terribad balance

Northwind

Balance on the bike is a learned response, more time on the bike will probably sort it, lots of good advice in here- especially slow speed practice, the slower you go the more input you have to make to balance. Trackstands, riding along white lines/kerb edges.

How's your balance normally? Stand on one leg OK?

andrewjoseph

I'm not sure standing on one leg is a good indicator of bike balance. Due to injury, I can't stand on one leg, and sometimes have a problem on two. (I use a walking stick)

I don't have too much trouble on the bike though.

dizzyduck

i'd say my balance normally is about average although hard to be sure. i can stand on one leg fine, but my balance on a bike seems to be poor, hence the post. will try to work on these skills suggested. what do you mean by practicing skidding the back brake? how do i do this?

andrewjoseph

dizzyduck wrote:

....

what do you mean by practicing skidding the back brake? how do i do this?

I thought all boys knew how to skid!

At a good walking speed, riding in a straight line, jam on the back brake to stop the wheel turning, it will skid and the back of bike may try to turn one way or another. Let go the brakes and continue on.

Repeat this at various speed until you get a feel for the bite point of the brakes, and the release point of the tyre (when it loses grip). Do this with your weight one side and then the other so you learn to control the skid.

Build up speed and repeat until confident.

Be aware: this can ruin your tyres in a very short time and can ruin a trail, so I recommend practising where it does no harm.

Also be aware that skidding a lot on trails is bad form and frowned upon and actively discouraged. It allows rain to erode the trail must faster than would otherwise be the case. If you find you are skidding a lot during your normal riding, then either you are going too fast or your tyres are crap.... or both.

diy

When I used to teach motorbiking with the plod we were required to perform a controlled front wheel skid.

Its doable by using the rear brake to keep you from low siding. while it teaches you about balance and control, it also teaches you just how much you need to brake to cause a front wheel skid. The same applies to cycles.

I think the advice about slow speed control here is spot on, for me it was something I learned from riding motorbikes, so trackstands are pretty easy, given that a mtb is about 1/10th of the weight.

Atz

As mentioned several times above DO NOT PRACTICE THIS ON TRAILS. Nobody will thank you for it.

Anonymous

If you're going in s straight line, andrewjoseph skidding the rear brake will not cause the rear to step out.

andrewjoseph

yeehaamcgee wrote:

If you're going in s straight line, andrewjoseph skidding the rear brake will not cause the rear to step out.

I beg to differ, hitting a stone, shifting weight, slightly slipperier patch: a multitude of things, can cause the rear to step out, even in a straight line. This is mountain biking we are talking about here, you know, mud and stones, gravel, sand, roots, cambers, ruts and numerous other obstacles, not pan flat sandpaper. it is extremely likely that the rear end will step out even on a flat fireroad.

However,I stated that the rear end MAY try to step out. Also, the skill I was suggesting practice in, is deliberately trying to make the rear step out, and then recover it.

Anonymous

Locking the rear will cause drag on the rear tyre as it skids. The point that drag is acting upon is behind the centre of gravity, and behind the front wheel.
Basically, the skidding wheel will act as a rudder, and will tend to straighten the bike out. Same happens in a car.
To perform a handbrake turn, you need to throw the momentum of the car off course, then lock the rear wheels to lose traction. Pulling the handbrake in a straight line won't do anything.

And honestly, why would it? In order to step to the side, the skidding rear would have to be travelling faster than the front. But the front is not decelerating, the back IS.

andrewjoseph

yeehaamcgee wrote:

Locking the rear will cause drag on the rear tyre as it skids. The point that drag is acting upon is behind the centre of gravity, and behind the front wheel.
Basically, the skidding wheel will act as a rudder, and will tend to straighten the bike out. Same happens in a car.
To perform a handbrake turn, you need to throw the momentum of the car off course, then lock the rear wheels to lose traction. Pulling the handbrake in a straight line won't do anything.

And honestly, why would it? In order to step to the side, the skidding rear would have to be travelling faster than the front. But the front is not decelerating, the back IS.

Perhaps in an ideal world, with no other loading, this would be true. In the real world, there IS other loading, many other forces that unbalance the vehicle to cause the back to step out.

A car can get into a skid quite easily with the back stepping out, the car may be travelling in a straight line but it may be on a camber with a strong wind and hit a stone. There are too many variables to state that the back end won't step out if going in a straight line, and that is for a car with four wheels and a low centre of gravity.

A bike has two narrow wheels, a high centre of gravity and a wobbly rider. Mountain bikers have the extra problem of uneven surfaces. It is even known for riders to deliberately lock the brakes to induce a skid and rear step out, so they go around corners faster.

You seem to be saying that you can't get a rear step out when the wheel is locked up because the braking effect will pull the bike back into line.

