Wheel sizes

I have a 1983 GS650GLD with 19" front wheel and 16" rear wheel.
Picked up some spare parts from a 1982 GS650G and for some reason it
uses same front wheel but its rear is 17"

Is there any advantage/disadvantage of putting the bigger rear on mine?
Presumably the weight difference is minimal, the distance travelled per
rev is slightly higher (3" not counting tire), seating height should be
minimally affected.

Now the manual does not say that the older bike had larger wheel but it
also does not say that the gas tank is 1/2" longer so will not mount.

Ian Singer
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Have you ever actually ridden that machine? Changes in wheel size and
tire profile can make a machine that is stable at high speed into a
nuisance that wiggles and weaves at highway cruising speed..

Don't ask how I know that. I used to think that wide tires were the way
to go, knowing nothing about profile. I though that putting a 1-inch
larger diameter wheel on a mchine so I could fit a wider tire was no
problem.

I recommend that you go to www.mawonline.com and find the tire section.
I don't recommend that you *buy* anything from MAW, it's just that they
have all the URL's for the most popular brands of tires.

You can go to the manufacturer's websites and look up the wheel size
and find out what tire fits each rim width optimally. You can look up
recommended replacement fitments for the 1982 and 1983, and find out
what the fitted diameter of each tire/wheel combo is.

Ideally, you'd like to come out with wheels and tires that have the
same diameters as the original equipment wheels and tires so the rear
end doesn't sit too high (or too low) and the same for the front end.

You want the axles to be at the same height above the ground that they
were when the machine rolled off the showroom floor, if at all
possible.

Then, if the tires have the correct profile, the machine should have
the parking lot nimble handling it had when new, as well as the same
high speed stability. You won't have changed the fork rake and trail if
you get the right size tires.

High speed stability doesn't go on forever though. Every motorcycle has
a critical speed where it begins to weave. You just don't want to fit
tires that make the machine weave at speeds where it's scary to cruise
down the highway.

 

If you go a higher diameter in wheel and install a lower profile tire it
might end up feeling the same way on the road. I really dunno never tried
it.

 

Oh. The voice of inexperience, huh?

I've tried it all. Spent a lot of money on tires and wheels.

The results were usually not at all what I'd expected. I need to change
my last mistaken selection to restore my Yamaha's handling to what it
was before I accepted Usenet concensus and bought a damned Bridgestone
BT-020 front tire. POS out-tracks on countersteering and shimmies and
speed weaves at freeway cruising speeds.

The factory test riders *know* what a motorcycle should feel like. They
try various tire and wheel combinations and make recommendations. OTOH,
testers do a lot of testing on the race track, and most street riders
will never set a wheel on a track.

Sometimes the bean counters at the factory will recommend a really
crappy tire that they can get for a nickel less per tire, and overrule
the experienced riders' recommendations.

But, generally, if you use the original equipment tires recommended for
your machine, you'll have a motorcycle that handles just like it did
from the showroom floor.

When you talk about"lower profile", what do you mean? Low profile car
tires have a different section height than the older E-section tires
which were as wide as the carcass was tall.

But a low profile motorcycle tire may have a very high crown for quick
handling. Or, it may have a lower crown and the rider has to struggle
to make the motorcycle turn.

One experienced rider I know roadraced for 20 years. He found a very
cheap Suzuki GS-450L with a 16-inch rear tire and tried to race it on
Willow Springs without changing to the 17 inch wheel that came stock on
other GS-450's.

The 16-incher had such a large contact patch it gripped the road too
hard and the GS-450L wobled fiercely in the highspeed turns 8 and 9,
unnerving him.

GS-450's were very popular at the time, riders could run them wide
open, flat out, at about 110 mph and humble riders of much larger
machines.

Don't ask how I know that...

 

Did more checking in the manual to see what's supposed to be stock
1983 GS650GLD Front J19xMT1.85 with 90/90V19 (mine had 100/90v90)
Rear J16xMT2.75 with 130/90V16

spares I have
1982 GS650G Front J19xMT1.85 with 3.25H19
Rear J17xMT2.5 with 4.50V17
(manual says rear should be 4.25H17)

After putting air in, as all 4 leak, the spares look like they should be
off a chopper as front is really skinny and rear is fat in cross section
looking like it's too wide for rim.

