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Technical FAQ: Corroded rims and hot heads

Lennard Zinn answers reader questions about tire sealant corrosion, making the tubeless transition and those funny Team GB helmets

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Editor’s Note: Lennard Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn.

Dear Lennard,
I had to put my road bike in storage for two months for an arduous move. In a week of riding after the move, my front Shamal 2-way Fit wheel would lose 20-30 pounds of air overnight. I added 40cc of Caffélatex to no benefit. Taking the Fusion 3 tire off, the valve stem hole is cracking almost to the tire bead with a jagged edge. There was random corrosion, most catastrophically at the valve stem. I’ve used acetone to clean the rims once or twice a year, and the valve area always seems to require the most attention. Using only Caffélatex and Acetone leads me to wonder about rim imperfections.

I take tires off in the Spring/Fall, remove residual latex (usually a dozen or so pin holes filled; I can’t imagine what, if anything, would have happened with tubes), clean the tires, and clean the rims. I have a couple of dull dentist tools that I use to scrape latex attached to the rim. It really reminds me of dental hygienist cleaning, scraping the crud while not hurting the enamel (rim). I can’t imagine how this could happen. Do you have any thoughts on it?

I sent the wheel to Campy USA via LBS. Campy USA says it’s not a warranty issue. (I bought the wheels from a European website.)
— Lindsey

Dear Lindsey,
I’ve often heard about rim corrosion from sealants and have been sent many photos of rims corroded due to them. Shimano specifically recommends against using sealants with its rims due to this problem, and I imagine Shimano would also say it’s not a warranty issue, were you to send in one of its rims with this issue. That is against the backdrop of every sealant maker I’ve talked to about this insisting that their sealant will not corrode a rim.

I personally have had one Mavic Ksyrium ES rear wheel that I was running with road tubeless tires and Stan’s sealant corroded so badly around the valve stem that it would no longer seal. There were also small corrosion pits here and there at many spots on the rim bed and rim sidewall. Of course, this was after I’d told a reader that corrosion from sealant was nothing to worry about!

Nonetheless, I have many wheels I’ve run tubeless for years, both road and mountain, with both Stan’s NoTubes and Caffélatex sealants without seeing corrosion. I also received a gallon of Hutchinson sealant at least a year ago that was formulated specifically to not cause rim corrosion, but it doesn’t seal anywhere near as well as Stan’s NoTubes or Caffélatex, so I long ago stopped using it.

I did ask the maker of Caffélatex about your rim with a crack at the valve hole, and here is his response:

Excluding corrosion from Caffélatex (but I’d be curious to learn when/how Lindsey used acetone on the wheel: as you know by using it to soften old tubular mastik, it is very aggressive!), the crack at the valve hole could be started also by mechanical stress in the area. I’m thinking about an over-tightened valve, or the valve could have been pushed laterally by accident after being tightened, for example, by hanging the bike on one of those ceiling hooks… where the bike is held by its front wheel (exactly the wheel that failed). If the hook is holding the wheel on the free rim space between two spokes there’s no problem… but if you happen to hook the wheel by the valve you can easily damage it. — Alberto De Gioannini, Effetto Mariposa”

Despite that single Mavic Ksyrium ES rear wheel that became corroded on me, I still run tubeless tires with sealant on all of my non-carbon road wheels, as the benefit of elimination of flat tires far outweighs the downsides for me. I do check them more often for corrosion, but, like I said, that remains the only rim that has become corroded on me running tubeless tires.

Corrosion can be a conundrum. Being in the business of making metal bicycle frames and cranks for decades, both anodized (like your rim), and painted or powder-coated, sometimes there seems to be no rational explanation for why one person can have corrosion issues with a frame or a crank while others using theirs in similar or seemingly much worse conditions will not experience any corrosion. I also have no explanation for why, in all of these years, I have only had one rim corrode with tubeless tires and sealant while not only did its mate not corrode, but also neither did a lot of other rims I have subjected (and continue to subject) to seemingly identical conditions.
― Lennard

Dear Lennard,
I am considering changing to tubeless tires. My Campy rims are tubeless ready.

My problem is that none of my local shops or fellow riders have much experience with tubeless tires. I am 6-feet-2-inches, riding at 200-215 pounds. Can you provide pluses and minuses and recommendations?
— Thom

Dear Thom,
Just get the tires — probably Hutchinson Intensive Tubeless for you, install them by hand, and add some sealant. If you need more detail, there’s plenty of that in chapter 6 of “Zinn and the Art of Road Bike Maintenance.”
― Lennard

Dear Lennard,
I’ve been reading your postings avidly for years, but am still often amazed at the depth of your knowledge of anything related to bike technology. I especially enjoyed your article on gearing and the effect that changes over the years have had on the grand tours (in the 2012 Tour de France preview issue). So here is my question on gearing: I do not understand the reason behind the current trend move to an 11-speed rear cassette. It appears to me that the only advantages of more gears would be either a wider total range reduced gaps between available ratios in order to better maintain cadence in the most effective range.

