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PostPosted: Mon Jun 16, 2014 8:37 am 
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Location: Adelaide, Australia
Thinking about building up a cheap climbing/training wheel. I'm debating on whether I should get the Kinlin XR-200 or XR19W rims as the basis of this build. I know neither of them are particularly aero, but which ones would be the more aero of the two? Is the ~20g weight penalty of the XR19W worth it (slightly wider?). Both rims will hit the target weight and have a "Kamm" shape...

I guess I'm just wondering which will be better under the criteria of aero with a 23mm tyre. I'm 57kg so I doubt stiffness would be an issue for me.

Are there any other 400g alloy rims that can be had for under $60? I know carbon tubular is where its at for aero and light (and chinese for cheap :lol: ), but I can't ride tubulars or carbons in junior ranks :| .

P.S. If I'm using the BHS SL210 and SLF71W (or SFL85W to get some colour) hubs with laser spokes what spoke count would people recommend? I'm thinking 20/28 would work? Maybe 24/28 if I go down the XR-200 route? Thinking of lacing radial front and 2x rear, would there be a better lacing pattern?

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PostPosted: Mon Jun 16, 2014 9:22 am 
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Here's a mock up of a 24.8mm tyre fitted to the two rims if someone wants to make aero predictions...

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PostPosted: Mon Jun 16, 2014 10:49 am 
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At 57kg you can go with the lowest spoke count available. I'm 80kg and ride 20/28 on my low profile alu wheelset. Fewer spokes will make more aero difference than rim profile.

Theoretically, the more rounded rim on the right will probably be more aero following the latest thinking/trends in U- vs. V-shaped profiles.

At 57kg you could easily go for a 21mm front tyre and again save more air resistance than with a different rim profile.

Again, at 80kg (ok, 78 actually) I ride 25mm tires which would scale down to to 21 for you :)

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Marin


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PostPosted: Mon Jun 16, 2014 1:37 pm 
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But what goes up must come down. If you a proficient descender, and are braking late into turns, you don't want a flexy front wheel. That's not to say you couldn't get away with a 20h front at your weight, but it really depends how you are weighing the "training" vs "climbing" duties against each other. Same goes for tyre width, a wider tyre at lower pressure will give you better traction in the corners. The weight and aero gains from narrow tyres are easily outweighted by traction advantage from a bigger tyre.

You can see it like this, at climbing speed, there is basically no aero difference. For descending, grip and (front wheel) stability are more limiting than wheel aerodynamics (between the options you mentioned).

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PostPosted: Mon Jun 16, 2014 10:53 pm 
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#I hate the term climbing wheel because the time saving of try to save 100g or even 300g from a wheelset even for a light 57kg rider is very small indeed. Also consider that training should be hard so for training a heavier wheel should be no penelty. I would wager that a wheel built from the wider Kinlin XC-279 on someone hubs in a 20F/24R spoke count may weight c.1500g but you will be no slower on it. It will be alot stiffer and the wider rim will make it more aero (as the tyre width will match the rim width more closely) and cornering when coming down those hills will be improved too. So no slower going up and slightly faster coming down. What's not to like.

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PostPosted: Mon Jun 16, 2014 11:49 pm 
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Thanks for the opinions above.

I guess I forgot to mention that I already have a set of easy on ea70, which are a similar profile to the xc-279. I'm looking for something that'll be as light as possible, why? Because Ive never had a sub 1400g wheel and I really want to try it. I guess in an ideal world I can afford the dura ace c24s, but I can't so these two rims look like the next best thing

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PostPosted: Tue Jun 17, 2014 1:15 am 
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Either rim... your call.

Might want to spring for CX-Rays if you want less aero drag, with heavier DS spokes.

At your weight you might be able to do 20f and 24r ... definitely 20f and 28r.

Lacing.. might be best to do 1x heads in on the DS and 2or 3x NDS if you *aren't* going to run 11spd.

Are you a good wheel builder?

