Saving circa 500g on wheels………

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  • Saving circa 500g on wheels………
  • bigsi
    Member

    …… is it worth it?

    I’m building a bike for enduro racing this year but am on a budget.

    I know the theory that weight saving at the wheel is more noticeable than anywhere else but my question is this –

    Would you consider spending £200 on saving 500g at the wheels over spending the same amount of money elsewhere on the bike for a greater weight saving as a worth while exercise?

    Any thoughts?

    Premier Icon Northwind
    Subscriber

    It depends on the rest of the spec. Especially tyres- the differences are all relative, my traversees are noticably very different to my 721s and that’s about a 500g difference, but if I stick dualplies on them then the higher overall weight diminishes that difference if you see what I mean.

    It’s all relative. What about the tyres, brakes, tubes/tubeless and cassette? Are these at an optimum?

    Premier Icon vinnyeh
    Subscriber

    I’m really unsure how spending £200 can save you 500g anywhere other than wheels, unless you’re doing something like ditching a dropper post for a carbon one and swapping dh tyres for xc racing jobs.

    Mind if you’re going enduro (stage), rather than endurance racing I’m not sure why you’d bother doing that really.

    Stick with the wheel change if you reckon you’ve got nothing else to spend the money on, and really want to spend it on the bike.

    You can lose about 100g just by spending £50 instead of £25 on a rear cassette.

    crikey
    Member

    I know the theory that weight saving at the wheel is more noticeable than anywhere else, but it doesn’t really equate to a difference in performance on a mountain bike, and especially not in enduro racing, when you’ll be carrying stuff and getting wet and covered in mud.

    Spend the £200 on good B&Bs the night before the race.

    Premier Icon Northwind
    Subscriber

    Oh, also… What sort of enduro racing? Proper enduro, or endurance xc?

    bigsi
    Member

    sorry i mean 12 hour endurance not enduro.

    The drive train will be the current stuff I’ve got, X9 rear mech, XT front mech, X0 cassette & XT crank so going any lighter will cost more than £200

    vinny – It would be tough to be honest to save 500g for £200 outlay but with some careful shopping around.

    +1 for spending slightly more on a light cassette – best bang for your bike. Bikeradar ran an article saying that it costs about £2.48 to lose one gram http://www.bikeradar.com/news/article/bike-weight-saving-more-costly-than-silver-32960
    Tyres and tubes also offer economical weight savings.

    bigsi
    Member

    Will be tubeless with rim strips if using current wheel set or without needing the rim strip if i go for the new wheels.

    Tyres will be the same no matter which wheels.

    Premier Icon kelvin
    Subscriber

    Crest rims.

    Premier Icon seosamh77
    Subscriber

    I went for 2 x 900g tyres, to 2 x 570g tyres(nobby nics). I noticed quite a difference.

    cynic-al
    Member

    If you are spending money to save weight then save it at the rims/tyres for sure. It probably won’t make you much faster but it will fell like it did.

    bm0p700f
    Member

    Remember that lossing weight at the cassette is not the same as lossing weight at the rim/tyre/tube. The same weight saving at the rim will reduce the moment of inertia of the wheel far more than the same weight saving at the hub/cassette area so I would pick lightweight rims/tyre/tubes before splashing out on expensive cassettes.

    curvature
    Member

    My recent experience –

    Changed Orange Five aluminium bars to Syncros Carbon bars – 150g saving

    Converted wheels to Stans No Tubes – 100g saving per wheel

    The difference to the way the bikes rides after going to tubeless is really noticeable, it’s a lot faster to pick up.

    Remember rotating mass has a big influence on the way a vehicle accelerates whether it be a push bike or motorbike.

    I would say change the wheels and go tubeless.

    b r
    Member

    If you are riding for 12hrs whatever weight you can save will help, also look at your Camelbak and contents too.

    But weigh everything you have first, before spending.

    crikey
    Member

    Rotating mass in bicycle wheels has an insignificant effect, however often the myth is repeated.
    If anyone can show it makes a difference, rather than claiming it does, I’m open to having my opinion changed.

    cynic-al
    Member

    TBF crikey me sober chum, so does non-rotating weight.

    whatnobeer
    Member

    Rotating mass in bicycle wheels has an insignificant effect, however often the myth is repeated.

    Can you show me anything that says it doesnt make any difference?

    crikey
    Member

    Indeedy, my mechanically adept acquaintance.

    It’s interesting how it’s become so widely accepted..

    skywalker
    Member

    Rotating mass in bicycle wheels has an insignificant effect, however often the myth is repeated.
    If anyone can show it makes a difference, rather than claiming it does, I’m open to having my opinion changed.

    TBF crikey me sober chum, so does non-rotating weight.

    🙄

    crikey
    Member

    Can you show me anything that says it doesnt make any difference?

    It’s not that it doesn’t make any difference, just that the difference is very small, and is lost in the complexities of the operation of the bicycle.

    It’s also almost invariably considered in an isolated way; no thought is given to the whole bike/rider/kit involved.

