What is the maximum height of a carbon steerer tube? I am NOT worried about aesthetics at this time. I am worried about safety and catastrophic failure of the carbon!
Most manufacturers recommend 40mm of spacers or less.
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According to True Temper, you can cut an Alpha Q Z-Pro fork steerer to 144mm longer than your head tube (I’ve included the 14mm for the bottom headset cup: 130 + 14 = 144). I then ran your question past Bert Hull at Alpha Q:
Dear Lennard,
Spacer stack height limit on the Z-pro is 130mm from frame to top of stem. With standard stems and headsets, that works out to about 90mm of spacers, which is quite a lot. There is no magic to this number, but we need to set a limit somewhere. The issue is not so much safety as it is stiffness. The steerer is not going to break because you put extra spacers above the upper bearing. As you know, the deflection of a cantilevered beam increases exponentially with distance. Adding spacers quickly adds up to a less stiff cockpit. We set recommendations on spacer stack height so that people who use our products will enjoy the performance we design them for.
Sometimes people ignore our guidelines to customize their ride, and if they can live with the compromise of performance in order to get their position more comfortable, then for them it is a situation they can live with.
As for the question about bearings not working with tall stack heights, I don’t see why there would be a problem with going higher. Perhaps that bike shop owner could enlighten us all with his logic on that one.
I could run a special test if you like.
I can set up a 100000 cycle CEN test on a handlebar mounted on a stem above a ton of spacers and see if the bearings give out before the test is complete. I will take a week or so to run it.
Bert Hull
Product Manager, Alpha Q Componentshttp://velonews.competitor.com/2008/04/bikes-and-tech/technical-faq/technical-qa-with-lennard-zinn-big-bikes-have-special-needs_74382
Some of the guys who own my bikes are running 8cm of steerer tube above the headset with no problems.
I’ve always wondered why many people on this forum freak out at the idea of running a few cm of spacers on their steerer tube but then have no worries about riding seatposts sticking 30cm plus above their seat collar. I wonder if they know some secrets about bicycle physics.
What is the maximum height of a carbon steerer tube? I am NOT worried about aesthetics at this time. I am worried about safety and catastrophic failure of the carbon!
I’m not sure what every manufacturer says, but based on what I was told by the head mechanic at the shop I used to work for: 8cm. He claimed that every manufacturer had different specs but his experience told him that 8cm was the best place to go for the highest on all but the lightest of forks. I’ve never met a mechanic I trust more (20 years of wrenching, one of USAT’s mechanics for World Championship races), so 8 cm it is in my book.
Also Leonard Zinn’s column is often filled with hacktastic tricks. Certainly neat but not something I would ever recommend on the internet anonymously much less knowing that there are lots of people who don’t know about bicycle maintenance who will read his column as the word on how to do things. It is like when my coach who won’t ride anything but tubulars because he’s been racing for 30 years tells the juniors that the best way to glue their tires is with 3M Fast Tack, you just kinda want to shoot yourself because while yes it will likely work alright it is TERRIBLE ADVICE.