Technical Q&A with Lennard Zinn

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By Lennard Zinn

VeloNews technical writer Lennard Zinn is a frame builder, a former U.S. national team rider and author of several books on bikes and bike maintenance. Zinn’s VeloNews.com column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn. Zinn’s column appears each Tuesday on VeloNews.com.


Question:
The question about the MTB carbon steerer tube and the recent column about carbon forks begs the question – what do you think about carbon steerer tubes in general? I recall reading that Armstrong insists on a metal steerer tube. I found I had to be very careful to get very well made bar ends for my Easton carbon bars. A set of poorly made bar ends cracked my first set. Is the same true of stems for carbon steerer tubes? –Steve

Answer:
As long as you have a support plug inside and the steerer extends above the top of the stem so that it does not get squished inward at the top (i.e., you need a spacer above the stem), then I think carbon steerers are great. They are clearly very strong; the trick is not damaging them on installation.

One reason that Armstrong doesn’t use a carbon steerer is because the Kleinfork on the Trek USPS team climbing bike, which has two different bearingdiameters – a standard-size bearing on top and an oversized one below, comeswith an aluminum steerer.–Lennard

Question:
Just wondered what your opinion of the whole 29er mountain bike movement is? I am 6 foot 3 inches and have read reviews saying that 29er’s are good for taller riders. I am feeling cramped on my current mountain bike and am thinking of trying out a big-wheeled mountain bike. Good idea? or fad? –Michael

Answer:
Almost all of the mountain bikes I have built this year are with 29″ wheels. The size is perfect for tall riders. I have one myself (I am 6’6″). They make a tall bike look normally proportioned, they roll over obstacles way better, and, best of all, they improve the position for tall riders.

The length of the available fork steering tubes (252-275mm) can be a severe limiting factor for tall riders, preventing them from being able to set their bars as high as they like, particularly if they are using a straight bar. With a 29″ wheel and fork, the bottom of the head tube is 3″ higher than it otherwise would have been, and the same length steerer (272mm for Marzocchi 2-9 forks) and the same length head tube puts the stem clamp up 3″ higher. I have built bikes for several 6’9″ riders with these. They look quite normal on their bikes. From a distance, the bike and rider are so well proportioned that they look like average-size riders and bikes. They don’t need funky riser bars and stems to get the position to work out.–Lennard

Question:
I have a 1-year-old Flight Deck computer on my 2-season-old Dura Ace drivetrain, and it generally works well, except when you trim the front derailleur (move it towards the big ring) while using anything smaller than the 16 rear cog. This seems to trick the computer into thinking that you have actually shifted to the big ring. This used to happen only occasionally, but has become more frequent, almost every time now. Not only does this tell you a different gear than you are in, but more important to me is the cadence error.

I have tried adjusting the cable slightly without noticing any change. My local bike shop doesn’t have any more info.

Another question, concerning the Dura Ace pedal you reviewed on this site recently: is the cleat only drilled for 3 hole Look style? Does Shimano not support their own shoes? I have the R212 shoes; they are great, but only drilled for Shimano’s own SPD-R. I was considering upgrading to the new pedal, but am not willing to invest in new shoes also. –James

Answer, from Shimano:
I went downstairs and fooled with a couple of bikes. I have a feeling that the front derailleur is not properly adjusted. The first thing that I would check, is the position of the front derailleur in reference to the front chainrings. Is the “low” limit screw adjusted so that the inner cage plate is just about to start rubbing the chain when the bike is shifted into the lowest gear in the front and rear. If the derailleur is adjusted too far in, the rider may be pulling excessive amount of cable and causing the computer to think it is shifted on to the large chainring when using the trim feature.

That is the only scenario that I can come up with. Let me know if this works out. If not, get back to me and we will try a different avenue. I have a strong suspicion that is the problem. Let me know if you need any other tricks or the Flight Deck. Just in case, The Shimano R212’s and the R214 shoes are both drilled for three hole pattern cleats. The rider needs to use what is referred to as cleat nut #3 adapter, which is provided with our shoes to accommodate the SPD-SL cleat pattern.
–Jason W. Leith
Technical Representative/Cycling Components Division
SHIMANO AMERICAN CORPORATION

James tries the fix:
I did re-adjust the front derailleur limit as per instruction, no improvement. I then dug out my Shimano instructions for adjusting both limits, and cable tension (really weird. They have you shift to 53 X 23, then trim the front derailleur and adjust cable tension till 0-.5MM clearance on the inside of the cage) I tried cable looser, tighter, no change in the Flight Deck, but I did manage to make my shifting worse! Do you recommend any different method to adjust cable tension?

