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PostPosted: Tue Feb 17, 2004 4:28 am 
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Florian wrote:
....I had a long technical discussion with Jo Klieber (engineer behind Syntace) about 4 bolt stems last summer:
any 4 bolt stem stresses the handlebar more than conventional 2 bolt faceplate stems.

There's even more stress with two divided clamps (like on the F99 or the new Ritchey WCS V3), because the clamping force applies in a very small area.
He had several 4 bolt stems from different manufacturers (incl. his F99) on his testing machine and all stems cracked handlebars earlier than 2 bolt designs.
That's why he decided to reinforce his bars in the clamping area and strongly recommends to use only bars which are explicitly approved for 4-bolt use by the manufacturer....


I'll second that! And I guess that there's more stress on the 4-bolt divided clamp itself, too, because I cracked my Deda Newton today, sheared at the top two bolts...had checked the torque when I last overhauled, it seemed alright.
Too bad...Anyone have any suggestions on a good new 31.8 stem, light and reliable and strong?

(Deda Newton bars, I don't really want to change them right now, but of course bar/stem suggestions also welcomed).

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Posted: Tue Feb 17, 2004 4:28 am 


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PostPosted: Tue Feb 17, 2004 4:31 am 
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Ritchey WCS. No fuss, light weight, low price. Bomb proof.

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PostPosted: Tue Feb 17, 2004 12:05 pm 
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3ttt Zepp XL, very stiff


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PostPosted: Tue Feb 17, 2004 12:20 pm 
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wcs better than zepp
big difference


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PostPosted: Tue Feb 17, 2004 1:50 pm 
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just as important as torque spec (which is much lower on 4 bolts than people realize) but torque sequence.

Quote:
I cracked my Deda Newton today, sheared at the top two bolts


did the stem crack or just the bolts shear? post a pic please.

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PostPosted: Tue Feb 17, 2004 9:49 pm 
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Tsielio wrote:
wcs better than zepp
big difference


But Zepp lighter I think :-)
and you can shave qain some weight with shaving and Ti bolts, like mine :wink:


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PostPosted: Wed Feb 18, 2004 6:59 am 
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nicrump wrote:
just as important as torque spec (which is much lower on 4 bolts than people realize) but torque sequence.

Quote:
I cracked my Deda Newton today, sheared at the top two bolts


did the stem crack or just the bolts shear? post a pic please.


The stem clamp cracked in 3+ places; I had checked torque but not "torque sequence" :?: Bolts are SRP. Perhaps I overtorqued?


Attachments:
117_1730_text.jpg
117_1730_text.jpg [ 49.03 KiB | Viewed 1017 times ]

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PostPosted: Wed Feb 18, 2004 7:04 am 
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You over tightened it BIG TIME! :D Notice how th ehandle bar pushes through the clamp causing it to split. Oh boy.

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PostPosted: Wed Feb 18, 2004 7:59 am 
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Ye Olde Balde One wrote:
FRM has this on their website, which is in favor of 2-bolt stems according to tests made by Easton allowing for better distribution of force and stress on the tube of the bar;

"2 VITI CONTRO 4 VITI
Come dimostrato da test della Easton, le chiusure a 2 viti offrono più sicurezza rispetto ai sistemi a 4 viti quando si devono serrare manubri a spessori sottili. Le 2 viti distribuiscono più uniformemente il carico sulla intera superficie che abbraccia il manubrio. Con i sistemi a 4 viti è molto più difficile distribuire uniformemente il carico. Anche se serrate correttamente, le viti alle estremità del coperchio tendono a creare una zona di pressione maggiore sul manubrio, proprio nella zona dove più il manubrio flette durante l'uso e dove ovviamente si concentrano gli stress massimali. La concentrazione della pressione creata dal sistema a 4 viti può portare a rotture a fatica. I coperchi a 2 viti sono autocentranti: permettono cioè ai carichi di serraggio di dissiparsi prima di raggiungere il bordo dell' attacco manubrio nel punto di uscita del manubrio. Gli attacchi con coperchio a 4 viti NON sono quindi consigliabili con il montaggio di manubri di basso spessore e quindi basso peso e neppure con manubri in fibra di carbonio."

