Wednesday, August 01, 2007
Tubulars: Part III, Gluing the tire to the rim
As you may have gathered from Part II, repairing a tubular tire is a lengthy process; so too is gluing the tires to the rim. To do the job properly it can take several days to allow the glue to cure and the tires to settle on the rim.
You can’t just fit the tires and go out and ride immediately as you can with clinchers; it is necessary to plan ahead.
Let’s assume we are starting out with brand new tires and new alloy rims. I have no experience with carbon fiber rims so I can’t advise on those. I understand there may be issues with tires not adhering so well to CF rims.
Before you even apply any glue to the rims, mount the tires and inflate them to the recommended pressure, and leave them on the rims for at least 24 hours. New tires are extremely tight on the rim and you really have to “muscle” them on.
Once they have been on the rim and inflated for a period of time, the tires stretch out and are easier to fit the second time around. You do not want to be dealing with glue and trying to get a brand new tire on at the same time.
By the same rule, don’t forget to pre-fit and inflate a spare tire; because if you get a flat you will not want to be trying to fit a brand new, un-stretched tire, by the roadside.
If you can’t get the tire on the rim the first time, it may be necessary to stretch the tire by putting it over your shoulder, diagonally across your back, and the put your knee inside the tire and push on it.
Before you apply any glue to a new rim, the concave inside surface where the tire sits, needs to be roughed up. This is to make sure the glue bonds to the rim; glue doesn’t stick too well to a shiny surface. Use some coarse emery cloth, and just scratch up the surface.
There are two types of tire adhesive; double sided sticky tape, or glue in a can that you apply with a brush. Some people like the double sided tape because it’s quicker and less messy that the glue. I don’t like it for the simple reason, when it comes time to change a tire, I never know if the tape will stay on the rim, or come off stuck to the tire. Glue is cheaper, I get many applications out of one can.
Getting back to our brand new rims that we have just roughed up with emery cloth; apply a coat of glue with a brush. I buy cheap glue brushes that come in a packet of five for a little over a dollar, and are cheap enough to use once and throw away.
When I apply glue to the rim, I deliberately miss a spot. The space between two spokes that is opposite the valve; that is the place where the manufacturer’s label usually is. (I am not talking about the new wheels with a large space between spokes. About 2 ¼ inches [56 mm.] is good.)
The reason I do this is, if a tire is stuck on correctly, it is hard to remove, even when deflated. This little dry spot with no glue gives me a place to start. The tire will not roll off because 2 ¼ inches of glue is missing. I choose the space opposite the valve so I remember where it is.
The first application of glue should be allowed to dry overnight. The next day, apply a second coat and allow to sit for 15 minutes. The tire manufacturers will tell you to apply a coat of glue to the base tape of the tire; I do not do this. I find it hard enough to get a new tire on a rim, with glue on it, it gets on my hands, then all over the sidewalls of the tire and the rims. Just a horrible mess.
What I do is; I put the tire on after two coats of glue to the rim. Inflate it and allow it to sit for several hours or maybe overnight again. Then I remove it and give the rim a third coat of glue. (The recommended initial amount.)
Now the tire has glue residue on it because it has been on the rim, but not as much as if I had applied it with a brush, plus the glue is partially dry. Also, because the tire has been on and off the rim twice now each time it gets easier to put on.
On the final fitting, I spin the wheel and make sure the tire is aligned. Partially inflate, and look at the edge of the base tape. Is there an even amount showing all around the rim, and is the tread central on the wheel? If satisfied the tire is straight, I fully inflate.
After allowing the bike to sit overnight, on the initial ride the next day, I take it easy and not push my speed to the limit on corners. By the next day, and after riding the bike, the tires should have bedded down and the glue should be cured.
A final test is to physically try to roll the tire off the rim with both hands and pushing with the thumbs. This is the test that officials will perform before a race. If the base tape lifts at all from the rim the tire is not sufficiently glued.
Whether you choose glue or double-stick tape, both types stay tacky for a long time. This means the tire can be removed when necessary, and if you change a tire on the road the glue is still tacky and will hold the tire well enough to get you home. (Riding with caution of course.) Once you get home you can remove the tire, give the rim a fresh coat of glue, wait 15 minutes, replace the tire and after the bike sits over night, you are good to go again.
At least once a year, or sooner if you make several tire changes, it will be necessary to clean off the old glue and start over. Use any kind of paint solvent to do this; I use lacquer thinner, it is probably one of the least toxic. Once the rims are clean and dry, start over as you would for new rims, although it may not be necessary to rough up the rim surface again.
Disclaimer: I have just explained how I fit my tubular tires. I have never had a tire roll off, but I weigh about 150 lbs. It would be remiss of me if I recommended you follow anything but the manufacturer’s instructions.
As I have often said, I am retired from the bicycle business, I have no connection with any company and I am not trying to sell you anything. I have given you the pros and cons of tubular tires. This is free information intended only to assist you in making your own decisions as to what type of tires you use.
Some of you have been asking about wider tubulars. Vittoria makes the Pave EVO CG, 24 mm wide, and the lower price Vittoria Rally training tire is available in 23 mm. Also, although tubulars are designed to be inflated to 120 psi or more, I find at my weight 100 psi is ample. Like the Sleep Number bed, find your own comfort level.
Footnote: This is the final in a three part series on tubular tires. Here is a link to Part 1 and Part 2.
Posted by Dave Moulton at 8/01/2007 05:11:00 AM