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By Bayouboy 05/2005
Part1 - Tyre removal
Part2 - Fitting new
tyres
I start every new tire mounting job the same way. Once the old tire
has been removed from the wheel I thoroughly clean the wheel. Then I
carefully inspect the tire bead sealing surfaces for any defects
which might cause air to slowly leak from the tire. Finally I mount
the wheel on my tire changing station. (see Part1)
We all know that new tires are slippery and you have to be careful
on them until they get “scrubbed in”
I give my new tires a quick
scrubbing in the bath tub using dish detergent and a fabric pot
scrubber from the kitchen sink. This topic has come up before and
some folks will think this is silly but I’m sold on it. We’ve all
heard stories of bikes going down with freshly mounted new tires. It
always seems to happen the same way: forget to take it easy and used
the “normal” amount of throttle while making a turn after starting
from a stop. The back tire looses friction with the road and kicks
out in the middle of the turn and the bike goes down. This almost
happened to me once right after I put on a new set of Dunlop D208s.
Luckily I was able to muscle the bike back up and very luckily no
one was coming the other way or I would have been toast.
(AndyW: 'Scrubbing in' - 50 to 100 miles of reasonably gentle riding
gradually increasing lean angles in corners and throttle use . New
tyres are covered in the remnants of a 'greasy' substance, a release
agent, used in the manufacturing process to make it easier to remove
the tyres from the moulds. I also clean new tyres before use and so
recommend Mark's advice.)
It only takes about 10 minutes to wash the tire and when you take
your first ride on it, it will feel like a tire that has about 50
miles on it. The difference in feel between a washed and unwashed
new tire is “very significant”. I’ll venture a guess that something
like 90% of the bikes that have gown down on their maiden voyage
with freshly mounted tires would not have if those tires had been
washed before mounting. That’s enough motivation for me to spend the
extra ten minutes. Note........it's still recommended to show
care for a few miles as the 'release agent' does contaminate the
surface rubber of the tire and tires are not at their best for grip
until the surface is 'ruffed' up.
One of the techniques that helps a lot in mounting the new tire is
to warm it up a bit before you start. This will do two things for
you: 1) it will slightly expand the steel belts that are located
inside the tire beads and 2) it will make the rubber a little more
flexible. Both of these things make it easier to get the tire on the
rim
If you’re a racer and you’ve got a tire warmer you’re all set, I’m
not so I use a heat gun (take care and don't use a heat source that
might over-heat or burn the tire!). Most good tool and home
improvement stores have heat guns. First I sweep an area of the
garage floor then position the tire on the floor and put the heat
gun in the middle. I position the heat gun so the nozzle is as far
away from the tire as possible and set it to low heat. Then every
two or three minutes I reposition the gun rotating the spot the heat
is aimed at by 90 degrees. I do this for two complete revolutions of
the gun, which takes about 20 minutes. By then the tire is pretty
hot. You can easily pick up the tire bare handed without getting
burned but if you tried to hold if for any length of time it would
get “uncomfortable”.
Once the tire is warm we are almost ready to place it on the wheel
rim and begin the mounting process. There are two issues regarding
the proper alignment of the tire with respect to the wheel that must
be observed. The first is the rotational direction. Many tire tread
patterns are directional. That is they work better at removing water
from under the tire when the tire spins in one direction as opposed
to the other. Hence many tires have an arrow on their side wall that
indicates the preferred rotational direction. Most wheel rims also
have an arrow indicating the rotational direction. You must make
sure the arrows on the tire and wheel rim point in the same
direction. The second thing you want to be sure to do is to position
the tire on the wheel rim so that the lightest part of the tire is
aligned with the heaviest part of the wheel rim. This situation
requires the minimum amount of balancing weights to be added to the
wheel later on. Pirelli uses two red dots while Dunlop uses one
yellow dot to mark the tire’s light spot. I don’t know about other
tire manufacturers but their web sites probably have this
information.
You will need some type of lubricant to help the tire beads slide
over the wheel rims. I use commercial tire mount lube/seal spray but
soapy water works fine also. I would recommend that newbies use
soapy water for their first couple tire changes because it stays
slippery for a long time. The commercial stuff is slippery for about
10 minutes then it starts getting tacky. Lubricate both tire beads
and push the tire down onto the rim. The first bead goes on easily
without the need for any tools. Then push part of the second bead
under the wheel rim and put on a Bead Buddy. A Bead Buddy is simply
a small C-clamp with a tail. It creates a barrier that prevents any
of the tire bead that you’ve succeeded in getting under the wheel
rim from popping back up while your working on a different section
of the tire. If you have a friend who is going to help you mount the
tire then you won’t need a Bead Buddy, your friend can do the same
job by holding a tire iron steady while you work other tire irons
around the circumference of the tire.
(a) Wheel rim protectors (b) Bead Buddy
(c), (d) & (e) Tire iron (tyre levers)
After you’ve got the Bead Buddy in place clip on a few rim
protectors - NB: I place a small coin covered in Duct tape under the
end of the Bead Buddy bolt so the wheel rim doesn't get marked. I tie string to my rim protectors to help recover them
if they fall off the rim and end up inside the tire. Slide the rim
protector away from the Bead Buddy as far as it will go. This will
be where we start using the tire irons.
When you get your first bit of tire bead under the lip of the rim
using the tire irons put on another Bead Buddy. Now it’s simply a
matter of working your way around the circumference of the tire. Be
patient, work slow and steady. At this point I place a couple rubber
stoppers in between the wheel rim and the tire bead. As I mentioned
in the section on getting the old tire off this is a crucial step.
