Just in: Vitus Dark Plasma

I rather conflated two separate issues in my original post, sorry. Firstly, fitting the stem so that it sits a few millimeters beyond the end of the steerer tube is a bad idea, because the clamping is uneven, and you can damage the vulnerable exposed ends of the crabon layers. As Leonard "at least one spacer above the stem" Zinn says, it is safer to choose your stem angle and steerer length such that the latter sticks out a couple of millimeters above the former, then put a 5mm spacer on top, giving you the few millimeters needed for proper headset adjustment. (Incidentally, the ultimate authority on bicycle maintenance on the web, Sheldon "Mr. Sobriquet" Brown didn't seem to have much of an opinion on the subject, but then I think he probably preferred quill stems.)

The second issue is that having as many spacers as shown in the photo above puts more lateral strain on the steerer. This is more of an issue with steerers than seatposts because (a) seatpost walls are often thicker (b) some of the seatpost is exposed so cracks can sometimes be seen before failure (c) sudden lack of support for the posterior is uncomfortable but nowhere near as dangerous as sudden loss of all steering, and (d) the weight on a seat post is mostly directed down its length, especially with the decreasing amount of offset many manufacturers are offering (I wonder why) whereas the stem acts as a lever on a steerer, applying a not-inconsequential torque every time you ride over a bump in the road.

While I choose not to purchase "all carbon" forks, I wouldn't go as far as saying they are unsafe for all riders in all circumstances. My comments was more concerned with the lazy use of the material of the fork steerer in reviews as a way to instantly classify bikes as either good value or ridiculously antiquated rip-offs that their manufacturers should be ashamed to let out the door. Not necessarily on this web site, although I notice there is no mention of the materials used in the construction of any other parts (but it is a "Just In" piece not a full review.)

Even though I am close to obtaining a Masters in engineering with some specialism in composite materials I dont feel qualified to post on this topic with any authority. Or perhaps it is that I have a better understanding of what would constitute qualified.

A carbon fibre reinforced plastic is substantially stiffer than aluminium when load is applied in line with the fibre direction. However the material is heavily anisotropic and heavily dependent on the volume ratio of fibre to matrix.

Basically I feel that it is an uninformed opinion that concludes that carbon head tube is bad thing with out knowledge of the exact material specification and fibre lay up, combined with a good understanding of the loading conditions its subjected to. Thats why we rely on a review to determine if there is "some thing funny" going on up front whilst its been ridden for a few hundred miles.

I would also postulate that on a road bike with a good position set up, perhaps except for under frontal braking, the load on the headtube is substantially smaller than load a 70kilo rider sitting on the saddle puts on seatpost (carbon or otherwise), espcially bearing in mind your seat could be seperated by 300mm from the clamp.

I do agree with Daves reasoning for aluminium stems.

However as I said, take my words with a pinch of salt.

With a *carbon* steerer many manufacturers recommend no more than 35mm of spacers. A longer length of unsupported carbon steerer is presumably more prone to failure due to increased leverage on the unsupported steerer between the stem clamp and the top headset bearings. Steel steerer tubes should be much more tolerant of 50mm of spacers - though the bike aesthetic police might not be

Quote:

That's mated to a full Carbon fork which on the Vitus website ends with a couple of spacers and a nice Control Tech stem, but on our test model you get eleven – count 'em – spacers for some serious fine tuning ability.

Hopefully that is just to cater for different size reviewers, and they don't actually sell them in that configuration. It is my understanding that clamping a stem right on the end of a plastic steerer, especially with so many spacers between it and the pivot point of the upper headset, is asking for trouble. Yet another reason why the totemic quality assigned these days to "all carbon" forks is misguided. I have read some reviews that basically praise a bike but conclude that the single fact that its fork steerer is constructed out of metal makes it a terrible value proposition. Alloy steerers can be just as light, are generally stronger (although nothing is perfect as George Hincapie found out at the 2006 P-R) and never splinter if you cut them down. You can use a star nut instead of struggling with a fiddly and weighty bung. Even if there is any weight or stiffness advantage, there are other areas of the bike where spending your budget to improve either quality will bring more significant gains.

"theory that postulates the existence of invisible lifeforms in the dark matter that makes up a major part of the universe"

you want to ask "MrChrispy" about that one I think.