Bike weight - how important??

Discussion in 'Cycling Equipment' started by kneighbour, Apr 30, 2003.

  1. kneighbour

    kneighbour New Member

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    I guess this is a topic dear to most road rider's hearts! But I wonder if things have gone past the physics of the matter, into mere myth and custom?

    I own a Softride Solo - a fairly heavy (14 kg) road bike. But it is very comfortable as it uses a carbon fiber suspension beam (no seat post). I have recently ridden a more normal and slightly lighter road bike, weighing in at 10kg. It was a LOT faster than the Softride, both on the flat and climbing hills.

    I am trying to work out why so that I can either talk myself into buying a new bike, or so I can fix my Softride so that it is just as fast.

    Argument 1 - Total weight (rider+bike)
    Looking on the Softride website, I see they put forward the fairly reasonable argument that it is the complete weight of the rider, plus, bike, plus water bottle, mobile phone, etc that is important.

    This seems a good scientific argument. If a rider weighs 100kg, and the bike 15 kg - total weight is 115kg. If we drop the bike weight to 10kg, this is only a total decrease in weight of 4% - no big deal.

    Argument 2 - Bike weight alone
    Most cyclists (And my local bike shop) assert that the bike weight is the big thing. Take off a couple of kilos on the bike, and you make a big difference in speed, etc. ie drop the weight from 15kg to 10kg. This is a drop in weight of 33% - a big change.

    Never mind that you have a 110kg rider on the bike, loaded down with 2 kg water, mobile phone, digital camera, food bars, etc.

    This does not make sense to me - but it has the advantage in that this seems to be what everyone has found to be true by experience. Or is it what they have heard at the bike shop, or read in bike magazines?

    I have to admit that my slight experience shows me that the bike weight is the big thing. And it is what my local bike shop guy insists is the fact in real life.

    Here was my "test" situtation.
    Bike #1 - Softride Solo
    Aluminium frame, 105 groupset, 700x23 wheels, flat handlebars. 14kg. Suspension beam seat post. Here in Australia costs around AUD$4,000. A road bike, but probably more of a tourer than a flat out speed machine.

    Bike #2 - Raceline
    Aluminium frame, Tiagra groupset, 700x23 wheels, dropdown bars. 10kg. Fairly cheap (entry level) road bike. Around AUD$1200.

    Same rider (me), with basically the same equiment (ie water bottles, etc). The Raceline was MUCH faster than the Softride. Climbing hills was markedly easier on the Raceline.

    So what do other people think? Is there a good scientific reason why the bike weight itself seems to be the over-riding factor? When it comes down to it - working out the physics of the matter is not so important to me - but is it true?
     
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  2. clever_guy

    clever_guy New Member

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    kneighbour;

    I have had guys hop off mid-range Treks and Cannondales (~$5K), hop on my Solo and say the same thing about the Solo - that it rides better than their bikes. I think a lot of it is the "toy" effect, hop on a new bike and it feels better for a while.

    No reason you can't upgrade the Soloflex to what you want. At the end of the day it may be slightly heavier than a comparable mid-range traditional frame racing bike - but unless you are competative I don't think it makes much of a difference. At 110kg I don't think a few kg's on the bike is going to make much difference - personally I would look at performance modifications, and try to optimize the feel of the bike. I don't know if your Solo was properly fitted for you, and that makes a difference in the feel and how it performs (as with any road bike).

    -CG
     
  3. maarten

    maarten New Member

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    Weight is more important when going uphil and when accelerating. On flat sections with constant speed the effects from more weight are smaller.

    About bike weigth versus human weight. The weight of the frame groupset and person has the same influences. Its only when going to moving parts that weight loss is more important(saving 200gram on wheels is way better(performance wise then saving 200grams on frame or fat)).

    But note at high speed aerodynamics are very important. Wheels with good shape may way 200-400 grams extra but the aero benefits may be much higher then the weight disadvantage.
     
  4. MidBunchLurker

    MidBunchLurker New Member

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    Forget about the weight!! On the road just go for the one that feels better to ride - be it for stiffness, handling, smoothness, cool looks or whatever blows your hair back.

    If you're racing your bike the most important thing is your fitness and leg strength, NOT the weight of your bike (well, not for almost all the kinds of cycling us mere mortals do).

    Having said all of that though :) , 14kgs is real heavy for a road bike...

    HTH
    N.
     
