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PostPosted: Mon Sep 23, 2013 12:56 am 
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I thought the purpose of using tape when gluing cross tires has nothing to do with creating a "stronger" bond. Let me rephrase that... it does create a stronger bond, but that is due to the revised shape of the rim bed as a result of building it up with the tape. In other words, didn't it evolve from gluing wider cross section cyclocross tires to rims which were actually designed for narrower road cross section tires. Since the radius of the wider cross section tires is larger, building up the rim bed a bit was the method used to lessen that radius in the rim, and better match the inner radius of the rim with the outer radius of a fatter cross tire, ultimately creating a better contact all the way across the base tape instead of primarily on the edges with a weak spot in the middle. I see this method of gluing becoming obsolete with the adoption of wider rims with a more appropriate rim bed designed specifically for wider tubulars.
Feel free to correct me if I'm wrong, but that's always been my understanding of the "why" behind the "Belgian tape" method as it applies to cyclocross.

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PostPosted: Mon Sep 23, 2013 1:18 pm 
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A question for you all ...

I am a gluer (don't worry...) though have used tape a couple of times in the past.

Considering going back to tape for one set of tubs (I have three sets of carbon tubs) for races away from home where there is a risk of a flat the day before, or even the night before the race, making gluing a new tub very difficult / unsafe.

What do others do to cover this situation?

My biggest issues with tape (Tufo Extreme) were the odd air bubbles / noise when combined with Vittoria tubs, and the hard to remove residue left on the rim, but I'm told the former is related to the imperfect Vitt base tape, so I can use another make of tub, and the latter is a ballache but worth it for the last minute change away from home.

What do others do to cover this eventuality?


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Posted: Mon Sep 23, 2013 1:18 pm 


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PostPosted: Mon Sep 23, 2013 1:39 pm 
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I think that there may be two things at work: first, as Calnago points out, the profile of the rim bed versus the profile of the much larger 'cross tires may need some 'build-up' to better fit a road rim; and, to introduce some 'structure' into the glue, better allowing it to resist the shearing forces that result from running low pressures with knobby rubber. Personally, I believe that the latter is more descriptive of what is happening.

First, the product used by Stu Thorne is pretty thin. If the reason the method works was due to a build-up of material to compensate or the difference between road and 'cross tire sections, then the thicker tape should work better. Secondly, the tape should not be applied across the whole rim bed, but only in the centre.

Frank, I am very surprised to hear that is not how you glue-up 'cross tires in Belgium! Until I got back into 'cross about 5 or 6 years ago, I had not glued-up a 'cross wheel in almost 20 years. I have found the 'Belgian' tape method to be very reliable.


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PostPosted: Mon Sep 23, 2013 2:34 pm 
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@geoff: Exactly. The tape, provided its weave is open enough to allow the glue to squish through, acts exactly like rebar in concrete. And how much you build it up depends on the tire you're using and the curvature of the rim. And yes, the middle needs to be built up more for fat tires, less for less fat tires. But I do think all this becomes moot if the rim bed matches the tire radius, as is the case with newer cross specific rims. But this was less likely in the past when all rims were essentially made for road and adapted for cross, hence the use of tape in the build up of the bed. It is also the reason I don't think using excessive layers of glue on regular road tubulars is a good idea. Without that reinforcement, it has the potential to become a thick gooey soft mess underneath.

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PostPosted: Mon Sep 23, 2013 8:03 pm 
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So I picked up a pair of chinese ebay tubular wheels for CX, and followed the embrocation tubular gluing guide. I prepped the rims by giving them a very light sanding with fine grit paper. In the process, noticed that there was little to no clearcoat on the rim bed - black carbon dust was apparent on the sandpaper. I wiped the rim surface off, everything seemed fine.

