Davis criterium, it's hot, hot, hot. The pace is fast and the corners tight. Inevitably some riders are going to have problems due to poorly glued tires, happens every year. What can you do to insure that your sew-up tires stay glued when the mercury rises?
There is no one cause of poor tire-rim adhesion so let's start at the beginning, new rims and tires. Most rims are shipped with a coating of anti-corrosive substances that closely resemble grease. This has to be thoroughly removed with solvent and a clean rag before you can put down the initial layer of glue. After cleaning put a thin coat of glue all the way around new rims and leave them to dry for at least 12 hours.
While this glue is drying you might check your tires for any latex covering the base tape. If there is any latex whatsoever give it a good roughing up with coarse sandpaper before coating it with a thin layer of glue. You shouldn't normally apply glue directly to the tire unless its base tape is non-porous or coated with latex. This glue should be left to dry for a few hours. If you're a light rider or don't plan on doing any hard cornering on hot days you can usually leave out this step but always roughen any latex found on base tape.
After the base coat of glue has dried it's time for the adhesive layer. This should be thicker than the first layer but not so thick that it can squeeze out and get on tire sidewalls. Glue is like solder in that you only need enough to fill the gap. More glue than that can actually be less adhesive. Let this layer set for 10 to 30 minutes before mounting the tire. You'll know it's too long if the glue doesn't set. Be sure not to mount the tire too soon after applying adhesive, however, as the evaporative vapors could compromise your base tape's glue.
New tires usually need a good stretching before they will go onto the rim without tending to roll and get glue on the sidewalls. To stretch a tubular route it around both feet and knees then pull up with your hands while pushing out with your knees. Pull the stiffness out of a new tire for a few moments or mount it on an old rim for a few hours. You might want to try mounting the tire on a dry rim first to see just how much stretching it will need.
Finally, mount the tire beginning at the valve and stretch it in both directions until there are only 4 to 6 inches remaining. To get this last section of tire onto the rim without smearing glue grab what's left and lift it away from and over the rim. This can be difficult if the tire isn't adequately stretched beforehand.
When using traditional sew-up glue wait at least 12 hours before doing serious cornering. If you need to race right away try shellacking the tire to the rim. In all cases spread the glue evenly over the surface of the rim using the tube itself or a brush (no fingers please, these are petrochemicals with toluene and other unhealthy ingredients).
Some glues work better than others in heat. Wolber tends to do better than Clement or Vittoria in hot weather whereas Tubasti is only recommend for cold conditions. Continential and Hutchinson glues are not recommend at all. 3M Fast-Tac, a popular choice years ago, is no longer recommended since its latest formulations are water soluble! Other 3M adhesives are not appropriate for this application.
On rare occasions, after years of use, a rim will need to have layers of older glue removed. The best tool for this job is a screwdriver or small carpenter's chisel.
It is important to note that even in warm weather tubular glue is rarely a factor in rolled tires. Glue does, however, prevent tubulars from rolling to one side and bunching up at the valve. When a tire does come off the rim 9 times out of 10 it is due to some unusual sideways force such as that caused by high-siding. Any reasonably tight tire needs very little adhesion for even the hardest cornering.
Be careful that whatever glue you use has not separated in its tube. If it has, take a spoke and stir it well. I have also heard of mixing different glues before application, however, this can yield unpredictable results. Traditional tubular glues will re-adhere tire and rim through 3 or 4 changes. Racing tires though, should be reglued when changed. Base tapes can also come apart from the tire in hot weather and underinflation can cause poor adhesion as well. Check these things as well as the tread for wear or cuts before every race and you'll be able to descend and corner with confidence.
Roger Marquis (www.roble.net/marquis)