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  1. #1
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    Race day wheelset: half pound savings for decreased stiffness?

    I had this in the Weight Weenie forum but someone suggested posting the question in the XC Racing....so here goes.

    Will you go with a wheel set that is considerably lighter (say 200 grams total) if it means it may be slightly less laterally stiff? Presume the fork/axle is the same and the wheelset is in the mfg's weight range for your body weight. Say each rim is 80 grams heavier and the rest is in spoke and hubs. The weight weenie thinking of making up time on climbs versus sensible foundation of stiffness and efficiency for racing and its sprinting, out of saddle hammering, downhill runs, etc.

    Depending on if you race in slower rocky courses or faster marathon type events with lots of climbing which would you go for in a race-day wheelset?

  2. #2
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    I'd run the race day wheels. They're called race day wheels because they're just for race day and you can give up a little durability for weight savings. of course as you've already alluded to you don't want to go crazy light that'll fold under you either.

  3. #3
    AZ
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    I would ride the lightest wheels that will not fail.

  4. #4
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    Get a wheel sponsor...
    I'm a member of NSMBA and IMBA Canada

  5. #5
    Fat-tired Roadie
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    I have enough trouble keeping my bike on the trail as it is.

    If I noticed I had tracking problems with the lighter wheels, I'd ebay them to someone who read the other posts in this thread.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  6. #6
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    I'd pick the one with the prettiest graphics-- I don't think 200g / 7oz is going to make a significant difference.
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  7. #7
    Rod
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    Can you feel the wheel flex? If you can't feel it flex then the decreased stiffness wouldn't matter to you. That's common sense, but a light rider wouldn't feel the flex that a 180 lbs rider would. I wouldn't want to ride a wheelset that flexes, but it appears I'm in the minority.
    There is not much choice between rotten apples.

  8. #8
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    I would buy the race wheels after your current wheels are worn out.

    Your wheels only contain about 5% of the kinetic energy. 95% is in the body and bike system as a whole.
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  9. #9
    Fat-tired Roadie
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    Interesting numbers.

    I'd been meaning to work it out. I knew they have a little more than proportional by weight alone, but had been too lazy to actually set up some equations.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  10. #10
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    Quote Originally Posted by Poncharelli View Post
    I would buy the race wheels after your current wheels are worn out.

    Your wheels only contain about 5% of the kinetic energy. 95% is in the body and bike system as a whole.
    Where does this come from? I know I changed out my wheels and I definitely noticed a difference on climbing.
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  11. #11
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    Quote Originally Posted by jrastories View Post
    Where does this come from? I know I changed out my wheels and I definitely noticed a difference on climbing.
    math, physics
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  12. #12
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    Quote Originally Posted by brentos View Post
    math, physics
    Yes. All the formulas are right here:

    Kinetic energy - Wikipedia, the free encyclopedia
    List of moments of inertia - Wikipedia, the free encyclopedia

    Conversion factors are sure a pain in the butt (holy crap, radians??, ). Assumed a velocity of 18mph, and Inertia of a hoop for the wheels. (mr^2).

    As Andrew mentioned, mass is the dominant factor, and most of that is in your body.
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  13. #13
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    Go for carbon wheels. I have seen several sets of Enve/King wheels for $1000 lately. Light, stiff and virtually indestructible. Also, rotational weight is much more important than non rotational weight.

  14. #14
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    Where?

    QUOTE=Salespunk;8562398]Go for carbon wheels. I have seen several sets of Enve/King wheels for $1000 lately. Light, stiff and virtually indestructible. Also, rotational weight is much more important than non rotational weight.[/QUOTE]

  15. #15
    Bro Mountainbiker
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    I would hope my crest race wheels would only make me faster. I'll know this week when I build em. Im thinking that I would rather have comps than supercomps. But it's all ordered and done.

    Has anyone noticed that they are faster on heavier/ stiffer wheels? Comparing light al to heavy al. No carbon you jackwagons. Not everyone can afford $1400 in rims alone! But we can dream!
    Raised in a Chicken-Coop by Chickens

  16. #16
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    Quote Originally Posted by Salespunk View Post
    Also, rotational weight is much more important than non rotational weight.
    Some more great stuff from Wikipedia:

    Another place where light wheels are claimed to have great advantage is in climbing. Though one may hear expressions such as "these wheels were worth 1–2 mph", etc. The formula for power suggests that 1 lb saved is worth 0.06 mph (0.1 km/h) on a 7% grade, and even a 4 lb saving is worth only 0.25 mph (0.4 km/h) for a light rider. So, where is the big savings in wheel weight reduction coming from? One argument is that there is no such improvement; that it is "placebo effect". But it has been proposed that the speed variation with each pedal stroke when riding up a hill explains such an advantage. However the energy of speed variation is conserved; during the power phase of pedaling the bike speeds up slightly, which stores KE, and in the "dead spot" at the top of the pedal stroke the bike slows down, which recovers that KE. Thus increased rotating mass may slightly reduce speed variations, but it does not add energy requirement beyond that of the same non-rotating mass.

    Lighter bikes are easier to get up hills, but the cost of "rotating mass" is only an issue during a rapid acceleration, and it is small even then.

