Engineering types... check my work!

I did a time trial with my college team this past weekend. The location is
11 miles away, and during the ride there, I got 2 flats! I managed to get
enough air in the two wheels, and managed to get there in time to do the TT
before everyone left. I ran a 20:19 for the 7-mile course, which was a lot
better than the 22:00 I had gotten the last time I tried it. It wasn't
until I got home and discovered that my tires were only inflated to 30F/35R
that I realized I could have broken 20 minutes. Oh well.

So I pumped up the tires to 120 later that night, and within a few minutes,
psssssssss. The 3-mm slit the glass made in the tire tread was too big for
the tube. So I cut out some water bottle and used duct tape for a boot.
Works well.

Today in class I was mulling over whether I should repair it, not because
I'm worried about the tire failing in the future, but whether I could
actually sew the casing back together. Then I thought about the kind of
tension the thread would be under if I sewed it. I remembered that I have
some Kevlar thread from a digital camera fix a year ago, and it was rated at
25lbs. I did some calculations he

http://plaza.ufl.edu/phillee/tireslit.jpg

and determined that I would need one thread to hold at least 14.5 lbs to
keep the tire closed, given a 3mm slit parallel to the direction of travel
in the center of the tread of a 23mm road tire at 120psi.

Ignoring gross uncertainties such as actual tire size, the fact that the
slit isn't so much parallel as diagonal to the tread, am I anywhere near a
correct answer?

Ignore the secant and bisection methods in the picture... that was class
notes. The FBD in the bottom right of the pic is the pressure distribution
perpendicular to the tread. I wasn't sure how to calculate it though.

--
Phil, Squid-in-Training

Search "hoop stress".

"Phil, Squid-in-Training" wrote
in message . ..

So I pumped up the tires to 120 later that night, and within a few
minutes, psssssssss. The 3-mm slit the glass made in the tire tread
was too big for the tube. So I cut out some water bottle and used
duct tape for a boot. Works well.

tension from hoop stress is pr (lb/inch)
for a 7/8 inch wide tire at 120 psi this will be 120 x .44 = 53 lb/inch
for a 1/8 (3 mm) width the tension is 53/8 = ~ 7 lb

Phil H

Phil, Squid-in-Training wrote:

I did a time trial with my college team this past weekend. The location is
11 miles away, and during the ride there, I got 2 flats! I managed to get
enough air in the two wheels, and managed to get there in time to do the TT
before everyone left. I ran a 20:19 for the 7-mile course, which was a lot
better than the 22:00 I had gotten the last time I tried it. It wasn't
until I got home and discovered that my tires were only inflated to 30F/35R
that I realized I could have broken 20 minutes. Oh well.

So I pumped up the tires to 120 later that night, and within a few minutes,
psssssssss. The 3-mm slit the glass made in the tire tread was too big for
the tube. So I cut out some water bottle and used duct tape for a boot.
Works well.

Today in class I was mulling over whether I should repair it, not because
I'm worried about the tire failing in the future, but whether I could
actually sew the casing back together. Then I thought about the kind of
tension the thread would be under if I sewed it. I remembered that I have
some Kevlar thread from a digital camera fix a year ago, and it was rated at
25lbs. I did some calculations he

http://plaza.ufl.edu/phillee/tireslit.jpg

and determined that I would need one thread to hold at least 14.5 lbs to
keep the tire closed, given a 3mm slit parallel to the direction of travel
in the center of the tread of a 23mm road tire at 120psi.

Ignoring gross uncertainties such as actual tire size, the fact that the
slit isn't so much parallel as diagonal to the tread, am I anywhere near a
correct answer?

Can't help you with the thread tension, but put in several stitches with
anything as strong as dental floss or stronger, and the threads won't
break. The bigger concern is whether they will pull out of the casing
cord. Make sure to engage several cords on both sides of the cut with
each stitch.

If you're using ultralight tubes, stick an inner tube patch over the
stitches to avoid abrading the tube (not sure if this is necessary, but
it won't hurt).

Have fun with your thread tension calculation.

Mark Janeba

Phil, Squid-in-Training wrote:

So I pumped up the tires to 120 later that night, and within a few minutes,
psssssssss. The 3-mm slit the glass made in the tire tread was too big for
the tube. So I cut out some water bottle and used duct tape for a boot.
Works well.

