Tubular Tire Gluing (Sew Up)
This article will discuss the mounting and gluing of tubular tires. The tubular tire is made from a tire casing that is then sewn around an inner tube. The stitching is covered with a strip of cloth called "base tape". The tubular is then glued to a special rim, called a tubular rim. The tubular system is not interchangeable with the common "clincher" system.
NOTE: The tubular tire system, even when mounted properly, is still susceptible to failure during use. Every precaution should be taken when bonding the tubular to the rim. At this time there are no industry standards for tubular mounting.
The basic principles that apply to gluing and adhesive bonding apply to tubular mounting. Generally, there should be enough adhesive to bond the tire and rim but not excessive amounts of glue. Excessive amounts of glue can become especially susceptible to failure from heat. There will be limits on the strength the bond between rim and tire.
- The tubular tire shape may not be a good match with the radius of a particular tubular rim. The tubular bond strength comes from the outer edges of the rim more than the center. If the tire is too small for the rim, there will not be good contact at the outer edges. In the cross section image below, there will be poor contact between tire and rim at the outer edges.
- Contact cements tend to soften and loose strength when they are heated. Hard braking during a descent can cause enough rim heat build up to soften tubular glue.
- Wet conditions tend to weaken the bond. Never glue a tubular out in rain or when the base surfaces are wet. Use care when washing tubular and avoid scrubbing the rim/tire interface.
- The tire is held on to the rim by glue, tension from the cord, and by air pressure. If a tire flats, the grip to the rim is weakened, and the tire is susceptible to coming off the rim.
- During use, the wheel and tire are subjected to several different types of stresses. The worst stress for the tubular system is a lateral load or lateral impact. Hitting bumps during a corner, where the wheel comes of the ground and then lands with an impact tends to push the tire sideways. This may cause the tire to come off the rim, either partially or entirely, which may result in a crash of the rider.
Most bicycle tubular glues are variations on contact cements. Tubular cement must hold the tire to the rim, but yet be somewhat flexible and giving when the tire is impacted laterally. Expoy or hard glue would tend to shatter when impacted rather than yield during a shock. Tubular cements tend to use volatile solvents that must bleed or dry out before the bond is fully secure. While the application technique is critical to maximum bonding strength, glue brands will vary in quality and adhesive strength. For more detail on tubular bonding see the technical article by Dr. Colin Howat on the subject of Tubular Tire Adhesive Performance at the Kurata Thermodynamics Laboratory.
The safety of the rider depends on the best possible gluing procedures. A clean work area is important, as is time and patience. Ideally, it would be best to have three days to bond a tubular to the rim. This would allow for full drying of base coats. It is possible to glue a tire in a shorter amount of time, but it is important to understand that tubular adhesive require time for proper curing. The bond strength increases after the tire is initially mounted.
Gluing Procedure - New or Bare Rim
As with all bonding procedures, clean surfaces are important. Use a clean rag and a solvent that will not leave an oily film, such as acetone or alcohol, to clean the rim surface. An oily surface will tend to repel the adhesive. Allow rim to dry completely before continuing. Wipe with a clean cloth only. Always take precautions when using strong solvents such as acetone. Use protective gloves.
Carbon gluing surfaces have special considerations. Most manufacturers of carbon rims state that acetone is acceptable for cleaning the gluing surface. Contact manufacturer for their recommendations. Abrading the carbon can be useful for cleaning surface. This is especially true if there is “mold release” on the rim. This is a slick substance that allows the carbon to come out of the mold during manufacturing. Use only a medium grade sand paper or emory cloth (approximately 120 grit). Do not abrade down to the fibers themselves. Clean with an oil-free solvent after any sanding.
The tubular tire can be a tight fit to the rim. It can help to stretch the tire on a dry rim and inflate it to full pressure. Allow wheel to sit overnight. If time is an issue, the tire can be manually stretched by placing it over your back “bandoleer” style. Place a knee in the tire and stretch, using your back.
Inspect base tape. If the base tape is covered with latex, attempt to scrape clean with a sharp edge. If scraping does not appear to remove any glue, do not scrape further. If scraping appears to clean and clear the tape, continue until full width of tape is finished.
Ideally, a bonded joint should have a little glue as possible but without “starving” the joint. It typically takes quite a bit of glue, however, to get a full bond with many tubulars. If you are using the typical tube of glue, you can expect to use one tube per new wheel set. If the rim has a good base coat already, you will need less glue.