Cut to mounting the tire - I kind of messed up the job on the rear rim - definitely had a hard time getting the basetape onto the rim opposite the valve-hole, and there was a LOT of working the tire to get it centered all the way around. In the process, I noticed that the worst problem area actually started to un-stick from the rim. Glue that had previously been on the rim was pulled up onto the belgian tape, I could see fine black grit (carbon) on the underside of the glue, and could feel that the rim bed itself was totally bare. Once I got to the point where the tire was reasonably centered/I didn't want to do any more damage, I pressed the tire onto the rim using a broomstick, pumped it up to pressure, and it's now hanging out at home curing. I have yet to take the wheels out for a test run.

Whats the move? Outside of "buy better wheels" I'm thinking I can either:
A) test it as is. Hope for the best.
B) peel the tire back and forth a bit - if glue hasn't set up to the rim fully, take a syringe and needle and inject a little bit of glue onto the rim bed of problem areas. Re-pressurize tire and re-cure.
C) rip the tire off, start from scratch.

Thoughts?


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PostPosted: Mon Sep 23, 2013 10:50 pm 
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Hi,

Quote:
Frank, I am very surprised to hear that is not how you glue-up 'cross tires in Belgium! Until I got back into 'cross about 5 or 6 years ago, I had not glued-up a 'cross wheel in almost 20 years. I have found the 'Belgian' tape method to be very reliable.


@Geoff:
I'm not saying it isn't, it's just that I don't see these guys using a mix of Jantex (and its accompanying Tubasti cement) and Mastik One on their rims.
So, if not that, then what do they use for tape?
From yours and Calnago's explanation basically any strip of easy to handle and strong cloth stuck in between layers on the center of the rim bed should work provided it allows the cement to "attach" to it firmly on both sides, right?

Quote:
Considering going back to tape for one set of tubs (I have three sets of carbon tubs) for races away from home where there is a risk of a flat the day before, or even the night before the race, making gluing a new tub very difficult / unsafe.


I've been in similar situations like this and resorted to using Jantex tape on a clean rim. It worked fine but I limited the use of these wheels to pretty basic regular rides. No fancy high speed descents at high ambient temps or other foolish extremes.
The nice thing about it is that it easily peels off the rim afterwards and any residue is swiftly removed using a rag dipped in a bit of plain household petrol.

Ciao, ;)

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Last edited by fdegrove on Mon Sep 23, 2013 11:59 pm, edited 1 time in total.

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PostPosted: Mon Sep 23, 2013 11:03 pm 
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Hi,

Quote:
I could see fine black grit (carbon) on the underside of the glue, and could feel that the rim bed itself was totally bare.


There's no need to sand down the rim bed on a carbon rim. It just needs to be free of mould release agents (Teflon and what have you) and generally grease free.
Any carbon dust (which is really not good for you) means a number of fibres have been cut, reducing the strength of the composite in the process.
Nothing major in this case, just saying.
Also, no cement will ever stick to a rim bed or base tape when it's covered in tiny dust particles. Likewise, rim cement being a contact type of adhesive, injecting some cement in between two layers of material will not form a proper bond.

Sorry to bring all the bad news but I'd go for option C) (better safe than sorry).

Ciao, ;)

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PostPosted: Mon Sep 23, 2013 11:55 pm 
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fdegrove wrote:

Quote:
Considering going back to tape for one set of tubs (I have three sets of carbon tubs) for races away from home where there is a risk of a flat the day before, or even the night before the race, making gluing a new tub very difficult / unsafe.


I've been in similar situations like this and resorted to using Jantex tape on a clean rim. It worked fine but I limited the use of these wheels to pretty basic regular rides. No fancy high speed descents at high ambient temps or other foolish extremes.
The nice thing about it is that it's easily peel off the rim afterwards and any residue is swiftly removed using a rag dipped in a bit of plain household petrol.

Ciao, ;)


Thanks - this would be for balls-out riding I'm afraid so the bond needs to be no compromises.

