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 Post subject: Re: Aero vs Light
PostPosted: Tue Aug 30, 2011 4:19 am 
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Joined: Sat Jun 13, 2009 4:02 am
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Location: NoVA/DC
User Name wrote:
... but I occasionally felt that the brick-like rims on my old Mavic Cosmic Pros (38mm-deep alu) held speed better than my shallower rims.


although a heavy wheel reduces speed at a slower rate than a light wheel, ignoring the very, very slight increase in rolling resistance from the entire rider/bike system being slightly heavier, it takes exactly the same amount of energy to maintain speed on flat ground. you are only working against rolling (mentioned earlier) and wind resistance (constant, and equal in both cases). the sensation, even the noise, can make the wheel seem faster, when it is merely different.

i agree with the "standard wheel comparison" argument, however. it would be nice to see a modern wheel used as the "standard wheel". i think some companies do (rolf prima?) use the Mavic Ksyrium SL, which aerodynamically is a very, very bad wheel. I cant remember if it might be WORSE than a 32hole box rim... I don't necessarily blame the wheel companies in trying to show themselves in the best light, as long as all the fine print is actually printed.


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 Post subject: Re: Aero vs Light
PostPosted: Tue Aug 30, 2011 3:18 pm 
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So basically nothing actually matters, right?

A bike is a bike, a wheel is a wheel. This is gonna save me a lot of money!


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 Post subject: Re: Aero vs Light
Posted: Tue Aug 30, 2011 3:18 pm 


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 Post subject: Re: Aero vs Light
PostPosted: Tue Aug 30, 2011 3:30 pm 
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Joined: Fri Dec 15, 2006 7:45 pm
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Location: Natovi Landing
At the extreme end of the spectrum you can notice the increased flywheel effect of a heavy rim. I have in my quiver a pair of WH-R540s that weigh c.1900g with hugely heavy rims - must weigh not far off 700g each as the wheelset only has 32 spokes in total. It certainly feels different to riding my Zipp 202s which come in just under 1100g with rims at 294g.

Obviously weight is not the only, or perhaps even the main difference one can perceive between these wheels - but it is perceptible, and when riding very close in a pack requires a subtly different power output to maintain position.


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 Post subject: Re: Aero vs Light
PostPosted: Wed Aug 31, 2011 4:51 am 
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Joined: Tue Jun 07, 2005 3:32 pm
Posts: 501
thisisatest wrote:
although a heavy wheel reduces speed at a slower rate than a light wheel, ignoring the very, very slight increase in rolling resistance from the entire rider/bike system being slightly heavier, it takes exactly the same amount of energy to maintain speed on flat ground. you are only working against rolling (mentioned earlier) and wind resistance (constant, and equal in both cases). the sensation, even the noise, can make the wheel seem faster, when it is merely different..

So, it was my imagination? Good :thumbup:

thisisatest wrote:

i agree with the "standard wheel comparison" argument, however. it would be nice to see a modern wheel used as the "standard wheel". i think some companies do (rolf prima?) use the Mavic Ksyrium SL, which aerodynamically is a very, very bad wheel. I cant remember if it might be WORSE than a 32hole box rim... I don't necessarily blame the wheel companies in trying to show themselves in the best light, as long as all the fine print is actually printed.

Yeah, I'd like the 'standard' wheel to be something that's not hideously 'unaero', like, say, a 28-spoke Deep V.


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 Post subject: Re: Aero vs Light
PostPosted: Wed Aug 31, 2011 5:15 am 
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Joined: Tue Jun 07, 2005 3:32 pm
Posts: 501
sawyer wrote:
At the extreme end of the spectrum you can notice the increased flywheel effect of a heavy rim. I have in my quiver a pair of WH-R540s that weigh c.1900g with hugely heavy rims - must weigh not far off 700g each as the wheelset only has 32 spokes in total. It certainly feels different to riding my Zipp 202s which come in just under 1100g with rims at 294g.
.

Hmm, nah, I'd be very surprised if they were that heavy. That obviously only leaves ~500g for the hubs about spokes. I'm kinda sure those hubs have steel axles and rear hub body, so the rear would be about 350g, and the front about 120g, without skewers. And 32 steel spokes would be about 240g.

Also, my 30mm DT RR 1.2s are ~580g, my 50mm Gigantex alu/carbon rims meant to be 690g, and my old Mavic CXP30s are 590g (30mm). New Velocity Deep Vs are supposed to now be 520g (30mm deep), and the older ones were around 550 to 570. Road rims over 700g are usually really beastly stuff, like these 43mm alu Velocity B43s:
http://www.velocitywheels.com/store/pro ... 273&cID=18

My guess is that those Shimano rims would be under 600g, but I could be wrong.
Anyway, who really cares? :thumbup:


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 Post subject: Lose 400g or go aero?
PostPosted: Sat Feb 16, 2013 5:04 pm 
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Joined: Sat Feb 16, 2013 4:44 pm
Posts: 12
Hi!

I have a pair of Shimano RH550 wheels on my ride that I'd like to upgrade in the near future, they weigh approximately 1900g. On a fairly limited budget but can afford secondhand clinchers that'll weigh in around 1500g, saving me 400g (Shimano RS80s for example).
Thing is I've been reading around a little and wonder if I'd benefit more from a pair of deeper profile wheels instead. In my price range however it would mean no or little weight saving.

