Stems...according to Chip, a follow up to Roofs fork

Triathlon Forum
1

Being as stems and forks are not the same failure, I thought I would start a new thread. In my 15+ years on road bikes I have seen my fair share of stem/bar failures…mostly caused by either a crash, or by a mechanic who just swears that his wrist has a built in torque wrench. One thing to know very well…if you crash your bike and the bar has ANY scratch on it, Alu or Carbon…consider it dead and replace it. (note, referring to drop bars…)

Now, much of my personal technie mindset comes from Barnetts Bicycle Institute as well as United. It comes from teching for USCF races and RAAM. It comes from frame building courses and of course living past the days of “drillium”…but, “drillium” is on its way back into fad.

Some of this is out of context as it started with a carbon bar question…MOST important with Alu or Carbon bars, forks, stems - PROPER TORQUE and Proper spacer configuration. This means that little clear plastic washer with your King headset, make sure it is there! They sent it for a reason. Make sure you have the proper expansion plug in your carbon fork…the one that came with it, not one the shop had around. Make sure that if you have a Wolf or AlphaQ the inserts are properly installed.

That is one of the big issues with carbon. Often there are no signs of stress fractures prior to destructive failure. My thoughs about the high modulous as opposed to woven (again this is MY thought, not based on any science)…is that a woven carbon structure will possibly fracture, but the weave of the fabric may have a chance to sort of hold things together. I have seen this on impact destruction as well as as over stress failure (impact on frames, stress on carbon weave fishing poles that cracked but helt together by the weave).

Every point to create a ridge is bad for any handlebar, or steer tube. Now, if you look at my BigOne Stem, you can see there are three potential ridge points, one on each side of the clamp area, one at the closure area…same with the steer side of the stem. A BIG thing that many folks may look past…sand and other pollutants. If you have sand, metal shavings or any other crap that is common in a shop get under a clamp - it will cause a defect in the material and possibly a wonderful start to a future failure.

Now, how many potential areas are there for crushing damage on this stem? This is other than the fact that the rider has a VERY small area of contact for the stem to secure the bar…or transfer the stress load. One thing you cant see here is the rubber insterts that ship with the F99 that go between the stem and bar (could get a photo from my Bianchi though). Also, the F99 stem REQUIRES a special “lube” that has “grit” in it to keep the bolts torqued (got me, I got the packages of the goop)

http://syntace.com/imgserver/syntace/images/1000/1800/1847/picture1847_Syntace.jpg

Now then there are stems like this super nice Thompson. I have seen bars carbon and Alu very damaged by this stem but not with out allot of help from a mechanic who has no clue or torque wrench for that matter. This stem also leaves the steer tube open to the same crushing damage as the bar…again, with a bad mechanic.

http://www.lhthomson.com/images/x2proto.jpg

This is the stem that is currently on my Litespeed road bike with a TTT Prima220 (NOS) bar. As you can see, there is a solid clamp for both the bar and steer tube. On the other side what is nice is the torque spec is etched right onto the stem next to each bolt.

http://www.troc-velo.com/images/img0n47062.jpg

But, as you can see here http://www.biketechreview.com/...links/bigonefail.htm the ITM can also be broken (this example was broken on a machine).

http://www.biketechreview.com/stems/images/bigone/extensioncrack.jpg

2

Here is a perfect example of a bar with out a torque wrench…imagine this with carbon…

http://lh6.google.com/mike.blackmountaincycles/RtGaDho-SwI/AAAAAAAAAQU/dV4ImVt59lw/s400/IMG_0010.jpg

3

Being as stems and forks are not the same failure, I thought I would start a new thread. In my 15+ years on road bikes I have seen my fair share of stem/bar failures…mostly caused by either a crash, or by a mechanic who just swears that his wrist has a built in torque wrench. One thing to know very well…if you crash your bike and the bar has ANY scratch on it, Alu or Carbon…consider it dead and replace it. (note, referring to drop bars…) …

So if you fall off your bike (e.g. clipping in) is that the same thing as a crash?

4

With Alu, if you HIT something, bend the bar or put a scratch into the Alu…that scratch is a potential failure point. Now, if that sctatch is on the lower back bend side of the bar near the end caps - screw it as that is not a place most folks put their weight.

Carbon my test is…did a well tightended lever fold over? Did the bar tape get ripped away? Are there any scratches on it. One telling sign of this is the very aggressive crash replacement policies many brands have. Profile replaced a crashed CarbonX for me for $125.00…Their guy Patrice??? Saw it at IMLP and demanded that I swap the bar before the race…they were what I thought were minor scratches on the bull horn area.

