake' and have both brakes on 'the limit' of traction.
+++++++++++++++++++++++++++++++++++++++
Following this posting are two articles, a technical article about weight distribution and grip and an article from an advanced trainer.