  5. Kraig Willett

    Kraig Willett New Member

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    Hello,

    I have written a couple of online articles on this subject in the past. If you have time, you might check them out at the following page of links:

    http://tinyurl.com/3x36

    The articles are titled:

    8/1/2001 - Bicycle Wheel Performance

    6/5/2002 - Is Time-Trial Equipment Selection "Significant"

    Basically, these articles suggest that weight is a distant second to aerodynamics when it comes to impacting performance.

    ==================
    Kraig Willett
    www.biketechreview.com
    ==================
     
  6. carmender

    carmender New Member

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    I feel it is a matter of simple physics involving mass. The less an object mounted on wheels weighs the easier it is to move.You can take away two things....body weight and gravity. The first is doable and the second is impossible cause we're stuck on this planet. Bikes have reached the technical end of minimal mechanical friction. The only thing left is making the vehicle as light as possible.
     
  7. Evo

    Evo New Member

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    I ride an old Shogun Selectra (steel frame, shimano tourney Goupo). I wouldn't like to even think what it weighs! I'm also in the process of buying a new bike and test-rode a modern aluminium-framed one the other day....The differences are like chalk and cheese. The bike accelerated quicker, stopped faster and I had no inclination to get up out of the saddle on climbs. But, then again, once you get the old Shogun going, there's not much that'll stop it (Except for steep hills!).

    I think that to a certain degree, weight does matter, as I found out the hard way, but only to a certain degree. For us mortals not doing mad time-trials and worrying about whether I could save 20 grams on some part.

    Has anyone else found this as well?
     
  8. JohnO

    JohnO New Member

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    I read a writeup on the new aero framesets used by Postal to win the team time trial in the TDF. They were described as being slightly heavier than the standard road bikes, but superior for TT due to better aerodynamics.

    If you like the ride of a beam (I sure do), but want less weight and better aero, you might look at a Trek YFoil
    (link is to my personal ride)

    Now out of production due to the UCI banning beam frames for competition, it was (and still is, as far as I know) one of the most aero frames ever produced. Frameset weighs around 3.2 pounds, my bike built up to a little over 19 pounds. Personal opinion, but I think it's one of the sharpest looking bikes ever made.

    My personal experience is that this bike will fly on sprints and downhills, noticably quicker than other similarly equipped bikes. The Vector Pro wheels are also as aero as all get out, albeit with a rather stiff ride.

    Trek discontinued the Foil in 2000, but new/unbuilt framesets turn up on ebay from time to time in the $500-750 range. (was $1700 new)

    Short of replacing the entire frame, you might also try a set of aero wheels.
     
  9. fatbadger

    fatbadger New Member

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    I find with my current mtb as its a hardtail its a hell of a lot lighter and that rly helps me on the hills and at the start of races when i need to get off the line fast, also i only weigh bout 7stone so tht helps lol
     
  10. JUS

    JUS New Member

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    This is not true.....much to the contrary, modern bikes are highly INEFFICIENT. For starters, think about the driveline. Chains are grossly inneficient. They have 100 or so mechanical links that all scrub off friction and thusly reduce energy transfer. The interface between chain and gear is even worse....more friction, more drag, even less power transfer. This problem is multiplied by our need for rear deraillieurs. The solution to this problem would be a belt driven driveline, running on only two variably (and automatically) sized kinesium rings. No chain, no gears, no shifters, no derallieurs, = less drag and ROTATIONAL MASS....which is probably the modern bicycle's biggest problem. I believe that too much emphasis has been put on lightening frames, when heavy tires, wheels, spokes, cranks, gears, etc...are diffusing energy.



    And I will not even begin to talk about suspension.


    -JUS-
     
  11. carmender

    carmender New Member

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    JUS has a point and I agree. I forgot about chain drag. It would be interesting to see CV drivetrain devloped for bikes. Carmender
     
  12. Eldron

    Eldron New Member

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    It all depends what you want from a bike...

    If you're a weekend warrior then put comfort first and worry about weight second.

    If you're a time triallist then aerodynamics first and don't even worry about the weight (as most TT courses are flat).

    If you're a road race don't worry about aerodynamics too much as you'll have the bunch to protect you most of the time - unless you're Jacky Durand the breakaway specialist.

    If you're a sprinter (my fave past time) then stiffness comes first.

    Ultimately everything needs to be a trade off. Some trade offs I make are:

    Carbon fork with aluminium head tube - the ally head tube makes the front end more rigid but adds a bit of weight. I ride a Turbomatic saddle - not the lightest on the market but really comfortable.

