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CXP 30- aero at all?

Old 12-15-09, 09:46 AM
  #1  
Basil Moss
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CXP 30- aero at all?

I'm wondering how you' rate the aero/weight benefits of my wheel options.

So I usually race on Ultegra/CXP 33's built with DT revolution spokes, 28 front 32 rear. They weigh about 1,750g. I've got some GP4 tubulars with more spokes for really horrible races like the Dengie Marses tour, but generally won't use them for road races. I've also got Dura Ace/Gel280's which weigh about 1,200g, for really nice roads in a hilly race or hillclimbs.

I've got most of the bits to build some wheels with the old CXP 30 tubular rims, 24 spokes front and 28 rear. Is a 30mm rim much more aero than a box section rim? Better than the CXP 33 set? More importantly, does their aero benefit outweigh the fact that these rims weigh a ton (the wheelset would be over 2 kilos)? How flat or steady paced would a race have to be for you to chose such a wheelset over my other options?

Don't tell me to get some carbon 50mm set, that'll have to wait until I can afford it, probably a few years. Just want to know what you've got to say about the options I've got now. I mostly road race, and many of my races are quite flat (Cambridgeshire), only a few crits at Hog Hill, otherwise I do Thursday evening timetrials, and hillclimbs in the season. Should I build these wheels, or sell the rims to some cyclocross nut?
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Old 12-15-09, 10:04 AM
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Sell them.

I'd race the GEL280, at least the front, and that GP4 rear.

If you can, buy another front hub for the other GEL280. You can ride them forever as a front. Rears, not so much.

Regretting bending all my GEL280s at the back of the bike,
cdr
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Old 12-15-09, 10:12 AM
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What's wrong with gel 280 rears? It's got more spokes (28 front 32 rear), but still, don't think I'd take either out on really potholed roads. I wear out front rims sooner, because I use the front brake way more. I've buckled 2 rims, one front, because it hit the tree before I did, and one rear, in last years Dengie, because I went down trying to avoid a fall in front on the farm track, and then got my wheel ridden over by the rider behind me.

I suspect that the aero benefits of my cxp33's over box section rims is negligible. Just wondering if the deeper CXP 30 is any better.
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Old 12-15-09, 11:03 AM
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I would use them for crits. The weight won't hurt there and the aero will help. One issue I have found in the GEL 280 (and GL 330) is that the sidewalls wear very quickly and unevenly (more near the spokes than in between). For that reason, they are great for the velodrome but have a short lifespan with brakes. The CXP30 has a machined sidewall.
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Old 12-15-09, 11:07 AM
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Surely excessive rim weight is going to hurt more in a crit than anywhere else? Especially at our Redbridge circuit (Hog Hill, named for a reason). I was thinking more for our flattest races, maybe the aero benefit (if there is any) would help when I go on some doomed attack off the front, or if I'm trying to string out the field in the last few K's for my mate who can actually sprint. I never do well in the flat ones, but it's not for want of trying.
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Old 12-15-09, 11:12 AM
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Originally Posted by Basil Moss View Post
Surely excessive rim weight is going to hurt more in a crit than anywhere else?
Definitely not.
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Old 12-15-09, 11:17 AM
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Explain? I'll be in amongst the wheels for most of the time, making any aero benefit pretty negligible, and repeatedly having to accelerate and slow down. Plus as I've said our crit circuit has a big hill in it.

But most importantly, is a 30mm rim actually much more aero than a box section one?
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Old 12-15-09, 11:20 AM
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you can't afford $600 for a set of carbon tubular neuvations ?

please. lol Some people will think you are in the wrong sport !!!
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Old 12-15-09, 11:37 AM
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That's about 400. No I can't, not right now. Anyway, they aren't available over here, so far as I know.
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Old 12-15-09, 02:07 PM
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Originally Posted by Basil Moss View Post
...But most importantly...
If we're going to talk about importance, let's take a step back and look at your racing resume. How many wins have you missed by just a few cm? I used to really want deep carbon wheels, but looking at the people who were beating me by meters on Open Pros convinced me that the aero benefit of any equipment is negligible compared to my ability.
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Old 12-16-09, 04:25 AM
  #11  
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I missed winning the ECCA Festival race by a few meters, having been out alone for about half the race- the field blew past me as a sprint finish. I was once lent a set of Zipps, 404 front and 808 rear, and they felt noticeably faster. Like, as much faster as the difference aerobars made in a time trial. I have since then wondered if having those wheels would have won me that race.

How much difference do deep section wheels really make to your top speed? I remember there being a list of all the commonest wheels and their aerodynamics- what happened to that? How much slower are my 32 spoke handbuilts than something with a 50mm rim?
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Old 12-16-09, 04:56 AM
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Your 30mm rims are much more Aero then box section rims. This is coming from someone who rode Mavic CXP 21's laced to Sora hubs, then went to a $1600 wheelset from Pinarello (MOst Panther CX) with an alloy 30mm rim and bladed spokes.