It's one respectable argument in favour of tape as far as I can see


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PostPosted: Tue Sep 24, 2013 12:11 am 
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Hi,

Not saying it won't work but I wouldn't trust it 100% when used with carbon rims as it was not formulated for that.
Beware as well that riding "balls out" often invites "cock-ups" :oops: :lol:

As far as bonding strength goes, it does not guarantee anything by itself really, the highest strength bond I'm aware of would be (god forbid) Tufo's Extreme.

Ciao, ;)

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PostPosted: Tue Sep 24, 2013 2:18 am 
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fdegrove wrote:
Hi,

Quote:
I could see fine black grit (carbon) on the underside of the glue, and could feel that the rim bed itself was totally bare.


There's no need to sand down the rim bed on a carbon rim. It just needs to be free of mould release agents (Teflon and what have you) and generally grease free.
Any carbon dust (which is really not good for you) means a number of fibres have been cut, reducing the strength of the composite in the process.
Nothing major in this case, just saying.
Also, no cement will ever stick to a rim bed or base tape when it's covered in tiny dust particles. Likewise, rim cement being a contact type of adhesive, injecting some cement in between two layers of material will not form a proper bond.

Sorry to bring all the bad news but I'd go for option C) (better safe than sorry).

Ciao, ;)


It's possible I wasn't thorough enough with cleaning the rims post-sanding, but I thought I did a decent job. What I was getting at, if there is bare carbon (and was effectively bare carbon before I started. Black dust was immediate), is this normal/not/can I expect the glue to stick well instead of glue sticking to clear coat. That make sense?


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PostPosted: Tue Sep 24, 2013 3:26 am 
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Also - just got home to check on cureing. Everywhere on the rim seems pretty solidly stuck on, it's only the worst part that I really had to wrestle that isn't adhered well. I may try B, then A, then C as last resort.

Anyone else?...


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PostPosted: Tue Sep 24, 2013 11:04 am 
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Hi,

Quote:
What I was getting at, if there is bare carbon (and was effectively bare carbon before I started. Black dust was immediate), is this normal/not/can I expect the glue to stick well instead of glue sticking to clear coat. That make sense


Rim cement should stick even better to a bare, uncoated, CF surface than it would to a clear coated surface. The reason is that bare carbon presents a number of voids for the cement to adhere to whereas a clear coat (especially a polished one) is essentially devoid of voids.

Hope this helps, ;)

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PostPosted: Tue Sep 24, 2013 1:09 pm 
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+1. Tubular glue is very sticky. It is so sticky that the biggest concern of a proper glue job should not be whether it will hold-up to aggressive riding, but how the heck to get the tire off of it if you flat it due to road hazards. If you can tell it is not well-adhered already, that is not confidence-inspiring.

So, Frank, how do you glue race tires for 'cross in Belgium? Do people not use any fibre tape? What is the Belgian secret to 'cross wheels. Whatever you guys do, it obviously works (I mean, other than having an endless stream of genetically gifted people, living in a magical place that loves and embraces one of cycling's greatest disciplines and is blessed with the terrain and weather for epic battles).


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PostPosted: Tue Sep 24, 2013 3:11 pm 
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Hi,

Quote:
So, Frank, how do you glue race tires for 'cross in Belgium? Do people not use any fibre tape?


AFAIK, they do use a cotton strip which are being sandwiched in between layers of cement depending on the width of the tyre and rim.
Thx for the compliments but I'm certainly no expert in cyclo-cross. :oops:

Ciao, ;)

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PostPosted: Tue Sep 24, 2013 5:33 pm 
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Pulled tire off rim. Virtually all the glue pulled from the rim, and everything is stuck to tire, with the outermost (rim-side) of glue looking grey-green. Not the amber-color id expect from dried glue. Going to re-prep the rim and re-glue.

How much should i focus in re-prepping the tire? I definitely want to get colored gunk off, but should I strip Belgian tape too, and other glue down to the base tape?


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Posted: Tue Sep 24, 2013 5:33 pm 


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