No I haven't ridden bike yet as having trouble getting clear title,
original gas tank leaked and chemical patches did not hold. Replacement
tank from the GS650G will not fit as is about 1/2" too long and the
third one I have on order is from an 83 GS1100 and it has not arrived,
and not even sure it will fit. If it doesn't fit I get the original
welded in a shop. Until I can get a tank can't even get it running. Bet
by the time I do it will be ready for snow.

The spare wheels and tires were from a parts bike I bought with
intention of swapping front forks and dual disks/calipers to my bike.
Whether I swap rear wheel is immaterial, and I need to buy tires, once I
confirm engine runs. If there are engine problems can always put spare
one in! If all is OK sell the spares. PLUS if the bike is too tall for
me to sit on properly then I sell it. My 85 V45 Magna with a really
chopped seat was just the right height for my 30" inseam.

B-12 was talking about changing wheels inducing wobble. Not sure I
understand why. As long as the rake isn't changed and the tires are
proper size for the wheels what causes it? Based on road conditions
here, and an ageing back, I need maximum tread on the road. I used to
hate it when I rode 15 years ago and suddenly the freeway would be
grooved when cruising at 70 mph. Luckily they seem to have stopped that,
but then there also was the problem with the cracks being patched with
that tar that stays super slick. Just what I don't need.


Ian Singer


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See my homepage at http://www.iansinger.com
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I am near Toronto Canada, can I tell where you are from your reply?
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Think "unsprung weight", birdbrain.

 

If that was the *only* change done to the machine, it would slow the
steering down and make it feel slightly less precise.

If you install a slightly larger tire on the rear and make no change to
the front, the front tire has to work harder to stabilize the machine
in a vertical position. The machine will steer a little quicker, as the
rear end is lifted slightly higher.

As any rear tire wears to flatten the rear contour, the front tire has
to work harder to stabilize and steer the machine. It wears to a
V-shape. As the front tire becomes more V-shaped, the machine becauses
less stable. The critical speed at which speed weaves behin is reduced.

If you install a slightly smaller tire on the rear, with no changes to
the front, you may notice that the rear end feels like it's falling out
from under you in a corner. But the rear end is lowered slightly,
raking the forks out just a bit more and incrasing the trail. The
machine steers slower.

That was the look the Japanese manufacturers were trying to achieve
with their "L" and "Custom" models.

It's hard to describe to somebody what the changes in chandling would
be when you change tire sizes, but the above is pretty much what
happens.

You should know about the effect of rim width on tire contour, though.
If you install a new tire on a narrower rim than is optimum (according
to the charts on the manufacturer's website) the tire will "crown" as
the profile becomes too round and pointy. The machine will steer
quicker.

The reverse occurs when you install a tire on a rim that is too wide.
The steering slows down.

Maybe you can relocate the metal cups on the underside of the tank. The
mounting rubbers slide into those cups. The cups are just spot welded
onto the tank, but you would have to drill out the spot weld to get the
cups loose to move them. This might require a 90-degree drill motor and
a really short drill.

Another way might be to cut the metal thingumbobs that the rubber
mounts slip onto off the frame and reweld them an inch forward or so.
But you'd have to be sure the triple clamp and handlebars and other
controls wouldn't hit the gas tank at full lock.

A bodge to fix *that* problem, if it should occur, would be to make the
steering stops on the frame longer by welding a nut on the end.

Ted M. should not have read this far, he will need pyschological
counseling for traumatic stress if he has done so, as your Suzuki will
no longer be a collector's item. ;-)

I found a very rare 5-gallon gas tank for a 1960's Yamaha production
racer which predated Yamaha's very successful TD-1 series. It wouldn't
fit the YDS-3 frame I was planning to put it on, so I did surgery on
the frame, fabricating new rear gastank mounts and a new seat mount.
Nothing was going to stop me from having that beautiful gas tank on my
cafe racer...

Speed weaves are often called "speed wobbles". I have written
extensively about the subject in this NG, boring TOG terminally.
Basically, a speed weave is caused by the front tire not having enough
traction to steer and stabilize the machine. The rear tire is much
larger, and modern tires have no problem with having enough traction.