    One thing I find make a huge difference is wheels - Vector Pros (as stated above) are light and strong. When I first rode them they were appreciably faster. Quite versatile too: light for the hills, aero for the time trialling and stiif for the sprints.
     
  13. coolworx

    coolworx New Member

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    Could it be the greater wind resistance slowing ya down? Maybe put some aerobars on the flat-bars of the Softride.
     
  14. madisongrrl

    madisongrrl New Member

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    I think that most any decent bike could prove to be faster than a softride. The are really meant for long comfortable rides (100+miles). I think the geometry is just way too radical. Much of the energy transfer is wasted. In a race situation, I would probably choose something else. For a century or double century, the softride would be great. As far as bike weight is concerned, my bike weighs 18.5lbs. It is fast as hell... If I added a few pounds, would it really matter? I don't know...
     
  15. dhk

    dhk New Member

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    Power needed to climb steep grades at a low speed is proportional to total weight (body plus bike). So, if you save 2 lbs on the bike, out of a total of 200 lbs, that means you'll get up the hill about 1% faster with the same power output. That's 6 ahead seconds on a 10 minute hill climb.

    Not a lot to most of us recreational riders, but if you're racing for the finish line at the top, 6 seconds is certainly a decent margin of victory.
     
  16. Mr_Potatohead

    Mr_Potatohead New Member

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    I come down on the total weight being important side.

    I think when it comes to comparing two different bikes it's too subjective and there are two many variables. What you may be feeling is ride quality. Which relates to tire pressure, saddle type and position, and spoke gauge among many other things.

    To be really scientific about it. Find your favorite hill and ride up it unloaded. Then go back down and pick up a couple of full water bottles, thats about 3 lbs or so. Ride back up the hill. Can you tell the difference? I doubt I could.

    On the other hand, I went up my favorite mountain road this last weekend and I took the ol' steel framed, triple crank 23 lbs bike with a Camelbak full to the brim with water. Thats about 5 lbs more for the bike and 5 lbs more water than I usually carry, and I could feel the difference.
     
  17. JTE83

    JTE83 Member

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    I have 2 road bikes -- a 2003 Cervelo Soloist Team that's 17.0 lbs with Ultegra / Durace & Ksyrium SSC SL's. My training bike is a 2002 Giant TCR Aero 2 with 105's, SHimano R535 wheels -- 20.4lbs.

    I have hit a top speed that is the same on both bikes -- 29.2 mph on the flats with no wind. So my $1500 bike goes as fast as my $3033 bike!

    But the Cervelo subjectively feels faster on the acceleration.
     
  18. dhk

    dhk New Member

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    Acceleration is similar to hill climbing. Good old Newton's Law says your acceleration will be proportional to total mass for a given force applied to the pedals. So, if 3 lbs is 1.5%, of your total combined weight, you'll get to the same top speed 1.5% quicker. (If the 1.5 lbs comes off the wheels, it's worth about double.)

    Agree the lighter bike will feel more responsive as it moves under you, but as you say, that's subjective. At top speed, believe about 90% of your power is going into aero drag. So, it's not surprising you don't see any easily-measureable difference between bikes.

    Plus, the ability to get into a good aero position on the bike is a lot more important than the height of your rims or number of spokes....that's why Lance spent so much time in the wind tunnel last winter.
     
  19. NJ Hewitt

    NJ Hewitt New Member

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    Something that's only been briefly touched on so far and deserves emphasis is that rotational mass is far more important than static mass on the bike; the same weight loss off your rims, tyres, even shoes is far more beneficial than than weight loss off your frame or saddle. I'd say at least five times more helpful in terms of the feel and effort of riding while cornering or accelerating, and still very noticeable on the flat and steady.
     
  20. dhk

    dhk New Member

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    Believe Mr Potatoehead posted the formulas on another related thread recently which proves that wheel weight costs almost double in terms of accleration. I say "almost double", since in his equations he assumed the entire weight of the wheel was concentrated at the rim...kindof a "worst case".

    Agree shoes and pedals are important also, but probably a bit less than the "times 2" factor since they have a smaller radius of rotation. Depends on the gear ratio of course....how fast they are turning compared to the wheels.

    The rotational inertia isn't all that great a factor overall, since the weight of the wheels and shoes/pedals is only a small % of overall weight. So, even if you save a pound on your wheelset, and it "counts" as two pounds off your total body/frame weight, that's in the 1% range for most of us.
     
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