    Explanations
    Possible technical explanations for the widely claimed benefits of light components in general, and light wheels in particular, is as follows:
    Light weight wins races with significant climbing because the heavier bike can't make up the gap on descents or on the flats: the rider on the lighter bike just drafts. Alternatively, if the identical riders of heavier and lighter bikes simultaneously reach the bottom of a climb to the finish, all of the advantage goes to the lighter bike. This is not the case in a hilly time trials (or riding solo), where the advantage of heavier, but more aerodynamic wheels would easily make up the distance lost in climbs.[citation needed]
    Light weight wins sprints because it accelerates more easily. But note that heavier aerodynamic wheels gain significant advantage as speed increases, and for a good part of a sprint a rider is doing little accelerating but is working hard against a high-speed wind. So many sprint situations may favor heavier but more aerodynamic wheels.[citation needed]
    Light weight wins in criteriums because of the constant acceleration out of every corner. Heavier but more aerodynamic wheels offer little advantage because the riders are in a group most of the time. The energy savings from lighter wheels is minimal, but it may be more significant that the leg muscles have to put out just that bit of extra effort at each jam.[citation needed]
    There are two "non-technical" explanations for the effects of light weight. First is the placebo effect. Since the rider feels that they are on better (lighter) equipment, they push themselves harder and therefore go faster. It's not the equipment that increases speed so much as the rider's belief and resulting higher power output. The second non-technical explanation is the triumph of hope over experience—the rider is not much faster due to lightweight equipment but thinks they are faster. Sometimes this is due to lack of real data, as when a rider took two hours to do a climb on their old bike and on their new bike did it in 1:50. No accounting for how fit the rider was during these two climbs, how hot or windy it was, which way the wind was blowing, how the rider felt that day, etc.
    Another explanation, of course, may be marketing benefits associated with selling weight reductions.
    In the end, the "incremental muscle power requirement" argument is the only one that can support the claimed advantages of light wheels in "jump" situations. This argument would state that: if the rider is already at the limit on each jump or each stroke of the pedals, then the small amount of extra power required for the extra weight would be a significant physiologic burden. Whether this is true is not clear, but it is the only explanation for the claimed advantage of wheel weight savings (compared to saving weight from the rest of the bike). For these accelerations, it makes no difference whether 1 lb is taken off the wheels or 2 lb off the bike/rider. The miracle of light wheels (compared to saving weight anywhere else in the bike/rider system) is hard to see.
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  17. #17
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    A lot of "Maybes" and "Ifs" in that article.
    Check out my SportTracks plugins for some training aid software.

  18. #18
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    Bikes and their riders are surprisingly difficult to model well.

    One of the reasons I hate it when someone I suspect hasn't made it through first-year physics, let alone dynamics, starts trotting out math and physics explanations.

    Here's something I've wondered about, especially with climbing out of the saddle - if work is change in energy (it is,) is the work performed when tipping a rotating wheel from one side to the other stored somewhere, or just lost? If it's lost, that would be one good justification for lighter wheels improving climbing, especially stand-and-hammer climbing.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  19. #19
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    Never underestimate the placebo effect... things that make me ride faster:
    -Lighter bike
    -New music on ipod
    -Less knobby tires
    -Beautiful weather

    Regarding the OP- I think there is probably more energy lost in the bikes suspension than wheels that are perceived to be less stiff.

    I also think that the gained speed of smooth and efficient pedaling and picking the best line and riding it smoothly will far outweigh both lighter and/or stiffer wheels.

    This is the interesting part- despite cycling being a multi million $ industry, there is no real data showing exactly what combination will provide the best performance. There are so many variables and lab testing does not really explain real world performance. Seems most is just anecdotal.
    Get it unlocked.

  20. #20
    is turning a big gear
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    ^ For example, rolling resistance tests on road bike tires are junk. Maybe on a velodrome they can be accurate, but otherwise not so much.
    Get it unlocked.

  21. #21
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    I have DT swiss 4.2 rims and XTR center lock hubs-28 hole laced up with thin gauge double butted spokes. Very light 1500g for the set. I'm 155# and they hold up well. I had a couple broken spokes on the rear because a shed the chain and it cut the spokes a bit and the shop didn't catch it.

    I ride the downhills really hard too-no problems.

    I'm an average (at best) climber and the wheel set (stans with regular karmas) has helped me roll up those hills MUCH better than my heavier wheelset.
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  22. #22
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    Science or no science - the difference in the weight of a wheelset is noticeable - if the weight difference is significant (200gms +). This applies only to the rims - as this is where the weight-noticeable difference is greatest.

    Example 1: on the road: changed from 450gm/rim GP4's to 290gms ti rims (back in the 80s) I found this to be lethal if riding fast in a strong side wind. The ti rims were so light that if I got out of the saddle to sprint the back wheel would come off the ground and I would go sideways. Went back to the heavier GP4s and felt much safer and more stable - slower windup but once there easier to maintain.

    Example 2: on the MTB: changed from a pair of Easton XC1s (rim weight 440gms) to Stan's crest (rim weight 320gms). When climbing in or out of the saddle and have to manual over square edge rocks/roots etc the stans win every time. The difference can be between clearing that last root in a 50m climb on the Stans or having to bail and walk it on the Eastons. The Eastons are stiffer but the Stans lack of stiffness doesn't matter as long as you can make it to race end.

    my 2c worth...

  23. #23
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    Quote Originally Posted by Poncharelli View Post
    Some more great stuff from Wikipedia:
    ... The miracle of light wheels (compared to saving weight anywhere else in the bike/rider system) is hard to see.
    This article seems to be general and applicable to road bikes? Has anyone put a Powermeter on a bike with heavier/lighter wheels to see if this is true? Seems like if you could test if the rider is pushing harder by recording the power output of the rider.

    This past year I shaved off a whole pound off my wheel/tire combo. I could notice a difference on acclerations (a huge difference), didn't really notice a difference on long substain climbes. Since there is such a huge difference in Utah to getting a good start (when you really have to acclerate) due to the fact we don't seem to have a very good shake out period before the single track - so I did see a difference in my results when I switched wheels.

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