Review: Forbidden Dreadnought

When Forbidden launched the 130mm-travel Druid way back in 2019 they were among the first to offer a high pivot trail bike. The Dreadnought first appeared on our radar in February 2021. With 154mm of rear travel and much more aggressive geometry, it's closer to the long-travel category where other high-pivot bikes are placed. While Mike Kazimer got a first impression back in February, I've been putting one through its paces for a few months now, so I'm ready to go deep into the details of how it works and how it rides.

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Frame Features

The single pivot design means there's only two main frame members: the mainframe and swingarm, both of which are made form carbon fiber. One of Forbidden's most interesting features is that the chainstay length is different for each frame size, but to save on expensive carbon molds, Forbidden use the same swingarm for all four sizes. To create the change in rear-center length, the main pivot moves back relative to the BB as the frame size increases, so all the change happens in the mainframe, which needs to change anyway. And thanks to the idler pulley, Forbidden can change the positioning of the main pivot relative to the BB without affecting the suspension kinematics. It's a pretty clever design.

The frame is tested to downhill standards and is dual-crown compatible. A 190mm-travel dual crown fork has a similar axle to crown measurement to the 170mm stock fork, so it's not an issue if you want to go there. But given the relatively short rear travel, I'm not convinced you need to.

There's plenty of room for a full-size water bottle, plus there's an accessory mount on the top tube for an inner tube, tool or whatever else. There's a little more storage space under the downtube with a two-bolt plastic cover which hides a space big enough for a tube or smuggled snacks. It also allows access to the internal cable routing for the dropper post.

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Geometry & Sizing

While many bikes have the same chainstay length in all sizes, and some brands change the rear-center by a few millimetres across the size range, the Dreadnought sees a whopping 40mm difference in rear-center between a small and an XL. Forbidden can claim to have genuinely proportionate sizing, because the ratio of the rear-center length to the wheelbase (which defines the weight distribution between the wheels) is 35% for all frame sizes.

But because of the high pivot, the rear-center gets longer as the suspension compresses: the XL has a 464mm chainstay at 0% travel, but this grows to around 480mm at sag and 495mm at bottom out. That makes it one of the longest rear-centers of any mountain bike. This means the ratio of rear-center to wheelbase increases throughout the travel, meaning more of the weight from your feet is loaded onto the front tire, helping it to grip.

The overall wheelbase of most bikes shrinks dramatically as the front and rear suspension compress together, as the axle path of the fork is highly rearward and the axle path of the rear is usually slightly forwards. But the wheelbase of the Dreadnought stays pretty consistent in this case. At bottom out, the wheelbase of the XL Dreadnought is longer than an XXL Geometron G1 at bottom out.

The reach is not overly long for an XL bike at 506mm, and the stack is on the shorter side too, at 639mm, making for a cockpit that's not the most stretched-out.

I measured all the major geometry figures on my XL test bike to check they match up with the above geometry table. The only discrepancies were that I measured the effective seat angle at my pedaling height at 75.6-degrees, the head angle at 63.2-degrees, and the bottom bracket height at 342mm from the ground.

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Suspension Design

The main pivot sits high above the axle, creating an axle-path that moves up and back (never forward) in an arc that starts at 70-degrees from horizontal, and finishes up near vertical. This means large, square edge bumps, which impart a partially rearward force on the wheel, will have an easier time pushing the suspension through its travel compared to purely vertical loads, such as the reaction force when you push the bike into the ground. The larger the bump, the more rearward the force, because the force acts radially inward from the point where the bump contacts the wheel. So for example, a 5cm-high square bump creates a force at 60-degrees from horizontal with a 29" wheel, but for a 10cm bump, it's 45-degrees.

The rearward axle path means that some of this rearward force is handled by the suspension, so the horizontal deceleration you feel when you hit a bump may be less abrupt. However, this doesn't necessarily mean that it helps the bike to carry speed, because although the horizontal forces may be less, they act over a longer time because the wheel is in contact with the bump for longer. Another potential benefit of the rearward axle path is that, by increasing the time the wheel has to get over the bump, it reduces the peak vertical speed of the wheel, which may lead to a smoother ride. The theory on axle path is more complex than it's often made out, so the proof is in the riding.

