23mm vs 60mm profile wheel

Discussion in 'Cycling Equipment' started by novetan, Mar 23, 2013.

  1. novetan

    novetan New Member

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    My current wheel is 23mm profile. I intend to change to 60mm profile that matches my bike colour. However, understand such wheel is not for climbing. Both wheel may not of the same weight but let say abt 400g different (either way). I know diff. in wt is not a big deal. I was told that the 60mm profile will only benefit if speed exceed 40km/hr. Is that true?

    Is there any test that shows the comparison between these 2 types of wheel over the mileage lost on flat or slope? Is it significant or minute. I’m not into racing but also wouldn’t want to sacrifice too much on distance.
     
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  2. alienator

    alienator Well-Known Member

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    Will you only benefit if going 40 km/hr or faster? No, whoever said that either misstated something or doesn't understand aerodynamics. Aero benefits don't switch on at a given speed. It is true the benefits are smaller at slower speeds. Whether the benefits are sufficient for you at a given speed is a matter for you to decide. Also note that one 60mm wheel is not necessarily just like another 60mm wheel. Aero performance varies between different wheels. 60mm wheels will tend to be more sensitive to crosswinds than lower profile wheels, so steering in gusty conditions will tend to be more challenging. With that said, some newer deep section wheels reduce that sensitivity greatly with newer cross sectional profiles (like those from Zipp and Enve). 60mm wheels may climb just as well as a lower profile wheel. It all depends on climbing grade, wheel mass, aerodynamics, and wheel moment of inertia. Note that aerodynamics and wheel mass dominate until the grade gets very steep, and even then it's wheel mass that is the driver. So the answer to how they climb is it depends on many things. Aero wheels definitely can help on descents, but as stated earlier they will tend to be more sensitive to crosswinds and gusts, which can make some descents "interesting". Any test that tries to say that wheel X save a given amount of time over Y distance compared wheel Z, will do so at a given speed. The manufacturers often make such claims. There is no set "number". Like many things, it depends on the wheel, the speed, the environmental conditions.....
     
  3. daveryanwyoming

    daveryanwyoming Well-Known Member

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    Good post above, but you can get a feel for the differences between weight and aero properties over at analytic cycling. They have some good examples such as comparing acceleration out of a tight corner with the same power for a lighter box rim vs a heavier deep section aero rim. They also have comparisons of the same wheel differences on climbs of varying grades. Play with the calculators to figure out how much extra wheel weight or how much extra slope gradient it takes before weight becomes a bigger issue than aerodynamics.

    http://www.analyticcycling.com/WheelsCritCorner_Page.html
    http://www.analyticcycling.com/WheelsClimb_Page.html
    http://www.analyticcycling.com/WheelsBreak_Page.html
    http://www.analyticcycling.com/WheelsSprint_Page.html

    Basically aero trumps typical weight differences in most situations unless your climbs are very steep or the aero wheels are much, much heavier.
     
  4. CAMPYBOB

    CAMPYBOB Well-Known Member

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    "...or the aero wheels are much, much heavier."

    And lately the 50 MM aero wheels are getting very light weight.

    I would have liked to seen a modern weight 50 MM aero 20-spoke/bladed wheel (as opposed to the Specialized tri-spoke) compared to a 16 to 20-spoke box section carbon climbing special (as opposed to a 32-hole 'tank' wheel used in the tests).
     
  5. daveryanwyoming

    daveryanwyoming Well-Known Member

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    Tom has offered the calculators right on the same page. Just enter wheel weights of interest and any swag at the differences in aero properties for wheels you're interested in comparing. The light carbon climbing wheels are likely very close to old alloy box rims aerodynamically but lighter and the 50mm rims won't be quite as aero as tri spokes but a lot lighter. Plug in what you want and see what happens.
     
  6. novetan

    novetan New Member

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    Tks all guys. Fully appreciated. Will play with the tabulation
     
  7. novetan

    novetan New Member

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    I look at the table, how do I determine the following as required under input. The manufacturer don't give out such info.

    1) front/rear wheel inertia
    2) ditto drag coefficient
    3) rear wheel shelter - what's that?

    Tks
     
  8. daveryanwyoming

    daveryanwyoming Well-Known Member

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    Simple answer, you take a swag at each based on what it represents, slightly more complex answers:
    I don't actually believe this is used in the calculations which Tom has done in some of his other calculators as well. But this is the Moment of Inertia (MOI) of the wheel which you can calculate if you know the rough distribution of weight in an object. A wheel is actually a complex structure but most of its weight is either out at the far radius or at the hub but the spokes do complicate things a bit as weight distributed radially. If you know the rim weight, hub and skewer (and cassette) weight and total wheel weight you can get pretty close but play with this value and I think you'll see it isn't actually used or at least the outcome is not very sensitive to exactly what you enter.

