Ultralight steel hardtail

A lot of the mountain biking where I live involves long climbs followed by what most would consider mellow singletrack descents. There are rocks to avoid, and the trails have almost no traction, but they’re not technically challenging.

Since I spend most of every ride climbing, I wanted to build a hardtail to make the climbing fun. And I can think of nothing more fun than climbing on a super light bike. Even though I may only shave a minute or two from an hour-long climb, a lightweight bike still feels like a rocket ship.

My current hardtail weighs around 25 pounds. It’s light for a steel hardtail. But I wanted to see how light I could go. Could I make a hardtail that’s less than 20 pounds?

I first had to design the frame and choose the components to find out.

Geometry

As with every frame I design and make, I consider rider weight and strength, rider preferences, and the bike’s intended use. In this case, I intend to use the bike as a lightweight singletrack climber, as a gravel bike when I know the terrain will be rougher than what’s comfortable on a rigid drop bar gravel bike, and as a bikepacking bike for fast and light excursions.

It’s safe to say that this bike is a proper XC hardtail. The 66.5º head tube angle is steeper than my typical trail hardtail. The 73.5º seat tube angle is downright slack for a mountain bike these days. Placing my butt further behind the bottom bracket keeps weight off my hands for all-day comfort. The longer 435mm chainstays combined with the short 712mm front center will keep more weight on the front wheel for steep climbs and downhill cornering grip. Unsagged, the bottom bracket height is 303mm. This bike is low but definitely not long and slack.

I made the seat tube long enough so the short travel dropper post is almost at the minimum insertion line. Small frames save weight.

Frame

It isn’t easy to shave a lot of weight from a steel hardtail frame without sacrificing durability. Mountain biking puts a lot of stress on a frame. So I had to be smart about where I could reduce the weight. I plan to ride this bike. It’s not going to be a showpiece.

Starting with the front triangle, I chose the Paragon Machine Works tapered EC34/EC44 head tube. It’s the lightest commercially available head tube for tapered steerers that’s robust enough for a mountain bike. Plus, it’s a beautiful piece of CNC wizardry.

I could get away with smaller diameters and thinner profiles than I would typically use for the top and down tubes. The XC geometry is more compact than a typical trail hardtail for drops, jumps, and general abuse.

However, the most significant weight savings came from using a 27.2mm seat post and an externally-butted 28.6mm seat tube. The standard 34.9mm seat tube I use for 31.6mm dropper posts is a total pig in comparison. Although I’d lose the ability to run a proper long dropper post, I felt the sacrifice was worth it. Even a few inches of drop can do wonders on the downhills.

For the chainstays, I stuck with the standard 3/4” tubing I use for almost all of the frames I build because I can bend it in-house. There are commercially available pre-bent chainstays that are lighter. I missed this opportunity to save more frame weight. But I prefer controlling the bends to maximize tire clearance.

The same is true for the seat stays. I used 1/2” tubing that I could bend in-house instead of going with something slightly lighter from one of the big bike tubing brands.

And finally, I chose the Paragon Machine Works UDH dropouts because I wanted to use Sram’s latest Transmission to test if I could recommend it to customers. My favorite Paragon snap ring dropouts are lighter, but I prioritized using the Sram Transmission over weight savings.

All in all, I was happy with the final weight of the frame when it returned from paint. 1824 grams for the frame with the bolt-on flat mount brake mount and titanium water bottle bolts is a significant weight loss from my regular hardtail frames. There were opportunities to make the frame even lighter, but I can live with the compromises I made.

Even though I designed this bike as a race thoroughbred, I wanted the paint scheme to match the pool party, beachy, summer vibe I planned for my booth at the MADE bike show: the sandy yellow bottom transitions to three darkening shades of blue to capture a coastal horizon. The bright coral for the graphics adds pop.

Fork

Choosing the fork was easy. The lightest fork on the market is the RockShox SID SL Ultimate. The 100mm of travel is perfect for the riding I plan to do with this bike.

While the pros are moving to burlier forks to tackle modern XC tracks, I won’t ride anything that gnarly on my hardtail. I think of this hardtail as a flat bar gravel bike.

I stripped off the stickers from the lowers and added some custom color-matched coral-colored Rockshox logos.

Components

Cockpit

Darimo made me a 720mm handlebar with reinforced holes for the tiny Zirbel twist shifters and a Sram AXS Blipbox that I tucked inside the 77mm Intend Grace XC stem. This is the most common solution for the Zirbel shifters. If you want to use a shorter stem, you can move all of the electronics inside the handlebar, but that involves way more tinkering than I wanted to do. The handlebar, stem, Blipbox, and shifters came to 270 grams. That combo is lighter than most aluminum handlebars!

