Hi,
I'm going to buy a new stem to my bike and I chosen Pro vibe, because heard a lot of good reviews.
I have a question:
Which version is more stiff:
- Pro vibe 7s
http://www.excelsports.com/Gallery/100542-1.jpg

- or Pro vibe UD carbon
http://www.backcountry.com/images/items ... ONECOL.jpg

Thanks for answers.

I have been using the alu version for about 2 years now. I have never felt my stem to have any undesirable flex. I am 170 lbs and a "sprinter" in cat-4.

I would recommend making your decision based on weight and price rather than stem stiffness.

Price and weight isn't very important for me, because of small diference in weight (less than 8g between), and $30.

Any other opinion?

If it's only $30 more, I'd get the carbon... just for the bling factor.

Both are very stiff and the weight is basically the same.

Carbon fiber is not the best material for every application. A stem is a good example of an application where carbon fiber is not ideal. Stems go through a great deal of stress and they are rather small in shape. Metal has always been a better choice as the appropriate material for a stem. Don't misunderstand me...carbon fiber stems work just fine. But carbon is better suited to larger items....that way the incurred stress can be distributed across a larger area and a larger number of carbon strands. It's really all about the resin of course.....the carbon fibers themselves can withstand a great deal of tension.
Addressing your specific question, it would not surprise me at all if the aluminum stem was stiffer than the carbon stem. But as other responses have noted, there's probably not enough difference between the two for you to notice. So the best advice is that you simply buy the one that looks best.

Not sure is you can still get this, but this stem has double the stiffness of the Pro vibe carbon stem.

http://www.pro-bikegear.com/publish/con ... _mark.html

The alloy Vibe 7s is really stiff. I would recommend an alloy bar, too.