When I see chopper riders installing 10-inch wide tires on the back of
their machines and still keeping
a 3.00 X 21 front tire, I have to wonder what is wrong with those guys?
The motorcycle cannot have any high speed stability at all, and it
cannot turn a corner. All it "wants" to do, is go straight.

If a rear tire was wide enough and the RUB couldn't find 40 acres to
turn his hawg around, he'd have to whip out his cell phone and call his
mom and tell her he wasn't coming home...

You might want to investigate more compliant rubber compounds then, if
your riding style demands comfort, instead of control. I knew a guy who
had a business installing 1200cc big bore kits on 883 Sportsters. He
was using Conti "Blitz" tires because they had better road compliance.
He said that they were "cushy".

That's the tread compound making the tire more compliant. When you
start getting into compliant rubber, you have to look at the size of
the tread blocks and the depth of tread. If you need to ride in the
wet, you'll want deep groved tread and small blocks, but if your riding
is all dry pavement, such a tire would feel "wiggly" and it would wear
in strange ways that I have discussed at length elsewhere.

Google for "cupping".

If you can get to a motorcycle shop that has an assortment of tires and
the salesman doesn't jump right on you trying to sell you something,
anything, to get your money, you can *handle* the tires and get a sense
of which tires have a softer carcass.

Cruiser tires will have a more limber carcass, you can even mount some
of them with your bare hands.

Go ahead, ask me how I know that. There have been some Michelin tires
that had such limber cases, I could turn them inside out!

Of course, something like that will have no "run flat" capabilities at
all, and may even come off the rim in case of rapid deflation.

At the other extreme are sportbike and sport touring tires that have a
very stiff carcass. One tire that has both compliant rubber *and* a
stiff carcass is Bridgestone's popular BT-4 Battlax tire, which comes
in "H" and "V" speed ratings.

I have a "V" rated BT-45 on the rear of my old GSXR because it's the
cheapest tire of that size. The
tread blocks are too tall, and the rubber is too compliant so the tire
wiggles too much. But the carcass was so damned stiff I had to pay the
tire monkey at a motorcycle salvage yard $15 to mount it, using his
tire machine.

 

Canadian rock drummer and lyricist Neil Peart wrote a book called
"Ghost Rider" where he said that all Canadian roads were either "closed
for the winter" or "under construction". or something like that.

But highway comfort has a lot to do with setting up your front and rear
suspension sag properly.

I remember when I first learned what the suspension travel of my front
forks was. I thought that if I had a fork with 5.5 inches of travel, I
should set the preload adjusters so that the forks extended all the
way.

I thought that it was more important to maximum full suspension travel
over that ONE great big bump than it was to get compliance with the
MANY much smaller bumps the wheel was constantly encountering.

The conventional wisdom that I was ignoring was that the proper set up
involves setting the preload adjusters on the forks(if any exist at
all) and the rear shocks so that the weight of the motorcycle uses up
about 25% of the travel.

And, if your own weight is about is somewhere between 200 and 250
pounds, the combined weights of you and the motorcycle should make the
suspension sag somewhere between 1/3rd and 1/2 of the possible travel
of whicever suspension unit you're looking at.

This setup will give you a comfy ride, but the steering may seem
imprecise. I wrote a long screed called "Good Vibrations" over on
alt.motorcycle.sportbike a few years ago, and the only response I got
was something like, "This has to be a joke?".

Most riders have no clue about how suspension frequency affects
steering feel and rider confidence versus rider comfort.

A lot of front tires had a center groove that would interact badly with
grooves and section lines. Dunlop eliminated center grooves and
supplied tires with large diagonally transverse tread blocks in the
K291/391/491/591 series. That solved *one* problem, but the typically
stiff Dunlop carcass prevented the tread blocks from moving freely, and
the tires cupped and scalloped and then they wiggled...

Tar snakes are no fun. The nature of tar is that it is a supercooled
liquid. The surface hardens, but the
asphalt under the surface remains semiliquid at ordinary highway
temperatures (maybe as high as 140 degrees during the California
summertime) and the tar *shears* diagonally when a rider tries to
corner across a lar snake.

 

B-12 wrote:

France used to ue those damn grooves on their autoroutes. 'Rainurages',
they were called, and some bikes used to dance the hokey-cokey on them.
Haven't seen them for at least 20 years, though: I think the French
relaised they were a bad idea.