    To really get your head around MOI for different objects you'll want to dive into a physics text book or read about it as applied to bike wheels here: http://velonews.competitor.com/2008/07/bikes-and-tech/calculating-a-wheel%E2%80%99s-moment-of-inertia_157317

    This you'll have to swag but it helps knowing the trispoke used as the default is a very aero rim, the box rim is not aero at all and something like a 46mm, 50mm or 60mm deep section rim will come in between the two extremes listed for the box and tri spoke. If you had listings of wattage saved for different wheels or grams of drag for different wheels and assumed the tests were performed at say sea level at nominal air density you could refine your swag.


    I'm pretty sure this was added to account for bikes with curved seat tubes that shelter the rear wheel. It isn't strictly a wheel parameter so leave it the same for both wheels you're comparing and it won't alter the comparative results which is what the calculator is all about. It will tend to diminish the aero drag of the rear wheel so leaving it as set in the default tends to give weight a higher priority for the rear wheel but not the front.

    I'd also adjust some of the other default parameters like Cd and frontal area. Their product is CdA and the defaults of 0.5 and 0.5 lead to a CdA of 0.250 which is a good but not incredible CdA for most folks on a time trial bike and crazy low for a road bike position. So especially for comparing the hill climbing scenario which is the only one where weight is likely to trump aero for real world wheel weight differences, I'd set it for a CdA of something like 0.350 or so to account for a rider on the hoods or tops on a road bike which you could get with a frontal area of 0.7 and Cd of 0.5.

    Similarly the default rider weight is low and the default Crr is pretty low for real world road surfaces and the types of tires most folks ride when climbing big hills which generally aren't the lowest Crr tires (that tend to be fragile and reserved for time trials).

    -Dave
     
  9. novetan

    novetan New Member

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    Tks Dave for explanation again.

    I'm really clueless by looking even with the addtional info you gave.

    Can I leave it as empty in the box? Or if need to input a figure, what safe figures shall I input for all of above?

    Tks again.
     
  10. daveryanwyoming

    daveryanwyoming Well-Known Member

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    I've got to say if you don't understand the principles it's probably best to just read their default examples and get an idea of how large or how small a difference weight vs aero properties make in different situations. You don't 'need' to run the calculators provided to get an idea of when weight trumps aero (which is not often outside of steeper climbing).

    It might help to read some of their overview such as: http://www.analyticcycling.com/WheelsConcept_Page.html

    If you follow the links on that page you'll also find some tables listing some of the properties you asked about earlier for a few popular wheels. That might help, but really the main concept is that so many cyclists evaluate wheels based on weight and in many situations it isn't as important within reasonable differences as most think.

    -Dave
     
  11. novetan

    novetan New Member

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    Ok, tks so much again. Will hv a cuppa later and run thru.
     
  12. novetan

    novetan New Member

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    Hi Dave,

    Just to clarify.

    As mentioned above, I know nothing to input figures such as drag coeff, wheel inertia, wheel shelter, air density, rolling resistance. When I open the webpage, there are figures already inside these boxes. So can I assume these figures are more or less accurate?

    Lastly, towards almost the bottom, Time at End is set at 1200s. What's this? Do we use this setting?

    Once again, thanks so much for all your help.


    [​IMG]
     
  13. daveryanwyoming

    daveryanwyoming Well-Known Member

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    Way too much in your post to explain and read those pages on Tom's website (analyticcycling.com) he does a very good job of explaining the physics.

    But the defaults are NOT in general great for all situations and not every input box is actually used in every calculation which confuses things a bit. For instance in the power given speed or speed given power calculators there are input boxes for crank length and cadence. For the purpose of calculating speed from power or vice versa these are irrelevant but allow things like average torque to be calculated as well.

    In all calculators he seems to default to frontal area of 0.5 meters squared (A) and a shape factor of 0.5 (Cd). The product of those two (CdA) is used in the calculators but not either individually. Those defaults set the CdA to 0.250 which is a good but not extraordinary time trial bike CdA but it's an insanely low road bike CdA especially for something like climbing a long hill on the tops or brake hoods where a CdA of 0.350 might be more appropriate. When playing with CdA in his calculators I usually just set Cd to 1.00 and enter the desired CdA in the Frontal Area entry box.

    Similarly in my experience unless you're running very fast tires over latex tubes his Crr estimates for different road surfaces are a bit optimistic. Again probably decent for time trialing on fast race tires and tubes but on the low side for day to day tires and tubes most people run. I's start the swag of Crr at 0.005 for good tires over butyl tubes and 0.006 might be more realistic if you're running tires with flat resistant layers or other more durable tires on many real world roads. And if you ride a lot of course asphalt as we do in the Pacific Northwet then the numbers can be even higher on our 'good' roads.

    Most of the information you need to become familiar with his calculators is already described on his site but things like what to expect in real world conditions for different parameters that's a huge discussion and really misses the point of those calculators which is to demonstrate how many people incorrectly focus on weight in situations where it's not that important.

    -Dave
     
  14. danfoz

    danfoz Well-Known Member

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    If not racing, and more specifically if not TT'ing, why not settle on a slighly lower profile but still aero wheel at around 30-40mm?

