So I’m going to be running carbon wheels for CX season this year and I started the process to glue up my new rims last night.
So I stripped the tires off my old wheels to discover that the tire was about 80% NOT in contact with the rim bed. The edges were glued tight, but the center of the tire and rim looked like they had never come into contact. I’ve been racing these for at least a season maybe two and had no indicators that there was such poor contact.
Any ideas why this was?
Should we assume that you glued-up these tires yourself? The how-to video from the link below seems to give a good demo.
You are hinting that the centre portion of the rim was not glued and therefore the tire was not in contact?
If you’re glueing a tubie for triathlons, you don’t want to glue 100% of the rim; there are a couple of techniques.
I leave about 1.5 inches of rim unglued opposite the valve, then glue the rest of the rim, sounds like the guy who glued your wheel left the the glue off the middle to facilitate a quicker punctured tire change
For cross, after the tire is mounted roll it on broom handle while pushing down on the wheel. You want as much tire rim contact as possible.
How many coats of glue are you laying down on the tire and rim before the final coat? To paraphrase the method used/tested by USA Cycling:
-Be sure to get full edge to edge coverage on the rim. Sounds like you have that part down.
-Cross tires are wider and will not seat as low into the center of the rim. Thats why its important to build up a bed of glue to help match the circumference.
-I know this will be an unpopular comment on a tri forum but why the hell would you want your tubular tire to peel off easier?? The whole bit of leaving a section opposite the valve stem is wide spread but very counter intuitive. I’ve even seen people apply glue like a dotted line, glue, space, glue, space, etc. Bad things happen when a tubular rolls off the rim. And for Cross, leaving that section unglued would be begging for trouble.
I hope this helps some.
Hey TTW,
Seems no one is answering your question. Actually, only you can answer it. If you glued it yourself, you should recall the process and determine why the center portions are not sticking. Perhaps it did at some point and just lost the tackiness? If someone else glued it, then they did a poor job. I don’t reglue my tubulars until after two years of use and even so, the whole tire is still stuck to the rim. Although my glue is somewhat dry, it’s still about 90% glue, mostly in the center and not the sides.
I guess at this point you will have to periodically how your tires are holding up before CX races.
.
For cross, after the tire is mounted roll it on broom handle while pushing down on the wheel. You want as much tire rim contact as possible.
i like this as i’ve wondered about rolling it on the flat floor.
but really, if you inflate the tires after you glue them on, i’d think they are in contact as much as the ever will be… (i inflate then, put on bike and roll/ride STRAIGHT down the driveway once)
Maybe, but by rolling the deflated tire down a broom handle, you know the glue and rim have a solid contact. If you run cross tubies at 18-25 psi, they have to be on tight!
i will admit my NON cross experience…
on a side note;
if someone were to help you put your kit on for a cross race…would they then be a cross dresser?
Thats one of the big issues with tubulars. Ideally the rim and the tire would be a perfect match. Thats not going to happen hence the better performance with AFMs proper gluing method using quite a bit of glue.
You had a rim that had a radius meant for a smaller tire, the big cross tubular bridged between the edges. You need to use enough glue to fill that gap.
I’ve always thought that the amount of glue Al uses could be improved upon. Ideally you would use the least amount of glue that gives full contact between tire and rim. Sort of getting it just right, too much is likely much better than too little.
Were your old wheels carbon as well? Did you “rough” up the carbon before you applied the glue to it? I was told to do this on carbon rims, or else the glue might not adhere well to the rim. Whether or not this is actually true, I don’t know, but I’ve always done this, and never had a problem.
Richard
To answer the questions
I’ve raced them a bunch at very low pressures and they were a bitch to get off the rim, so the glue job was sound, I just found it odd that the center portion of the rim was covered in glue but never tacked to the tire. FWIW it was Kinlin TB-25 Al hoop.
My guess is that when you inflated it the base pulled away from the rim, leaving a gap. Even if you press it down it will likely happen. Try inflating, then when you are sure its centered correctly, deflate and either press it down or wrap a cord around the circumference of the wheel and tighten it then leave over night.
Styrrell
I have a cross set built up with those TB-25 rims. The wheels are just barely 1400 grams, but I don’t think they are ideal for cross.
Keep in mind I have had NO issues, but the mavic reflex rims I’ve used in the past just seems like a much better fit. Next set I build will be with the major toms. Those should be perfect.
Certain rims fit certain ccx tires better. If there is a huge gap between the tire and the rim channel, and you followed the gluing procedure as indicated above, and you did some trick to seat the tire into the rim, then you might want to try the glue/tape/glue on the rim method. I think I saw a velonews article on the subject recently (http://velonews.competitor.com/2010/10/cyclocross/technical-qa-with-lennard-zinn-getting-those-cross-tires-on-right_101235).
I second the broom handle trick. Also, once the tire is mounted and inflated to pressure, I like to press the wheel/tire down against the floor, rotating till you’ve gone all the way around. Spin it in a truing stand to make sure the tread is straight.
As for scuffing up the carbon surface, this is not recommended. The bond between the glue and the rim is a chemical bond, not a mechanical one. For a fresh rim, use acetone or naphta to clean the rim surface and allow to dry before applying glue. For a rim with glue already on it, just make sure the old glue is firmly stuck onto the rim. Otherwise, peel as much of the loose stuff off as possible.
If you’re still having problems with the center of the base tape not adhering to the rim then you can try the “Belgian” taping method, specifically for cross applications. Never tried it but if you’re still having problems its worth the effort. http://velonews.competitor.com/2010/10/cyclocross/technical-qa-with-lennard-zinn-getting-those-cross-tires-on-right_101235
(btw, the tape described in the article is NOT tufo tape)
I think styrrell is onto the problem: the rim was probably designed for a road tire (19-23 mm) but your mounting a cx tire with a bigger diameter. The middle of the cx tire can’t reach down into the bottom of the rim. You need to build up the bottom of the rim so that the shape of the rim matches that of the tire.
What wheels are we talking about?