BMW K Series Lower rear profile rubber?

Thanks for the help, advice and encouragement earlier on this one gents.
I am now in the detail...

The orig spec for the K100RS is 130/90 but I have found a new 130/80 locally
at the right price ...very much!

Am I right in considering the only change will be feet reaching the floor
now?
Given the speedo recalib ... running cycle computer too.

Thanks
Garry

 

So, the tire is "free"? Sometimes "free" isn't such a bargain...

I recommend sticking with the standard tire sizes, and the original
equipment tires, unless you like to experiment and go through a lot of
work to learn all this stuff the hard (and expen$ive) way...

I used to spend hours poring over mail order catalogs and scheming on
how this or that oversized or wider or lower profile would affect the
handling of my motorbike. I tried all that stuff, it didn't work out
the way I expected...

Been there, done that, learned not to experiment with tire sizes, it
ain't worth the hassle, expen$e, and generally weird handling resulting
from fooling around with the rear end...

The steering feel will change with the 130/80, because the rear axle
will be half an inch lower. So the rake angle of the front fork will be
kicked out a little and the trail will be increased...

Increased rake and trail usually have the effect of making the steering
feel heavier, but lowering the rear end half an inch has the effect of
shifting the center of mass a little further back, so the steering will
feel lighter in this case...

If the reason for the 130/80 having a lower profile is lower sidewalls
and the tread profile remains the same, the motorbike will probably
give the sensation that the rear end is falling away from you in the
turns. That "weak arse" feeling destroys your confidence in corners...

If the sidewalls are the same height and the tread profile is flatter,
the motorbike will be averse to turning, and the steering will feel
heavy. You'll feel like you're fighting the rear wheel every time you
want to turn a corner, the bike just won't "want" to turn...

If you just insist on doing the size swap and you're not going to mount
a lower profile front tire to level the bike, investigate whether you
can pull the fork stanchion tubes up through the triple
clamps. This will return the axles to their same relative positions
above the ground, but the bike still won't handle exactly the same,
because, while the rake and trail will be restored, the *wheelbase*
will be slightly shorter, and the center of mass will move forward and
lower, just a little bit...

And you *will* notice these changes when you ride the bike...

 

No. The steering will be slower at least. There are other things which
may have an adverse effect too. Do not save money on tires, wheels,
brakes or suspension of your bike.

 

Thanks one and all for the one going advice on this one ... without the
personal abuse often seen on other lists.

Completly standard sizes fitted this afternoon.

After equally lengthy discussion from suppliers who had their bikes parked
outside the bay!

Only done 2-3 VERY careful miles but the difference is phenominal.
Bike turns in quicker, seems lighter on the steering.
Still nervy but "newness" afecting grip, cofidence and bowel control!

oooh sorry they are Michelin Macadams.

Guys said they felt the side walls were stiffer than the Battalax and
mileage may be better too? .... could be it just what they had in who
knows.
Dealer was personaly recommend by other 2 wheelers ...

Thanks gents .. just got to keep off the gas and keep it upright for a
couple of hundered then Ill report back.
TA!
Garry

 

I would recommend the "knobbies".
:>o

 

We do strive for professional and courteous treatment of our customers.
You may send us each a cyber beer ;-)

Way to go!

A genius engineer at Michelin figured out formulae for the coning
angles and wheelbases and tire widths that work together. I wish that I
could find it on the web, but never have. Basically, the coning theory
says that the tires have to roll in a circle like a
styofoam coffee cup rolls on a flat surface cause of the difference in
diameter from the center of the tire's cone to the edge...

In practical terms, both tires now match each other as well as they
ever will, so the front tire doesn't have to "fight" the rear tire just
to keep the bike running straight down the road and the curvature of
the rear tire is such that it falls easily toward the side you want to
go...

Michelins had a reputation in the 1970's for being very rigid and
difficult to mount on a rim because of the steel wires in their beads.
I had a flat front Michelin one time, and rode the bike home carrying a
passenger, because the steel wire beads kept the tire on the rim...

Motorcycle engineers have been playing with hard rubber sidewall
stiffeners for years since radial tires were developed for motorbikes
in the mid-1980's...

The side wall can be used as a spring to support the weight of the bike
while it's leaned over. The reason the stiffener acts like a spring is
because the suspension system of a motorbike isn't designed to work at
high lean angles. Engineers say that the tire loads are "out of plane"
to the normal direction the suspension is supposed to work...

Without any stiffeners at all, the motorcycle and the tire could be
pointed in slightly different directions. It's OK for a radial on a car
to wallow from side to side like that, but a motorcycle would feel too
squirrely, and riders demand a precise steering feel...

Even with really rigid stiffeners, the rest of the carcass may be
fairly thin and compliant to small pavement irregularities...

One hopes that compliant tires of that sort will remain on the rim and
not handle too very weirdly if the tire is punctured and loses its air.
Engineers refer to this beneficial characteristic as "run flat
capability"...

One of these days when I'm in the big motorcycle emporium over the hill
I will have to visually compare the Michelin's cases with the
Bridgestones and see how they feel when I manually try to spread them
apart...

The last Michelin I used had such a thin carcass, I decided to try an
experiment with it. I thought I could turn it inside out, like a bicyle
tire, so I tried it, and I did turn the tire inside out...

I could have never done that with a Bridgestone or a Metzeler or a
Dunlop. Those tires have thick, heavy carcasses, and the ride suffers
for it...