The stem is the part that connects your fork steer tube to your handlebars. They are usually made from aluminium alloy or carbon fiber with steel or titanium bolts.
The most important feature of the stem is its length, as this contributes to your proper fit on the bike. Typically you would need a stem of 9 - 12cm if your frame is properly sized.
To get the pro look, buy a bike frame a size smaller than normal and fit a stem 2cm longer than normal. Ensure that the stem is 'slammed' i.e. no spacers between the stem and fork bearings. Actually many pros ride with plenty of spacers under their bars. For example Stijn Devolder won the Tour of Flanders solo in 2009 with a 2cm stack under his stem. It is more important to be comfortable.
I have noticed that bike fitters have a habit of putting the bars higher, due to lack of hamstring flexibility. I find that this puts more weight on the saddle, which can lead to back ache and saddle sores. Low bars are not necessarily less comfortable.
The angle of the stem is also important, as it affects the height of your handle bars. A 17 degree angle is preferred as it means the stem will be approximately parallel to the floor. Often stems are made in 7 degree angles, so the bars are lifted a little.
The stem needs to be compatible with the handlebars, so a clamp size of 31.8mm (most common- called oversized) or 26.0mm (the old standard size) should be chosen.
The part that attaches to the form will either be 1.25 inches or 1 inch. Stems are normally provided with an aluminium shim to allow standard stems to fit to 1 inch forks.
The stem should be stiff so that the bike does not feel too flexible when sprinting. However, it should also provide some damping qualities so reduce rider fatigue. Having tried about 10 different stems with different lengths over the past few years, I can say that I have never noticed any difference in damping or stiffness between them. There are differences, but I'm just saying that I can't feel them.
The stem should be light, as extra weight hinders climbing. Stems range from around 100g to 200g (for 11cm) so there is a fair amount of variance. There is hardly any difference in the weights of carbon and aluminium stems. This is because the stem needs to be designed to cope with loads in all three axes (isotropic). Since carbon is strong in one plane (anisotropic), a special lay up has to be used which negates the weight savings. You end up with a weight very similar to aluminium.
Furthermore, when a stem is made from aluminium with a carbon wrap such as the Pro Vibe Carbon, the stem is only marginally lighter and much less stiff than the aluminium version.
This is because:
- a layer of epoxy has to be put between the aluminium and carbon to stop corrosion which reduces stiffness.
- To justify a higher price, less aluminium is used to yield a lower weight than the pure aluminium version.
On the plus side, carbon wrapped stems may provide better damping than aluminium alone.
Titanium bolts do not make any difference to stiffness. Such bolts are more likely to snap or be rounded compared to steel. A small amount of weight is saved, Ti bolts don't rust but most of all it is good for marketing.
Looks and price
While most stems are of similar stiffness and lie in a range of 105-135g (for 11cm), the deciding factors are looks and price.
You might prefer the look of a carbon stem, since carbon is quite an exotic material. Bear in mind that carbon does not seem to offer any advantages over aluminium alloy for stems, and is considerably more expensive. You are better off sticking with aluminium stems like many pro riders.
Of course, for an ideal asthetic, stem brand should match your handlebars and seat post. Popular finishing kits are made by 3T, Deda, Fi:zi'k, FSA, Ritchey and Pro.
To consider price, an ENVE carbon stem Costs $265 and weighs 120g for 11cm. A PRO PLT aluminium stem costs $40 and weighs 115g for 11cm. Cheaper, lighter and stiffer - I recommend to save your money.
|3T||ARX Team||Aluminium||11cm||130g||Very Good||$110|
|Extralite||OC Road||Aluminium||11cm||88g||So so||$230|
|PRO||Vibe 7S||Aluminium||11cm||137g||Very Good||$100|
|PRO||Vibe Carbon||Carbon||11cm||138g||So so||$180|
Most stems are a similar weight, around 100 - 140g (3.5 - 5oz). They have similar stiffness. It is very rare to see a stem fail, so strength is adequate for all. The deciding factor then comes down to looks and price.
I like the Pro Vibe 7S, as seen on Giant-Shimano , FDJ, Orica and Sky bikes and the 3T ARX Team stem as seen on the BMC and Garmin Sharp bikes. Both 3T and Pro make excellent handlebars and seat posts, so you can match them up on your bike.
For extra bling factor you could get an ENVE stem, but what's the point? Better to get something in aluminium, and money.
slamthatstem.com - site about slammed stems. Remember, fit is more important that slamming. If you don't fit a bike that's a frame size too small with at least a 12cm stem, then get stretching until you do.