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Neutral steering is very important for stress free long distance riding.
Just what is it and why is it important? Neutral steering is what makes some
motorcycles so easy to ride, so effortless to go through turns and allows the
rider to go for long distances. It is the tire profile and geometry of the
forks and frame that determine it.
Test for neutral steering
First you must test for straight tracking. With your hands off in the
30-50 mph range, it must go in a straight line. If it does not, then maybe
the frame is bent.
It is very easy to test for neutral steering. Make sure that your tires
are in good condition and are properly inflated. It is an absolute must to
have the throttle lock to keep it at one speed. If you can't hold a steady
speed, you can't perform this test. The steering bearings should be
correctly adjusted. Remove any steering damper friction. You should
also know that your bike has little or no tendency to have a low speed wobble.
If you have any question about that, go to my page on wobbles.
Find a curvy road where a fast rider could easily go through the curves at 50
mph, but 30 mph is easy and "normal" for the average rider. Find a time
when you have little traffic with which to be concerned. As you go through
a turn, sort of lighten up on your hand pressure on the bars. As you
lighten up, the bike should stay in the same line as before. If you feel
that the bike wants to "fall over" or "go straight" then maybe you don't have
neutral steering. As you feel your bike want to stay in the same curve,
lighten up even more. If you can get to the point of having your hands
completely off of the bars and the bike still stays in the same curve, then you
definitely have neutral steering. It may take several "runs" though the
curves to do all of this. You should discover that your airhead BMW will
go through the turn without your hands even on the bars. One can even put
it into the turn and pull it out without even touching the bars. It won't
be done as quickly as with your hands on the bars, but it certainly can be done.
I have ridden miles through many curves without even touching the bars, just by
using my body to steer.
Oversteer
This is where the bike seems to want to fall over into the turn, or turn
tighter as you relax your pressure on the bars. If you had a remote
throttle, you could accelerate and that would tend to "pick" the bike up.
As it is, you have to "grip the bars" in a curve and that is a most unsettling
feeling to have. You sort of have to "hold the bike up" to feel confident.
Many of the older Japanese bikes were designed this way and it was "normal" for
them.
This will cause a change in geometry, basically too short of a wheel base and
too little trail. If the front end sits too low, this will be the result.
One of the reasons for this to occur on a BMW is to have sacked out (collapsed)
fork springs. A common reason is when the Earles fork was bent back from
an accident. We saw a few telescopic fork models do this too, but usually
they bind up so badly that the owner can't/won't ride it.
Low air pressure will allow the front end to sit low too. A tire that
is too small for the front will do it too. One of the most common reasons
is that the owner mounted a too large tire on the rear. This sets the
front lower by comparison and it will oversteer.
The /2 Earles fork series used the same sized tire front and rear, a 3.50 X
18" and that worked very well. The US models with the "new" telescopic
forks used a 4.00 X 18" on the rear and it had neutral steering when all was in
top condition. Don't confuse the two types of forks and get some wild hair
to use a 4.00 on the rear of your Earles forks BMW if you value neutral
steering.
On the /5, and later bikes, it was common for owners to overload the bike
with accessories and ruin otherwise good handling. I have no experience
with BMWs after 1981, but geometry and human nature probably haven't changed
very much.
Understeer
This is where the bike doesn't even want to lean. It will try to stand
up in the curve if you reduce pressure on the bars. This is far rarer than
oversteer on a BMW. It makes you really work to go into a curve and stay
there. I have seen it from a variety of situations on a BMW. Once a
/2 came in with a 4.00 on the front and it was a real bear to ride. Once I
found a 3.00 or 3.25 Metzler C on the rear. I didn't even know that they
made them that small.
Tire profiles
The shape of the tire profile greatly alters how a bike goes into corners.
The old Dunlop K81 had a triangular profile and that caused it to give one a
scare as it transitioned from straight ahead to medium cornering. After it
was in the corner it really held well. Take a look at the profile and see
if it has any irregular shape to it. I have seen some new (meaning in the
last 10 years) tire profiles that would really mess up an old airhead. The
cafe racer could easily give up some smoothness in transition for some other
advantage, such as greater traction while in the corner.
The Metzler and Continental tires recommended by BMW really had a profile
that felt good. I well know that better compounds exist today, but I would
like to keep a regular profile and keep the neutral steering.
The result of neutral motorcycle steering
Neutral steering makes it easier to ride long distances, go through curves
with confidence and save your shoulder and back muscles. When a rider
becomes really comfortable with a bike like this, the rider only needs to "see a
curve" and the bike seems to just "go through the curve." I have often tried to
do nothing consciously when approaching a curve and the bike just seems to have
a mind of its own and do the right thing. It is this characteristic that
causes some bikes to be very easy to ride and others seem to be a wrestling
match. On the older stuff, the European bikes tended to be neutral
steering and the Japanese were often guilty of oversteer.
Stay with the tire sizes suggested by the manufacturer. I do not know
the size conversion to the newer modern metric tire sizes.
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