Much more aero.
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Old 12-16-09, 09:41 AM
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Originally Posted by Basil Moss View Post
I missed winning the ECCA Festival race by a few meters
Sounds like you need to get a credit card and get those 60mm Zipps.
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Old 12-16-09, 11:51 AM
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Originally Posted by Basil Moss View Post
I was once lent a set of Zipps, 404 front and 808 rear, and they felt noticeably faster. Like, as much faster as the difference aerobars made in a time trial.
I doubt it.
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Old 12-16-09, 03:23 PM
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I said they felt faster, I can't say how much. But that it was noticeable, seemed like it was that order of difference, not the kind of difference that you really wouldn't notice. I don't think this was placebo effect kind of faster, if you see what I mean.

Maybe I should just save up, see if in a year or so I can get some secondhand Zipps on ebay. No credit cards for me though- student debt is debt enough for me...
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Old 12-16-09, 11:04 PM
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Originally Posted by Basil Moss View Post
What's wrong with gel 280 rears? It's got more spokes (28 front 32 rear), but still, don't think I'd take either out on really potholed roads. I wear out front rims sooner, because I use the front brake way more. I've buckled 2 rims, one front, because it hit the tree before I did, and one rear, in last years Dengie, because I went down trying to avoid a fall in front on the farm track, and then got my wheel ridden over by the rider behind me.

I suspect that the aero benefits of my cxp33's over box section rims is negligible. Just wondering if the deeper CXP 30 is any better.
I bent all my GEL280s on the rear wheel, usually in crashes. I'd unlace a front to rebuild the rear. I went over to Record Crono rims, and did the same thing.

Rode 28H f/r, so I could move the rims back and forth.

The front wheels lasted forever, at least until eyelets started to fail.

At the same time, I've never bent a GL330 or Isidis rear. For a long time my default "fast" wheelset was a GEL280 or similar wheelset, 28H. My super heavy duty wheels were GL330/Isidis 28H.

I'm just saying that a GEL280 would last a while up front, not as long in the rear. But with 32H the point is moot.

Personally I don't think even a 38mm rim (Zipp 340) is aero, based on some experiments I did with different wheelsets. They were marginally faster than the Record Cronos but significantly slower than old aero Ventos, Rev-X, 440 (58mm), and the TriSpokes. I think about 60 mm is where it really makes a difference in rim height, probably a bit less with the newer shapes available now.

cdr
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Old 12-17-09, 01:56 AM
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Originally Posted by carpediemracing View Post
Personally I don't think even a 38mm rim (Zipp 340) is aero, based on some experiments I did with different wheelsets. They were marginally faster than the Record Cronos but significantly slower than old aero Ventos, Rev-X, 440 (58mm), and the TriSpokes. I think about 60 mm is where it really makes a difference in rim height, probably a bit less with the newer shapes available now.
This is what I'd suspected- I think the aero benefit might be so slim I'd be better off racing on some of my lighter wheels, and worry about aero when I can afford to do it properly.
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Old 12-17-09, 07:11 AM
  #18  
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A lot of people like 38mm carbon wheels because they have some aero benefit (of course not as much as deeper wheels), but don't have very much crosswind penalty. They are also usually pretty light and so are easier to spin up faster in a crit or climb in a rr.
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Old 12-18-09, 08:12 AM
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http://www.rouesartisanales.over-blo...-15505311.html

that should shed some light
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Old 12-18-09, 08:47 AM
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Originally Posted by Basil Moss View Post
Explain? I'll be in amongst the wheels for most of the time, making any aero benefit pretty negligible, and repeatedly having to accelerate and slow down. Plus as I've said our crit circuit has a big hill in it.

But most importantly, is a 30mm rim actually much more aero than a box section one?
Acceleration is a minimal concern with wheel weight. Looking at this graph, you can see how much energy is burned going from 0 to 30km/hr. I eliminated the first and the last result, and you get a span from 77J to 147J going from 0 to ~18mph. This means that the 2nd heaviest wheelset in the test would cost you 77J more to accelerate from a stop to 18mph, compared to the 2nd lightest wheelset.

In a crit, consider a corner that requires you to go from 18mph to 24mph (30km/hr to 40km/hr), which are round numbers for the table. That's 1/3 of the acceleration covered in the graph, so it would be ~23J from a really heavy $200 wheelset to the $5000 wheelset. (I know the Gipiemmes aren't $200, but most 2040g wheelsets are)

In a 60', 4-corner crit, I'm looking at about 240 corners. Let's say I am slowing 6mph each time, and getting back up to speed, as in the example above. In that crit, I am likely to burn 1000kJ. That's 1,000,000 Joules. The 240 corners with the heavy wheels would cost me 240 * 23J = 5,520J more than with the light wheels.

5,520J/1,000,000J = ~0.5%. Half a percent of my race energy expenditure. Half.