I weigh 64kg and ride on mostly flat, open roads that can get windy at times. My average speed on a good day is 32kph. So, save 400g or go deeper...?


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PostPosted: Sat Feb 16, 2013 7:06 pm 
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If you ride a fairly constant speed then a weight loss will make no difference as lossing wheel weight only make a difference when accelerating (mostly). In this case a more aero wheelset would be more benefical but at 19mph the difference may not be that noticeable. Non aero wheels are better for training anyway.

The difference between a shallow rim 32 spoke wheel and a good aero wheelset may ammount to 20W at 30ish mph. You can get that from tyres if you are using the "worng" ones at the moment. If some one has more accurate data then pleasee add.

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PostPosted: Sat Feb 16, 2013 7:24 pm 
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Joined: Fri Jun 01, 2012 6:40 pm
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You can lose 400g and gain some aerodynamic gains for a similar price. The RS80s cost about the same as a Kinlin XC279 rim built up with sweet hubs (for example Zen Cyclery's Katmandu) or even the new Pacenti SL23. You'll get the benefit of more aerodynamic wider rims, profile, albeit with less depth than true aero rims, and build up a wheel around 1500 grams.


Last edited by dvincere on Sat Feb 16, 2013 8:21 pm, edited 1 time in total.

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PostPosted: Sat Feb 16, 2013 8:04 pm 
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Formerly known as wassertreter

Joined: Tue Apr 12, 2011 8:08 am
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Always go for weight reduction, unless you think it will actually help you with placings in races. A light bike is just so much more pleasant to ride. Spinning up after each traffic light, intersection etc, it's a noticeable difference. The WH-R500 was my first wheelset a few years ago, and when I swapped it for AC420 the riding was worlds apart (they might be a tad more aero, too, but the spin-up was most significant).

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PostPosted: Sat Feb 16, 2013 8:29 pm 
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Joined: Fri Aug 26, 2005 8:13 am
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You'd need to be going waaay slower for aerodynamics to not be important. Yes you save less power per minute than a faster rider, but you take longer to cover the same distance so actually gain more.

I''m facing a similar dilemma. Do I stick with my Mad Fiber wheelset, or go for a more aero but heavier 808 firecrest/ enve 8.9? Tough call. For flat stuff the balance swings in the favor of aero but I do lots of pretty hilly events...


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PostPosted: Sat Feb 16, 2013 8:42 pm 
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Location: United Kingdom of Great Britain and Northern Ireland
Riders pre-occupied with losing weight from their machines in large part do not understand that reducing resistance to the air is far more important than overcoming inerta. If you want to go faster you are most likely to do so with a heavy pair of deep section wheels as opposed to a light pair of box sections. When riding your bike you typically use about 80% of your energy 'pusing air out of the way'.


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PostPosted: Sat Feb 16, 2013 8:51 pm 
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Just look how steep it has to be before the pros use light road bikes instead of tt-bikes in a tt. Aero is faster.


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 Post subject: Re: Aero vs light wheels
PostPosted: Sat Feb 16, 2013 10:31 pm 
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in the industry

Joined: Sat May 12, 2012 7:25 pm
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Location: Glermsford, Suffolk U.K
I think we all get slightly obbessed with having every last advantage. Ultimatley there is no subsitute for training.

Power output = 0.5XCdA(ro)v^3
Ro is air density and CD is drag coefficent, A is frontal area.
Wheels only affect Cd really. The biggest factor is rider frontal area.

A 20W change in power from a change in wheels will end up being a very small change in speed.

Let say for example it require 260W to sustain 26mph and changing wheels saved say 25W at that speed.
With the new wheels a new speed of 26.9mph is possible at 260W output. So while that is a big difference this would be like moving from a 36 spoke box section rim to a low spoke count deep rim wheelset, Moving from Shimano R550 to something more aero will likely lead to a smaller change.

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 Post subject: Re: Aero vs light wheels
PostPosted: Sat Feb 16, 2013 10:35 pm 
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Posts: 12
Thanks for the quick and concise answers, as a new convert from 20 years on a mountain bike, I'm a bit wet behind the ears when it comes to road equipment. Racing is not on my agenda at the moment.

I agree wassertreter, I love the feeling of a light bike and would certainly feel the loss of 400g rotating weight. However my rides are usually on quiet roads where I can keep a fairly constant tempo, so reading further suggests aero would suit me better. Also, thanks for the tips on non-factory options dvincere, perhaps a compromise is the answer.

I'll also read through the 'Aero vs light' thread that my question has now been filed in :wink:


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 Post subject: Re: Aero vs light wheels
Posted: Sat Feb 16, 2013 10:35 pm 


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 Post subject: Re: Aero vs light wheels
PostPosted: Sun Feb 17, 2013 4:04 am 
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Joined: Thu Aug 16, 2012 12:56 am
Posts: 435
Location: YYZ
Don't forget your position on the bike makes way more of a difference than shallow vs. deep wheels ever will. Ask Greg to show you his Yellow Jersey for proof...

RBA just did an interesting piece with Neil Shirley in a wind tunnel - he saw simply moving to an aero jersey lowered drag as much as moving from the hoods to the drops. All in all his position changes (and new jersey) saved about 500g of drag.

Just a thought....

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