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October 01, 2014 6 Comments
Twice reminded of a very important but often overlooked subject: first reminder - mention on the Classic Rendezvous group of a recent instructional video about mounting tubular tires by Rhys Bateman (courtesy of hackcycling). Second bell-ringer - the upcoming USAC Mechanics Clinic (sold out but there’s always 2015).
Why these, why now? Glued on tubular tires were the original pneumatic tire. But 30 years ago, they all but died out except for high level racing. Clincher tires became standard and, despite numerous issues, none include adhesives. With this switch came a broad amnesia among riders and mechanics about vital tire gluing rules.
End of story except tubulars staged a stunning comeback powered by the carbon rim. Making light, inexpensive, and safe carbon clinchers is elusive. A tubular carbon is not. The weight and aerodynamic benefits of carbon (not to mention marketing bling) pushed tubulars back into the market (they never waned among professional racers). But there is a scarcity of knowledge about mounting them.
Most of us never have the opportunity to learn from mechanics of high level teams about rules for gluing. One of the single most important missions of the annual Mechanics Clinic is instilling a combination of fear and expertise into attendees about tubular gluing. The techniques they learn from others, read from product box tops and glue containers, may work locally but actually be dangerous under many conditions. If tubular riding customers are mostly triathletes (less descending and extreme cornering) or track riders (no brake heat), then your technique may seem adequate.
When a tubular leaves a rim, the rider crashes. The fall is sudden, unrecoverable, and injury inevitable. Other riders are also at risk. However, think of the various perspectives. A rider suffers such a fall, hopefully not season-ending. It’s miserable but riders fall for other reasons as well, so it feels like a risk of the game. However, if you are the mechanic who glued the tire and the glue job was flawed (easy to detect), you have more than abrasive wounds. Depending on the situation (think: Worlds), this can be a career ending event, a misery never forgotten. Ironically, the rider might be less of a victim than the mechanic. Here is where our concern really becomes acute.
The World’s Best instruction for tubular mounting and all the related principles is a direct outgrowth of the Mechanics Clinic. An early attendee was Chip Howat, Emeritus Professor of Chemical Engineering and former Director of the Kurata Thermodynamics Lab at University of Kansas. As he joined the ranks of race mechanics (part time of course) a question arose, “what is the most urgent chemical or thermodynamic issue in cycling?” The answer was a resounding chorus: tubular gluing. There are lots of tire-induced crashes and a dozen recipes for gluing. What is best?
Over several years, Chip supervised lab study to sort this out. Now the world of cycling has data and authoritative prescriptions for gluing all types of tires to all types of rims. Here is the archive. Click “Bicycle Research” and “Online Articles.” Illustrated demonstrations are also helpful but only if they are consistent with the engineering. Two come to mind: Calvin Jones (Park Tool) shows some great techniques to ease the procedure. And Rhys Bateman’s demo is well informed and presented.
One take away tip? Use a brush to spread the glue on the rim and on the tire bed (they both need it). Toothbrush, acid brush, no matter. You paint the glue to textured surface. A brush does the job best.
Let's finish with two last points:
1) Tire gluing is inherently flawed. It cannot work under all conditions. So, flawed gluing is NO option.
2) Sanding rims can be miss interpreted. Adhesives and sanding are not related the way most think. It is critical you know this. Really!
The goal of gluing is to attach a tire so securely that no combination of extreme conditions can pull it off (heat, sideways skidding, panic deceleration, partial wheel deformation, tornados, etc.). At the same time, we insist the tire can be manually removed in case of a puncture or wear. These are mutually exclusive. No such thing. Result? Under rare and unwelcome conditions, a properly glued tubular will come off. The only solution would be high temperature epoxy, so strong that removal requires ripping the tire to shreds. No one is ready for that.
Do any of you question my assertion that tires will come off? An imaginary scenario to prove a point:
Start a mountain road stage from a picturesque village spread along the alpine route. Begin with a controlled start, a parade for the locals in which a race vehicle heads the peloton at low (20-30kph) speed. Make this control section a 5% descent out of town. At 5k, the pace car pulls off and the peloton starts racing, descending for 1km more accelerating quickly. At 6k, we insert a steep hairpin turn. Riders jockey for position, take the corner aggressively on over heated tubular wheels. The whole peloton crashes at once. Tires flying everywhere.
Sorry, gruesome. What do the experts say about this catastrophe? First, the promotor and the course designer are hung. Anyone schooled in the basics of bicycle racing knows that tubular tires cannot survive the course described. Race courses are intentionally designed to produce safe challenges for competitors. Course induced crashes rare because we know the limit of tubular glue and design races around it.
However, this presents special issues for recreational “competitors.” Respect for weather, traction, heat, etc. are part and parcel of our collective space. And mechanics cannot be under gluing tubular tires. Ever.
Read Chip’s discussion of sanding and tire gluing. Data! Notice aluminum and carbon beds. Answers are there for you.
Be aware that sanding does not improve adhesive strength. The ONLY reason to sand a surface prior to bonding is to clean it. There are contaminants that resist all solvents. The only way to guarantee 100% cleanliness is to lightly sand the surface, removing contamination.
However, the sanding is counterproductive if its debris (may be microscopic) is not removed. Use a strong solvent (lacquer thinner, acetone, MEK…beware, all highly flammable) and a perfectly clean, white cloth or towel. Wipe, turning the cloth, until there is absolutely no color coming off the rim. Now, until airborne contamination begins landing, your rim is ready. That's why we try to store tubular wheels with a tire aboard. Even a flat, throw away will shield the rim bed from airborne contamination.
It is NOT a matter of removing shine. Perhaps a useful target to assure sanding is minimal but shine is not the adhesives enemy. Rough surfaces can be repellant to adhesives and shiny ones permit 100% strength.
Oh yes, for cyclocross gluing, conditions are so different, you deserve advice from specialists. In the meantime, hope you know more about tire gluing. For many of us, tubulars remain the most rewarding, exciting, and desirable ride. In spite of all the scary stuff above, the tires of our forefathers are still pretty damn sweet.
Do not be shy about posting your opinions on this subject. No topic is a closed discussion. We are all learning!
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