The idler pulley is connected to the swingarm, but offset from the main pivot such that the chain passes through the pivot on its way from the idler to the chainring. This gives a small amount of upper chain growth and therefore pedal kickback as the suspension compresses, but much less than a conventional design with no idler. Another advantage of the high pivot & idler design is that it provides a generous amount of anti-squat while having very low levels of pedal kickback. That means if you land hard at low speed or hit a bump with the rear wheel locked up, you won't feel the cranks being rotated backward by the chain.



The swingarm pulls a link, which rotates a rocker just above the BB, which in turn drives the shock. All the pivots, including the shock mounts, run on bearings and there's very little friction in the system. The leverage ratio (the number of millimetres the axle moves for every millimetre the shock moves) starts fairly high, at 2.675, and ends very low, at 1.825. That gives it an overall progression of 32%, making it among the more progressive suspension designs. The shape of the leverage curve is a bit out of the ordinary too. The leverage ratio falls quickly to start with, then levels off a bit in the mid-stroke, then plummets downwards again towards the end of the travel. Especially when combined with an air shock, that makes the forces at the wheel build steeply towards the end of the travel.

The low final leverage ratio also amplifies the damping forces towards the end of the travel, which means the high-speed rebound should be run pretty light or the rebound from deep in the stroke will be slow.



The high single pivot design means that if the brake is locked on, the wheel rotates with the swingarm as the suspension compresses. The high pivot means it also moves backwards relative to the mainframe. The combination of these two factors means that when you pull the brake while riding, the rearwards and rotational forces from braking both act to cause the suspension to compress. This counters the suspension's tendency to "rise" due to the transfer of weight onto the front tire when you brake, so this effect is called anti-rise or brake squat. The Dreadnought has particularly high levels of anti-rise, which means the chassis is more stable under braking (less brake dive) but, in theory, the suspension may be harsher due to the fact that it sits deeper into its travel under braking. But personally, I have never noticed this supposed harshness under braking with the Dreadnought, or other high anti-rise bikes.

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Climbing

The Dreadnought climbs well enough for an enduro/park bike, but not so well for a 150mm-travel, full-carbon 29er.

The progressive rear suspension needs to be set up with pretty generous sag in order to use its travel effectively on the descents (I'm running 32% which is the minimum recommended). This has an effect on the climbing performance. A 76-degree effective seat angle is not to be sniffed at, but once riding up hill with over 30% sag, the seated position is a little off the back by modern standards. I slammed the saddle all the way forwards, but I'd still prefer a more upright position especially when tackling steeper climbs. It's not that the front wheel was lifting - the long chainstay sees to that - but in my view a more upright position feels more comfortable and efficient, making the same climbs feel less of a chore.

The relatively high and consistent anti-squat figures mean there's not much bob under power, and if anything the bike lifts slightly when you pedal hard. But there's not much mid-stroke support from the shock itself, so when set up with light damping, it's quite active, moving around under weight shifts and oscillating slightly at high cadences with the movement of my legs. Fortunately, I found the suspension worked better for descending with relatively firm low- and high-speed compression damping, which was enough to cut this chassis movement considerably while climbing. Just goes to show that anti-squat isn't the only thing that matters for climbing performance and stability.

But still, I ended up reaching for the climb switch pretty regularly on this bike, not just to stabilize the suspension movement, but also to make the bike sit up a bit higher. The X2's climb switch isn't a particularly firm platform so the suspension can still move over bumps but it will still bob when sprinting. The Dreadnought doesn't feel as dynamic and responsive on the climbs as a lot of other bikes in the enduro category, even among those with ten or twenty millimeters more rear wheel travel.

The flip side is that the position is nice and roomy on flatter pedaling sections and the suspension is superb at soaking up undulations in the trail under power. During technical climbing, the traction is superb and pedaling over bumpy terrain is smoother and more consistent than with conventional bikes, even with the climb switch on. Just keep spinning and it will get to the top of tricky sections more easily than most bikes.

How much drag does the idler create?

I've done quite a lot of testing to find out if the Dreadnought is less efficient than non-idler bikes when climbing. There's a whole feature on this project on the way, but the bottom line is that in my tests the Dreadnought was six Watts, or about 2%, less efficient at delivering power to the rear wheel than a non-idler bike with the same chain at a 250W power output. That's too small a difference to justify anyone claiming that they can "feel" the extra drag, even if the slight noise of the idler gives a psychological sense of inefficiency. But on the other hand, if someone could make me go 2% faster up hill for the same effort, I wouldn't say no to that. I'm sure for some riders a 2% drop in efficiency will seem like nothing, but to others it's worth consideration.