It should. The thickness of a PET strip from a bottle is overkill.

What I thought about a while ago would be strips of Kapton with a really
good adhesive to glue into the inside of the tire. Kapton is a
lightweight, high strength plastic. It's expensive if you buy a pound
of it (waaay back in 1985 it cost $75/pound) but if you only have a few
strips of 2 or 5 mil Kapton, plus adhesive, it shouldn't be terribly
expensive.

Sewing up the slit in the tire should be belt-and-suspenders. Use silk
thread, maybe. It's really strong.

--
BMO

"Boyle M. Owl" wrote in message
news:R_JFd.26857$jn.2417@lakeread06...
Phil, Squid-in-Training wrote:

So I pumped up the tires to 120 later that night, and within a few
minutes, psssssssss. The 3-mm slit the glass made in the tire tread was
too big for the tube. So I cut out some water bottle and used duct tape
for a boot. Works well.

It should. The thickness of a PET strip from a bottle is overkill.

What I thought about a while ago would be strips of Kapton with a really
good adhesive to glue into the inside of the tire. Kapton is a
lightweight, high strength plastic. It's expensive if you buy a pound of
it (waaay back in 1985 it cost $75/pound) but if you only have a few
strips of 2 or 5 mil Kapton, plus adhesive, it shouldn't be terribly
expensive.

Sewing up the slit in the tire should be belt-and-suspenders. Use silk
thread, maybe. It's really strong.

I used one of the really cheap house-brand plastic bottles that are much
thinner than bottles from Dasani, Zephyrhills, etc.

I've split open a Park tire boot before... I didn't want to take any
chances.

--
Phil, Squid-in-Training

On Fri, 14 Jan 2005 01:36:04 GMT, "Phil, Squid-in-Training"
wrote:

Ignoring gross uncertainties such as actual tire size, the fact that the
slit isn't so much parallel as diagonal to the tread, am I anywhere near a
correct answer?

I can't say, but here's something to consider...

Some of the tubeless tire makers are recommending a variety of
cyanoacrylate adhesive as the repair method for punctures in their
products. By extrapolation, using the adhesive might be a reasonable
addition to the stitching. I have seen a couple of small cuts
stitched up in tires that were either expensive or hard to get under
the circumstances, with mixed results. The thread gets worn off on
the outside if the sewn area is in the tread region, breaking the
stitches in the process; the adhesive might help to keep the repair
together.

I suspect that while it may be possible to repair the tire well enough
to get it to work for some period of time, the chances are good that
any repair will fall short of an undamaged tire's durability. It's
just something to keep in mind when balancing effort versus cost and
results.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

"Werehatrack" wrote in message
...
On Fri, 14 Jan 2005 01:36:04 GMT, "Phil, Squid-in-Training"
wrote:

Ignoring gross uncertainties such as actual tire size, the fact that the
slit isn't so much parallel as diagonal to the tread, am I anywhere near a
correct answer?

I can't say, but here's something to consider...

Some of the tubeless tire makers are recommending a variety of
cyanoacrylate adhesive as the repair method for punctures in their
products. By extrapolation, using the adhesive might be a reasonable
addition to the stitching. I have seen a couple of small cuts
stitched up in tires that were either expensive or hard to get under
the circumstances, with mixed results. The thread gets worn off on
the outside if the sewn area is in the tread region, breaking the
stitches in the process; the adhesive might help to keep the repair
together.

I thought CA was extremely brittle and would fracture under stress.

I suspect that while it may be possible to repair the tire well enough
to get it to work for some period of time, the chances are good that
any repair will fall short of an undamaged tire's durability. It's
just something to keep in mind when balancing effort versus cost and
results.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

I suspect that while it may be possible to repair the tire well enough
to get it to work for some period of time, the chances are good that
any repair will fall short of an undamaged tire's durability. It's
just something to keep in mind when balancing effort versus cost and
results.

Sent post off too early:

This bike is my road racing bike and commuter bike. Old GT Edge with old
105 group. Handbuilt ME14A with spokes from a customer's tacoed wheel.
Cost me $250.

So yes, it's worth the effort

--
Phil, Squid-in-Training

Phil, Squid-in-Training wrote:

I thought CA was extremely brittle and would fracture under stress.

Yeah, but the weather's hard to beat.