Parts guide
MTB Stems and Bars: Length, Clamp Size and Fit
The cockpit is the easiest part of a bike’s fit to change. Here is how to check the sizes and choose a stem and bar that suit how you ride.
- By
- Collective, London
- First published
- Updated
- Reading time
- 2 minutes
Swap a stem and bar and the same bike feels different: quicker or calmer, more upright or more aggressive. Two sizes decide what fits, the steerer and the bar clamp, and then it comes down to length, width and rise.
This guide covers the sizes, what changing them does, and how our ST1 and S1 stems and riser bar fit in.
Chapter 01
The two sizes that matter
Steerer and bar clamp.
| Size | Common values | Notes |
|---|---|---|
| Steerer | 1 1/8 inch (28.6mm) | Standard on modern MTB forks. Tapered forks are 1 1/8 at the top, where the stem clamps. |
| Bar clamp, MTB | 31.8mm or 35mm | 31.8 is the most widely used; 35mm is newer and stiffer. |
| Bar clamp, BMX | 22.2mm | BMX bars and stems. Not interchangeable with MTB stems. |
| Bar clamp, older | 25.4mm | Older and some city bikes. |
The ST1 takes both 31.8 and 35mm bars. The S1 takes 31.8mm. Both clamp a 1 1/8 steerer, so they fit nearly every modern mountain bike, whatever the brand.
Chapter 02
Stem length
Shorter is quicker.
A shorter stem puts your hands closer to the steering axis, so the bike reacts faster and feels more precise. That’s why dirt jump, trail and wheelie riders run short stems. A longer stem stretches you out and calms the steering, which suits long climbs.
The ST1 is 35mm, the S1 is 50mm. Our C100 V3 comes with a 50mm stem; dropping to the 35mm ST1 is a popular change.
Chapter 03
Bar width and rise
Wider gives leverage.
A wider bar gives more leverage and control, but a bar that is too wide for your shoulders feels awkward in traffic and tight trails. Most MTB riser bars come between 720 and 800mm, and many riders trim them. Rise lifts your hands: more rise is more upright.
Our MTB riser bar is 750mm wide, 31.8mm clamp, 20mm rise, with 7 degrees back and 4 degrees up sweep, in triple-butted 6061 aluminium.
Chapter 04
Fitting a stem
Torque matters.
- Set the headset. Tighten the top cap just enough to remove play, then the steerer bolts.
- Clamp the bar evenly. On a four-bolt faceplate, tighten in a cross pattern so the gap is even. The ST1 faceplate is designed to close with no gap.
- Use the torque printed on the stem. Over-tightening damages bars and steerers.
- Check by holding the front wheel between your knees and twisting the bar. Nothing should move.
Upgrading the whole front end? See MTB headset sizes explained.
Chapter 05
Questions
Will the ST1 fit my bike?
Yes, if your fork has a 1 1/8 inch steerer and your bar is 31.8mm or 35mm. That covers almost every modern mountain bike.
Can I use a BMX bar with an MTB stem?
No. BMX bars are 22.2mm at the clamp and need a BMX stem.
Does a tapered fork need a different stem?
No. Tapered forks are 1 1/8 inch at the top, where the stem clamps.
35mm or 50mm stem?
35mm for the quickest, most precise steering. 50mm for a little more stretch and stability.
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