This forces the part of the tire bead that you already have under
the wheel rim into the center part of the wheel where the
circumference is less. This makes it much easier to get the rest of
the tire on with the tire irons. Previously I used a twisted up
towel for this but that is not a good idea. Once when removing an
old tire I found some fabric fibers from the towel on the wheel rim.
Any debris on the sealing surface is bad as it might contribute to a
leak. So I switched to the rubber stoppers so I would be sure to
leave nothing behind.
When you get a new section of the tire on, reposition the Bead Buddy
and slide the rim protector over and continue. When you get close to
being finished always make sure the two rubber stoppers are
approximately centered across the wheel from the part you are trying
to lever under the rim. It’s the part of the tire directly across
from where you are working that you need to force into the center of
the rim. Before too long you’ll have the tire on the wheel.
Then you need to seat the beads with high pressure air. First
replace the valve core, I always put in a new one since they’re
pretty cheap, but you could probably reuse the one you took out. I
use a delivery pressure of 60 PSI which works fine on the Pirelli
Diablos. But its not just the pressure that matters you need to be
able to deliver a decent volumetric flow rate of air or you won’t be
able to seat the beads. A hand pump might not do the job. Before I
got a compressor I used to take the wheel to a gas station and use
the compressed air there. I’m not sure what pressure the tire
actually sees during the bead seating process. I always have to add
more air to the wheel to get the recommended 36 PSI after both beads
seat.
The last thing we need to do before putting the wheel back on the
motorcycle is balance it. This is a fairly simple but time consuming
process. As I said earlier when positioning the tire on the wheel we
want to align the lightest part of the tire, which is marked, with
the heaviest part of the wheel. Usually but not always, the heaviest
part of the wheel is where the valve stem is located. This makes
sense as the valve stem usually weighs more than the metal removed
to make the hole for it. Therefore if you're going to change your
own tires one thing you should do early on is determine where the
heavy spot is on both of your wheels. Make sure you do this with the
brake rotors and sprocket attached.
Finding the heavy spot is also the first thing you do to the wheel
with a mounted tire when balancing. As I said above I use a static
wheel balancer for balancing the wheel. This is a simple device
consisting of two pairs of low friction roller bearings attached to
a supporting frame. It’s a good idea to level the wheel balancer in
the axle direction before you start. One simply places the wheel on
its axle and then rests the axle on the roller bearings. The wheel
and axle can now rotate almost freely. The theory being that if you
give the wheel a nudge it should come to rest with the heaviest part
at the bottom. Repeat a few times to be sure. When the wheel is
balanced there should be no preferred resting spot so the wheel
should stop at random locations.
We need to find the heavy spot first so we can add our balancing
weights to the opposite side. If the wheel is quite far out of
balance then finding the heavy spot is easy as the wheel will always
come to rest with the same spot at the bottom. If the wheel is only
slightly out of balance then it’s much more difficult to find the
heavy spot. In this case many spins are needed and you’ll need to
keep track of all the resting positions so you can take an average.
I set up my wheel balancer near the computer and I keep track of
what’s happening by placing dots around the circumference of a
circle in Photoshop (pencil and paper will work fine though!). When
finding the heavy spot the dots represent the position of the valve
stem when the wheel comes to rest. After I add some balancing weight
to the wheel the dots represent the position of the weights when the
wheel comes to rest. If the wheel stops at the same place as before
I place another dot along an imaginary line that connects the first
dot with the center of the circle. Here’s a pic of the data I got
before adding any weights. The data shows that every time I spun the
wheel it stopped in about the same place making it easy to identify
the heavy spot.
Now it’s simply a matter of determining what is the proper amount of
balancing weight to put on the wheel. As you get closer and closer
to the correct weight it gets harder and harder to tell what’s going
on so more spins are needed. I use a minimum of 20 spins when I get
close. The only time I would spin less than that is when it’s
obvious that the added weight is too little or too much. Finally
when I think I have the proper weight determined I always get two
additional sets of data with plus and minus two grams. This is a
final verification check I use as if I have correctly determined the
weight needed both of these data sets will show worse balance.
When you spin the wheel use different amounts of force. I try to get
data with 1, 2 and 3 rotations of the wheel mixing these up at
random while I collect data. If you always push the wheel the same
amount of force you would get crappy results. When you’re in the
stage of determining what the proper weight should be don’t stick
the weights on with the sticky back adhesive they come with. I use
scotch tape. Only use the included adhesive after you have
determined the correct weight and are sticking the weights on
permanently
As you can see balancing a wheel this way is a time consuming
process. I recommend doing it when you’re not in a rush to go ride
the bike. I always do it at night while I’m watching TV or using the
computer.
Here’s a few more sets of data, I ended up going with 14 g. You can
see that with 14 g the rest position of the weight is distributed
pretty well around the circle. With 12 g there is a clear bias for
positions at the top meaning the weight is too little. Finally with
16g there is a clear bias for the weight ending up at the bottom
indicating too much weight.
**Disclaimer!**
Properly installed tires are an absolute necessity on a motorcycle.
Your bike's tires can make the difference between life and death.
Just because I chose to do the work myself does not mean you should.
If you have any doubt about your ability to change your tires
properly, get a professional to do the job for you. In the
discussion above I describe the method I use to change my tires. I
make no claims that this is the best way or the only way, it is
simply the way I do it. I cannot accept any liability for the
outcome of any error or omission in these guidance notes nor your
misinterpretation of them.
Bayouboy May2005
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