Fantasy Bike

["Tom Brown" <tbrown@xxxxxxxxxxx>]

Bob:

>An ideal bike would be one with the K75 engine in an RS frame.  I know,
>the K1200RS or the K1200GL, but those bikes are too heavy for me. Bob
>Silas '94 R1100RS

Or a "K90" engine....(900cc-100HP?)

The magic of the Oilhead bikes is that they ARE the frame.   The front "frame"
is a piece of aluminum about 6" long.   It weighs about 2 lbs and connects
then engine block directly to the front steering head.  The boxer engine
design is smooth enough that an 1100cc twin can be used as the frame and the
bike is still pretty damned smooth to ride.

The R1200 engine has balance shafts to cancel the off-centeredness caused by
one piston/con rod being in front of the other on the crank.   It worked
pretty well on the 1200GS I rode last year, but I must admit, I expected more.
It's still not as smooth as my Aprilia Mille R with a 60degree V twin.
Aprillia's balance shafts really work.   I think BMW may have more development
opportunity with this balance shaft idea.   The sales literature from the UK
on the R12RT mentioned a "modified balance shaft system".   I think this may
be a step toward more smoothness.  One thing I did notice with the new engine.
There was no point in the RPMs where vibration suddenly increased.  The upper
revs were totally useable.  There used to be a "shelf" at just under 5,000
where things started to shake on every 1100 I ever rode.  This is less
pronounced on the twin spark 1150, but still there.   Generally, I was out
flogging the thing on some back road in 3rd gear anyway at this RPM, so it
didn't matter so much to me.

Both the 1150 and the 1200 exhibit some shudder at lower RPMs that the 1100s
don't seem to have when a little power is applied.   I thought this was
surprising and out of place.   It's minor and controllable with practice, but
it's there.

Could they make an engine-as-frame design with the new k bike engine?   I
dont' know.   Does a triple offer advantages that a quad does not in terms of
balance?   Don't know.   The old K75 also used a balance shaft, as I recall.
It is one of the smoothest engines around.    The K12RS is a very smooth bike.
Without aftermarket exhaust, you really have to use the tach and shift
indicator to know where you're at much of the time unless you're really
humping with it,  but its engine rides in shock mounts on the frame. This has
always resulted in less frame rigidity compared to an engine as frame design.
This is why all K-bikes, at least the ones up until the K12S, are at a
disadvantage on bad roads in the turns.

I rode a K1100RS once and it was not smooth except at one or two small sweet
spots on the rev band.  There was a highter frequency buzz most of the time
that I found objectionable.   I don't think 4 cylinders water cooled designs
are inherently smooth.  The K12RS and LT do it with isolation mounting to the
frame and with balancing tricks.   A triple might not require so much of
that.

Triumph triples are very smooth and quick.   I tested a Sprint ST in 1999 and
thought it was a really good bike.   If I'd not already owned my RT, I might
have gone for that.   Hard to imagine going back to a chain drive design for
touring after you've had shaft drive for a while.   It's so nice to not think
about your chain after riding all day.

- -TB

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