Getting my head round this ?

[the addict]

Another example

Take your sports bike buddies out to the car park and set some cones out to ride slalom between. - take your sports bike and try to ride round the cones in first gear and then try it in 2nd.

Whats easiest?

Best explanation I have seen so far Jimmy, lowering the gearing gives a rider more time and more control over the bike in normal riding, a higher gear ratio speeds everything up. In road racing you gear a bike so the rev range is kept in maximum power/acceleration at all times and when you change gear the drop in revs does not go below the bottom of the power curve. Trials and road racing have nothing to do with each other in gearing.

Edited March 2, 2011 by The Addict

[perce]

I always put a one tooth smaller front sprocket on a gasser & did the same on the last 4rt I had. Simply gives you more time.

[pete_scorpa3]

I run my SY250 on standard gearing, but the DRZ400 that I use for Long Distance Trials is geared 2 down on the front and 9 up on the back. This has the effect of slowing the bike right down and more importantly helps to stop it stalling mid section.

For enduros I go back to stock gearing which gives a much better top speed, but the bike does tend to rush me into the tricky going and also stalls far more.

In this context, the lower gearing does indeed calm the bike down.

On a road bike, doing the same thing would turn it into a wheelie machine. This is always the dilema on the race track, gear down to use top gear (but make 1st unusable) or keep the gearing higher and forget top.

[paul w]

info for your other forum.

when converting a road 600 into a race bike you normally fit longer 1st and 2nd gears and shorter 6th possible even 5th (albeit its a few years scince i built one) you can then gear for the track on the sprockets. Some tracks you geared for 6 gears some for 5. back in the TZ250 days you had cassete gear boxes with differnt ratios for several gears. (sounds difficult but you could swap gears in about 30 mins)

This is why i like trials, give the bike a good wash when you get home, a couple of hours tinkering in the garage through the week and your good to go.

[stevec]

I think of dropping teeth at the c/s sprocket (or adding to the rear) as if I'm changing from a fast to slow throttle. It results in slower rear wheel speed per amount of throttle rotation. Sure, there's more torque but slowing down the reaction of the rear wheel is what I think people are talking about.

[copemech]

One is propelled a lesser distance at a given throttle or RPM.

[billyt]

In my humble opinion

When it comes to a trials bike, one changes front or rear gearing for torque either more or less, not speed.

If that is so, then we change the rear sprocket i.e. make it bigger to gain more torque but loose speed.

Changing the front sprocket usually results in limited choices due to chain wrap and we can not go to small.

The rear sprocket affords us more choices in the way of changing things up!

When changing gearing we in trials really need to ask our selfs "do I want more or less torque" not speed.

Torque and speed are inversely opposed. Gear up in the rear get more torque, loose speed.

My half a crowns worth!

[hrcmonty]

As others have said, You can't compare gearing of Trials Vs Track bike.

Trials you want the engine to NOT drive you too fast on low throttle. Easiest way is to spend a few quid on a front sprocket, 1 tooth bigger and 1 smaller than what you have. Go down the woods and try it.

Here some toilet reading for you.

Introduction to TORQUE, WORK and POWER

Torque is the twisting force about a point, sometimes called a 'moment'. The torque is defined as the force multiplied by the distance from the pivot perpendicular to the force.

Torque = Force x Distance Perp. to Pivot

For example: One foot pound of torque is the twisting force necessary to support a one pound weight on a weightless horizontal bar, one foot from the pivot. You might directly measure torque when tightening a nut to a specified torque using a torque wrench. Here, a twisting force is applied to the nut, until the resistance to rotation of the nut is equal to the torque required.

Work is the the transfer of energy. The work done is equal to the force applied multiplied by the distance travelled in the direction of that force.

Work = Force x Distance Travelled

Power is the rate of doing work, the amount of work done in a unit of time. The power produced is the work done divided by the time taken.

Force x Distance Travelled

Power = ----------------------------------------

Time

For example: If a weight is fixed solidly to the floor and you try to lift it, you are applying force. However the weight cannot move, so no work is done on the weight. Although force is exerted by your arms, no energy is transferred to the weight. If you lift a one pound weight one foot, then by definition one foot pound of work has been done. If you take one minute to do this then you will be producing power at one foot pound per minute.

One horsepower is 33,000 foot pounds per minute. To find the horsepower of an engine, the torque produced by the engine is measured and the horsepower calculated. This is done using a dynamometer which is essentially a brake with a measuring device - hence the term brake horse power (bhp) which is often used. A torque curve is produced by plotting the torque measured against the engine speed.

With torque in foot pounds:

Torque x RPM

Horsepower = ----------------

5252

Using this equation a power curve can be produced from the torque curve.