I had made an error in my original question; the shoes are actually R211, not 212. They look the same, perhaps were a year older? (They were bought new 2 years ago from my local dealer, but were discounted, as they were not the current model.) Anyhow, I don’t see any way to adapt them to LOOK drilling, no matter what “cleat nut adapter” they have. –James

Answer:
It sounds like you have done everything to make it work. I basically do not use the front derailleur inner limit screw or the rear derailleur outer limit screw. Heck, on super-light bikes, I remove those screws entirely. I let the cable tension take care of stopping the front derailleur to the inside and the rear derailleur to the outside (obviously, the other limit screw on each derailleur must be adjusted properly).

On the front derailleur I back the inner limit screw way out so it does not contact the arm through any of its normal travel. I then dial in the cable tension so it lets the chain drop easily to the inner ring and not rub on the cage when on the largest cog. That’s it, save for the outer limit screw (and of course, the height and angle of the front derailleur cage). If the Flight Deck does not work then, I don’t see how it will ever work correctly.

As for the shoes, unless you drill three big holes in the sole like the 212 has (which I am sure is discouraged for warranty reasons), they are not going to work with Look cleats. –Lennard

Question:
I have a quick question regarding Prolink chain lube. Both your review and the Web site suggest that it is best to apply shortly before riding. However, most people that I have talked to that use Prolink say that if you let it dry overnight before riding, then the chain stays “dryer” and subsequently cleaner. Does this minimize the magic of the voodoo metal friction reducer? If you apply Prolink and wipe the chain vigorously after a few minutes do you remove most of the good stuff along with the bad?

I’ve also noticed that my chain will start out the ride “dry” and clean, but when I get done it is wet again. Is this old lube working itself out of the rollers? Can I expect this phenomenon to disappear eventually after the chain finally rids itself of all old lube? –Eric

Answer:
According to ProGold, it does not matter when you apply it for the function of the product. There are some mineral spirits in it that will evaporate overnight, giving the appearance of a dryer chain in the morning.

Lubing after your ride is probably preferable, because if you went through a lot of water, you won’t have the surface rust in the morning. The surface rust is irrelevant, since the area is still protected between the links where the ProGold treatment works, thanks to the heat there during use. However, it is unsightly, and lubing after your ride will prevent that. You can wipe it just before you head out, if you don’t like the dirt or wetness.

In answer to your final question, in my experience, the chain will always be wet throughout its life, if you use this every day. Consequently, it will always be dirtier than with chain wax, but it will last longer and run better. –Lennard

Question:
I have a one-piece carbon fiber frame that has developed short hairline cracks in the gel coat. Is there any way to tell if the cracks go through to the carbon fiber? Is this a safety concern? –Bob

Answer from Kestrel:
Tough to give an easy answer, based on the amount of info he gives.”Hairline cracks” could be something just in the finish, or due to damage from crash/impact, or some sort of manufacturing defect, etc. It is something I would need more info on, or preferably see, to determine the type/extent of damage.

I like to be safe rather than sorry, so I would tend to have the manufacturer check it out, or at least contact the manufacturer to see what they recommend. In my experience, cracks appearing in carbon fiber frames are usually a structural thing, unless there is something wrong with the paint/clear coat materials or application. BTW, I don’t know of any carbon bike using a “gel coat” finish – they are usually hand-sprayed paint/clear.

So not so common to see the type of surface cracks/crazing that occur in a gel-coated fiberglass structure, for example.
–Preston Sandusky
Kestrel Bicycles (Sand Point Design)

Answer from Colnago:
At Colnago we have some chemical products which allow us to understand if the cracks go through the carbon fiber. Naturally you must take the gel coat away, first. Normally, if Bob sends back the frame to the producer, they must be able to give an answer.–Alessandro Colnago


VeloNews technical writer Lennard Zinn is a frame builder, a former U.S. national team rider and author of several books including the pair of successful maintenance guides “Zinn & the Art of Mountain Bike Maintenance” and “Zinn & the Art of Road Bike Maintenance.”