Until recently, headtubes were available in two dimensions: 1-1/8 inch and 1.5 inch. 1 inch headtububes were also common in the past, but today they can be found only on low cost supermarket bicycles.
The new headtubes combine the two dimensions, as in the upper side their internal diameter is 1-1/8 inch, while at their bottom, the diameter is 1.5 inch. One of the main advantages of using such type of tubing is increased stiffness, as a tapered tube will always be more rigid then a cylindrical one, hence some other important advantages to consider, increased cornering precision and increased feedback while riding. The resistance of the frame is also increased for this particular area, lowering the risk of cracking the down tube or the top tube at their junction with the headtube. Last, but not least, a tapered headtube allows using one of the most common stems size, 1-1/8.
Furthermore, the large section (1.5 inch) of the headtube bottom allows using a thicker downtube/
Not only the headtube is tapered but also the fork steerer. This is not a rule, but rather an option. You can buy a tapered head fork or a cylindrical head fork, for which you will need to use an adaptor completing the difference from 1-1/8 inch to 1.5 inch. This adaptor will cost around 20 euros.
If you consider buying a frame with tapered headtube, you will have to consider which headseat you will be buying. There are two types of headsets, internal and integrated.
It is very easy to see the difference between the two types of headsets: internal headsets have a visible outer edge while an integrated headset will be hidden in the headtube.
You will notice slight difference on the track regarding stability if you use a bicycle with tapered headtube. Our stiffness measuring devices showed that a frame with tapered headset is more rigid than a cylindrical headset one. Also, for enhanced control we recommend using a QR 15 thru-axle. Of course, the fork must be fitted with such mount and the front hub will have to be replaced. However, results will exceed expectations, as we are talking about a difference which any rider will be able to appreciate.