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How does this apply to a motorcycle?

For the rider, torque is the all-important factor. A bike will accelerate at a rate that matches its torque curve (ignoring rolling / air resistance). The torque peak is the point at which the bike has maximum acceleration, either side of this peak it is less. For a given torque at the rear wheel, the acceleration of the bike is the same, irrespective of the engine speed. Horsepower increases with the engine speed until well after the torque peak, and only peaks when the decreasing torque compensates for the increasing rpm. (look at the equation.) The acceleration at the torque peak is greater than that at the power peak.

So why do we talk about horsepower so much? Consider a large waterwheel. While it's obvious that the water wheel generate a large torque, its rotational speed is very slow and hence its power (the ability to do work over time) is low. A waterwheel is therefore not generally very powerful. A powerful engine with lots of horsepower is one which produces high torque at high rpm.

Theoretically, producing torque at high rpm is better than producing torque low rpm, as at high rpm you can use gearing. A powerful engine is useful because it can then be geared down - you don't want the rear wheel of your bike doing 8000rpm anyway! Gearing down reduces the speed at the rear wheel with a corresponding increase in torque. This does not affect the power of the engine apart from frictional losses. Incidentally a properly lubricated chain drive is 98.5% efficient, significantly better than a geared drive. For road racing, this theory closely matches reality, but for offroad the above is not the only consideration. (still awake?!...)

But what does that mean about gearing...

The stock gearing of your bike is likely to have been determined by choosing a compromise ratio based on what worked best for test riders in "average" conditions. As soon as the bike is taken out of average conditions - by engine tune, terrain, track design or rider style the stock gearing might no longer be the optimum solution - a different setup might get you round the track faster.

Maximum speed occurs when the driving force is exactly counterbalanced by the air and rolling resistances. At this point the acceleration has fallen to zero.

Setting up the gearing of any vehicle is a trade-off between acceleration and top speed.

Gearing a bike up to produce higher top speed with less acceleration is done using a larger countershaft (gearbox) sprocket or a smaller rear sprocket.

Gearing a bike down giving it more acceleration with lower top speed is done using a smaller countershaft (gearbox) sprocket or a larger rear sprocket.

The ratio chart shows the gearing ratios for different numbers of teeth on the gearbox and rear sprockets. The numbers given are the number of revolutions of the gearbox sprocket required to cause one complete revolution of the back wheel. These figures are calculated by dividing the number of teeth on the rear chainwheel by the number of teeth on the gearbox sprocket.

From the table it is clear that changing one tooth on the gearbox sprocket has a significantly larger effect on the gearing than changing one tooth on the rear sprocket. To make a small change in gearing it is therefore necessary to change the rear chainwheel size by one tooth, as changing the gearbox sprocket makes a far larger difference in gearing.

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Edited March 3, 2011 by hrc_monty

[pete_scorpa3]

Just what I was thinking!

Edited March 3, 2011 by Pete_Scorpa3

[paul w]

crikey.....its all getting a little complicated for me.

[02-apr]

As an approximation, on the typical trials gearing, one tooth down on the front sprocket equates to four teeth up on the rear and is cheaper to do as you shorten the chain instead of adding to it and the front sprocket is generally cheaper than the rear.

My experience over the years is that one tooth on the front, while it sounds a lot, is what you need to do to feel a difference. But, having said that, my 200 Beta had the 250 gearing on it (one tooth smaller at the back) and changing to the correct size did make a difference to the very slow running in the higher gears but I wouldn't have experimented by one tooth on the back.

I suppose we have so many gears in the box nowadays that we can afford to be a bit low overall and just use the next gear up if required.

It's a very personal thing - I seem to recall the Fantic 300 was very low geared for the period and everyone geared it up but one chap (I think one of the supported riders) lowered his still further so he could use the high gears in sections - a novel approach at the time.

[stevecollie]

Now I see it

Edited March 4, 2011 by Stevecollie

[cabby]

Now I see it

You speak with fork tongue

[copemech]

I'm having a rather healthy debate elsewhere, on another forum, who are all road/track riders, I have said that I have read on here and on Trials UK vids that to calm your bike down, you can go a tooth down, however, they are all disputing this, although none of them are giving a reasoned argument as to why.

What year is your bike? For the most part the standard advice is to leave the gearing alone at standard as well and learn the bike.

In my opinion you need to learn the clutch.To do this , you must ride up a gear from normal, forcing you to use the thing. Most sections in second gear, feel for grip with the clutch, not throttle, works re the revs, you can rev till hell but won't change things. Gota giv a try,as after a while it becomes mor natural