    This is my best reference;

    http://biketechreview.com/reviews/wheels/63-wheel-performance

    Premier Icon Northwind
    Subscriber

    crikey – Member

    Rotating mass in bicycle wheels has an insignificant effect, however often the myth is repeated.
    If anyone can show it makes a difference, rather than claiming it does, I’m open to having my opinion changed.

    It seems I’m in the kind of mood when I ask people making unsubstantiated claims yet demanding proof from others, to apply their demands to their own posts.

    crikey
    Member

    skywalker, you can make a contribution if you want to.

    skywalker
    Member

    I would make a contribution, but I think my time will be wasted explaining it. Clearly you two know better than the laws of physics.

    crikey
    Member

    I would make a contribution, but I think my time will be wasted explaining it. Clearly you two know better than the laws of physics.

    Come on, don’t be shy. Explain the difference that 500g weight loss at the wheels will make in a 12 hour mountain bike race, Professor.

    Sam
    Member

    Having had practical experience (i.e. used) light frames and heavy wheels and also heavy(ish) frames and light wheels, I can tell you I’d prefer the latter any day.

    Premier Icon Northwind
    Subscriber

    crikey – Member

    Explain the difference that 500g weight loss at the wheels will make in a 12 hour mountain bike race, Professor.

    The mood can last for a long time sometimes. Explain why a 500g weight loss at the wheels will make an insignificant difference in a 12 hour mountain bike race, Professor?

    crikey
    Member

    …and then explain the difference from a 500g weight loss that isn’t rotating…

    Premier Icon Northwind
    Subscriber

    Well, if you’re feeling keen, feel free.

    Or alternatively continue demanding other people provide proof, while ignoring requests for the same. Up to you really.

    cynic-al
    Member

    A test a while ago, where a roadie went up Alp D’Huez 4 times on different set-ups, including with his tyres filled with water IIRC, showed **** all difference to his times (and IIRC his HR was recorded).

    That’s the “physics” that skywalker etc appear to be on about – no better test has been done AFAIK…while light wheels fell realy fast, they’re not actuallt significantly faster.

    I accept an MTB climb may be slightly different.

    Crikey, chum, how am I mechanically inept?

    radoggair
    Member

    crikey . Do you race, and if so any good?. Just wondering.

    If you look at the car world for instance, losing 3kg a corner ( according to pro testers) makes a noticeable difference.

    I ( unscientifically of course, but i’m using real data (me) rather than lab data ) notice a difference going from a heavy(ish) wheelset to a light race wheelset. Whether thats unsprung mass or just lightening of the bike doesn’t really make a jot of difference.

    Now, if the context of the question ( and OP mentioned saving 500g, a lot of weight) was would i feel the difference between say a 1250g wheelset and a 1050g wheelset, then i feel the difference would be negliable because of the flex and precaution taken on a really light wheelset would ofset the weight advantage. Think Njee on here said that a 900g wheelset was built but they prefer the ride and safety of a slightly heavier wheelset.

    So to the OP, spend that money on the light wheelset, you will notice a difference but also choose tyre and tyre pressures carefully. On a light wheelset keep them quite high, say above 33psi because you will feel a tyre roll of the rim any lower than that plus ( IMO) they roll better without losing too much on traction

    bigsi
    Member

    Skywalker if not for the others then I’m interested to know why.

    Once you’ve explained you don’t have to check back and answer any of the others comments as I will draw my own conclusion 😉

    My worry is not so much the speed aspect its the pushing an extra 500g or rotating weight when I’ve been in the saddle for 12 hours. How much will it have taken out of me having to rotate that extra 500g over the previous 12 hours 😕

    skywalker
    Member

    Come on, don’t be shy. Explain the difference that 500g weight loss at the wheels will make in a 12 hour mountain bike race, Professor.

    Consider the kinetic energy and “rotating mass” of a bicycle in order to examine the energy impacts of rotating versus non-rotating mass.
    The translational kinetic energy of an object in motion is:

    Where E is energy in joules, m is mass in kg, and v is velocity in meters per second. For a rotating mass (such as a wheel), the rotational kinetic energy is given by

    where I is the moment of inertia, ? (pronunciation: omega) is the angular velocity in radians per second. For a wheel with all its mass at the outer edge (a fair approximation for a bicycle wheel), the moment of inertia is

    Where r is the radius in meters
    The angular velocity is related to the translational velocity and the radius of the tire. As long as there is no slipping

    When a rotating mass is moving down the road, its total kinetic energy is the sum of its translational kinetic energy and its rotational kinetic energy:

    Substituting for I and ?, we get

    The r2 terms cancel, and we finally get

    In other words, a mass on the tire has twice the kinetic energy of a non-rotating mass on the bike. There is a kernel of truth in the old saying that “A pound off the wheels = 2 pounds off the frame.”