"Overbanding" we call this, in the UK. We don't have the problem of 140
dgeree heat (you'll be surprised to hear!) but we do have the problem
of rainwater on overbanding, which makes it slippery as all hell.

For this reason, there are very strict guidelines that road menders
must adhere to, covering total length of any single overbanding strip,
maximum permitted width, etc. Successful prosecutions and claims have
been made against local councils that broke the guidelines and caused
motorcyclists to crash.

 

Nice to know. I just bought an '83 GS450L . Yes, the one that had been
sitting. I've been running B12 in the gas, but I haven't ridden it enough
yet to get it completely clean. But it improves a little with each ride.

BTW, was this bike known as cold-blooded? Seems I have to leave the choke at
least partially on for several miles. Or is that just another manifestation
of the dirty carbs?

And as long as I'm asking questions, I read somewhere that all of the GS group
shared many common parts. Does anyone know of a website that covers these
equivalencies?

 

Never used to have a problem with set-up. I am too heavy and too lazy at
the moment and weigh 167 LB and am 5'6". So don't want bike flying on
its own or in the unlikely event it falls over when parked I need to be
able to pick it up.

When I used to ride V45 Magna front end would lift just enough to become
airborne and then torque a little. Maybe if I had adjusted the front
preload more, back too(?) that would not have happened.

I wanted to thank you yesterday for your detailed message on tires. It's
nice that you don't come across as too self important and egotistical.

Ian Singer



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See my homepage at http://www.iansinger.com
hosted on http://www.1and1.com/?k_id=10623894
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I am near Toronto Canada, can I tell where you are from your reply?
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You've been pointed to the gsresources.com?

--
Later,
John



'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk.

 

There is a guy on e-bay that advertises a CD thats supposed to be a
cross ref between models. Have not bought it.

I do know that gas tank, headlight shroud, turn signals, battery box,
rear tail light, rear wheel, rear tire, left handle bar control are NOT
the same between different GS models from 1982 and 1983.

Ian Singer

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I am near Toronto Canada, can I tell where you are from your reply?
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There are better ways to achieve anti-squat than spring preloading.
Unfortunately, the engineers haven't convinced the manufacturers that
we need anti-squat on UJM's.

Too much preload on the front springs will cause the front tire to be
less compliant,
it will lose traction and chatter across rough surfaces. This leads to
early onset of speed weave.

Heavy weight fork oil will do the same thing. It increases compression
damping too much.

If you increase the rear spring preload too much, the springs will kick
back after bumps. You can get a
rocking horse motion on the highway if your front and rear sag isn;t
set correctly for the speed you like to ride. I wrote about this
rocking horse effect in my "Good Vibrations" article on
alt.motorcycles.sportbike.

 

"Cold-blooded" motorcycles are like that because they are being starved
for idle mixture.

The spark plugs need to encounter mixture of a certain minimum richness
just to light the fire in the cylinder, and the EPA doesn't like
motorcycles that start easily and warm up quickly, because they pollute
the air while they are doing that.

The dirty carbs are affecting your performance to a certain extent.
But, the EPA clean air
regulations mandated that the idle mixture screws be set at the factory
and then sealed underneath an aluminum plug (on Suzukis, Yamaha uses
brass plugs).

The EPA anti-tamper plugs are probably underneath your carbs, forward
of the float bowls. But, they might also be on top, forward of the
vacuum chamber.

They can be removed by drilling a tiny pilot hole with a twist drill
held between your
fingers. After enlargening the hole to about 3/32nds of an inch, screw
a small sheet metal screw into the hole and pull the screw and plug out
with a pair of pliers.

Then you can set about the task of finding the original factory setting
of each idle mixture screw. Turn them CLOCKWISE until they just stop,
counting the turns and fractions of turns.

This might be anywhere between 1/8th of a turn and three full turns,
depending on the size of the idle jet. Then you can uncrews the screws,
making sure to save the small spring, washer, and tiny rubber o-ring
from the hole.

Then you can spray B-12 through the empty hole. Assuming you have the
carbs on the bench, you can cover two of the four orifices that the
spray should come out of with your fingers, to force the spray to come
out of the port that is plugged worst.