Descending


The long 464mm chainstay length in the XL bike - which grows to around 480mm at sag and gets even longer as you push into the travel - is something you can feel straight away. Initiating a manual or a bunny-hop takes a bit of re-calibration; it requires slower timing and a more forceful, exaggerated style. The same's true on short-sharp jump faces where it's harder to pop off the lip at first. It's not like trying to hop an e-bike though, and once you get used to it it's less of an issue.

The flip side of this long back end is that it puts a bit more weight on the front wheel with a neutral riding position. That makes it easy to carry speed through fast, flat corners without fear of the front wheel washing out. It's possible to overstate this - it still pays to put a bit of pressure through the grips to get closer to a 50:50 weight distribution and keep the front wheel gripping, but if you're riding tired and you're not proactively weighting the front wheel the balance is better than other bikes. It's one of the easiest bikes to rip fast, flat or off-camber corners without the front end washing out.

Cornering the Dreadnought has its quirks too. Because the Dreadnought's chainstay gets longer as you push into a berm, it's a bit harder when you actually want to transfer weight to the rear wheel when slapping into a short, sharp catch-turn. I notice the dependable front-end traction more often than I notice this cornering quirk, however, and overall I'd say the Dreadnought is one of the best cornering bikes once you're used to it. It makes me want to try longer chainstays (460mm plus) on more bikes.


Another area where the long rear center was an occasional hindrance was on steep and awkward technical descents. The long dynamic chainstay reduces the breakover angle - the angle from the rear contact patch to the bash guard - so it grounds out more easily than you'd expect given the BB height. This meant that on one familiar track with a few steep knuckles, I had to consciously unweight the bike (a bit like dropping into a quarter pipe on a BMX) where other bikes can just roll through. Like with the manuals, this is something you can adapt to by learning where you need to go light to avoid grounding out, but it's not ideal if you ride a lot of awkward, technical terrain. It's worth remembering that the chainstay length grows with larger sizes while the BB height stays the same, so the breakover angle will be steeper on smaller sizes. I can only report on how the XL rides.

On the plus side, when tackling steep trails I like how the high-single-pivot responds to braking. I didn't notice any real harshness under braking despite the high anti-rise suspension, which could be down to my fast rebound settings preventing it from packing down despite the brake squat. Better still, the anti-rise causes the bike to hunker down at the rear like a Sumo wrestler when hard on the brakes, which means there's less brake dive and a more stable platform on steep descents. This could help explain why Fabien Barel and Connor Fearon used braking arms designed to increase anti-rise.


I rode the Dreadnought a few times at Bike Park Wales and Innerleithen DH trails, where there's a lot of fast and rough terrain. As expected, the Dreadnought really starts to come into its own here. There's tons of stability when battering through rocks at speed, and it's easy to trust the grip in loose turns. While the bike can be hard to pop off tiny lips, I had no complaints sailing off bigger takeoffs or pulling for natural gaps. More to the point, the suspension does a great job of smoothing out the small to mid-sized bumps. Wrist-sized roots are softened with very little feedback or loss of traction. Holding rooty off-camber high lines is more about technique and commitment than anything, but I felt able to commit and make them stick more often than I'd expect.

But when the terrain gets really chunky - big rocks or heavy landings - there's no hiding the fact this bike only has about 150mm of vertical travel. It's not that that it bottoms out much, in fact I only used full travel occasionally, but that you can feel the very progressive final 25% of the travel quite regularly on chunky terrain, which sends a lot of feedback through to your feet. I tried increasing the compression damping (low- and high-speed) until almost closed in order to absorb more energy earlier in the travel and avoid the firm ramp at the end, but at a certain point this increases harshness on smaller impacts and robs speed over repeated bumps. A coil spring would increase the mid-stroke support further, possibly meaning less of a sudden ramp towards the end. But the fundamental problem is the rear wheel can only move upwards by 150mm. It's not the always-forgiving ride you might expect from the high pivot design and the enduro/park bike designation.