5

But stems have the torque spec (not the bars) and they give you one, not one if you’re using carbon bars and a different one if your using alum. Does this matter?

6

Thanks for the info. Makes me happy that I spent the money for the torque wrenches and that I did not spend the money I had considered on carbon bars and a stem for the road bike I am currently building. Now I kinda wish I passed on the all carbon fork.

7

But stems have the torque spec (not the bars) and they give you one, not one if you’re using carbon bars and a different one if your using alum. Does this matter?

No, you go by the stem. The bars should be set. The other thing that to me is really nuts about the market today is carbon bars that can, and cant handle aero clip on’s.

8

So basically, the spec on stems is such that it’s low enough to not damage carbon bars (and not allow them to slip), but also hold alum bars w/out slipping?

9

You guys are scaring the shit out if me! Now I’m thinking my stem or fork is going to fail. I did scrape my aero bars(PD carbon) in July 06 crash nothing major for the bike. I had two shops look at them both said they were ok. However, I put a hair line crack in my Zipp 808 ouch$$. As for the torque wrench thing who knows.

10

That is it
I am going to order a torque wrench this week!!!

You speak of the mechanic with the strong arm, what about the former football player who thinks everything should be very ahem Tight on a bike…

Good info, but I will agree with the other you are scaring the crap out of me.

Pete

11

So basically, the spec on stems is such that it’s low enough to not damage carbon bars (and not allow them to slip), but also hold alum bars w/out slipping?

Exactly. If the stem at its proper torque can not fix your bar in place - either scuff the surface of the bar lightly - or get a new stem. Again…contact area is EVERYTHING when it comes to a secure bar. Enough is Enough when it comes to that area…

There was about 2yrs ago a BIG recall on the F99 stem. This was not at all due to the stem…it was due to the torque spec!

12

One problem is the torque specs are for the bolts and the threaded holes,the specs are there to stop yopu from streating the bolts then breaking them,or so you do not pull the threads out of the base material,the bar you show might be made out of a softer material and another bar might not indent as much or at all,the cuttouts in stems like you show are for light weight not long lasting parts,i guess what i am trying to say is torque specs are not the only answer or a fix, get a solid steel bar put it in a steel part that has the same configure as that stem torque it all down and years later you will see that same indention but much smaller
.

13

One problem with torque specs is that they have to be used correctly. A sten with a torque spec is likely correct when used with a bar from the same manufacturer. Adifferent bar may be a bit bigger or smaller or have a diferent surface finish of be more or less round, which can all effect weather it will slip or not. I’ve know people who have had bikes built with a pro using the torque specs and still had things rattle loose or slip.

Styrrell

14

Good point. That’s exactly what I was getting at/wondering.

15

So basically, the spec on stems is such that it’s low enough to not damage carbon bars (and not allow them to slip), but also hold alum bars w/out slipping?
Is there a rational reason to even use carbon base/drop bars?

16

So basically, the spec on stems is such that it’s low enough to not damage carbon bars (and not allow them to slip), but also hold alum bars w/out slipping?
Is there a rational reason to even use carbon base/drop bars?

Maybe not, I am a long time user of Deda Newton bar/stem.
However, you gotta love the a-hole who buys carbon stem, carbon bar, wraps it w/ gel tape and puts those stupid bontrager buzz-kill thingies in the ends. Classic.

17

I’ve know people who have had bikes built with a pro using the torque specs and still had things rattle loose or slip.

Styrrell
That is what LockTite 242 is for.

18

Alright, this has brought up a troubling memory. I have (and use) two torque wrenches: the Park TW-1 (0-60 in/lbs) and the TW-2 (0-600 in/lbs). I recently replaced the loaner stem from the bike shop with a Deda Zero100 (NOT the SC with the Ti bolts) holding a Newton bar. IIRC, the torque specs for the stem are 8 n/m, so that’s above the TW-1, but way low on the TW-2. So I figure I’ll use TW-2 and just aim low. I’m torqueing them all down in order and while the wrench is still not up to where 8 n/m would be, I’m CLEARLY over torqueing these bolts. I start backing them off and pop goes the first bolt. I replaced all four bolts and used the TW-1 to get the bolts close to 8n/m. Probably not there, but the bar doesn’t slip. Yet.

So I have two questions:

  1. How should I have handled “in between” torque specs?
  2. Should I even be using this bar still? It looks OK, but should I take this opportunity to replace the yucky anatomic bend bar I don’t like with the pretty italian bend Newton? Stem as well?