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Aggressive Hardtails: Modern Geometry Explained

Aggressive Hardtails: Modern Geometry Explained

aggressive hardtail geometry

Every year, more manufacturers design aggressive hardtails with wild geometry. The massive wheel base and slack head tubes send the front wheel out like a custom chopper. These aren’t your typical XC, or even Trail, hardtails of years past.

You might think: they can’t be serious? This is just some kind of gimmick?

In this article I explain the freaky geometry of modern hardtails and why they look so unique. I’ll use examples from my experience with Rocky Mountain’s aggressive hardtail: the Rocky Mountain Growler.

Arguably one of the most “extreme” examples of aggressive geo is Chromag’s Doctahawk. In fact, a Pinkbike review of the Doctahawk by the designer is what inspired this Hardtail Canada article.

Check out the link to the Pinkbike article below. Fair warning, the piece is technical! But well worth a read.

In a previous article I discussed all the benefits of riding a hardtail. I won’t reiterate them here.

For this post I’m using the Doctahawk article as a primer, and my own personal experience as examples, across 4 geometry specs that I believe best define an aggressive hardtail: Head Tube Angle (HTA), Seat Tube Angle (STA), Reach, and Wheelbase.

I’m not a geometry expert. I’m not a bike designer. This is simply a “real life” reference for anyone wondering what it’s like riding a modern, aggressive hardtail and why they’re shaped the way they are.

Aggressive Hardtails: Modern Geometry Explained

Head Tube Angle

The HTA is probably the most obvious characteristic: the slack fork sets the front wheel at an unnaturally obtuse angle from the frame.

To understand the need for a shallow HTA, we need to have a look at what it’s like riding an aggressive hardtail.

The long wheelbase, big reach, and steep seat tube angle (which we discuss in more depth below) all put the rider’s weight forward on the bike.

This keeps the centre of gravity forward, which means less pressure on the rear wheel and more pressure on the front wheel/ over the front of the bike (compared to full suspensions I have ridden in the past).

Lewis (the authour of the Pinkbike article) calls this feeling “riding the fork,” which is exactly what I’ve experienced: these bikes HAVE to be ridden aggressively, in a forward position. This also frees your legs to absorb the terrain and control the big wheelbase.

I’ve found dynamic control over the back end of a hardtail is not only necessary, but makes these bikes much more fun than a full suspension.

The slack fork supports this aggressive riding position, since it decreases the chances of going over the bars.

Which brings us to one of the most insightful points Lewis raises in his article: the difference between static geo and dynamic/ sagged geo (for the sake of simplicity: Hardtail v Full Suspension).

A static aggressive hardtail looks radically different than a static full suspension. But, once the full suspension is loaded, the “active” (i.e. the sagged HTA and STA) specs are more in line with an aggressive hardtail.

Put another way: aggressive hardtails are designed to have the same “static geo” as a full suspension’s “sagged geo.”

Lewis wraps this up quite succinctly: “77 STA and 62 HTA on a hardtail feel the same as 79 STA and 64 HTA on a full suspension.” The aggressive hardtail has similar geo to an active full suspension. The important difference is that the hardtail needs to have those stats when the bike is static, since there’s no rear suspension to sag into “active geo.”

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Seat Tube Angle

Lewis’ (and my preceeding discussion) of STA introduces some contrary info: an aggressive hardtail can get away with a slacker STA than a full suspension, because it doesn’t sag. Yet, STA are typically steeper in aggressive hardtails.

There’s a couple reasons for this.

1-A steeper STA brings more weight forward, off the rear wheel. This keeps the rear wheel looser, and your legs are more effective at managing traction in the rear end. 

An important point Lewis mentions, which I can confirm, is because the weight is so much more forward on a hardtail, and more balanced front to rear than a full suspension, it isn’t unusual for you to run virtually identical tire pressures front and back.

2-Because of the big reach on aggressive hardtails, a steeper STA is necessary simply so you can actually reach the bars in a proper riding position.

Reach

The big reach on aggressive hardtails puts your weight forward.

This, and the steep STA, were the two biggest characteristics I adjusted to when I started riding my Rocky Mountain Growler.

The STA was much steeper than my old full suspension, yet the bars were further away!

If you are not an aggressive rider, this will probably be your biggest shock when riding one of these bikes, and your biggest point of frustration.

These bikes are not forgiving if you decide to coast or don’t pay attention on downhills. You must be dynamic and engaged with the bike’s front end. This may sound like a lot of hassle, but the payoff and strong response from a hardtail frame is killer and why I’ve come to love this style of riding so much more than a full suspension.

There’s another sport where I’ve experienced this level of necessary, aggressive biomechanics: whitewater kayaking in gnarly, steep rapids and waterfalls.

Those particular boats are designed to be paddled in an ultra-aggressive, forward body position. If you ever watch kayak videos or witness a group sending your local waterfall, take a note of their body position: they will all be aggressive, active, and fully engaged.

Those that aren’t, or relax and let up, instantly lose control and have their back end tossed around and likely flipped.

Sending fast downhills on a hardtail is the closest I’ve some to this feeling without actually being in whitewater.

The big reach is a key reason why these hardtails can be ridden so aggressively. Just make sure you’re willing to put the effort in!

Wheelbase

With massive reach and slack HTA, what’s a bike’s wheelbase to do?

Be long and slack!

I was shocked when I realized my new hardtail had a longer wheelbase than my old full suspension enduro. The old wheelbase felt long and I figured that much length on a hardtail would be even tougher to manage.

What I’ve found, between the forward riding position and the short chainstays, is the wheelbase doesn’t “feel” that long.

Some switchbacks are tight, but having the short chainstays means I just have to carve wider turns with my front end.

Focus is required on steep climbs to keep the bike traction balanced and prevent the front end from popping up.

This is doubly so with the lack of rear suspension: all power is immediately transferred forward since there is no suspension to absorb the energy.

But on descents, at speed, on anything steep, the massive wheelbase is extremely stable.

I see the wheelbase more as a necessary consequence of the reach and HTA, than a separate geo consideration on its own.

But when you see an aggressive hardtail on the showroom floor and think the massive wheelbase is obnoxious, now you know why it’s generally longer than a similar full suspension.

Aggressive Hardtail Geometry

That sums up the reasons why aggressive hardtails look so different, and the key geometry characteristics that separate them from many other bikes.

If you want a rewarding trail experience, something new, something simple that still handles DH terrain, a better workout, or all the above, you can’t go wrong with one of these awesome modern hardtails.

The Chromag Doctahawk is definitely at the “full send” end of the spectrum, and I hope to try one out sometime! Maybe next season.

In the meantime, the Rocky Mounain Growler, and its aggressive geometry, is an absolute riot and the most rewarding experience I’ve had on two wheels.

If you have your own hardtail geometry thoughts you want to share, or questions and concerns, please comment below!

As more people re-visit aggressive hardtails and realize how capable they are, these bikes will only continue rising in popularity.

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