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Old 11-10-07, 06:17 PM   #1
hbutler
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Ambrosio Crono F20 rim ERD

This is my first post on a forum (any forum) so please be nice.

I am planning on building a set of tubular wheels for my race bike and had planned on using the Ambrosio Crono F20 rims, but I can't find the ERD for the rim anywhere (the company will not e-mail or call me back, neither will Ital-Tecno). I don't want to buy all the parts unless I can get the ERD so I can buy the spokes at the same time. If anyone can help (like someone who has built some wheels with these rims before) I would greatly appreciate it.
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Old 11-10-07, 07:16 PM   #2
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I haven't reloaded an updated spocalc.xls in a while and my rim data doesn't show it, but have you checked there for possibly a newer list?
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Old 11-10-07, 07:43 PM   #3
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I checked on the Spocalc.xls that I found on sheldonbrown.com, and I found two values, 618mm and 610mm. Also, I got 615mm from DT Swiss' online spoke calculator. Any idea which one is correct? The only one I found that cited a source is the 618mm that someone posted on a google group forum, but I also would not expect DT Swiss to put wrong information on their site, but I really don't have a clue which one to trust. I'm in no rush to find out, my racing season won't start until April, which is when I am planning on using them.
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Old 11-10-07, 08:22 PM   #4
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I found this thread on a German forum saying DT Swiss shows 615mm, but the responder says he can't verify it.

If possible, I'd suggest you order the rims first, measure ERD, then order the spokes.

EDIT - Now the link doesn't seem to work.. Sorry.
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Old 11-10-07, 08:23 PM   #5
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ambrosio

618 off of this site.

http://www.mapleflow.com/demo/spoke-....php?title=get

I asked Ital-Techno if they knew the ERD or could measure the rims they were selling so I could buy rims/spokes from them, they nicely said no.
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Old 11-10-07, 08:44 PM   #6
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Thanks for all the help. I tried the two different ERD's in DT Swiss's spoke calculator, and it only made a difference in spoke length of 1mm for each kind of spoke (front, left rear, and right rear).

This is probably a stupid sounding question since I think I'm going to buy the rims first and measure it myself (thanks for the suggestion Scooper), but if you had to buy the spokes and rims at the same time, would you buy the shorter length and risk the spokes not being long enough, or would you buy the longer length and risk the spokes sticking out too far? I'm not going to do it, but which would be worse in your opinion?

Some thoughts: 1. I can make the long spokes shorter, but I hate messing up the threads
2. The nipples are 12mm long, so would 1mm short even be that big of a deal?
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Old 11-10-07, 10:13 PM   #7
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Quote:
Originally Posted by hbutler View Post
Thanks for all the help. I tried the two different ERD's in DT Swiss's spoke calculator, and it only made a difference in spoke length of 1mm for each kind of spoke (front, left rear, and right rear).

This is probably a stupid sounding question since I think I'm going to buy the rims first and measure it myself (thanks for the suggestion Scooper), but if you had to buy the spokes and rims at the same time, would you buy the shorter length and risk the spokes not being long enough, or would you buy the longer length and risk the spokes sticking out too far? I'm not going to do it, but which would be worse in your opinion?

Some thoughts: 1. I can make the long spokes shorter, but I hate messing up the threads
2. The nipples are 12mm long, so would 1mm short even be that big of a deal?
I always go shorter rather than longer; the risk in having a spoke too long isn't that it will stick out too far, it's that you'll run out of threads on the spoke before you can tighten the nipple enough to get the right tension. That happened to me on my first wheel set because I stupidly let the LBS saleman talk me into ordering the front wheel spokes and the non-drive side rear wheel spokes all the same length in spite of spocalc telling me that the rear non-drive side spokes should have been 2mm shorter. Well, I ran out of threads on the rear non-drive side before reaching 110 kgf tension and had to reorder eighteen spokes 2mm shorter. I've always rounded down since then.

