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Friday, October 14, 2005

Sticky Fingers

So, as promised I guess that I will give you the low-down on how I glue my cyclocross tubulars.

I should probably first point out that there is a pretty big difference between road tubulars and 'cross tubulars in terms of how they stay on the rim. A road tubular at 8 bar of pressure will stay on the rim almost by itself, sans-glue. The glue is essentially there to prevent any movement between the tire and rim from starting in the first place. You can try this if you have a new tire and new rim at home; just throw the tire on the rim, pump it up and try to push it off. Hard, yeah? Now release the pressure to 1.8 bar (about 25psi, a standard CX racing pressure) and the tire will slide right off. Scary. That is why standard tub-glueing knowledge does not necessarily apply for 'cross use - the only thing holding the tire on the rim is the glue, there is no help from air pressure.

Next up is the issue of tubular tape. Great for road applications, especially the Tufo variety, horrible for 'cross. Here's why. As has been repeated ad-nauseum in other tubular installation instructions, the bond between tire and rim at the very edge is über-important if you want to keep your rubber on. This is even more critical in 'cross because there is so much water flying around on the course and from the ubiquitous pressure-washers. If there is any gap in this area, water and dirt will penetrate into the bond and weaken it to the point where it may fail in cornering. Tubular tape is bad because it never completely fills the interface between tire and rim. It also causes the center section of the tire to sit a little higher than the edges, making it easier for a gap to form. This is true even of the so-called "Belgian Method", where glue is applied to both tire and rim and tape used to complete the joint. Another bone of contention here- if you are using glue and tubular tape, why not just use glue?

My solution to this problem is Vittoria Mastik´one - and lots of it. Next best is Continental. If you can get your hands on a big can of the stuff, so much the better. If not, be prepared to use about 3 (maybe even 4) litle tubes per wheel, if you are starting with new fresh rims and tires. My team-mate Jiri told me he uses 1 can for 4 wheels. That's a crapload of glue. Some people will say that's too much, but Jiri has also never had a rolled tub in 14 years of high level racing. You decide.

You should probably start by cleaning your rims, just a really quick polish with some light sand paper and then acetone should do the trick. Now you need to apply a relatively thin layer of glue to the rim, making sure that you get it all the way out to the edges of the rim. I don't really care how you spread it, just get it on there. Take your tires, put a little air in them to make them easier to handle and put a thin layer onto the base tape, making sure the entire surface of the tape is saturated (but not dripping) with glue. Now you wait. General rule of thumb is 8 hours of drying time between coats on the rim, but basically as long as it is dry to the touch and not too rubbery you can apply the next coat. Ideally you should do 3 thin-ish coats to the rim this way. For most people who aren't sitting around all day waiting for glue to dry this means three days. Somewhere in these 3 days you need to pull out the tires (remember them?) and put another coat of glue on the base tape. This layer should be über-thick - as thick as you can make it and not have it running off the tape as you apply it. This is when a brush of some type is required. Let that dry overnight too. Finally, on the fourth day you can put the tire to the rim. Put a medium-thick layer of glue on the rim, give the tire a quick stretchy-stretchy and fire it on the rim, starting at the valve. For God's sake make sure you put the tire on in the right direction first, otherwise you will make an atrocious mess peeling it off while the glue is wet (assuming you didn't make an atrocious mess putting it on. Sorry, can't help you there!). Make sure the tire is centered, put it up to 4 bar and leave overnight. Next day, deflate the tire and check the edge bonding by going around the entire circumference of the tire (on both sides), trying to peel it off the rim with your thumbs. If any gaps form, you need to poke some glue in there and inflate the tire again. Leave overnight again. Check the edges again. Now nothing short of a herculean effort should separate the tire from the rim - this a good thing. The glue generally requires 24 hours from the time the tire goes on the rim to reach full strength.

Like anything related to bicycle mechanics, there is a certain amount of feel involved with all this. With tires and/or rims that already have glue on them, less glue will need to be applied. The end result should be somewhere around 0.5mm of glue thickness (even up to 1mm is OK). Sounds like a lot, but it works. With Tufos you can get away with less because there is no seam on the underside.

That's the extent of my knowledge. Argue all you want, but I have never rolled a tub since I started doing it this way.

Please don't sue me


Blogger Dave Haygarth said...

Thanks for this - wonderfully in depth and I'll get the Duvel chilling in the fridge for those long eight hour waits...

8/27/2008 01:53:00 PM


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