    I've always been a fan of wheels that do everything well and while not doing anything great don't have any real downside, like the Zipp 303. Also if you settle on any of the FC Zipps, the rim shape has apparently been designed to move the center of pressure closer to the hub so crosswinds have a lesser effect.

    The biggest potential downside with any aero wheel (beyond the obvious crosswind scenario), and assuming the material is carbon is going to be wet weather braking performance. I can say with certainty that some cheaper CF wheels/rims do not brake well at all in the wet and if not racing I would have a hard time justifying any potential benefit. Even high end CF wheels brake in wet subpar to their alloy counterparts. While some folks may not ride in the rain, they may get caught in the rain some way from home. And I may be assuming boldly but anyone who says "cuppa" may be coming from good old Ingyland where it rains more oft than not. /img/vbsmilies/smilies/wink.gif
     
  15. daveryanwyoming

    daveryanwyoming Well-Known Member

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    That's pretty much my take on it, a good 45+ mm aero rim like the Zipp 303s, Reynolds Assaults, HED JET 4s, Boyd 45mms or others in that class tend to be great all around wheels that bring aero properties without being a handful in gusty crosswind conditions. It's just that a lot of folks will dismiss those or slightly deeper rims in the 50mm or 60mm class based on a look at weights and often they're missing the point. I'm currently racing road events on a pair of HED JET 4s and all around they're my favorite all around wheelset for mass start racing but they're not flyweights at somewhere around 1700 grams for the pair. I've owned wheels that came in as light as 1100 grams per pair but I'll take the JETs any day and in just about any race outside of a pure hillclimb over the lighter wheels.

    -Dave
     
  16. alienator

    alienator Well-Known Member

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    You'll do well to heed the points above. With that said, the new generation of deep section wheels are designed to play nicely in crosswinds. Without actually riding such wheels in crosswinds to see how they handle, the best way to get a handle on how they function is to read a comparison test between a number of wheels. Here's one such test with five wheel sets (Enve SES, Bontrager Aeolus, Psimet custom, Rolf Prima TDF, Hed Stinger). The interesting part of this test is that the test comparison includes both new generation "wide, blunt" aero rims, more traditional "deep V" rims, and some in between. The test also provides moments of inertia for the wheels, about which you should note three things:
    1. Moment of inertia doesn't necessarily track with weight. It's a measure, in part, of how mass is distributed in the wheel.
    2. The biggest difference in MOI for the wheels is 17.4%.
    3. Generally differences in wheel MOI aren't the magical performance deciders that they're made out to be. MOI is most often "felt" (I used quotes because people claim to "feel" a lot of things, but feelings are often deceptive and wrong) when accelerating, or in the case of a bike, when sprinting and climbing. Bike speeds when sprinting and climbing aren't huge and when coupled with a bicycle wheel's comparatively small MOI, the differences in acceleration isn't that great. The numbers from calculations don't lie. On the anecdotal side, I once had a set of CF wheels that weighed in between 800 and 900g. The difference in climbing performance between those wheels and and a 1380g set of mine was nothing to write home about. It certainly wasn't transformative, and phrases like "rocket ship", "mountain goat", and "anti-gravity machine" didn't spring to mind when describing that difference in performance.
    In reading the test you'll find that almost all the wheels handle differently in crosswinds and that the blunt, wide versions handle much better in crosswinds. The test also covers differences in braking. One area that has seen huge improvements is braking on CF wheels. This is reflected in the test. A lot of work has been done by a few companies to produce CF clinchers that stand up to heat from braking without failing. New developments have also improved braking in general, including braking in the wet. Zipp and Enve have made great strides there. With that said, the most important factor in braking is you. No one in their right mind goes into a wet corner at the same speed they would in dry conditions. You have to moderate your speed according to the braking power available, your braking skills, and the conditions. For some, CF rims are a non-starter for wet conditions. Me? I don't mind. I make sure to be aware of the conditions and any changes and change my braking accordingly. I've had no issues descending Colorado mountains in the rain with CF wheels, but I also didn't wait for the last possible second before counting 3 steamboats and braking. Be aware that the aero benefits that aero wheels offer isn't earth shaking. In fact, you'll just might be hard pressed to feel the difference on the flats. The old rule of thumb is that aero wheels will add about 0.5 mph of extra speed at 25 mph for a given effort. Newer generation wheels might do better than that. If I were in the market right now for CF clinchers, I'd be looking at Enve, Zipp, Shimano and HED. I also would not rule out hybrid clinchers (alloy rim with CF aero cap) from Mavic, HED, Fulcrum, Campagnolo, and Shimano. A lot of people have had great luck with Boyd wheels. In the past they've used open mold rims, but they have their own rims coming out this year. I would suggest buying from a company that will stand behind its product. I am sleep deprived so feel free to add any nouns, adjectives, articles, or other handy words to any place I've omitted such things.
     
  17. novetan

    novetan New Member

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    Tks so much dave for giving your time to explain
     
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