Last edited by waterrockets; 12-18-09 at 08:51 AM.
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Old 12-18-09, 08:55 AM
  #21  
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Originally Posted by waterrockets View Post
Acceleration is a minimal concern with wheel weight. Looking at this graph, you can see how much energy is burned going from 0 to 30km/hr. I eliminated the first and the last result, and you get a span from 77J to 147J going from 0 to ~18mph. This means that the 2nd heaviest wheelset in the test would cost you 77J more to accelerate from a stop to 18mph, compared to the 2nd lightest wheelset.

In a crit, consider a corner that requires you to go from 18mph to 24mph (30km/hr to 40km/hr), which are round numbers for the table. That's 1/3 of the acceleration covered in the graph, so it would be ~23J from a really heavy $200 wheelset to the $5000 wheelset. (I know the Gipiemmes aren't $200, but most 2040g wheelsets are)

In a 60', 4-corner crit, I'm looking at about 240 corners. Let's say I am slowing 6mph each time, and getting back up to speed, as in the example above. In that crit, I am likely to burn 1000kJ. That's 1,000,000 Joules. The 240 corners with the heavy wheels would cost me 240 * 23J = 5,520J more than with the light wheels.

5,520J/1,000,000J = ~0.5%. Half a percent of my race energy expenditure. Half.
You've got it wrong...err I mean the math is right but its still wrong...

CF aero wheels are not about being a more competitive racer they are about emotions and feelings. I feel fast, I look fast therefore I am fast.
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Old 12-18-09, 09:44 AM
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Originally Posted by RichinPeoria View Post
CF aero wheels are not about being a more competitive racer they are about emotions and feelings. I feel fast, I look fast therefore I am fast.
So that's what I've been doing wrong all this time.
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Old 12-18-09, 12:33 PM
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Originally Posted by a_thomasmr23 View Post
Thanks, that's really interesting. Also confirms my suspicion that Mavics carbon fiber cartwheels are by a long way the least aerodynamic wheel out there. But I'd like to see a test that included 32 or 36 spoke wheels, with old fashioned rims. Since pros still race on them in the classics, surely it's worth knowing how they compare? Has anyone done such a test? Are they as draggy as the R-Sys? A reasonably reliable friend told me they can be more aero than the Ksyriums, but that's not exactly an aero wheel either, with those ridiculous great alloy spokes. I wonder also how much difference there is with the thickness of spokes used in hanbdbuilts- DT Revolution are much thinner than the DT Comp spokes you see more often. Does that make much odds?

Also thanks Waterrockets, for the maths. So am I to take it you'd choose the 2 kilo CXP 30 handbuilts for a crit over any of my other homemade wheels? Even the CXP33 set which isn't so much of a deadweight? I suppose with good tubs on the CXP30 that would be an advantage to consider.

Richinpeoria, what you describe probably doesn't apply to me. I always feel fast. Before most races I feel like I've got the legs of Jens Voigt, regardless of what POS bike I'm riding. So I proceed to attack again and again, mercilessly and relentlessly, until I blow in the last lap. Kind of like Eddy Merckx, but without the whole fitness thing... So probably if I could find a way of taking myself down a psychological peg or two, that would be more productive!
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Old 12-18-09, 03:30 PM
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It is my understanding that the shape of the hub side of the rim is equal in impact as the rim depth. The justification is that once the air is on the side of the rim its in laminar flow and only add surface friction at that point. That is provide that the rim depth is sufficient to achieve laminar flow. So the 2 major contributors to drag is frontal area which is about the same on all wheels/tires and the separation point. Its pretty easy to see that a teardrop or airflow shape is better than a box.

But that just my 2 cents.
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Old 12-18-09, 04:14 PM
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Originally Posted by Basil Moss View Post
Thanks, that's really interesting. Also confirms my suspicion that Mavics carbon fiber cartwheels are by a long way the least aerodynamic wheel out there. But I'd like to see a test that included 32 or 36 spoke wheels, with old fashioned rims. Since pros still race on them in the classics, surely it's worth knowing how they compare? Has anyone done such a test? Are they as draggy as the R-Sys? A reasonably reliable friend told me they can be more aero than the Ksyriums, but that's not exactly an aero wheel either, with those ridiculous great alloy spokes. I wonder also how much difference there is with the thickness of spokes used in hanbdbuilts- DT Revolution are much thinner than the DT Comp spokes you see more often. Does that make much odds?

Also thanks Waterrockets, for the maths. So am I to take it you'd choose the 2 kilo CXP 30 handbuilts for a crit over any of my other homemade wheels? Even the CXP33 set which isn't so much of a deadweight? I suppose with good tubs on the CXP30 that would be an advantage to consider.

Richinpeoria, what you describe probably doesn't apply to me. I always feel fast. Before most races I feel like I've got the legs of Jens Voigt, regardless of what POS bike I'm riding. So I proceed to attack again and again, mercilessly and relentlessly, until I blow in the last lap. Kind of like Eddy Merckx, but without the whole fitness thing... So probably if I could find a way of taking myself down a psychological peg or two, that would be more productive!
I would choose as aero as you can afford. Deep, moderate spoke count, aero spokes. I like the KinLin XR-300s better than any other aluminum clincher. 30mm depth at the weight of an OpenPro or Aerohead.
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