When it comes to flat tires on the road
with a motorcycle, I have been luckier than I deserve. I started
riding again more than 16 years ago and, until the summer of 2019, I hadn't had
a flat. Its a good thing too. Almost all of my miles have been on
dirt bike, spoke rims with street tires with tubes in the tires. To be honest, I don't think I could
remove and patch a tube on the side of the road. These stiff road
tires on these narrow dirt bike rims make dismounting and mounting a
tire into about a half day of hard work in the shop. Nearly
impossible on the side of the road.
Realizing that I was pushing my luck,
this season I converted the spoke wheels on my KTM to “tubeless”
by sealing the spokes with a special 3M sealant tape. You might say
that the universe wanted me to practice my tire plug skills by giving
me a drywall screw in the rear tire on the first trip I took after going tubeless. And it did take some practice. My first attempt leaked some air, so I ended up plugging it again on
side of the road the next day. That one held long enough for me to complete the ride and ride the 500 miles home.
With my new interest in plugging
motorcycle tires, I discussed the subject with other riders and got a
range of opinions on the reliability of a plugged motorcycle tire. Riding home, I
started wondering what the expert opinion of plugging a motorcycle
tire might be. And then I remembered that I knew an expert or two
that I could ask.
I will tell you up front that, based on
my car experience, I was a proponent of plugging tires. I
assumed that, like a car tire, a well executed tire plug could last
the life of the tire.
When I got home, I got online and found
Dunlop's position on plugging tires. They say never
use a plug alone to patch a tire and the only acceptable repair is a
“plug/patch”.
My next stop
was to email my friend, Frank. Frank is a retired tire designer of
great expertise. Frank was the father of the original BFG Comp TA
and spent time at BFG, Michelin, Dunlop, and Kumho.
Frank's response was that a motorcycle
and a car tire are very different things. He pointed out that the
tread of a motorcycle tire does a lot of stretching and compressing
because of the curved crown of the tread. This means that it is much
easier for a plug to come out of a motorcycle tire, even when
properly installed. His advice was to get the plugged tire off the
bike as soon as possible. Now that's a little scary.
To be frank, I'm still going to use
plugs as an emergency road side fix, but I'm also going to be careful
of the stress that I put on a plugged tire and get it off the bike as
soon as I get home.
I thought it would be interesting to
look at the differences in tire construction between a motorcycle and
a car tire. There are 2 cut-away sketches of the inside construction
of a typical car and motorcycle tire shown below. The casing or body
ply of the tire is almost the same in a motorcycle and a car. Cords
run straight across from one bead to the other. The car tire shape
is flatter in the tread area, but otherwise similar. Both these
tires are radial ply.
The big difference comes in the belt.
The car has two belts (usually steel) that form a cross hatch because
of their cord angles. That structure is really strong, even when
punctured, and a car tire plug can often live the life of the tire.
On the other hand, the typical
motorcycle tire belt is a single cord that is wrapped around the
circumference of the tread. When punctured, the belt cord is cut and
can pull away from the hole. Also, as the tire rolls through the
contact patch, the belt compresses, then stretches making the loss of
a plug possible. As you can imagine, high speed and high load are
likely to make this situation worse.
So take it from a convert. If you have
to plug your tire along the way, take it a bit easy and keep close
track of the tire pressure. Then get that tire off the bike as soon
as you can.
Attribution - the cut-away sketches
were borrowed from Google Images with the motorcycle tire from
bareasschoppers.com and the car tire from overdrive.in. The picture of the rider with a flat on the side of the road is from roadrunner travel magazine.
Southern Grace and Manners
My last trip of this season was down to western Virginia, a favorite area for me. Once again, I had a puncture in my rear tire. Before the trip, I had installed a tire pressure monitor and it worked. I looked at the display and found a flashing red light with a rear tire pressure displayed at 19 psi.
I was up in the mountains in a National Forest with no cell signal and very little traffic, but I had the tools to plug the tire and inflate, so it was no worries. I was lucky to find a wide, shaded pull out on the side of the road and began fixing the tire. Part way through the process, a car pulled up and sat behind me watching me work. When it was clear that I was able to fix the tire and was starting to put away tools, the car approached with an older couple inside. The lady on the right put down her window and said, "sorry for your troubles" as they rolled back to the highway. It turns out that they had stopped and waited, just in case I needed some help. Now that is friendly.
A Funny Flat Story
This is a short but true story about
plugging motorcycle tires. A friend of mine vacationed in Cuba last
winter, including 2 weeks exploring with a guide and a rented
motorcycle.
It turns out that it was the season for
crabs to come out of the ocean and lay their eggs on the shore. My
friend and his guide came across the place where the crabs were
crossing the road and there were so many that they couldn't avoid
hitting a few of them. The crabs claws were so sharp that my friends
front tire was punctured and they had to try and find a repair place
nearby.
A motorcycle repair shop was found, but
the mechanic was out of tire plugs. Not to worry, he had a ready
solution. It turns out that condom is a useful replacement for the
traditional tire plug. The condom plug lasted the rest of the trip.
