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July 05, 2016 1 Comment
Removing tubular tires should be easy. Getting the tire off the rim should not require gorilla strength.
Over the past few years a new issue has arisen. Pulling tubular tires from carbon fiber rims can cause delamination of the rim bed. Creepy, to say the least. Is this normal? What is going on? What to do?
Carbon delamination - please, no!
No carbon rim maker wants to hear about structural delamination during tire removal. Every design effort is made so it cannot happen, as it is impossible with aluminum rims. We all have the same objectives. Under normal circumstances, the inter-laminar carbon layup strength is greater than contact cement on the surface.
Is the delamination important?
Plies (layers) of carbon cloth are extremely thin. Departure of several plies is visually dramatic but may not be a structural problem. It all depends on the design. The rim maker is your only reference. Hopefully, the departed plies are sacrificial, intended to be rugged and expendable.
Gluing is improving
We are seeing a growing appreciation for tire gluing integrity. More than ever, mechanics are using best practice for achieving strong bonds. In the past, when glue integrity was mainly a concern for high level road racing, technique could be less rigorous. Cyclocross, in particular, sees weird rim-to-tire combinations (where bed and tire form do not closely match), suffers water contamination (weakening bonds), and uses very low tire pressure (lower pressure = less tire grip to assist the glue). CX gluers are doing really good bonding.
How to minimize risk when removing a tubular
First, deflate the tire. Air pressure makes the tire grip the rim. Not enough grip to ride without glue but enough to interfere with removal.
You'll then need a narrow pry tool, such as a slotted end screwdriver, to push into the glue and separate the tire from the rim. Your goal is to push the screwdriver (or equivalent) all the way through between tire and rim, from one side to the other. A steel tool like this can damage the rim or the tire. Use it gently, pushing carefully, wriggling small amounts, separating the tire from the rim in tiny bites.
Once you achieve tool insertion, replace the slotted (sharp end) screwdriver with a round, Phillips type. My best luck is with a blade about 6mm (1/4") in diameter. A larger diameter dowel works but the rim and tire prefer the small steel shape. While seated, place the wheel between your legs, with the screwdriver handle in your dominant hand. I am right handed, so here the screwdriver handle is on the right.
Orient the wheel so the screwdriver is at the top. Pull the driver towards you with both hands while you rotate it clockwise (viewed from the right side). Pulling while rotating advances the blade towards you, rolling against the sticky tire bed and skidding against the smoother rim.
This rolling requires a strong turning hand (right for right handers) and a firm pull on both sides. The tire bond is no equal for this rotation. The tire will begin to separate from the rim as you pull and rotate.
You can also use a dowel but the screwdriver blade offers less resistance and a better separation angle. The glue joint is more susceptible to the small radius of the metal driver.
You're inducing a glue joint failure and the angle of separation is better for the small rotating blade than a larger rotating dowel. We're inducing a cohesive failure with glue remnant on both rim and tire, handy for future gluing.
As soon as enough tire is separated, pull the tire from the rim. Pull in the plane of the wheel so the tire is doubled over as it leaves the rim. This minimizes base tape separation as you pull it from the rim.
Back to our carbon rim problem, Using the small diameter metal rod induces cohesive failure and minimizes the chance of rim delamination. The final tire removal (over 50% of the circumference) is done without the metal rod, just arm strength. Doubling back the tire as it peels reduces delamination forces.
More than a few mechanics note that heat aids tire removal. At 70C (160F) rim cement is liquified. At 40C (100F) cement is substantially weaker than on a cool day. Using a heat gun to warm is impractical. A wheel is large and sheds heat. At least appreciate this principle and let wheels come to the highest available temperature before pulling tires.
Throughout tire removal, proceed slowly and watch the tire carefully. Stop if anything does not proceed smoothly. Some tires will disintegrate upon removal but it's rare except for limited use track tires.
There is much to tire mounting that you must know. Demounting is not the opposite of mounting. Great instructions are available in many places: mine (here and here), Calvin's, and Chip Howat's scholarly works, among others. Gluing tires is done thousands of times a day and each job carries immense responsibility for rider safety. Learn your stuff and be part of the reason cycling is known as a healthy sport.
As ever, practice is the best teacher. Try different techniques, pester experts with questions, listen to all opinions, and develop dependable techniques. There are too few tubular gluing guru's. Please join this club!
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