Trying a shorter stem length usually means buying a different stem, and if that length doesn’t work out, buying another. Stack is a little easier to play with. Lowering the bar is just a matter of moving spacers from below the stem to above it, but going higher may be impossible if the steerer tube has already been cut too short. Michał Piórkowski, a suspension design engineer in Poland, designed a stem that adjusts both length and stack.
His one-person company, Evidence Engineering, makes a CNC-machined stem with adjustable lengths of 20, 30, 35, and 45mm and two stack heights: 33 or 45mm. Laser-etched markings on the side show which configuration it’s in. After Piórkowski shared the design on Instagram, many commenters were eager to buy one.
The main selling point, Piórkowski says, is that it allows riders to “switch setups in a couple of minutes to make back-to-back comparisons between runs.” I spoke with him last week to learn more about the design.
Ultra-short stems often require cutting your steerer tube, which reduces your range of stack adjustments
An ultra-short stem can bring the bars into contact with the steerer, so many riders cut their steerer tube short to make everything fit.
“When you buy a short stem below 35 millimeters, like 30 or 20 millimeters, you need to cut down your steerer tube,” Piórkowski said. “And then you don’t have much adjustability left.”
Evidence Engineering’s solution makes it more likely that riders can get the stack height they prefer despite a shorter steerer tube, though clearly there are still limits. The shortest reach settings — 20 and 30mm — only work with the higher, 45mm stack setting, which might not be ideal for those who need the bars to stay low.
Evidence Engineering stem specs
- Reach: 20, 30, 35, 45mm (20 and 30mm with 45mm stack only)
- Stack: 33 or 45mm
- Handlebar clamp width: 58 or 70mm
- Handlebar diameter: 35mm
- Steerer: 1-1/8″
- Weight: 187g
- Material: 7-series aluminum, CNC machined and anodized
- Max system weight: 130kg (about 287lb)
The stem is built in two pieces: a steerer clamp on the bottom and a handlebar clamp on top, joined by M6 bolts torqued to 10Nm. Piórkowski started with the direct-mount bolt pattern but found it didn’t deliver the configurations he wanted, so he created his own. He said his calculations showed the forces on the bolts are slightly lower than with a direct-mount pattern.
Riders can choose between two different clamp widths, 58mm or 70mm. Going with the narrower width should make the bars feel more compliant, while the wider width should make the bars feel stiffer.
The stem fits 35mm clamp-diameter bars only and weighs 187 grams.
Very short stems are having a moment
As we noted earlier this year, mountain bike stems are getting weird. Hope now makes a 20mm Gravity Stem that raises the bar mount 35mm and Be More Bikes makes a Raised Reverse stem that can be set up with a negative 15mm effective length. Both are aimed at the same problem: riders who want a shorter, taller cockpit than their frame delivers.
That’s not surprising given how mountain bike geometry preferences are shifting. In a 2024 Singletracks survey, 45% of readers said reaches were getting too long, and only 5% wanted them longer. Yet average trail bike reach still grew by 7.5mm between late 2023 and early 2026, though a few bikes, like the Commencal Meta SX V5, have pulled reach back. Meanwhile, stack height has gotten more attention as riders look for a more upright, comfortable position, especially for descending.
Frame geometry tends to lag rider preferences by a few years, and swapping in a new stem is much cheaper than a new bike. An adjustable one means riders don’t have to commit to a guess, either.
From race cars to stems
Piórkowski’s background is in motorsport. He spent three and a half years working on suspension for his university’s Formula Student team, where he also learned CNC machining, and later spent six months machining small frame parts at Polish brand Antidote Bikes. For more than six years, he’s worked as a suspension design engineer at a small Warsaw company that designs suspension components for motorsport, including WRC teams.
“In some motorsport suspensions, there’s a lot of adjustment,” he said. “So that was maybe why I came up with this.”
The stem wasn’t his first bike idea. Piórkowski said he’d sketched out a set of mountain bike brakes, but when he saw the Intend Trinity he decided it was too big a project to do well on his own and moved to something simpler.
Stems are simple, but this one took plenty of testing. Piórkowski said he ran fatigue tests at the EFBE lab in Germany using forces higher than its standards call for, and he built his own machine for static testing. Those tests turned up a surprise: greasing the bolts significantly reduced displacement between the top and bottom halves, since greased bolts hold higher clamping forces at the same torque. He says he’s been riding the stem since February without issues.
The stem doesn’t carry an EFBE certificate. Piórkowski said the lab would have to test every configuration to issue one, which would be prohibitively expensive. So, he focused on testing the most extreme settings to give him confidence the design will hold up.
Availability
Evidence Engineering ships worldwide, and the stems are machined in Poland. Buyers can enter their email address on the Evidence Engineering website to reserve a stem. The stem is priced at 199 € (about $220) including VAT.
The first batch of 100 stems has been produced, though the wait list has over 300 people on it. Piórkowski told me he emailed the first 100 people on the waiting list, though many of those emails likely landed in spam folders, so anyone who signed up early should check to make sure they didn’t miss their chance to order one.
The adjustable design is patent-pending in Poland. He’s already planning other versions, and said a future design could add spacers between the base and the handlebar clamp, like a direct-mount stem, for even more adjustability.
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