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Bike Maintenance

Here I will be discussing the main control area of the bike and, indeed, for a 50cc the only control area.

 

BARS

Starting with the bars, the steel bars that come with the bike should immediately be removed and placed in the shed for use in straightening subframes etc. They are a compromise in material and fit. With the 80cc bike for instance, the one set of bars is supposed to fit everyone between the age of 9 and 16 with a range of different riding styles and a range of disciplines, like MX, minikhana, grasstrack, supercross etc. This is obviously impossible and for this reason a quality set of alloy bars should be in the bike purchase budget. There are many quality bars available, Renthal, Tommaselli, Fly, TAG, AFAM...and that is just a few! These have advantages over steel bars, namely tremendous strength and a multitude of bends and styles. Other advantages are vibration damping and of course colour.

 

Recently a new innovation has appeared, that being tapered bars. While I have no experience riding with these, I have spoken to riders who use them and they claim to have fantastic damping and flex qualities, eliminating arm pump and fatigue. On the down side is the cost - the bars and clamps cost roughly double the price of a set of Renthals, but for those on a large budget they seem to have a lot going for them.  

While the following holds true for all bars, I will use Renthal as an example in this article mainly because everybody has heard of them. They have been in production to my knowledge for over thirty years and they have a brilliant website - complete with the story of the factory burning down. I would strongly advise anyone fitting bars to visit this site as it is full of information on fitting etc. and has some nice diagrams of clamps. Renthal have recently discontinued knurling the centre of their bars as it was found to be a stress point - as are dings and dents, which brings us to the first part of this article - fitting.

 

FITTING

 

There are two very important things with fitting bars. Firstly, the edges of the handlebar clamps must be chamfered with a round file so that no sharp edge bites into the bar, as shown in these two diagrams

 

 

 

 

 

 

 

 

 

 

 

 

 

A couple of years ago a supercross rider found out the hard way what happens when this is not done. At present most manufacturers do not do this and to their discredit do not tell you about it either. What they do tell you is the next point and that is that there must be a gap between the top and bottom clamp when the clamps are tight, as shown below  

 

 

 

As for fitting bars for the rider, this is mostly a personal choice, but as a starting point they should be straight up and down in line with the forks. Slightly forward of this will encourage an aggressive riding stance with better cornering, but do not go too far or front wheel landings will happen. If the bars are rotated back, the rider will look like a nerd. Remember, it is your responsibility as head mechanic, pit crew, marshall and parent to watch your child, and if they keep landing on the front or back wheel after a jump, the solution is often a simple and minor rotational adjustment of the bars.

 

Bar selection is a personal choice, but even though new bikes come and go, Renthal Mini Racers for example will always be the same bend and put a constant value in the equation. As the rider progresses to larger bikes they can get the same bend and style of bars in a larger size that they learnt to ride with, but my advice is to sit on lots of bikes, when you find the bars that suit you, you will know. Suddenly that bike fits you and begs to be ridden.

 

GRIPS

Onto grips - these again are a personal choice. Once more Renthal make an excellent grip in three compounds and three patterns (I should be getting paid for this). I have found for MX and minikhana the medium compound half waffle to be as good as they get with durability and vibration absorption. The soft compound will give better vibration control, but at a price - you will be replacing them every few weeks and certainly if the bike is dropped. Needless to say they should be fitted with the correct glue or WD40 and preferably wired on with stainless steel locking wire in the grooves provided, and finally, always replace them before they look like Nick Thompson's - they are not expensive.

 

Next, if you have not already plugged the bar ends with wood, we are going to cut holes in out brand new grips and fit a pair of gripsaver bar ends (not made by Renthal), a strange name as you have to ruin the grips to fit them. Be careful when you fit these that the throttle rotates and returns freely. There should be a slight gap between the plug and grip on the throttle side and always check this after the bike has been dropped.

 

LEVERS

Finally, to the levers. Start by setting them in the 30 to 45 degree down range. The lower lever will encourage a good attack position, but the downside is that the rider will find it difficult to move back when braking. It is impossible to suggest the right position for every child, due to differences in height, hand/finger size and experience at riding. When fitting the levers, never fully tighten the perches so that in a fall the lever will merely rotate, allowing the rider to knock it back into position and race on - difficult with a broken clutch lever and nearly impossible with no front brake. It is also a good idea to wrap pipe (Teflon) tape around the bars where the lever perches clamp on - this is available from plumbing suppliers or out of the back of my van when my back is turned.

Lastly, a trap that many parents fall into is that they set the clutch freeplay for their own hand. Children even as old as thirteen have very small hands. The end result is that they are trying to control the business end of the clutch with their fingertips, causing involuntary wheelstands and stalling. A good portion of clutch freeplay eliminates this problem