Elite 31.8mm X4 Stems


The X4 is absolutely the best combination of strength and weight available. Enduro and downhill riders can run Thomson confidently, yet X4 is light enough for cross country and cyclocross. X4 offers precise steering and tracking for the ultimate in control while riding.  40-60mm stems are available in block style only.

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Too many modern mountain bike stems sacrifice strength and torsional stiffness for a few grams of saved weight. The Thomson X4 is the leader in strength and stiffness.

The Thomson X4 stem allows you to realize the benefits of stiffer forks and stiffer 31.8 bars. X4 offers precise steering, tracking, and more control while riding, all wrapped up in a beautiful design.

Certified to: EN 14766 2006 MTB and DIN CERTCO: 2006 MTB

The Thomson X4 is stronger and 30 grams lighter than the Thomson Elite 25.4 mountain stem. It features a traditional steerer clamp that is shaped to save weight and to be knee friendly. X4 is absolutely the best combination of strength and weight available. Thomson stems are the strongest in the industry, meaning enduro and downhill riders can run Thomson confidently.

The stem is one piece of solid 7000 series aluminum extruded billet precision, machined by Thomson in our Macon, Georgia factory. It’s built and tested to the same standards as our aerospace parts, and it’s the best stem for all-around mountain bike and cyclocross riding.



Can I flip a Thomson Stem?

You may flip the X2 and X4 Thomson stems to create different rise options. The logo on the 10° X4 stems is reversible so you may run negative and the logo will not be upside down.

Can X4 be used on a road bike?

Yes, X2 is lighter and allows better aero-bar compatibility, but if you want to use X4 on a 31.8 Road or ‘Cross Handlebar you may.

Is X4 safe for carbon fiber?

X4 is engineered to work very well with both carbon handlebars and carbon steerer tubes. All torque requirements in our instructions must be strictly followed for carbon components. Our carbon bars work nicely with X4!

Does a Thomson 1.5″ stem fit Cannodale® Forks?

Yes and no. Some Cannondale bikes are now shipped with 1.5″ traditional forks and our 1.5″ stems will fit. Newer Lefty’s use the OPI combination steerer tube/stem, and none of our stems will fit. Older Lefty and Headhshock stems are 1 9/16″ and our stems will not fit. If you are not sure, measure the steerer before you buy. This is a good time to go to a bike shop!

Why did you change steerer clamps on X4? Were there problems with the old clamp?

We changed to save weight. There were no problems with the old clamp but it did add about 20 grams.

What is the stack height of the X4 Stem?



X4 Instructions
X4 Line Drawing