Wheels and Weight Distribution

by notfastenough   May 21, 2014  

Hi all, I have a pair of Mavic Ksyrium Equipes, (admittedly only used on my other frame, I haven't tried them on the Madone) but I noticed that they didn't feel as stable on descents as my winter wheels (Omega Mach 1), and nowhere near as good as the stock Bontrager Race wheels on the Trek. The Mavics are the lightest of the three, but anything above about 35mph and the front starts to twitch and wobble. I had the spoke tension checked out but that was good. Anyone know why this is happening?

I'm asking because I would like to buy a wheel upgrade. This is because when I really drop anchor, the Bontrager Race wheels have a rather grabby brake track. My first club outing on my new bike resulting in a nice face/hedge interface in front of a concerned motorist.

The Madone has really neutral, predictable handling, and I'd like to ensure that continues. This isn't a thread asking you to recommend wheels, I'm trying to work out whether any lighter wheelset is going to have that same 'flightly' feeling as the Mavics. Thoughts? Is it the wheel weight? Is it my fore-aft weight distribution? Is it just that my arms are too tense?

On a related note, I've noticed that weight distribution seems to come into play quite a lot for me. Every time I read something about descending, someone advises hanging right back on the bike, but for me, this seems to induce front wheel wobble. If I get my weight over the front, the handling settles down. Why is it advisable to shift your weight backwards?

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Interesting questions. I've never had issues with front wheel wobble on fast descents but my husband did with his Masi. On descents in excess of 25 mph the front end would shudder violently to the point where he felt he'd be thrown off the bike. Ultimately the LBS where he bought it discovered a crack on the carbon fork where it went into the head tube. But I doubt that's what's going on with your bike as something structural like that shouldn't change based on your wheelset I would think.

In terms of weight distribution, I've found that when I'm on a steep (>10% grade) I feel more stable when I'm in the drops because it lowers my center of gravity so I can control the bike better with minute weight shifts, especially in turns, and I go faster because it's a more aero position. When I'm on the drops it definitely feels more squirrelly to me as I'm pushed around by the wind more and I just feel more tippy. I would assume that the physics of lowering your body shifts your weight balance as it pushes you slightly back on your rear wheel but still maintains enough weight in front so that you don't get that unbalanced feeling like the front wheel is going to wiggle out from under you. Theoretically, if you shift your weight too far forward there's not only the risk of end-overing the bars but also having the rear wheel slip out from under you as there's not enough weight on it (similar to how you can fishtail when standing up on climbs as your weight shifts mainly to the front) Is this similar to what you've felt with the wobble?

Here's also a much more eloquent article with tips from Antonio Cruz about descending position and front/rear body weight positioning http://www.bicycling.com/beginners/bike-skills/descend-rocket

Melancholy is incompatible with bicycling. ~James E. Starrs

movingtarget's picture

posted by movingtarget [134 posts]
22nd May 2014 - 0:41

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Is it the frame characteristics? Planet X Carbon Pros are known for having vague steering at speed. For years I thought it was me or the wheels. I now happily ride the same wheels off my Ridley.

If you look at the physics, centrifugal forces will be higher on a heavier rim and there for the stability on the bike is increase. Think of a flywheel or even spin a wheel in you hand and try to alter it's angle. Therefore a light rim may wander at speed and any input could result in over compensation and a wobble.

Weight distribution, the idea of shifting weight back I think is to allow the front wheel to follow it's own track to a point. Also under braking it allows your body to move forward without feeling like you are going over the bars.

Like with most things bikewise, experiment and find what feels right for you. Ultimately, if you have confidence you will go faster.

posted by Yorkshie Whippet [296 posts]
22nd May 2014 - 8:39

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movingtarget wrote:
Interesting questions. I've never had issues with front wheel wobble on fast descents but my husband did with his Masi. On descents in excess of 25 mph the front end would shudder violently to the point where he felt he'd be thrown off the bike. Ultimately the LBS where he bought it discovered a crack on the carbon fork where it went into the head tube. But I doubt that's what's going on with your bike as something structural like that shouldn't change based on your wheelset I would think.

In terms of weight distribution, I've found that when I'm on a steep (>10% grade) I feel more stable when I'm in the drops because it lowers my center of gravity so I can control the bike better with minute weight shifts, especially in turns, and I go faster because it's a more aero position. When I'm on the drops it definitely feels more squirrelly to me as I'm pushed around by the wind more and I just feel more tippy. I would assume that the physics of lowering your body shifts your weight balance as it pushes you slightly back on your rear wheel but still maintains enough weight in front so that you don't get that unbalanced feeling like the front wheel is going to wiggle out from under you. Theoretically, if you shift your weight too far forward there's not only the risk of end-overing the bars but also having the rear wheel slip out from under you as there's not enough weight on it (similar to how you can fishtail when standing up on climbs as your weight shifts mainly to the front) Is this similar to what you've felt with the wobble?

Here's also a much more eloquent article with tips from Antonio Cruz about descending position and front/rear body weight positioning http://www.bicycling.com/beginners/bike-skills/descend-rocket

I don't think it's the fork on that frameset. I do agree about the position on the bars - I shift to the drops as the speed increases and agree that the handling improves. Previously, I was concentrating on keep my arms relaxed, but perhaps took too much weight off them, leaving the front too light.

It's weird, because the advice I read re descending is to hang back on the bike and take the weight into my feet and off the saddle slightly, but I find that both of these decrease my stability - of the front and the mid-section of the bike respectively. I find that if I concentrate my weight on the saddle and the bars and keep my feet at the horizontal pedal position, that's the best I can find so far. Cruz's article lists all the things my rational self knows, but that I sometimes find difficult to practice. (Or, as Steve Peters might say, my inner chimp keeps getting in the way of the computer!)

Yorkshie Whippet wrote:
Is it the frame characteristics? Planet X Carbon Pros are known for having vague steering at speed. For years I thought it was me or the wheels. I now happily ride the same wheels off my Ridley.

If you look at the physics, centrifugal forces will be higher on a heavier rim and there for the stability on the bike is increase. Think of a flywheel or even spin a wheel in you hand and try to alter it's angle. Therefore a light rim may wander at speed and any input could result in over compensation and a wobble.

Weight distribution, the idea of shifting weight back I think is to allow the front wheel to follow it's own track to a point. Also under braking it allows your body to move forward without feeling like you are going over the bars.

Like with most things bikewise, experiment and find what feels right for you. Ultimately, if you have confidence you will go faster.

Well you could have a point about that frame - it's essentially a generic far-east thing. I bought it from Graham Weigh in Deeside, but as the guy there said, it's basically the same frame as sold by Dolan, Ribble, Planet-X and a host of others. I suppose I should swap the tyres/tubes from the Bontragers and see how the Mavics feel on the Trek. I have also thought it was me, so I'd be quite happy if it turned out to be the frame!

Last night I would have considered trading a very loud baby for a really nice bike.

posted by notfastenough [3307 posts]
22nd May 2014 - 11:25

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