BTW, in Roger Musson's e-Book Wheelbuilding he shows how to simply and very accurately measure ERD:

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Last edited by Scooper; 11-10-07 at 10:21 PM.
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Old 11-10-07, 10:24 PM   #8
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Thanks for the wisdom, it sounds like you've built more that a few wheels in your life. I've trued tons of wheels before, but this will be my first shot at building a set from scratch. I'm fairly confident that with all the talent I can call (the LBS that sponsors us and my teammates that used to work in a bike shop) the wheels will come out like I want. I may not build them until after Christmas rolls around, I wouldn't want to spend all my money on myself and look bad by not buying any presents.
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Old 11-11-07, 02:05 AM   #9
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I have a spare one and I get 610mm from nipple seat to nipple seat. I measured twice to be certain. This rim is 2 years old, has an orange sticker that says "tubular Formula 20" just want to make sure we're talking about the same rim.

Be careful building the rear; the rims are soft and there's a fine line between enough tension and a bent rim.
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Old 11-11-07, 08:12 AM   #10
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I think that is a different rim than the one that Ambrosio makes now. I've seen a set on ebay (here) with that orange sticker, and they look like a different model than the ones I am planning on getting. I am just going to buy the rims first and measure them to be sure now though.
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Old 11-11-07, 08:47 AM   #11
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F20

Quote:
Originally Posted by hbutler View Post
I think that is a different rim than the one that Ambrosio makes now.
http://www.ambrosiospa.com/catalog_e...pper&Itemid=52
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Old 11-11-07, 09:53 AM   #12
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Quote:
Originally Posted by Scooper View Post
I always go shorter rather than longer; the risk in having a spoke too long isn't that it will stick out too far, it's that you'll run out of threads on the spoke before you can tighten the nipple enough to get the right tension.
-1

In which case it can be filed. You can't lengthen a spoke, but you can shorten one.
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Old 11-11-07, 10:21 AM   #13
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-1

In which case it can be filed. You can't lengthen a spoke, but you can shorten one.
We'll have to agree to disagree. If the nipple bottoms out on the spoke threads before achieving the desired tension, you'll have to either pull the spokes and use a die to add additional threading to the spokes, or you'll have to buy shorter spokes. It's not as simple as shortening the longer spokes. Also, spokes - especially butted ones - stretch under tension.
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Old 11-11-07, 03:43 PM   #14
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The rim soil sampler put up is the one I measured.
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Old 11-11-07, 04:00 PM   #15
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Quote:
Originally Posted by operator View Post
-1

In which case it can be filed. You can't lengthen a spoke, but you can shorten one.
??? Too Long = Out of threads. You filing some extra threads onto that spoke? Maybe filed in the round file
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Old 11-14-07, 12:11 AM   #16
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Just to set the record straigt, I finally heard from Sergio from Ambrosio s.p.a. The ERD for the Crono F20 is 610 mm, for anyone else that may have been looking for the info. I wonder why it took such a long time for them to get back to me? Maybe they were all on vacation. I heard that Europeans get some awesome vacation time...
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Old 11-14-07, 06:30 AM   #17
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Erd

Was it measured with Rim Rods, or just a tape measure?

http://www.cyclingforums.com/showpos...11&postcount=4
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Old 11-14-07, 07:41 AM   #18
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I'm not sure. My guess is that since it came from the company that manufactures these rims, it is an accurate measurement, though. It could have even come from the CAD drawings, or whatever blueprints they manufacture the rims from. It might be 5mm short, that might be where the other meausrements are coming from. Still, the best bet is to buy the rims first and measure them before you order spokes. I've been looking around a lot more since I got serious about building a lightweight set of tubs for racing, and I might even go with an old pair of Super Champion Medaille d'Or rims I've found. They're super light, even if they aren't too strong. I'm only 130 lbs in full kit with a water bottle in my jersey pocket, so I don't think that they will fold up under the massive power my legs are producing, ha ha.
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