This clearly doesn't happen. A locked wheel is no longer braking, it is sliding and may even be sliding faster than the front. It is skidding and not braking.

diy

yeehaamcgee A bike is articulated, the rear will track independently to the front within reason. So its path will be determined by the terrain, camber, balance of the bike etc. Unless you are on smooth flat tarmac or going uphill, its almost impossible to ensure that the inputs on the front are the same as the rear.

A locked wheel will always slide in the direction momentum dictated and under the influences of gravity and friction.

If you think I'm wrong, jump on a motorbike take it up 70mph on the straight and then lock the rear wheel. you'll low side within a few seconds, unless you make corrective inputs.

andrewjoseph

diy wrote:

A bike is articulated, ...

I forgot about this bit, thank you.

Anonymous

diy wrote:

A locked wheel will always slide in the direction momentum dictated and under the influences of gravity and friction.

Precisely. And when going in a perfectly straight line, momentum is in a straight line.

andrewjoseph

Yeehaa, sometimes it strikes me that you either argue for the sake of it, or don't ride a bike.

diy

Momentum is always in a straight line. Even angular momentum is many straight line "momentums" acting on each other at different trajectories.

It doesn't matter if you are going round a bend, up a hill, down hill or sideways, momentum will be in a straight line.

Anonymous

diy wrote:

Momentum is always in a straight line. Even angular momentum is many straight line "momentums" acting on each other at different trajectories.

It doesn't matter if you are going round a bend, up a hill, down hill or sideways, momentum will be in a straight line.

Ok, then, wording. The momentum of the rear wheel will be perfectly in line with the direction of motion when going in a straight line.
As soon as you corner, the wheel will slide sideways. But when going in a straight line, it will continue in a straight line.
Hell, not even "it will", more like, " it actually DOES".

andrewjoseph

yeehaamcgee wrote:

...
Hell, not even "it will", more like, " it actually DOES".

Not in most peoples experience.

I don't know why I bother, I'll say no more on this matter.

diy

that is because normal people's experiences are subject to the forces of friction and gravity, which have been conveniently ignored.

Anonymous

diy wrote:

that is because normal people's experiences are subject to the forces of friction and gravity, which have been conveniently ignored.

No. They have not.
You are claiming that a rear tyre being dragged along the floor will tend to cause either a sideways motion, or want to accelerate past the front wheel - the two conditions that could cause it to step out of line.

It could go sideways if the bike is turning, or trying to turn (i.e., banked)

It could try and overtake the front if the front was decelerating effectively, and the rear completely lost all traction, whilst going down an incline with very very little effective friction. For example, front has a spiked ice tyre, rear does not, and the downward slope is covered in ice.
However, that does not constitute "skidding with the rear", as this would require the bike to be decelerated using the front brake - which WOULD lead to the rear of the bike to try to pas the decelerating front.

In a straight line, neither of these things happen. Go and try it. You can skid the rear for ages, it won't just suddenly get distracted by the bushes and start heading left or right to sniff out the musk of wheel that recently passed by, or to take a leak.
As soon as you bank the bike, or initialise a turn, then YOU are influencing the rear.

diy

Ok lets take this scenario to its logical conclusion. Firstly I didn't say the rear could push to over take the front due to friction, that was another poster. I agree without braking from the front it is very unlikely that the locked rear could have sufficiently weak friction to pivot the front. But on a steep muddy down hill it could happen as the front digs in under transferred mass while the rear skips along the surface.

You keep saying "in a straight line", but your straight line not only has to be straight, it also has to be completely smooth, and without any camber (you are thinking in 2D and need think in 3D) Because its perfectly possible to ride along the side of a hill "in a straight line" when I'm sure you would agree that skidding the rear would slide the rear downwards (sideways), under the effects of gravity.

How many times do you go down a flinty or rooty trail and find that your front wheel clips a stone or root that your rear doesn't or that they strike it differently due to the impact of the front hitting it first? Or that your front takes a slightly different path to the rear due to the banking, dips and rises of the trail as you strive for balance grip, thrill? This is the point that andrewjoseph has been making that you seem reluctant to accept?

Due to the articulation and inherent properties of tracked vehicles, each wheel follows its own slightly independent path to maintain balance. You can then factor in differences in the trail which will apply different grip to each side of the tyre, the fact that bikes only have a brake on one side which will always cause some flex, that humans are not actually symmetrical in terms of mass. etc. In summary to get the results you are describing requires lab conditions.

