1984 K100RS Tyres?

Its tire time again and the option to swap out both?
Its an old K100RS sitting on BT45s.
They have done about 6K.
I find I have to lay the bike a long way down for an old git on an old
beemer?
They cope with it VERY well though.

The rear centre is down.
The sides of the front are well feathered!
Front centre OK.
The rear is a 140 (optional) rather than the 130 (recommended).
Has this contributed to the feathering of the front and increased lean
required?
Will going back to a 130 rear reduce under steer or do I need to slow down
more?

Books recommend sticking with cross ply?
Motobins here in the UK don't stock BT45s are they going out of favour?
Mate runs Conties on his boxer and recommend them for longevity?

Garry

 

I couldn't get any K-591's to replace the aged set on one of my bikes,
Dunlop discontinued them, and I didn't want to try the replacement
Dunlop offered, so I tried a set of BT-45V's in the original sizes. The
Bridgestones felt squirmy, the tread blocks could be easily moved just
by squeezing them with my fingers...

Some brilliant tire engineer at Michelin came up with a formula for
tread radius and width and cornering radius to figure out what tire
sizes would be best for a bike of any given wheelbase. But the
existance of his formula is unknown to most riders, who install wider
rear tires because they think they'll get more traction...

A wider tire makes the front tire's job harder. And, when the rear tire
wears flat in the middle, the front tire's job is even harder, it wears
more to a Vee-shape as the rear tire's profile flattens out and the
steering effort at the handlebars increases...

The narrower tire may (or may not) feel like you've got power steering
on your bike, but that depends upon the profile of the curvature of the
tread. Some profiles are rounder, others are flatter. To be safe, stick
with the OEM tires. If you can still get them, that is...

Just looking at my new set of BT-45V's before mounting them, it looked
like the rear tire was going to have a very flat profile, but once it
was spooned onto then rim and aired up, the profile was a lot rounder
than the K-591 I was replacing. It didn't have the distinct lip at the
edge that the K-591 had. That lip gave me confidence, I would know when
I was getting to the edge of the tire...

But I wanted to go back to the original rear tire width so the bike
would steer quicker on tight, narrow mountain roads that I planned to
ride on...

And, with the overly wide K-591 on the back (it was a 170, where a 140
was supposed to go, most roadracers used a 170 or a 160 on the track),
the motorcycle was more stable in crosswinds. The handlebars would feel
very rigid, but the bike would stay where I wanted it stay in the lane
I was in. But the narrower stock-sized tire doesn't feel that stable.
The first strong gust of wind blew the bike right across the double
yellow line, into the oncoming lane. Forunately, no car was coming my
way...

Maybe. It depends upon the rim width and case rigidity of the radial
tire you're thinking about experimenting with. Most radials require a
wider rim, check the charts on the manufacturers' websites for
recommended rim widths to see what rim size you need...

One of the reasons for recommending staying with bias ply tires instead
of switching to radials was that the suspension would have to be
retuned, using softer springs or less preload and letting the
tires absorb more of the bumps, but that didn't always hold true...

Bias ply tires *generally* have a stiffer case than *some* radial ply
tires but the tire engineers found that they had to add rubber
stiffeners to the radials' sidewalls to make the sidewalls more rigid.
So the sidewall rubbers are controlling the springiness of the tires,
especially while leaned over, when the suspension loads come in at a 45
degree angle to the direction the forks are intended to work..

favour?

They are out of favor with me, and I've only used one set...

I found the Contie that I used (Blitz) to be soft and cheap and they
wore quickly. They did have a soft, cushy ride, which was okay for
touring, but I preferred the rigid case of the Dunlops...

The Conti Blitz also lacked the lip that I mentioned above. It felt
like the tire was falling off the edge when I leaned the bike into a
corner...

There was a section height problem with the Conti Blitz, too. If the
tire was one size over the original specification to get more width,
the section height proportion meant that the tire was also taller and
the bike's seat was higher off the ground and the extra circumference
of the tire lowered my cruising RPM and slowed down the acceleration...

It seems that changing any little thing, changes a lot of unexpected
things. The German government doesn't allow *anything* to be changed on
bikesregistered in Germany...

original tire is approved for use on whatever model they ride. Problem
with that is manufacturers keep on discontinuing their old tires and
"improving" the new ones for the latest greatest sportbikes and sport
tourers every year...

What do German riders do, when they have a 22 year old BMW?

Enquiring minds want to know what the German riders are wearing this
year, on their wheels...

 

Are Metzelers and Pirellis still being made in the same factory?
Several years ago, I wanted new Metzelers for my Yamaha, but couldn't
get them, as there had been a fire at the factory, and then the Pirelli
run was going to take place before they would switch back to making
Metzelers again. I got stuck with a crappy Michelin instead, as I
didn't want a Pirelli tire...

The Sport touring Metzelers are slippery, that's a fact...

I was riding the Angeles Crest with a friend who had Dunlop 207's on
his GSXR, while I had the older MeZ2 sport touring Metzelers on my
Yamaha. He couldn't understand why I was taking the corners so slowly.
I told him that the rear tire would slip away in the exact same turns
every time, at rather low speeds.

In his view, spending $300 for a set of new Dunlops every 3K to 4K
miles made sense, but I want a back tire to last twice that long, so I
accept a slower pace...

Metzeler has been offering some pointy profile tires recently. I don't
want any of those, as I'm not concerned with getting the fastest turn
in possible...

I did like the smooth round profiles of the MeZ1, and the MeZ2, but I
tried a set of Bridgestone BT-020's and the front tire is too tall and
too pointy, so the bike feels just like some old 1980's UJM, now. It
even begins to speed weave at a lower speed instead of feeling rock
stable at 90 mph...

To make the Yamaha feel right again, I'll either have to go back to a
Metzeler like I had on it before, or try a BT-010 on the front as other
riders have recommended. The BT-010 is supposed to have more traction,
but isn't so pointy...

 

If you used the BT020 and didn't like it, there are also the Mich Pilot
Road (rounder profile) and the Avon Azoro 45/46ST (sharper profile).
Both handle better than the BT020 while also lasting longer. I got 6k
out of a rear BT020 with the front badly cupped by 4k. With the Pilot
Road I could have gotten 10k miles out of it but changed at 9200 due to
an upcoming trip.

 

Do you know anything about the "run flat" capabilities of the current
crop of Michelin tires? I want my tires to stay on the rims when they
are punctured, and I want the carcass to be stiff enough
so the motorbike doesn't get impossibly squirrelly if the tire deflates
rapidly...

When I couldn't get a Metzeler due to the fire at the factory, the
closest thing I could find was a Michelin, which was an M-89X, as I
recall. I did my usual pre-installation examination of the tire,
checking for balance marks, stickers inside the tire, and general
weirdnesses...

One thing that struck me was how light and flexible the case was. I
worked it with my hands to get an estimate of how hard it would be to
spoon it onto my rim, and I realized that the carcass was so flexible I
would be able to *turn the tire inside out* just like a bicycle tire.
And I did that, just for giggles. Imagine that, an inside out MC tire.
No way in hell I could do that with a Dunlop or Metzeler or
Bridgestone. I wondered what's up with The Michelin Man, anyhow...

That rubber balloon only lasted 2K miles and I got a puncture and I
couldn't use an internal patch or plug because of the weird reticulated
rubber ridges inside the tire...

Older Michelin tires that I used, like the old PZ-2 and the original
Hi-Sports were nothing at all like that rubber balloon of an M-89X...