Various articles (on the VeloNews website, of course) have led me to believe that the max rear gear that pros use, even for mountain stages, is 25-tooth (except for maybe a few stages with climbs that I would have a hard time walking up). So the pros aren’t taking advantage of the max range that is possible with 10 gears, which, I believe, is 11-28. That leaves the only apparent advantage of an 11-speed cassette to be narrower gaps. From my spreadsheet, the 11-gear cassette does smooth out gaps a bit in the midrange compared to a 10-speed 11×25 (using a 53-39 crank), but the biggest gap for either occurs between the 19- and 21-tooth gears – and both cassettes are identical there. So is there a real benefit behind the 11-speed cassette, or is it just marketing?
— Gary

Dear Gary,
I am not sure why it’s relevant what gear range the pros use when considering your own gearing. I, for one, ride a lot lower gears than pros generally do. I have compact 34-50 cranksets on all of my road bikes, and my SRAM and Shimano bikes have 10-speed 11-26 cogsets, while my Campy bike has an 11-speed 11-25. Clearly, I have a bit smaller jumps on the 11-speed cogset, but I can’t say that I notice it; when I climb a mountain road on one bike versus another, I really don’t notice the larger jumps on the 10-speed cogsets relative to the 11-speed. Maybe if I did the same climb back-to-back on one bike, followed immediately by another, I could notice something, but even on Flagstaff Mountain, which I’ve probably ridden around 500 times in the last 30+ years, I don’t notice the difference in gear jumps from one week to the next on different bikes.

I think Shimano and Campy are offering 11-speed because people will buy it, not because it offers more gear range or smaller gearing steps. It’s the same with amplifiers. When we were at 5-speed cogsets 35 years ago, I never imagined an 11-speed cogset, so I won’t be too shocked if we see a 12-speed cogset a few years down the road, too. And I imagine that if that time comes, I’ll eventually end up with one on my bike, too, even though it probably won’t make me any faster than a 10-speed would.
― Lennard

Dear Lennard,
The most insane thing in the world seems to be these helmets.

They have nearly the drag of a ventilated helmet without the ventilation! In my opinion, if you’re racing in cool weather and don’t want a perforated helmet, GET A SMOOTH HELMET!!!!!!!!!!!!!!!!!!!!! Then you’d be warm/dry and have an aero advantage. Those non-perforated rough helmets are the stupidest things ever.

Also, the GB men’s team raced them in 70F for 150 miles, and also used booties and sleeves to their elbows. duhhhhhhhhhhhhhhhhhhh. No wonder they cracked.

Am I missing something here?
— Alan

Dear Alan,
The helmets on the British Olympic team are obviously carryovers from the Sky methodology in the Tour de France, and I have to assume that the Sky team knew what it was doing in the Tour — both aerodynamically and body-temperature-wise, since it appears to have left no stone unturned for its assault on the race. I can understand the urge to try to save small amounts of energy throughout the race with a more aero head on the shoulders of riders who are at the front all day long. I do agree that those helmets don’t look very aerodynamic, but I have no wind tunnel data to back it up, whereas I’d be amazed if Sky did not have such data. It’s also hard for me to imagine Bradley Wiggins wearing something different from the norm without data to support making such a change. [Lazer, Giro and Kask are proponents of solid-bodied aero road helmets, claiming noticeable differences in the wind tunnel, and have put them on a number of sponsored teams. —ed.]

As for cooling, I know I want every bit of ventilation my helmet offers on most summer days, and those helmets look stifling to me. But I haven’t worn one, and I’m also not privy to any data Sky may or may not have from continuous monitoring of head and body temperature in training on hot days with remote data capture. It would have made sense to remotely record temperatures with half the team on ventilated helmets and half on unventilated ones on the same rides, and I don’t know whether the team did this or not. I think that it should have done so before making such a change, and if it did not, it lucked out that this Tour was not as hot as some have been. In the Olympic road race, the British team had way bigger problems than the helmets and clothing alone, but I’m not sure that they hurt themselves on balance with those helmets, half sleeves and booties.
― Lennard

Dear Lennard,
I have used the Photoshop fitting method as well and it has worked really well for me. Where it’s particularly helpful is transferring a fit between dissimilar bikes, like road to ’cross. I have also gone a step further to put a marker on body points (hip joint, ball of foot, knee joint, etc.) and sit on the bike for the photo. This helps when two bikes have different saddles or different shoe/pedal systems.
— Dave