I was excited when I received my Cutter carbon handle bars. Reviews were good and they came in under weight at 175 grams for 40 cm. As I was installing them, I started to hear a cracking noise as I was tightening the bolts. I used a 5 NM Ritchey Torqkey Wrench and the bars started to fail before torqued to 5nm. May be hard to tell in the pics below, but there is a small bulging line where the carbon failed. Not sure if the one I had was just defective, but these will definitely be returned. I think I'll just stick with aluminum for peace of mind.

all [carbon] bars I have used have a limit of 4Nm... did that same thing to a set of xXx bars... my bontrager 4Nm wrench did the trick sorry to see you had the same experience.

Oh. My stem requires 5Nm though.

I was actually the one who installed the bars. I brought over some tools to swap out some parts for him and when I was putting his new bars on I heard cracking the entire time as I was tightening it. It got crushed long before I got anywhere near 5 Nm.

MikeyBoyAZ- Where are you seeing all bars requiring 4 Nm? Ritchey Carbon makes carbon bars and their 5 Nm torque wrench tool is specifically designed to provide safe clamping force when using their bars. 3T also has a 5 Nm torque rating on all their stems, which are intended to be used with their carbon bars. Either way, 1 Nm should not make a difference. These POS bars started cracking well before 4 Nm was seen. I kept hearing a cracking noise and I was like hmm okay, maybe it's the bolts on the stem because it had some cheap stem that I haven't seen before. Then I ran my finger along the side of the stem and felt the huge ridge that was created on the bars. I knew they were effed at that point.

The pics don't do it justice. The bars got crushed bad. It happened with very little force. It honestly didn't surprise me though. $65 bars can be 175 grams or safe, but not both. I highly suggest that anyone running these bars remove them right away because you are playing with your life just to save a few grams. Totally not worth it.

Sorry about that bad luck today bro. You'll be better off with some aluminum 3T bars anyways. They are MUCH lighter than those beastly 460 gram bars that came on your bike! LOL

ilc, just because a stem is rated to 5Nm doesn't mean a carbon bar is rated that high... just saying. I have been loading my bars to 4Nm and have never had one rotate on me... ever... so why add any more torque?

I said all carbon bars I have used... not all made... I have most definitely not seen all carbon bars that are made and have no idea about all of them... though zipp is 8Nm... I would never go that high... ick.

you stem does not require 5Nm it is limited to no more than 5Nm

hyperbole.

1. they did not crack the entire time (when the first thread of the first bolt was screwed in).

2. reduce friend to friend only position.

3. utilize bicycle shop.

4. why would you continue after hearing cracking?

What diameter are the bars and what diameter is the stem clamp?

I'd be interested in seeing the faceplate of the stem that was clamping these bars.

If it was as described, a cheap arsed alloy stem meant for cheap arsed alloy bars then there is a good chance that the stemp clamp was not 100% round and/or the mating surface was not designed for carbon and concentrated all the clamping force in too small an area.

Sorry to hear about the bars failing regarless of the reason.

Bummer.

Bars and stem should probably be aluminum anyway, IMO.

At least for now.

Mine have been rock solid. I had to tighten my stem on it on the road once because some ass hat thought it would be funny to loosen my bolts when it was on the bike rack at work. Not sure what I tightened it to (obviously didn't have a torque wrench on me) but I snugged it up pretty good. Ritchey WCS stem.

I went with 4Nm because of thinking that 5Nm would be too high for my aerobars (5Nm max). Hit a slight crack in the road and I was suddenly looking a inch further down at my wheel.

I prefer to just go to the max now.

The diameter of the bars should be measured and compared with the stem. More than likely, the fit between the two was wrong. No carbon bar should fail because it was torqued to 5Nm or 6Nm instead of 4Nm.

After reading similar stories about stems and carbon steering tubes, I did some experiments of my own. I've taken cutoffs from steering tubes, clamped a husky stem (with two M6 clamping bolts) onto them and applied a ridiculously high torque with a long-handled hex wrench. I was never able to cause any damage. Most cases of damage result from a poor fit and/or raised metal along the edges of the clamp.

