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RBA Q&A: Answers To YourTech Questions

March 15, 2012
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When you’re descending, always be on the lookout for speed wobbles.


I was reading one of your threads on speed wobbles and couldn’t really come to a conclusion what the real cause is. My bike is a carbon fiber 2007 Specialized Tarmac, size 56.5, with a Ksyrium Anniversaries Red Spoke wheelset, front 18 spokes and rear 20 spokes. I’m 5 foot 11 inches and weigh 190 pounds. I changed out the stock wheels that came with the bike to the wheelset listed above, which have a lower spoke count and are lighter. Since the change, I have encountered speed wobbles at around 25 mph on downhills. Any help or suggestions would be greatly appreciated.
Keith Bolechowski
Rancho Cucamonga, California
Craig Calfee from Calfee Bikes responds:
Speed wobble is caused by a bicycle rider responding to asymmetrical steering inputs. While there are a few ‘natural’ situations that can cause it, like gusty winds on deep-section rims and your own shivering, most speed wobbles are caused by equipment. Wheels are the first place to look: check for unevenly tensioned spokes, flexy rims with not enough spokes, or a lack of balance. This last one is interesting to test on the repair stand. With the bike clamped by the seatpost, spin up a rear wheel to a fast cadence in your highest ‘downhill’ gear. Watch how much the bike starts oscillating. This is caused by unevenness in the tire and inner-tube rubber, as well as heavy valve stems and some unevenness in the wall thickness of the rim. The same reasons apply to car wheels. On heavier wheels, the unevenness of the rubber is a smaller percentage of the overall weight of the wheel. On light wheels, it’s a bigger percentage and therefore more out of balance.
One can measure and fix it easily. While still in the stand, take the chain off the cassette and let the rear wheel settle into its ‘heavy-side-down’ position. Clamp a wheel magnet on the uppermost spoke, counterbalancing the heavy end. You can slide the wheel magnet towards the outside of the wheel for it to have the greatest effect. You may need to add another one. You’ll be surprised at how much weight you have to add to balance some wheels. The wheel is balanced when it can be rotated to any position, and not move when you let go of it. Once balanced, do the spin-up test again and note how little the bike jumps around. Now do the front wheel. Then see if that prevents the dreaded wobble. If that doesn’t help on evenly tensioned, true wheels, then you might be too heavy for the wheelset.

Did any of the teams you raced for impose a curfew when you were at the races? You hear of baseball and football players getting in trouble for partying before a game every so often, but I hadn’t heard of it being a problem with cyclists until the 2010 Vuelta a Espana when Andy Schleck and Stuart O’Grady were out until 5 a.m. and then sent packing by their team manager.
Grants Pass, Oregon
Good question, Bruce. For me, personally, being out late during a stage race was never an issue. I could barely make it through dinner before wanting to hit the sack! None of my former teams ever had to impose a team wide curfew. Maybe at some point the Aussies on the team would be pulled aside and given a specific curfew since they were always up for a good time with their mates, day or night. For the most part, the professionals are just that, professional. Not many riders would want to jeopardize their race by staying up late partying the night before and letting down their teammates by not taking their job seriously. Once the race was over, it was a different story. The post-race party was always quite a sight. As long as everyone behaved themselves to a certain extent, the team management didn’t mind post-race celebrations.

If you’re having shifting problems, the culprit could be a bent derailleur hanger.

I hope you can help me out with a problem I’m having with the shifting on my bike. My chain is jumping around on the cassette and no matter how much adjusting I do, it doesn’t seem to help. I’ve tried every adjustment that I can think of. I changed the inner cable and housing after my gears started jumping around, but that didn’t help at all. There aren’t any stiff links in the chain, but I’m thinking of changing that next. Do you have any suggestions?
North Hills, California
John, without knowing the condition of your derailleur and shifter, I’m going to assume that they are in good working order. From the description of the problems you’re having, it sounds like a bent derailleur hanger rather than a derailleur adjustment. Sometimes the derailleur hanger can get bent without you even knowing it. If your bike got knocked over and landed on the drive side, or the derailleur got bumped while in the garage, it could be enough to bend the hanger and affect the shifting.
A good way to know if your hanger is bent is simply by looking at the derailleur cage from the back of the bike. If it’s not at a right angle with the ground, then it’s bent. As gear spacing gets narrower and narrower due to the addition of 10- and 11-speeds, the adjustments become even more finicky. A slight bend in the derailleur hanger can be the cause of many shifting frustrations, and the only fix is to have the hanger realigned. Fortunately, just about every bike shop will have a derailleur hanger alignment tool and can do a quick and relatively inexpensive ($20-$30) fix. If the hanger is severely bent, it might be necessary to replace it. If that’s the case, you better hope your bike has a replaceable derailleur hanger; otherwise, a simple fix could turn into a nightmare.
I live in Phoenix, Arizona where temperatures can regularly exceed 100 degrees, and although I try to get my rides in early in the morning, I still get stuck out in the heat occasionally. On my normal two-hour ride, I would drink 32 ounces of water, but sometimes afterward I would feel lethargic and parched. Is it possible that I’m not drinking enough? Would a sports drink be better than water? What do the pros drink during a race?
Phoenix, Arizona
It’s easy to underestimate how much fluid is lost during a ride, especially in dryer areas where sweat evaporates quickly. Since as little as 2 percent of lost body weight due to fluid loss can decrease performance, it’s critical to stay hydrated.
A few years back, during the 156-mile Philadelphia Invitational race, the temperature was in the upper 90s with high humidity. I knew if I was going to make it through the race, in any kind of shape to contend for a result, I needed to pound the fluids. I ended up going through 18 bottles that day. Fortunately, getting that many bottles was easy since we had follow cars in the race, but since most cyclists don’t have that luxury, it can be tough to get all the fluids necessary to stay hydrated in warm weather.
First off, during exercise, I would recommend using a carbohydrate/electrolyte sports drink. There are tons of options available that taste good and have the necessary ingredients. Secondly, try to consume 16 ounces of fluid every 30-45 minutes of riding. That should be enough to keep you adequately hydrated, unless it’s insanely hot. If that’s the case, I would probably recommend staying inside with the air conditioner blasting.

Pedialyte, or similar drinks, have ample electrolytes without the sugar commonly found in most sports drinks.

One trick of the trade that I learned was to drink Pedialyte the night before a hot race to ensure proper hydration going into the big day. It has the perfect amount of electrolytes without the sugar of a sports drink, and you can find it at any grocery store. Pedialyte would also come in handy post-workout to get my body rehydrated if I wasn’t able to take in all the fluids I needed during the ride.
A good way to see if you’re taking in enough fluids during a ride is to weigh yourself before heading out, and then again as soon as you get back. Be sure to wear the same amount of clothing on both weigh-ins. If you’ve lost more than 1 percent of your body weight, you should try to take in more fluids during the ride.
Neil Shirley is a former professional cyclist, current Road Bike Action assistant editor, and a coach of both amateur and elite-level cyclists. Got a question for Neil? Send it to RBA Q&A.


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