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A Complete Guide To Marin's Steel Frames

We've been making steel mountain bikes, steel road bikes and steel gravel bikes for 35 years and have no plans to stop any time soon. Here's why we love building bike frames out of steel here at Marin Bikes and what our Marin Series 1, 2 and 3 frames are all about.

Steel Is Real

Here at Marin Bikes we’ve made steel-framed bikes since day one (that's somewhere around 1986 donchaknow!) with plenty of steel MTB, road and gravel options in that time.

Along the way, we’ve diversified into aluminum frames, carbon fiber and even titanium, but we’ve stood by the humble steel bike frame for over 35 years. While bike technology has developed enormously over that time, steel is still a great choice for a road, gravel, city or mountain bike frames and at the heart of many of our favorite bikes.

Why steel bike frames? There’s a lot of romance around steel frame bikes - people idolize their looks and their ride quality and wax lyrical about how “steel is real.” But here we’re going to try and cut through some of the mysticism and look at what actually goes into a Marin steel bike and why we think they’re worth your attention.

We'll also explain why Marin's Steel bike frames are grouped under those 'Series 1', '2' and '3' headings.

Marin El Roy hardtail mountain bike

Steel Isn't Just Steel

In their simplest sense, nearly all bike frames are a collection of tubes, regardless of what material they’re made from. Steel bicycle tubing seems the most straightforward and easy to understand, but there’s more going on than meets the eye.

For starters, steel isn’t just steel. The basic version, mild steel, is just iron and carbon. But there are lots of slightly different types depending on what other materials are added to the alloy. Only the very cheapest bikes are made from mild steel, whereas most quality frames, including ours, are made from Chromoly, also known as CrMo steel.

Chromoly has some cool properties which make it especially suitable for steel bike frames, including the fact that it resists corrosion and becomes stronger when you heat it up.

mountain biker jumping in summer on Marin hardtail

Billets and Buttings (Funny Names, Serious Business)!

While some bike companies make a big deal out of using branded steel tubing, we prefer to do things our own way. Rather than buy-in pre-made tubes from a steel bike frame tubing manufacturer, we design and build our own, to our own specifications.

The tubing we use for our Marin's steel bikes starts life as a solid billet (a lump of steel). This billet is turned into steel tubes in a painstaking process involving a lot of heat and some serious machinery. Using this, we can control the diameter, thickness and profile of each individual tube.

And that’s not all, during the process we can vary the thickness of a tube along its length. A tube that ends up in one of our bike frames will be profiled so that it has more material at the ends, and narrower walls in the middle for less weight and better ride quality.

This process is called “butting” (no snickering at the back!) and it’s used in all our steel bike frames. The more changes in thickness a tube has, the more complicated and costly it is to produce. Making special one-off tubing for a particular steel bike adds time and cost but means we're able to make something that's exactly how we want it to be.

Steel bicycle tubes can also be ovalized so they’re stiffer in one direction than another, and shaped to do some really clever stuff. Take a look at the rear triangle of one of our steel hardtail mountain bikes and you’ll be able to see this in action, with the tubing shaped to nicely meet our forged and cast frame parts, and fit around big-volume tires.

Handmade Quality, To Take On The World

Before a Marin steel frame goes off to the paint shop, it needs more stuff adding to make it functional: bottle bosses, rack mounts, luggage or mudguard eyelets, disc brake mounts and dropouts (the bits your back wheel attaches to).

As with tubing, there are different ways to make these parts, and some are more expensive. For example, investment cast dropouts are more expensive than stamped dropouts, but look and perform much better.

Blue Marin Pine Mountain 1

So Why Steel?

You might well be asking 'why steel bike frames?' Are steel frames good? Are still frames better than aluminium ones?

Our decision to make steel bike frames is part head, part heart.

Steel has an incredible strength-to-weight ratio, which is why we can use those cool-looking skinny tubes to build a bike that’s just as strong as one made with alloy or carbon fiber.

A good steel frame bike has a great ride quality that’s hard to replicate with other materials. It’s relatively easy to repair, and easy to make into something else at the end of its life. That ride 'feel' becomes particularly noticeable when you're hammering rough, off-road trails on a steel mountain bike or a steel gravel bike.

Reliability and cost are also factors to consider. Steel is a frame material that’s been used for years, which means you know what you’re getting, and production and tooling costs are kept reasonable. But it’s also got a classic aesthetic that harkens back to the BMX, road and mountain bikes we all lusted after when we were kids.

Steel bike frames just have the right mix of reliability, longevity and looks, which is why you still see so many older ones still in use, and why so many bike companies are still making them today. In the steel vs aluminium debate, we love both but have a definite soft spot for ferrous metals.

Rider on Marin Gravel Bike

Marin Bikes Series 1, 2 and 3 Frames.

And this brings us nicely back to those mysterious numbers we attached to our steel bicycle frames.

Marin Bikes steel frames are all given a designation as Series 1, 2 or 3. You can find that number printed on the frame if you're not sure. These give you a clue as to how the frame has been made and the level of detail we've put into it.

That number doesn't simply refer to the tubing though, it's the whole frame. It's the tubes, the pieces that join them together and the fine details down to the bottle bosses and brake mounts.

And, of course, bikes from the same series don’t all use the same type of components; it wouldn’t make sense to build a steel gravel bike frame in the same way as a mountain bike steel frame for example. But they do go through the same processes to get to the finished frame and the "Series" helps you to understand what you're getting.

Studio image of Marin Four Corners

Marin Series 1 Steel Frames

A Marin Series 1 CrMo steel frame will use simple, less costly processes to produce a reliable and great riding bike.

Generally, Marin Series 1 frames are our most affordable options and are designed to create the most bang for your buck, offering a brilliant bike that almost anyone can afford.

Series 1 frames will often have butted CrMo steel tubing, forged open dropouts, disc brake mounts and brazed-in eyelets.

The Marin Series 1 family includes the Nicasio, Nicasio+, Muirwoods and Four Corners bikes.

Marin Series 2 Steel Frames

A Marin Series 2 CrMo steel frame will use tubing that undergoes more shaping and forming, which means it’ll be slightly lighter and more compliant to ride. It's designed to be that middle ground of great value and great performance, offering a more premium package than Series 1.

Series 2 steel frames will share many of the features of Series 1, such as forged, open dropouts and brazed-in eyelets but are upgraded to have custom double-butted and formed CrMo steel tubing for a super comfortable ride. Series 2 introduces neat, stylish and functional upgrades such as IS Standard brake mounts and investment cast dropouts.

The Marin Series 2 family includes road and off-road bikes, with plenty of steel frame mountain bikes and steel frame gravel bikes in mix.

For off-road, there are the Pine Mountain 1 and Larkspur 1 & 2 and for on road there's the Nicasio 2.

Studio image of Marin Pine Mountain
Studio image of Marin ElRoy

Marin Series 3 Steel Frames

A Marin Series 3 CrMo steel frame is the top-dog, bells and whistles of the bunch, including some of the best steel hardtail mountain bikes around.

These best-of-the-bunch beauties have premium, custom double-butted and formed tubes that are specific to each individual model for the best looks and ride qualities.

Series 3 upgrades the fine details once again with investment cast dropouts and frame components, post-mount disc brake mounts and thru-axles, all of which create a great-looking, great-riding bike that mixes classic materials with modern performance.

The Marin Series 3 family is - for now - made up of the Pine Mountain 2 steel gravel bike and the El Roy steel mountain bike hardtail, but watch this space for more!

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