Look at this clip (50 sec on) its a lardy yank bike probably 400+kg with a very low CoG crap brakes in a flat car park. Vastly superior conditions to anything you would find on a trail. Even this theoretically experienced rider cannot maintain a rear wheel skid without some tracking of the back.

http://www.youtube.com/watch?v=M2keWo5R6_Q

The poster has missunderstood the technique, you don't ride the skid out by locking your arms, you ride it out by pushing on bars and keeping your eyes on the horizon, which allows the rider to instinctively make minor corrections - as he clearly does. If you are correct then he wouldn't need to do this as the rear would "act as a rudder".

bails87

I think we should have a thread where people can discuss theoretical, 'perfect conditions' physics scenarios. That way threads like these would be left free for people to give advice to OPs based on what actually happens on bumpy, rocky, rooty, off camber trais.

cooldad

Yeehaa is quite correct with his assumption but forgets real world body shape.
My obvious hangs to the left, and being unbelievably huge, causes the rear to skid to the right to compensate.

His obvious obviously creates no such problems.

bails87

cooldad wrote:

Yeehaa is quite correct with his assumption but forgets real world body shape.
My obvious hangs to the left, and being unbelievably huge, causes the rear to skid to the right to compensate.

His obvious obviously creates no such problems.

Ah, but which way does it fall in a vacuum?

cooldad

bails87 wrote:

cooldad wrote:

Yeehaa is quite correct with his assumption but forgets real world body shape.
My obvious hangs to the left, and being unbelievably huge, causes the rear to skid to the right to compensate.

His obvious obviously creates no such problems.

Ah, but which way does it fall in a vacuum?

Easy way to find out and kill two birds...

Vacuum

diy

On similar lines I had a thought the other day - Should I twist my saddle slightly to the right, because I dress on the left?

Northwind

cooldad wrote:

Ah, but which way does it fall in a vacuum?

Easy way to find out and kill two birds...[/quote]

Very good

Deputy Dawg

yeehaamcgee wrote:

diy wrote:

A locked wheel will always slide in the direction momentum dictated and under the influences of gravity and friction.

Precisely. And when going in a perfectly straight line, momentum is in a straight line.

Unless you change the direction of the momentum by shifting your position on the bike. Otherwise 'S' shaped skids would be impossible.

Anonymous

Deputy Dawg wrote:

yeehaamcgee wrote:

diy wrote:

A locked wheel will always slide in the direction momentum dictated and under the influences of gravity and friction.

Precisely. And when going in a perfectly straight line, momentum is in a straight line.

Unless you change the direction of the momentum by shifting your position on the bike. Otherwise 'S' shaped skids would be impossible.

Shock horror. Are you ACTUALLY saying that when you're not going in a straight line, you're... NOT going in a straight line?
My god! Give that man a nobel prize.


Right, anyway. About the camber. If you're riding across a camber and your body is NOT perpendicular to the camber, then what you're actually doing is failing to turn, in a roundabout kind of way. You're leaning and side loading the tyres to prevent the bike turning to the fall line (not sure what more accurate way there is of explaining that in English, Fall line seems to be accurate though, from Snowboarding).
You can actually ride, at speed, with you and the bike perpendicular to the slope, for a short amount of time, when the bike is naturally going in a straight line. Skidding the rear during that period would be the same as on flat ground.

If it helps visualise this, by taking it to the logical extreme, consider someone on a wall of death. This could be considered to be riding across a 90 degree bank, continuously.
At a certain speed, the rider will be able to be completely horizontal to the ground, or perpendicular to the surface of the wall, whichever way you prefer to think about it.
Once the bike is at a speed where the centripetal force is significantly outweighing the pull of gravity, you could perform a rear wheel skid, and the bike would continue as normal, until the speed was low enough that the rear wheel eventually succumbed to gravity.

Or yet another analogy. Take a well maintained, no stiff-link chain, and place it in a squiggly mess on the floor. If you pull the link at one end of the chain across the floor, the rest of the chain will follow behind it. the chain will not suddenly veer off to the side, since there is no way it can generate momentum in that direction. That's what your rear wheel is doing during a skid.

Furthermore, just go try it. Have you really never played the silly but fun car park/fireroad game where you try and pull the longest rear wheel skid before coming to a stop? It really doesn't matter what you're riding on, the rear will trail behind the front.

And have you also not noticed that if you lock and drag the back wheel on a steep descent, that it will keep the rear of the bike BEHIND you?

Do you actually ride mountain bikes at all?

Anyway, irrespective of this, dragging the rear is not an useful way for someone to pick up balance. Although on occasion it can be an useful thing (or just a fun thing) to do.

diy

Can someone explain how you change the direction of momentum?

I'm beginning to think the works of Sir Isaac Newton are obviously largely unknown here?

Jolly Swagman

Blimey, poor bloke opened the thread just to ask if he might have terrible balance and it has turned into a physics class. Are there no doctors out there could give us about 3 pages of post about inner ear problems as it relates to riding then we would have a full house.