Technical Q&A with Lennard Zinn-Mysteries of logic

Dropped chains - Why? Dear Lennard,

By Lennard Zinn

Dropped chains – Why?

Dear Lennard,
Last Saturday I was very fortunate to watch the Stillwater Criterium taking place in my very own hometown. It’s a great circuit with acrazy climb. Maybe you have seen it. Well, many racers in themen and women’s race dropped their chains when transitioning into the steepclimb. I am a randonneur rider, and I ride a triple with a granny 26-tooth granny ring. This helps me survive after riding for hundreds of miles and endless hills. I have fitted a Jump Stop to avoid dropping the chain.I wonder why these professional riders are not using such a simple and lightweight device to avoid such a catastrophic event in a fast-paced criterium. Once they drop the chain, they are really out of the race for all practical purposes.Maybe you can explain this mystery to me.


Dear Chris,
No, I can’t explain it, other than to say that many people are prone to think that bad stuff will happen to others and not to them. If riders were to train on similar courses under race conditions, they would see the likelihood of this occurrence. Of course, less panic during theshift and better front derailleur adjustment will help as well. In both of my maintenance books and in my “Cycling Primer” I recommend mounting an inner stop like a Jump Stop, a Deda Dog Fang, or a Third Eye Chain Watcher. I have one of these on each of my bikes that will accept one, and I install them as a matter of course on my customers’ bikes as well. (Some mountain bikes have a shock mount where the inner stop needs to go.)Some teams, Fassa Bortolo being a good example, have inner stops (Deda Dog Fangs) on most of the team’s bikes.Lacking an inner stop, rotating the front derailleur a hair on the seat tube so that the tail of the derailleur is inboard a bit more than thefront tip can speed downshifts to the inner ring while allowing the leading point of the inner cage plate to act a bit like a Jump Stop.


More on water trapped in wheels

I talked with a number of wheel manufacturers since last week about draining water from wheels, especially since I have since discovered a number of wheels without a drain hole, something I thought that pretty much all of them had. The reasons I received for eliminating the drain hole is that the area at the lower edge of the brake track, where the hole would need to be located, is the second most likely area for stress cracks to appear, after the holes around valve stems, nipples, etc. So even though many rims do have these holes, if yours do not, you might not want to drill one as I suggested last week. But without a drain hole,you have to remove the tire and tube, stand the wheel up with the valve stem down, and dry them out. Whether you have the drain hole or not, this is probably a good idea to do as frequently as you can stand to, it obviously being a bit of a pain, particularly with tubulars. Certainly you should do this any time you change a tire. Water, mixed with minerals picked up from the road, in an enclosed area with a number of different metals in contact with each other, has the potential to decrease the lifetime of a rim.


Dear Lennard,
Thanks! You were right. There are holes in each of the rims on the sidewall near the valve stems. Both of the things are cleverly covered up with solid plastic “Spinergy” decals. Those bozos. They drain fine now.


Dear Lennard,
I had an experience with Shamal wheels in a heavy rain/hail storm during a race of “high speed wheel wobble” on a steep descent.After the race I noted that the rims were full of water. This was the first and only time I ever experienced a high-speed wheel wobble with these wheels and I have always suspected that the water in the rim caused the imbalance. It felt like the bike was falling apart.


Dear Lennard,
It has been my experience that water will enter the rim by “creeping”up the spoke and into the rim through the nipple or other spoke entry hole via centrifugal force.

The wheel is turning too rapidly to have water enter through the valve hole or other weep holes, if any, when riding through puddles. Rather,any steady rain, however light or heavy, will cause plenty of water to accumulate on the wheels and thus move outward from the spoke and intoany hole available. I have had this happen on many different kinds of wheels and have no solution.


More on stem/bar clamp-size compatibility

Dear Lennard,

I have used mountain-bike stems for road bike bars for many years on my road and cyclo-cross bikes. I have never had a problem and have never noticed any damage to either the stem or bars (I check periodically and don’t use carbon road bars). I do not use road stems for MTB, however, because the 26.0 road clamp is too big and does not sufficiently secure the 25.4 MTB bar.


Dear Tre,
While this may have worked, you can be assured that no manufacturer warranty will cover you on this if one of those parts were to break. A 26.0mm road bar and a 25.4mm mountain stem were not designed to go together,and stem and bar manufacturers are getting so squeamish these days that many of them will not even honor a warranty claim if the bar and stem arenot both of their brand, much less a mixture of sizes.


Dear Lennard,
Nitto and Bontrager make road bars that fit a standard 25.4mm mountain bike stem. The Nitto is a classic shape. The Bontrager is designed for cyclo-cross but is certainly fine for general road use, especially if one is searching for a wide, roomy bar. However, it is best to use a stem with a removable face plate because with the older one-piece stems it is often impossible to spread the stem enough to go around the curves of a road bar.


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 including the pair of successful maintenance guides “ Zinn & the Art of Mountain Bike Maintenance” and “Zinn & the Art of Road Bike Maintenance.”Zinn’s regular 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 here each Tuesday.