THIS WEEK IN PRO CYCLING »

Get the VeloNews Email Newsletter FREE

  Learn More | Archive
Home » Top Stories » Tech »

Technical Q&A with Lennard Zinn: Dialing in those new wheels

Published: Jun. 16, 2009
Zipp 404s.
Zipp 404s.

Dear Lennard,
I recently received a set of Zipp 404 tubulars, and for me they represent a first in many respects. They are my first carbon wheels, my first tubulars and my first super light wheels. I taught myself to glue on the tires.

I have ridden them several times and I have noticed a significant pulsation whenever I coast at 20-28 mph. I don't notice it when I am pedaling although it is probably there.

I have tried to assess the problem. The wheels are true vertically and laterally. As you sight the rear tire near the brakes, there is a small (2-3mm) variation in the height of the tire as it rotates. When the wheels are allowed to "settle" by gravity, the valve stems of both wheels end up precisely at the bottom even though there is a small magnet opposite the front valve stem.

When I hold the bike by the saddle and spin the rear wheel at high speed, there is a very significant, vertical, pulsating rhythm which correlates to the speed of the wheel. It moves the bike visibly even when I try to hold it still. The same rhythm exists in the front wheel although less dramatic.

My buddy says I glued the wheels poorly. That’s very possible. I wonder if the wheel/tire/valve stem complex is out of balance.

Do you have an explanation for this phenomenon? Is it normal? Is there a solution? It is a very unnerving sensation while riding.
Rich

Dear Rich,
Indeed, I believe that you are right: the wheel is out of balance.

Your car will also pulse at speed with unbalanced wheels. I have had good luck with balancing lightweight road wheels by locating what part of the wheel always ends up on the bottom when it winds down to a stop and counterbalancing the other side of the wheel until it has no preferred stopping point. Obviously, good bearings are necessary for repeatability, but good bearings are usually a given in most Zipp wheels.

By locating the magnet opposite the valve stem, Zipp has indicated that it knows that the valve stem will be the heaviest point on the wheel. Incidentally, that is not the case with shallow-section aluminum rims. Generally, these will stop with the valve stem at the top, because the weld or the splint at the rim junction will outweigh a short valve stem. They are easy to balance, because you can just screw on more knurled nuts onto the valve stem until the wheel comes into balance.

But on a carbon rim, there is generally not a seam, and the valve stem will be the heaviest place on the wheel. And the lighter the wheel, the greater the same valve stem will throw off its balance. You could try slotting little fishing weights and putting them on the spokes opposite the valve stem and taping them down against the rim. Or just tape little weights to the rim.

The bulge in your tire may also add to the bumpy sensation, but my guess is that will be much less noticeable once you balance the wheel.
Lennard

Dear Lennard,
In your June 2nd column , you mentioned to a reader that he might use new Campagnolo Centaur shifters with his existing Campy 10-speed group to have the new ergonomics without replacing most of his drivetrain.

That inspired me, and I ordered a set and installed them today. I had a very hard time installing the shift cables without bending them. I finally got them installed, but the right shift cable was bent, and I will have to replace it as soon as I can buy another one.

How on earth do you get the cable up from the bottom and bend it to go into the beige cable guide without damaging it? I tried to bend just the end, but couldn't get it to work.
Mike

Dear Mike,
This is the instruction on how to get the cable through an Ultra-Shift lever that I just included in the soon-to-be-released 3rd edition of Zinn & the Art of Road Bike Maintenance :

On post-2008 Ultra-Shift Ergopower levers, the cable will pop up out of its passageway and continue in one of two grooves in a light-colored, low-friction material before passing through another hole back into the black lever body before exiting it. One groove routes the cable in front of the handlebar and the other routes it behind the bar, so choose the one you wish (I recommend routing the cable in front of the handlebar). The cable will not want to follow either groove and pass through that hole without some coaxing. First, push the cable out so it extends above the two grooves and put a little bend in the end of the cable. Pull it back in a bit until that bend is just visible. Now push the cable forward again, and push down on the end of the cable with a 2mm hex key or other thin implement to get the cable to pass through the little hole at the end of whichever groove you chose and exit the lever.

This method has worked great for me and for the other mechanic in my shop who does the assemblies on Zinn bikes.
Lennard

Dear Lennard,
I recently bought my wife a Guru Chron-alu. It is outfitted with an FSA standard crankset that, I believe, has an ISIS bottom bracket. I have a Ritchey WCS Compact Cranset that does not have a bottom bracket with it but is an Octalink compatible set.

Will the Ritchey crank work with the bottom bracket on the bike now or am I going to have to by a new bottom bracket or find an Isis compact crank somewhere.

I am very new to trying to work on my bikes as I have always just had my local bike shop do it.
Jeff

Dear Jeff,
Yes, if you want a compact crank, you’ll have to buy a new bottom bracket or a new crankset. ISIS and Octalink are not compatible.
Lennard

Dear Lennard,
I wanted to drop this new program on you. In an effort to promote tap water use and raise awareness about the waste bottle water creates, Swobo started a new effort last week:

Message in a bottle
Message in a bottle

Swobo has a new water bottle program called the "Message in a Bottle Project." We feel that the world doesn't need more water bottles with company logos, but we also know that water bottles, in and of themselves, are a good thing because they promote tap water use over bottled water use. So we created a program that allows the bottle to do the deed of holding tap water, but then it acts as a soapbox once the user is done with it.

This particular soapbox focuses on how much bottled water sucks up natural resources, and what a waste it all is come the end of the day.

Our first program within the Message in a Bottle Project is Tap Water Rules. We've written a letter on one side of the water bottle to the Nestle Water Bottling Corporation that announces the Swobo water bottle user's lack of stoke on bottled water. The consumer then places the appropriate postage on the water bottle itself, and sends the well-used and now-retired water bottle (with their message on one side) directly to Nestle.

Message in a bottle: Let them know how you feel
Message in a bottle: Let them know how you feel

Our goal is to flood Nestle with the idea that maybe creating containers that hold tap water is a better business than trucking water all over the world. We'll see. And like everything else we do, this seems like a lot more fun than just making water bottles. All Swobo water bottles are biodegradable/recyclable/recycled.
Sky Yaeger
Swobo

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.

Photo Gallery