That's not to say the high pivot design doesn't deliver - the rearward axle path definitely seems to reduce harshness over small-to-medium bumps, especially when compared to other 150mm travel bikes. But on big impacts it can only absorb so much. It's not that the suspension is harsh, but given the idler design has a few drawbacks I'd like a little more travel to fully unlock the benefits on the roughest descents.

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Reliability

I've been riding this bike a lot over the last few months. In that time I've had two main issues:

Firstly, the rear shock eyelet bolt kept working loose even when torqued up to the recommended torque spec (or tighter). On one of the first rides, it worked loose to the point that it started rubbing on the carbon shock tunnel, where it caused some damage to the frame. This didn't cause any dramatic play, so I only noticed this when the suspension started to feel sticky and harsh. Loctite on the threads and regular checking of the bolt has solved the issue for now, but it's something to keep on top of.

Secondly, on two occasions the derailleur has gone into the spokes and ripped off, taking out several spokes with it and destroying the wheel, hanger and chain. Both times I was riding in the smaller end of the cassette, without pedaling or shifting, and without hitting anything obvious. On the second occasion, it happened in the middle of a smooth berm, so I'm sure I didn't hit the derailleur on anything. The second time, the derailleur hanger rotated such that it damaged the carbon swingarm too.

The question is, was this just a fluke or does the high pivot design, with a large amount of chain growth in the lower span, make this more likely? That's tough to answer - I've deflated the shock and compressed the suspension fully in all the gears, and I can't see any obvious problems: the cage has plenty of scope to extend and spool out enough chain. On the other hand, it's very rare to see two derailleurs break in the space of a few months, but broken derailleurs are a fact of life and it's not beyond the realms of possibility that two freak accidents could occur in the amount of riding I've done.

I've since rotated the chain guide clockwise so the lower chainline is more taut and has less growth. I've had no issues in the dozen or so rides since doing this, but whether that has anything to do with adjusting the guide, I don't know. Forbidden say this isn't a problem they've heard customers complaining of.

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How does it compare?

One of the main questions I wanted to answer in this test was this: does high pivot suspension make up for the lack of travel compared to other bikes in the enduro/park bike category? The answer is a resounding ... sort of.

If you compare it to other 150mm-travel bikes like the Orbea Rallon then yes, I would definitely say the Dreadnought's suspension does a better job of taking the sting out of trail chatter. Not only have you got the rearward component of the travel helping to take the edge off the bumps, but the more progressive linkage makes it suppler on the small-to-midsize bumps without bottoming out. But the Rallon is more of a trail bike than an enduro bike in the modern sense of the word. It's lighter, more upright and has less chassis movement when pedaling than the Dreadnought, so when going uphill there's no contest. This is why judging bikes relative to their travel makes little sense.

Instead, it makes more sense to compare it to bikes with similar (or better) climbing abilities. If I compare it to something with a bit more travel like a Privater 161 (which I've been using as a control bike to test various forks, tires and other components, so I have a lot of miles on it) it's less clear-cut whether the Dreadnought's suspension still has the edge. On the one hand, the Forbidden flutters over roots and mid-sized rocks better, but on the other hand, the extra 10mm or so of squish is noticeable when hitting bigger hits. The Privateer's suspension is more linear, with more mid-travel support; this makes it more predictable and keeps more travel in reserve to absorb those bigger impacts. And despite being a weighty beast, the Privateer also climbs better, both subjectively and against the clock with a power meter.

These days, in the Dreadnought's price range there are plenty of bikes with 170 or 180mm of rear wheel travel that are not only lighter but more pedal-efficient than the Dreadnought, such as the Specialized Enduro or Nukeproof Giga. The 170mm-travel Scott Ransom stands out as an example of a bike with very supple suspension that's still ridiculously light and efficient on the climbs. Does the Dreadnought's high-pivot suspension allow it to catch up to these longer-travel machines on the descents? I don't think it does.

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Technical Report


Shimano XT four-pot brakes: You probably know what I'm going to say here. While bite point consistency was better than many Shimano brakes, the lever would occasionally pull heart-stoppingly further than expected, especially when hauling on the brakes after long rough straights . Also, the brake pads rattled until I splayed-out the pad retaining springs to hold the pads still.

Fox 38 Performance Elite fork: The 38 is still the best performing single crown fork I've tested, and I've tested most of them. If there is a difference relative to the Kashima-coated Factory version, I can't feel it, although a data-logging comparison test is something I'd like to do in future.

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Pinkbike's Take