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PostPosted: Tue Jun 17, 2014 2:40 am 
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I'm running 11spd so 2 cross it is I guess. Is the 1x heads in just for extra stiffness or for nds tension?

Which rim is the stiffer of the two rims? Brandon recommended that I should go with 4 extra spokes for the 19w, does that make the 200 stiffer?

I've built wheels before, idk what makes a good wheel builder, but I'm fairly pedantic with my spoke tensions/ trueness?

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PostPosted: Tue Jun 17, 2014 1:33 pm 
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What's the average speed of your category, and what terrain do you mostly run on ?

Because the aero part of the equation matters alot if you're above 40 km/h (U16-U18 on flat terrain), or below 35 km/h (U14...hilly terrain) .....

In the first case, you can build an appreciably "aero" (and solid) sub 1400 g wheelset with 30 mm XR300 rims on 16-20 hubs.
+1 on 20mm front tire, 22 or 23 rear. Veloflex Corsas with light tubes :D !!
+1 on what WMW wrote.

The XR200 is a very soft rim. My 12 yr old (and 45 kg) daughter bent a 28h (2X each side) rim when she took a spill in a warm up run. Had to unbuid the wheel and bend it back the other way. I have XR 270 rims that took a serious beating and never went out of true.

OH! Someone has to explain to me the "tubulars forbidden" for juniors rule..... :|

Louis :)


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PostPosted: Tue Jun 17, 2014 1:47 pm 
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If u want the absolute lightest wheelset, get a pair of 1st gen Stan's ztr 340 rims from wiggle.com. About $100/apiece, probably as flexy as the kinlins but 40-50g lighter.
As far as aero, I'd guess that the rim width on a 22mm rim depth is pretty irrelevant. I'd gather the bigger difference is the change in rolling resistance by effectively having a wider clincher tire.


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PostPosted: Wed Jun 18, 2014 2:19 am 
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LouisN wrote:
sub 1400 g wheelset with 30 mm XR300 rims on 16-20


Will I notice the weight on the rim? Its nearly an extra 100g per rim... Doesn't sound like much but its rotational mass? Would I be better off saving up a bit and get something like the pacenti sl23?

I'd use these wheels on hillier courses, our averages are in the low 30s. Although some have downhill so aero does matter, but I've got no sprint and usually try to get away on the hill...

And the no tubulars for juniors thing is so there's no angry parents when a junior rolls a tubular... Or at least that's how my club president explained it.

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PostPosted: Wed Jun 18, 2014 3:05 am 
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My guess would be that they are equally "not stiff". I weigh a lot more than you (170 lbs at the time) and had no problems with the XR200 in 20f and 28r.

The lower rotating weight will improve initial accelerations slightly, and will make the bike feel lighter and more responsive to direction changes. It isn't a big enough deal to get anal about though, especially if you are on a low budget. You'll gain more by using the best tires (Conti Supersonic or Attack, Vittoria Tri or Corsa) with latex tubes.

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PostPosted: Wed Jun 18, 2014 4:27 am 
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So I guess I want to know if the slightly better acceleration worth the extra rolling resistance of a narrow rim? I assume because the xr-200 is narrow it'll have a higher crr? How would it compare to the xr19w which is only slightly wider/heavier?

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PostPosted: Wed Jun 18, 2014 4:38 am 
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I think what Ron (WMW) is saying is that it's probably wiser to dump all the money that you're reserving for this wheelset into getting nice, albeit less durable/long lasting, tires and latex tubes, as that will yield you a higher return in terms of watts/$$.

I'm inclined to agree with him. Even at your slim weight, the 100g means far less than the bump you'd get from having really low rolling resistance (which will help you up and down the mountain)


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Posted: Wed Jun 18, 2014 4:38 am 


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PostPosted: Wed Jun 18, 2014 5:10 am 
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Sticking with BHS, go Kinlin tubular TB-25 rims (~425g)! I have a set weighing 1340g thereabouts.

Save some more weight with Velocity Escape rims > under 1300g set.

You said you wanted something different, so go tubs!

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