+1. I think using a stem that's not designed or intended to clamp a carbon handlebar is the likely culprit.

That wouldn't be a big surprise - the ancillary components on the BMC are rather less than stellar, though they get the job done well as assembled. It would be easy to have a less than perfectly round stem "hole" that one would not notice on the aluminum bars. I am not moving as quickly as dayday82 to modify/trim weight on my BMC, but I will likely look at a stem replacement when I change the bars.

The other possibility that hasn't been explored is out-of-roundness on the part of the econo-carbon-bars. That would be an issue, too.

And to those who ask "Why would you keep tightening once you heard a cracking sound?" - what does it matter? Once you hear the cracking, failure is happening at some level. The bars are no less useable now than they were when the cracking sounds were first heard.

This is a good point.

When I worked with Deda they had a batch of bars that could have failed this way if we hadn't caught it.

The problem was that the carbon bars were to spec out of the mold but once the non-slip coating and clear coat were added they were quite a bit larger than tolerances would allow.

Clamping these bars (even with a perfect stem) would have resulted in failure.

Looking at the photos this might be another possible answer.

I like the design of the Easton faceplate for use with carbon bars. It makes it hard to screw up aligning the faceplate and crunching the bar.

I believe aerobars have more torque due to their length (something about the distance from the fulcrum... the math teacher should chime in here sometime) the farther away, the more torque you can apply with less force... I would hesitate putting aerobars on carbon drop bars in general... aerobars on alloy drops shouldn't be an issue, because they can withstand more than 4Nm... I have a friend with aerobars on some alloy, over the last few months he has noticed the bars drop a little over time... its about time to adjust them... they are alloy on alloy torqued up to 6Nm... I think it has more to do with his technique and posture though.

Definitely interesting. Puts in a good word for having solid QC.


I'm wondering if the Cutter bars in question were Bonktown specials (I've never seen Cutter as a brand anywhere but Bonktown). And if something's on Bonktown, it's there for a reason (hopefully just last year's color of whatever, but it is a bargain rack). Still, you'd hope that a defective product wouldn't get into the wild.

Ha ha; that happened to me in the British university TTT championship several years back - except the whole handlebar assembly rotated down at the stem by about 30 degrees. TT bars pointed down at that angle are true terror when you're inches off a teammates' wheel. Then it turned out I'd picked up a slow flat at the same time... Got the wheel change but it was all pretty much game over for us by that point.

(Though we thankfully didn't DFL... and our university's other squad - we were definitely the 'B team' - took silver so we could still party.)

This was my thought. Sounds like the bars are bigger than the stem clamp to me.

It definitely could be an out-of-round stem or the handlebar itself. I'm putting my money on the handlebar being out of spec though. There were no unusual marks on the clamp area of the stock aluminum bars. If the stem was out of round it would have at least marred the surface of the handlebars. Pretty sure it was just an out of spec handlebar due to poor QC from cheap Chinese labor.

Out of spec or not, the bars took no real force to crack. They are junk. Even if you are successfully using them right now I'd swap them out for something else asap. The chances of them being durable long-term are not good. Do you really think a $65 handlebar that weighs 175 grams was well engineered? Highly unlikely.

I too would put my money on this likelihood.

It could be I guess, but I've purchased several Cutter items and quality was top notch. I've got two of these handlebars and they appear to be beautifully made.

The torque spec on a 3mm bolt means next to nothing. Torque specs are pretty much worthless for bolts less than 1/4" due to high variance in thread friction. To illustrate, insert the bolts dry and 5Nm will might have the bars slipping. Put grease on the threads and at 5Nm you might have enough bolt tension to crush the bars. The important is bolt tension; in big bolts, tightening torque correlates well with bolt tension. In a little bolt, thread friction is a huge factor and the correlation between bolt tension and tightening torque is not good.

Also, the 5Nm spec given for stems is 1) a maximum to keep for stripping the bolts, and 2) for the stem, not the handlebars.