Wheel locking

[Fire_Eyes]

I hear it everywhere but what is it? Why does it happen? What do you do to avoid falling off incase it happens?
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Kawasaki ZZR 400 | K5 GSX-R 600

[mchaggis]

Wheel locks? I presume you mean wheel locking, sliding etc. Generally, the wheel locks when you apply too much braking for the road conditions. When the road is slippery, your tyres cannot generate as much braking force; if you try and make them brake too hard they'll stop spinning and start sliding.

Generally, when your tyre is sliding, it can only generate forces along the line that is sliding in. (E.g. lock your front wheel going straight forwards, it can only slow you down, no matter how much you turn the bars, there will be f-all steering effect.)

The main thing about locking wheels is that it most often occurs under hard braking (emergency braking) and causes you to slide to a stop rather than roll to a stop. The dynamic coefficient of friction (sliding) is lower than the static coefficient of friction (rolling). If you slide, you will take longer to stop.

With locked wheels under braking, you lose directional stability as the front tyre sliding will mean that you can't input any steering, and the rear tyre sliding tends to make the rear want to swap places with the front, so your rear ends up sideways/ forwards, and you end up on the floor.

General sliding when leaning is caused by trying to make the tyre generate more lateral (sideways) force than is possible to be generated given the road conditions. The tyre starts slipping more than the threshold and it loses grip and ends up sliding towards the outside of the turn. Generally this is a lowside condition, where you fall towards the inside of the turn, but slide towards the outside with the bike.

The tyre can only generate a particular amount of force at once, as it does this by the rubber deflecting, which is limited. Putting the power on whilst leaning and trying to force the rubber to deflect enough to generate both the required longitudinal (in line with the bike) force as well as the required lateral force will also cause the rear to slide out as the tyre cannot generate enough of either.

Anyone else can explain the highside condition if they wish, or if you really want to know more about tyre force generation with slip (or ABS), you can ask and I shall endeavour to explain.

Sorry it's a bit mix and match, but it's a rather broad topic.



As far as avoiding it, don't touch the front brake when cornering, and try and avoid using the rear brake during the corner. If possible, have all your braking done before the corner, so that your tyres only have to do one thing at once. Take corners more slowly so that the amount of lateral force they need to generate is smaller. Hang more off the bike so that you can get a greater force towards the centre of the turn (by shifting the centre of gravity) without needing the bike to be as far tilted over.

If you can feel the front or rear trying to slide sideways, then the best thing to do is to get the bike more vertical, slowing down and possibly get ready to stave off the lowside by putting a boot down if at low speeds.

Someone will need to tell me whether throttling back is really a good idea or not, I saved a front slide situation last week by getting back upright, throttling right off and (over) correcting with steering, but it almost put me into a sort of tankslapper where the front was see-sawing from side to side for a second or two.

Was throttling back the wrong thing to do? It was instinctive behaviour really.
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I must not be a troll...
Mmmm, Guinness
Discovering the delights of Hammerite and a 3/4" brush.

[stinkwheel]

I presume you are taslking about when the wheel suddenly stops turning on a moving motorcycle as opposed to a device to prevent your vehicle being stolen? The latter will only make you fall off if you forget to remove it before riding off

There are three main reasons that the wheel would 'lock up' on your bike.

1) Excessive braking
Fairly self explanatory, pull brakes on too hard, lock up wheel. If you lock the wheel under braking, back off on the brakes a bit.

2) Shifting down too many gears at once.
If you change down too many gears at once (so are in far too low a gear for the speed you are doing) and let the clutch out, the resistance of the engine can cause the back wheel to slide. If this happens, pull the clutch in again and either change up or apply the brakes to slow you down to a speed that matches the gear. Plan things better next time.

3) Catastrophic mechanical failure.
One thing that you should be aware of on a 2-stroke is that they can be prone to engine seizure, especially if oil is neglected, they are thrashed to the redline everywhere or have been 'tuned'. This is where the piston that goes up and down in the engine gets too hot, expands and sticks in the cylinder bringing the whole engine to a complete halt. If this happens, the back wheel will also stop turning. Should this happen, pull in the clutch to disengage the engine from the wheel and it should start turning again. In most cases you would experience a sudden drop in power, funny noises, burning metal smell and/or a sudden increase in engine temperature just before an engine seizure. That is the time to pull the clutch in and stop the engine before damage is done.

Other causes are a lot more unusual but things like getting an object stuck in the wheel, collapsing wheelbearings, a broken chain and a gearbox seizure are all possible. Pull in the clutch, it doesn't work for all of them but is worth a try. If that doesn't work, hang on as best you can and look for somewhere soft to land ...jumping off the bike is always an option if it is going really pear-shaped (don't panic, that kind of thing only happens once in a blue-moon)
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Fire_Eyes]

Thanks a million mchaggis .but can you tell me what to do if the wheel locks while im turning? Or is there no way to survive if it happens while leaning?
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Kawasaki ZZR 400 | K5 GSX-R 600

[AcIdBuRnZ]

If it locks up whilst leaning over, you're pretty much guaranteed to come off.

Just hope you don't hit anything hard
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Past: Honda NSR125R >> Kawasaki ER-5a2 >> Kawasaki ZZR-600e1 >> Suzuki GSXR-750Y >> Honda VTR 1000 Firestorm
"Chickity China the Chinese Chicken..."

[Fire_Eyes]

[Kickstart]

Hi

If you lock the wheel then get off the brakes immediatly. That is pretty much your only hope of saving it.

Trouble is that a bike stays upright largly because of the gyroscopic effect of the turning wheels. Have the wheels stop turning and the bike tends to loose all the will to stay upright.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[stinkwheel]

[hustler]