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We have been prompted to produce this article by a recent posting on the RCBikes Smartgroups, asking for advice on a steering issue. The silence from the group was deafening! Its not meant to sound smug, big headed or belittle other peoples ideas, it's just that these are ours. See read, digest and then make up your own minds. If you agree or disagree then pleased tell us. If you can contribute anything then we will be happy to bring it to the world through http://www.teambenwell.co.uk. We strongly believe that any information right or wrong, is good information as it encourages experimentation, discussion and forwards the sport. We are knocking huge chunks off of lap records this year and a large part of that is because the bikes are now not only faster but easier to ride, and this has to be good for the future of the sport.
1/5th scale bikes are still a relatively new and developing class of RC vehicle so no firm and accepted rules of behaviour have yet been established. In the car world you will always find some one to give you advice on dealing with bumps, kerbs, oversteer, understeer etc; with varying degrees of accuracy. In our experience the number of people that truly understand car dynamics is very few. The people that understand bike dynamics are even less….. In fact we could go so far as to say that there aren't any! But we will do our best. Before we begin we are going to make a VERY BIG assumption. Your bike is correctly built, straight, true, balanced, everything is tight and rigid and nothing binds, catches, snags or is sloppy etc. This is because when describing some of the symptoms we are only going to discuss the steering related solution. If for example your rear damper has air in it, or if the steering link rod catches on the rider or even if the steering link rod ball joint binds on the ball, then the solution we give may not supply the results you require. That doesn't mean that we are wrong (although it is quite possible) just that other factors may be influencing the outcome. OK, now lets get started. First things first, ditch the steering damper. It is only a partial cure to some problems and it provides no solutions just confuses the issues, it often does more harm than good. You will put it back on later but leave it off to start with. Second point of note. There is only one correct steering spring tension for any given bike set up. If you raise or lower the back, change the rake angle or move the centre of gravity then you will have to adjust the steering linkage to maintain your perfect set-up. Which by the way doesn't exist? And we don't mean It can't be found, we mean it doesn't exist! Because we don't steer a bike, (we just lean it) we have to set the bike up to steer itself and we can't expect to find a single set-up that can cope with a fast smooth corner as well as a slow bumpy one by just using a link and a couple of springs! But we can find a good compromise. So what's involved. In this article we are going to ignore the rear of the bike so set your rear swing so that with everything fitted, ready to race, it is parallel to the ground. This is the most neutral position and lets us concentrate on the front. Now let's try and understand what's happening at the sharp end. As we all know a turn is initiated by us by turning the steering, in what seems at first glance the wrong direction, and thus leaning it to the side that we want to turn in. Once in the turn it's the angle of the wheel to the road, the weight of the steering assembly and the side ways offset of the front wheel's contact patch as a result of the offset at the headstock, which all contribute to the bikes willingness to turn. The trick is to get the bike to turn at exactly the right rate. Too much and it will just pick itself back up again out of the turn and too little and it pushes the side guards into the tarmac taking the weight off of the wheels and reducing its turning ability.
So, how do we control all this? Well we have two adjustments, rake angle and steering linkage tension. Put simply the lower the rake angle (the closer the forks are to the vertical) the more the bike will turn, but the less stable the steering becomes (category two wobbles, remember them :) It also has the effect of making it harder to pick a racing line, or be smooth and carry speed through a turn, hence all Team Benwell's earlier advice about running the forks at their maximum angle to start with. Were not going to give a recommended angle here because there are so many factors that come into play, suffice to say that you should end up with the adjuster at least 1 to 2 turns down on a BD4, double that on a kit bike. So, set everything approximately and go testing. Get used to what's happening and have a play with the rake angle. Now once you have settled on a rake angle you like you need to set the steering linkage spring tension. Too little and it probably wont turn very fast, it may fall onto the crash bars and stay there and may suffer from cat 2 wobbles. Too great and it may bounce off the side guards when turning in and could be hard to keep in a turn. We should point out here that you can go too far in reducing the rake angle. If the bike seems to tuck into a turn and lock the front wheel over to one side as it skids to a halt or if its really hard to ride to a chosen line you've gone too far. The point at which this happens is dependant on the strength of the steering linkage, the speed at which you're travelling and the grip of the tarmac so just be aware of these symptons when you're testing, and change things if they happen. In our experience if it's happening at all then your running too little rake. So, back to spring tension. The other primary reason for tightening the springs up is to help eliminate the cat 2 wobbles. In our experience if you get rid of them totally then you probably have them too tight, so for that last little bit of control put the steering damper back on. NOTE it's only for the last bit of control the bike should be totally ride-able with it off it's just that fitting it helps. If you need any more than light damping then you haven't got it right. If you have any kind of oil filled damper fitted then something is wrong. Just the drag of the oil seals should be enough regardless of the weight oil you have in it! Back to the linkage. We should have talked about the length of the arm and the transmitter you're using first really but one thing at a time. Now that you have got a rake angle and linkage tension you like you need to adjust the responsiveness of the bike to suit your riding style. If you have a bells and whistles transmitter with a steering rate adjustment then fit your linkage to a long steering arm (double the normal length!) and then adjust your steering rate to set the servo through too as much as you can handle. Start off with too little and gradually increase it as you get used to the bike's responsiveness. Too fast a response is worse than too slow a response as it leans the bike too quickly pushing the side guard into the tarmac which lifts the front wheel and the whole bike then pushes wide. If your steering is slow the bike still turns just as well, remember its the bike that turns not you!, you just have to initiate the turn earlier. Lets say that again the speed at which the steering responds has no bearing on the rate at which the bike turns. Got that… Good because its one of the easiest pitfalls to fall into if you have come from the car world where response is nearly always connected in some way with the cars turning ability.
Right now that's just about it except for one thing. When you first started this you left everything alone and started with the rake angle. The trouble is you were probably miles off with the other settings so the rake angle you settled on was probably not quite right. Now that you have got everything a little closer to the ideal go back and do it again. When everything is correct the bike should run straight and true. The kit steering springs are such that you should be able to move the steering to lean the bike into a turn and then let it go back to centre. If you have to hold it into a turn then it's quite probable that you still haven't got the steering linkage tuned correctly to the rest of the bike. Clearly there is another lesson here. You shouldn't have to hold the stick over very much through a turn. You can make the bike work like this but it's not ideal. Remember you just lean the bike it steers itself. Ok a few quick fixes. The nature of bike setup dictates that there is never one answer and that any changes have more that one effect but the following may help…. or it may just confuse things more! Q. My bike seems to turn well enough but it's slow to
respond to rider input. Q. My bike is slow to respond and when it does it doesn't
seem to turn tight enough. Q. My bike turns well enough but its response is vague
and it is hard to put on a racing line Q. My bike is twitchy and falls onto the side guards excessively Q. My bike turns in ok but bounces off of the side guards
and needs to be laid over again Q. My bike responds well, seems to turn well enough and
doesn't display any excessive wobbles yet it still won't go round a
turn with out excessively dragging its side guards Most of the above issues can be caused by other factors other that just steering problems but that will have to be the subject of a follow up article. So that's it. We hope this helps. Please feel free to email us with any comments or questions but we can assure you that if you follow this set up, and then learn to ride it!, you will find the bike quicker and ultimately easier to ride. Have fun Team Benwell
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