Apply a single coat of glue to the base tape. Inflate tubular until base tape rolls outward. Handle the tire by the sidewalls. Pinch tire in the middle to form a “figure 8”. Apply a bead of glue a few centimeters at a time. Use an acid brush or tooth brush to spread the adhesive evenly across the base tape. Continue applying small sections of glue at a time until entire base tape is coated, including the area at valve.
Use care not to get glue on sidewall of tire. However, if glue does get on sidewall, do not remove with solvent. Simply allow drying and leave it alone. Hang tire off ground in a dust free environment allow to dry completely. A dry tire will be easier to handle when mounted to the rim.
It can be useful to hold the wheel in a truing stand. Place rags to protect the stand from glue. Set the calipers to drag slightly on the rim braking surface. This will keep the rim from rotating while glue is applied to the top.
If rim has no base coat, apply a first coat. Apply an adhesive bead a short section of rim. Spread evenly the full width of the rim with a clean brush. Allow this first coat to completely dry, ideally overnight. Apply an additional coat and allow this coat to dry as well. The third and perhaps final coat will be used to mount the tire while it is tacky, and not completely dry. If there is a poor fit between tire shape and rim shape, more coats may be required.
It is important the adhesive be applied fully to the edges of the rim. Most of the holding power will come from the outer edges of the tubular rim. Test edges for glue, as seen in the image below:
After applying the final coat the rim, allow to only partially dry. This may take 60 seconds to a few minutes, depending upon the glue and atmospheric conditions. Deflate the tubular until it is soft, but leave enough air so the tire holds its shape. This will help keep the sidewalls clean during mounting. Find a clean floor area to work on, such as tile, or even a toolbox lid. Do not mount on carpet, grass, or any surface that may contaminate the rim. Place the wheel vertically and place the valve in the valve hole. Begin to pull outward on the tire, holding the tire approximately 12-inches (30cm) to either side of the valve. Work the tire on a section at a time, while continuing to maintain pressure on the tire. The last section may be especially tight and difficult to get on the rim. Use thumb pressure to force tire onto rim.
After the tubular is mounted, IMMEDIATELY begin to true and align the tire on the rim. Sight the base tape on both sides of the rim. Generally, the base tape should appear even and centered. Check that the center of the tire is if fact centered on the rim. Pull and twist the tire as necessary. It can help to deflate the tire further to align, but re-inflate to check final alignment.
Check proper adhesion at this time. Roll the tire back in several places and inspect the glue at the rim and tire interface. Glue should be apparent at this area, as seen in the two images below.
A lack of glue will again show up at the edge of the tire and rim. The image below shows evidence of an inadequate amount of glue, referred to as a “starved joint”. Remove this tire and apply more glue to the rim.
After the tire is aligned, inflate tire fully. High tire pressure will help press the base tape fully in the radius of the rim. It can also help to roll the tire along the floor while applying downward pressure.
Clean braking surface of any glue. Use a strong solvent and a rag is the rim is aluminum. For carbon rims, wipe off glue as best possible without solvent.
Lastly, the tire MUST be allowed to fully cure. This will require time for the glue solvent to bleed out. It is recommended that a tire be allowed to cure for 24-hours. Gluing and using a tire in a short amount of time will not allow proper bonding, and can lead to failure, no matter the brand of glue.
Gluing Procedure - Used Rim
The gluing procedures will vary depending upon of the condition of the used rim. If the rim already has a base coat, it typically can be reused. The old tire must first be removed. This may in some cases damage the tire and make it unusable. Deflate the tire completely. Pull back at the tire to work it loose in one spot, and then insert a dull edged straight tool, such as a steel tire lever or dull tipped screwdriver. Work the tool between the tire and rim. Lever the tool back and forth, then slide the tool along the rim to remove the tire.
The old tire, once removed, will give indications of the previous gluing. In the image below, the base tape shows very minimal contact.
There will often be a layer of dirt on the edges of used rims. Use a scraper and remove this glue and dirt. Remember, it is the edges that do most of the holding. It may be necessary to build up the previous coat. It is also possible that the old coat is thick in some area and bare in other. Apply glue accordingly. If the base coat is very old, or if it is dirty and contaminated, it should be stripped off. It is possible to use heavy bodied paint removers. Use a biodegradable remover when possible, and follow stripper directions.
NOTE: Do not use paint stripper on carbon rims. Many manufacturers recommend acetone to cut old glue. Contact manufacturer for their recommendations.
The base tape of a tubular is adhered to the tire with glue. If the base tape comes loose from the tire, it is difficult to repair to a “like new” condition. Use a thin coat of glue on the base tape. Install tire to a dry rim and inflate fully to push tape to rim.