TRANSLATION:
2 BOLTS VERSUS 4 BOLTS
"As demonstrated in testing conducted by Easton, clamps with 2 bolts offer more security with respect to 4-bolt systems when using thin-walled handlebars. The 2 bolts distribute the load more evenly over the entire clamping surface. With 4-bolt systems it is much more difficult to evenly distribute the load. Even if inserted correctly, the bolts at the extremities of the clamp tend to create an area of greater pressure on the bar, precisely in the area where the bar flexes most during use and where, obviously, the maximum stress is concentrated. The concentration of pressure created by the 4-bolt system can cause fatigue stress. 2-bolt clamps are auto-centered: that is, they permit the clamping force to dissipate itself before reaching the edge of the clamp where the handlebar exits. 4-bolt clamps are therefore NOT advised for use with thin-wall bars (and therefore light weight) nor with carbon-fiber bars."

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PostPosted: Wed Feb 18, 2004 9:54 am 
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cadence90 wrote:
The stem clamp cracked in 3+ places; I had checked torque but not "torque sequence" :?: Bolts are SRP. Perhaps I overtorqued?

I think it's a clear design flaw:
you can see both cracks starting on the inside of the front plate.
The edges are way too sharp and thin, should be more rounded than they don't start to crack so easily.

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PostPosted: Wed Feb 18, 2004 2:44 pm 
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I have to agree with superlite on this one. However, I also agree with Florien But this can be cleaned with a de-burr.

Given the consumer market, this is a far too complicated design for the consumer to use safely. I have been using two Newton stems for a sum total of about 18k miles with no problems.

As for sequence, follow the order in the pic, 48"lb (5Nm) on the first pass and 70"lb (8Nm) on the second. If you dont follow sequence then although your bolt torque might be right, the cap is not loaded correctly.

Just like the head bolts on your Benz

Thats a lot less than the usual 100-120"lb (14Nm) of old school stems.

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PostPosted: Wed Feb 18, 2004 2:46 pm 
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sorry, pic wont load but looking at your stem from the front its upper left then lower right follow by upper right then lower left.

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PostPosted: Wed Feb 18, 2004 5:12 pm 
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Joel wrote:
Tsielio wrote:
wcs better than zepp
big difference


But Zepp lighter I think :-)
and you can shave qain some weight with shaving and Ti bolts, like mine :wink:


:shock: Please tell me you are joking! I used the Zepp stem last year up until the Ti bolts suddenly broke causing me to crash. Then I bought a second one and tightened it with a torque wrench and I stripped the threads. I learned that the Zepp stems were recalled for the same two exact problems and I was able to get my money back for both stems. I would never trust my life to a Zepp stem again let alone shave it in order to save weight.

I bought a Stella Azzurra Vice Versa stem because it uses a four bolt face plate. The bolts are steel and the face plate is substantially thicker than most other stems and it is a solid piece, not a split face plate like some. After crashing because of a broken stem I'd rather use a slightly heavier stem (Advertised at 125 grams but real weight is higher) and lose the weight somewhere else like my body.


link to stella azzurra stem


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PostPosted: Wed Feb 18, 2004 7:59 pm 
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I'll post a pic soon, I'll think it has no standard bolts. They're M5.


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PostPosted: Thu Feb 19, 2004 12:23 am 
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I had two 25.8mm Zepps with mega miles and no problems but also heard of the period where problems arose with a batch of Zepp XL's due to lack of depth with a countersink on the faceplate which resulted in stripped threads. And the little 5mm Ti bolts did not inspire confidence. But note that the 3TTT "LESS" stem now replaces the Zepp - it uses 20 mm long 6mm steel bolts at the faceplate in place of the 15mm long by 5mm Ti bolts on the Zepp.

I've got enough confindence in the new LESS to have replaced all the steel 6mm bolts with Ti......


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Posted: Thu Feb 19, 2004 12:23 am 


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