The idle mixture circuit is arranged so that air comes in through the
pilot air jet in the carburetor inlet. Fuel comes in through the idle
jet in the float bowl. They mix in a passage. Fuel air mixture can come
out into the mixing chamber downstream of the throttle butterfly
through a triangular pattern of three transition ports.

The throttle butterfly just covers half of the transition port that is
furthest downstream. The transition ports are very important and
mystifying to the amateur tuners. The transition ports are there to
give the engine just a bit more fuel when the throttle is cracked open.

But, if the amateur tuner misunderstands the fact that the idle mixture
screw only controls ONE of the FOUR idle mixture outlet ports, he will
turn the idle mixture screw too far out, expecting the idle RPM to
follow the turning of that screw.

So the amateur tuner gets the idle mixture screw open too far, and the
idle RPM actually DROPS because the mixture is so rich. So he adjusts
the master idle knob to increase the idle RPM back to what the manual
specifies.

Then, when the tuner twists the throttle and releases it, expecting
engine RPM to follow the throttle, he is surprised to discover that the
idle RPM hangs up around 4000 to 5000 RPM.

That's because the transition ports are uncovered too soon by the open
throttle butterflies.

To solve your cold blooded running, you only need to open the idle
mixture screws about 1/8th to 1/4th of a turn more than they were open
when the carbs were sealed at the factory. So, reinstall the idle
mixture screws by screwing them in until they just stop, and then
screwing them back out to however many turns they were originally
screwed out, plus 1/8th or 1/4th of a turn.

 

*Splutter*

Nice bikes in their own humble way, but for ****'s sake, get real.

 

I should clarify my remarks about the GS-450. I didn't mean that they
would outrun an XS-1100 between the French riviera and the Chunnel.

They amazed me on Willow Springs, where they could run flat out almost
everywhere and actually walk away from me on my GS-1100EZ.

Willow Spring was called "The Fastest Track In the West" even back in
the days when
GS-450's were a popular racing class...

Google up a track map, if you care.

The western half of the track is called the "slow" half. You can get
away with doing only 120 mph around the omega-shaped Turn 2. But the
east side is the fast side. Nowadays, you have to run 140 mph through
Turn 8 to Turn 9, or you will get passed before the 115 mph Turn 9.

It doesn't matter that your machine will go 150 mph down the 1/2 mile
long front straight.

It's what you do from Turn 6 thru the slight bend of Turn 7 and through
Turn 8 to Turn 9
to get onto that front straight that makes your lap times drop down to
1:30.

Ignore the fact that a fierce cross wind comes up in the afternoon and
tries to push you off the track. Professional racers and
motojournalists say that you have to develop "wind balls" to get around
Turn 9 without fear.

But, the Willow wind respects nobody, it tosses them all around...

Back in the mid 1980's, a well-ridden GS-450 could circulate the track
in the 1:45 range, and they were getting away from my powerful but
wobbly GS-1100...

 

I rode one to the bike show in Germany in 1986, and then on down to the
South of France for the Bol d'Or, and then back to the UK. A 2000-mile
round trip. I must say it bashed along at 80+ all day quite happily.
Nice torquey little engine.

I never knew they raced them, mind. A bit like racing cruisers, IMHO.

 

The GS-450L was a cruiser. It didn't handle well becasue the rear wheel
was too large.

But the GS-450 with normal sized wheels formed the basis for a popular
box stock racing class.

However, box stock racing in the early 1980's didn't live up to my GP
imagination.
I thought that a racebike should alternate between high dB screaming
and 2-stroke cackling. I had a yearning for a TZ-250 or a TZ-350 but
didn't know how to get one on a limited budget.

When I saw the the hoardes of GS-450's and GPZ=550's circulating Willow
Springs in muffled silence, I thought of them as electric utility
bikes. I didn't gain respect for the unpretentious middle class box
stock machines until they humbled my 1100, even in the higher speed
portions of the racecourse.

One of the GS-450 racers I knew bought the first Ducati 851 that I ever
saw. He just had to bring it to the Griffith Observatory to try it out
on the twisty park roads and show it off to the gang, but a motorist
did an unexpected U-turn in front of him and his $12K Duc was wrecked
the very first day.

 

Just took a quick look - looks good. Thanks.