The Extralite foam grips and headset added very little extra weight.

Going this light with the cockpit is scary. You don’t want something to break up front, or you’ll be helping your dentist buy a boat. But as long as I use my torque wrench and carefully follow all the installation instructions, I’ll feel fine using the bike for its intended purpose.

Saddle and seatpost

I could have saved a lot of weight using a cable-actuated dropper, but instead, I used the Sram AXS XPLR 27.2 dropper with 75mm of travel. The Zirbel shifters can control the rear derailleur and dropper while keeping the cockpit tidy. I saved about 10 grams by replacing the steel saddle clamp bolt with a Better Bolts titanium bolt.

The saddle hails from the hands of Jure Berk in Slovenia. He makes some of the lightest saddles in the world. I chose the unpadded Ploh, which weighs a mere 81 grams. After a quick lap in my neighborhood without a chamois, my first impression is that the saddle is stiff. But I’ll reserve judgment until I get it out for a proper ride.

A 9-gram Carbon-Ti collar holds the seat post in place.

Brakes

I originally wanted to get some of the Trickstuff Piccola brakes for the build since they’re the lightest on the market, but the long lead time and super high cost ruled them out. Instead, I stole the Magura ST8 SL brakes from my current hardtail. They weigh around 200 grams each. Not the best in class, but pretty close. The rear uses a flat-mount caliper, again to save weight. I’ve been happy with their performance.

The calipers will squeeze some Carbon-Ti rotors: 180mm up front and 160mm in the back. The lightweight carbon spider allows Carbon-Ti to keep more material for the braking surface, where it belongs. The lightest brake rotors have so much machined away from the braking surface that they don’t provide enough surface area for the pads to do their job.

I routed the rear brake through the down tube to keep the frame looking clean. The brake hose is housed in a foam sleeve through the frame to eliminate rattling. The foam sleeve is a lighter option than a stainless guide tube brazed inside the frame, but it does add a few more minutes to the build time.

Drivetrain

When Sram announced its new Transmission system, I was eager to try it. I’m already sold on wireless shifting. My gravel bike uses Sram AXS. The perfect shifts and reliability make up for the hassle of dealing with batteries.

Transmission is not the lightest option out there. I could have gone with an 11-speed mechanical group for maximum weight savings. But customers have already been asking me about Transmission. I owe it to them to test-ride it first before I can form an opinion.

I chose the XX SL group to minimize the weight penalty. The rear derailleur is massive! The GX version is supposed to shift identically to the fancy XX SL group for a minor weight penalty. I foresee a lot of customers opting for the GX Transmission in the future.

Installation of the system was quick and easy. I watched one short Sram instructional video and had everything installed and dialed faster than regular AXS and much faster than a mechanical setup. Two thumbs up!

I grabbed my E-Thirteen XCX Race cranks from an old bike to save more weight. Lucky for me that they make chainrings that are already compatible with the new flattop chain. With a new 34t chainring, they’re a scant 410 grams!

Although not shown in the photos, I will use the Xpedo M-Force 8ti pedals. You have to include pedals in your total bike weight!

Wheels

The easiest place to shed a massive amount of weight is in the wheels.

I chose Extralite HyperBoost hubs, laced to Light Bicycle carbon rims with Berd fiber spokes. Without rim tape, valves, sealant, and tires, the wheelset weighed 907 grams!?! That’s freakin’ nuts. Is it stupid light? I guess I’ll find out.

I went with Specialized S-works tires in the 2.25-inch width because they might be the lightest XC tires on the market. Getting accurate tire weights is challenging. The sidewalls are pretty thin and flimsy. I bet they’ll be fast, but we’ll see how well they handle all the rocks in the Sierra Nevada.

Stan’s sealant, aluminum tubeless valves from Industry Nine, and Whisky rim tape round out the complete wheelset.

Although I’m excited to try the new Sram Transmission, I’m most excited to see how these wheels feel. The Berd spokes are supposed to add a bit of compliance. And the featherweight wheels should feel super snappy when accelerating.

TL;DR

The bike with pedals and King titanium cages weighs 19.69lbs or 8.93kg. Woot, woot!

This is by far the lightest bike I now own. Once the MADE bike show is over, I have a few rides in mind to give it a good test, including a 100-mile bikepacking route in the Lost Sierra with tons of long, steep climbs.

Unique projects like these are super fun. If you've always wanted to build an ultralight hardtail, give me a ring and we'll make it happen.