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VeloNews’ resident techno guru takes your questions.

By Lennard Zinn

Hanged by the wheel - it's okay.

Hanged by the wheel – it’s okay.


Dear Lennard,
I am considering storing my new full suspension bike using a vertical type rack that stores a single bike hanging vertically from the wheel.

I was wondering if that could cause any damage to either suspension, front or rear.
Does it make sense to hang the bike from the rear wheel?

Dear Nir,
Hanging it from the front or rear wheel will not hurt it unless either of your shocks leak oil through the upper seals. In that case, hanging it could still be a good thing, because it will alert you to the problem and motivate you to fix it.

Dear Lennard,
What may be causing my “new” bike to be so unstable? It’s an older bike (but with no miles), it has Shimano WH-550 16 spoke wheels and it flexes like a twig, is this due to those wheels or is it the frame?

Dear Harry,
It could be either or both, but even if only one of them is flexy, the whole bike will be even more flexible that that single item.

To understand this, we can go back to the same metaphor I used my column in VeloNews magazine two issues ago. Think of a steel plate being held up by four vertical springs. Adding four more vertical springs supporting the plate doubles the force required to push the plate down a given distance. (The springs work in parallel, analogous to the two bulb strands on a three-wire set of Christmas lights.) However, if the four additional springs were instead placed atop the plate and an identical plate were placed on top of them, the force to push the top plate down the same distance is cut in half. (The springs work in series, analogous to Christmas bulbs on a single strand.)

Perhaps even more surprising to some people who buy super-stiff components and use them on a bike with a flexy frame or wheels, if softer springs were instead used only under one plate, the system is softer than just one plate held up by the four softer springs regardless of how stiff the other four springs are.

On a bike, most components are in series, including your wheels, frame and crank (seatstays, fork legs and chainstays are in parallel). So, if you have flimsy wheels or a flimsy frame, you can put the stiffest components possible onto the bike, and it will still feel flimsy. To eliminate one or the other possibility, try the wheels on another bike and see if you feel the same problem.

Dear Lennard
In reading your magazine column this week on bottom bracket and frame flex I thought of my fav’ bikes and I began to wonder if flex is okay — sometimes. My Merckx MX Leader is very stiff, and tires me more quickly than my less rigid Gunnar, which I can ride for hours longer than the Merckx. I am talking about fatigue in the legs, not comfort, or fit, or ride. While a sprinter might favor complete rigidity, a stage racer — or recreational rider — might not benefit from such efficiency. Some people claim that the energy absorbed in a slightly compliant frame is returned to the drivetrain and aids propulsion. What is your take on this hypothesis?

Dear Charles,
Yes, there is no question that there is a balance between rigidity and rider fatigue that must be found when designing a frame. An analogous situation would be riding a cyclocross bike on a rough trail and then doing the same ride on a mountain bike. You will be much more tired after riding the ‘cross bike. Or riding a Harley hardtail across the country vs. a softtail. Vibration of your muscles is fatiguing. So if you were to race that Merckx on a smooth track, you might not feel the fatigue and would expect to perform better than on the Gunnar, but over a long period on a rougher surface, that may not be the case.

Now that may be a completely different question from the one about returning pedaling energy, since the first one may be dependent simply on compliance. But certainly some bikes absorb more energy in torsional and lateral flex than do others, and it may be that sometimes it is returned in phase with the pedal stroke so that it does aid propulsion.

More on rim corrosion related to sealants — including overlap of the last two column subjects: inflation gases and sealant corrosion:

Dear Lennard,
On the subject of corroding wheels.
For the past nine years we have been using my sealant to convert tires on every brand of rim including Mavic UST and Shimano UST rims. We have never had any customers tell us sealant was corroding their rims. Nor have we in all of our testing and riding seen this problem.

I’m sure we have 100 times more people riding MT bike conversions with my sealant over the Road tubeless. If the problem was with my sealant Mavic and Shimano would have seen problems years ago.

The rim in question is the newer Shimano road tubeless. I feel the problem is with the propane injection systems. Some propane is very corrosive to aluminum. If you do a search on Google for propane corrosion, look at this .pdf and read down to #8:

“8. Propane and other LPG gases are generally non-corrosive to steel and copper alloys. Precautions against corrosion may be necessary if aluminum or aluminum alloys are used.”

If we could talk with the customers affected I feel we would find they all, at one time used propane inflators to seal or inflate their tires. I have been told these inflators contain a propane byproduct. Well, the ones we tested in the past were like blow torches. Is it possible the byproduct they are using is the corrosive part of the propane? I will try to do some testing with Propane inflators and sealants to see if we can find the problem.

Dear Lennard,
I just checked the pH of my Stan’s tire sealant with pHydrion pH test paper: pH about 11, which is pretty alkaline. It does smell like ammonia, too. Sorry, Stan; I guess I’ll spend this rainy Wednesday cleaning out my tubeless tires and checking the rims. Alkali will remove anodizing from aluminum — remember how slick oven cleaner cleans scratched anodized aluminum components — and then the natural reactivity of aluminum will allow corrosion to take place.

pHydrion test papers are made by Micro Essential Laboratory.

The papers work well in dilute aqueous systems, so I think the alkaline pH test is fairly accurate. As always, your mileage may vary.

Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of numerous books on bikes and bike maintenance including the pair of successful maintenance guides “Zinn and the Art of Mountain Bike Maintenance” – now available also on DVD, and “Zinn and the Art of Road Bike Maintenance,” as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.”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.

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