    There you go, young grasshopper.

    cynic-al
    Member

    Radiogaga, Windy and Skywalker…jeez…did you even read crikey’s linked-to article?

    crikey
    Member

    Al, I said adept, y’know, as a complimentary thing…

    Interestingly enough, we have done this before…

    http://singletrackworld.com/forum/topic/rotating-weight-does-it-make-any-difference-and-why

    Anyway, a quote from the above article;

    So, what do all these numbers mean? It means that when evaluating wheel performance, wheel aerodynamics are the most important, distantly followed by wheel mass. Wheel inertia effects in all cases are so small that they are arguably insignificant.

    How can it be that wheel inertial forces are nearly insignificant, when the advertisements say that inertia is so important? Quite simply, inertial forces are a function of acceleration. In bike racing this peak acceleration is about .1 to .2 g’s and is generally only seen when beginning from an initial velocity of 0 (see criterium race data in Appendix D ). Furthermore, the 0.3kg/0.66lb difference in wheels, even if this mass is out at the rim, is so small compared to your body mass that the differences in wheel inertia will be unperceivable. Any difference in acceleration due to bicycle wheels that is claimed by your riding buddies is primarily due to cognitive dissonance, or the placebo effect (they paid a lot of money for the wheels so there must be some perceivable gain).

    crikey . Do you race, and if so any good?. Just wondering

    Not anymore 😥
    Old age has crept up, hidden by a job and kids, then jumped out on me and scragged me. I crawled around the 3 Peaks this year, might have another go, but a 17 year gap added well over an hour to my time.

    crikey
    Member

    ..sorry, forgot; changing wheel weight is very noticeable, in that we/you/me can all tell that it’s changed, but it doesn’t have the effect in terms of actual, measureable performance that we assume.

    radoggair
    Member

    well get back racing 🙂

    Anyway, firstly it does say that the vest wheels are those that are light, aerodynamic with no brake rub. ALso this test was on a road bike where (admittedly) wheel weight isn’t as important, wheel aerodynamics are because most of your time your spend at speed. MTB’ing on the other hand is far more stop/start, so ( and its written in there) lighter wheels allow faster acceleration where in many events time can be gained.

    So , cynic-al did you read this as well and realised the biase of road riding or are we just jumping on the scientific road bandwagon?.

    +1 for light wheels. I’m considerably faster on my ZTR 29er Race Golds 1345 g, tubeless RR and RRon, XTR cassette, ti skewers, and than my Shimano MT75 UST wheelset 1900 g with 2 x NN I use for training.

    radoggair
    Member

    well get back racing 🙂

    Anyway, firstly it does say that the vest wheels are those that are light, aerodynamic with no brake rub. ALso this test was on a road bike where (admittedly) wheel weight isn’t as important, wheel aerodynamics are because most of your time your spend at speed. MTB’ing on the other hand is far more stop/start, so ( and its written in there) lighter wheels allow faster acceleration where in many events time can be gained.

    So , cynic-al did you read this as well and realised the biase of road riding or are we just jumping on the scientific road bandwagon?.

    skywalker
    Member

    .sorry, forgot; changing wheel weight is very noticeable, in that we/you/me can all tell that it’s changed, but it doesn’t have the effect in terms of actual, measureable performance that we assume.

    http://en.wikipedia.org/wiki/Bicycle_performance#Advantages_of_light_wheels

    Read that, it explains it all, the contents in your link are just someones view.

    If we were on about road bikes then aerodynamics would play more of an important roll, but we are talking about mountain biking where you are constantly braking then accelerating. Aerodynamics will not help you climbing a hill, the speeds are too slow, whereas less weight will.

    Change of direction is also easier with lighter wheels due to less inertia, something you do a lot of in MTB’ing and not so much of on the road.

    crikey
    Member

    🙂 I’ll have to retire first!

    I suspect, and it’s only a suspicion, that the overall greater weight in mountain biking makes the change less significant.

    But.. It seems to be the case that the rougher the terrain, the more wheel weight is significant; not to any great extent, but you can calculate a difference.

    http://www.analyticcycling.com/ForcesLessWeight_Page.html

    and worth having a play if you are bored;

    http://www.analyticcycling.com/

    crikey
    Member

    skywalker, from your own quoted article;

    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.

    So, rotating mass is not really all that.

    The miracle of light wheels (compared to saving weight anywhere else in the bike/rider system) is hard to see.

    Really not all that.

    Dickyboy
    Member

    Bigsi – it is possible to do the maths to show that 1g off the rims/tyres is worth 1.5g off elsewhere on the bike. However it can also be shown that the difference between an average weight rider & heavy bike (say 30lbs) & an average rider weight rider & light bike (say 20lbs) is only worth about 5% advantage & that is only on the ascents. Up to you if that makes a worthwhile difference & it also assumes all else is equal re feel of bike etc.

    Having done a couple of solo Mayhems I would say that weight is one of many factors to be considered but your psychology is paramount, if the 5% advantage above gives you an extra psychological advantage then it could well be worth every penny.

    radoggair
    Member

    well i enjoyed this 🙂

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