King of the Mountain

ABP Explained

Alrighty, class. Welcome to Suspension 101. In today's lesson, we're going to go over what ABP is, what it does for you, and how it works. Ready? Let's jump in.

ABP: What is it?
Pivotlocations The active brake pivot puts the rear suspension pivot concentric to the rear wheel axle, as opposed to Trek’s current design or the ‘Horst’ link where the pivot is located above (Trek) or Below (Horst) the rear axel.

What is the Benefit?
-The ABP keeps the suspension active and the rider in control while braking. Lock-up, or stiffening of the suspension under braking is virtually eliminated. Skidding is reduced; the tire stays in contact with the ground. Because the tire stays in contact with the ground, the brakes are more effective when they are used, and thus the time spent braking is reduced. Less braking also equals better handling and suspension by not loading the front fork.
Less time braking = more time going fast!
-Wide stance pivot bearings – same as the main pivot. Because the rear pivot bearings are spaced wider apart, the frame structure is torsionally stiffer.

How does it work?
The ABP allows the suspension to be active and independent of braking by separating the braking and drive-train components. The ABP allows the brake caliper to keep a near constant relationship to the brake rotor, so the caliper doesn’t rotate around the brake disk as the suspension moves through its range of travel.

What’s the science behind ABP?
Abp_explaination_revkb Think that claim sounds too much like unsubstantiated marketing speak? Here’s the real deal, in-depth explanation (in other words, most of us will now tune out, and simply go riding and experience a ride like never before…)
The ABP allows the brake caliper to keep a near constant relationship to the brake rotor, so the caliper doesn’t rotate around the brake disk as the suspension moves through its range of travel.
Brake force occurs between the ground and the tire. There is a contact patch on the bottom of the tire that is in contact with the ground. All modern, current suspension designs move the rear axel in an arcing motion. So when the brakes are applied, the wheel has to move in an arcing motion because it is fixed to the swing-arm. What this means is that the ground and the tire don’t exactly move together.
If you look at the bike with the suspension fully extended (bike completely un-weighted), there is a contact patch the tire has with the ground at 6 o’clock on the tire. With the wheel (and the tire) fixed to the swing-arm because of the brake being applied, when the suspension tries to move in the arc we described earlier, that original contact patch the tire had with ground moves.
However, because of friction between the tire and the ground, this contact patch doesn’t want to move. The rider feels this as “suspension stiffening” under braking, or a skidding, skipping feeling as the suspension bounces over bumps.
All suspension designs experience this to varying degrees, and all suspension designs can be analyzed to measure and quantify the amount of “contact patch rotation.” The lower or smaller the amount of rotation, the more active the suspension will be under braking.
ABP has the lowest rotation factor – lower than single pivot, lower than VPP, lower than FSR.
However, because the movement of the wheel is still based on our proven R1 design, all this active suspension comes without unwanted suspension movement. The bike is still highly efficient, bob-free, and without the need for suspension lock-outs.

Small bumps, big bumps, braking bumps, fast bumps – full time smooth, active, efficient suspension.

Here's how the Fuel EX compares to some of its competition. The first comparison is at the mid-stroke of the suspension, or at 50% travel. This is the most important measure because it's a bit past sag, and where the suspension is most likely to be during braking, and especially braking during high speed bumps.

Comparison of Contact Patch Rotational Factors – Mid-Stoke of Suspension Compression

2008 Fuel EX  -  2.3 degrees
2007 Stumpjumper  -  3.1 degrees
2007 Blur LT  -  4.5 degrees
2007 Mojo  -  4.0 degrees

Remember again, the lower the rotational number, the more active the suspension under braking.

Comparison of Contact Patch Rotational Factors – Full Suspension Compression

2008 Fuel EX  -  6.0 degrees
2007 Stumpjumper  -  7.3 degrees
2007 Blur LT  -  6.3 degrees
2007 Mojo  -  9.3 degrees



Bought a Superfly 100 AL Elite this spring. Best suspension I've ever ridden. Had a Specialized S-Works Epic, older model 26" before. This bike is as nimble and more fun than any brain can give.

John Morris

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John Morris

Thanks for sharing this great submit, i truly adore your weblog, but i have some problem i dont know whether it is my side issue or on your site? some words of the post on your weblog have charactor encoding issue, yes i use auto detecting, can u pls appear into this issue a bit?

John Morris

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My ABP creeks. How do I fix this?


Lim -- REPLY -- Lim, I too have heard of people damaging their frame. The bulk of the feedback has come from the downtube denting upon impact with sharp objects -- we've never been shy about positioning this bike as one of the lightest race bike setups you can find -- one way this is achieved is through tubeset profiles and butting optimization. We are aware that some customers are dissatisfied by this cosmetic damage and are working to solve the issue in the future. In the meantime, Session riders can be satisfied knowing that they have a leading-edge product that delivers world class performance, market-leading weight and a warranty backed by a company that's here to stay, staffed by people who care.

And to address your question specifically -- ABP and Full Floater in no way compromise the bike's durability or integrity. If anything, they make a stiffer design that requires fewer moving parts.


hi, i've heard of many session 88 damaged on the first year. can i know do the ABP or full floater system weaken the frame? or its other factors that make this bike easily damaged?


Hi there, Keep this simple can I run a hope pro 2 rear wheel with the ABP system? as I am lead to beleave the skewers from bontrager ABP to normal hubs are different? thanks for any reply.

Reply - Any 135mm O.L.D. QR hub will work with ABP. True, you do have to use the Bontrager skewer that comes with the bike. But the only difference to the skewer is that it is longer than standard to accomodate the wider dropout of ABP. Hope Pro 2 hub will work just fine with ABP.


I still don't understand all the techo jargon, but I know that I've taken my EX-8 with ABP down steep long stairways as well as steep terraced downhills and this design keeps my back tire on the ground when I hit the brakes. I couldn't even say that about my hard tail.

Pavol Kianicka

Hello Dylan,

I've been trying to figure out what forces, rotations & movements matter when braking during suspension. I have considered wheel rotation and caliper rotation but resulting brake caliper rotations, for Fuel EX, which came out of my method don't match yours that you published in "ABP explained" article. Please, could you describe your method that you used to calculate rotation of brake caliper around brake disc? Or even some suspension related article/book would be a great help.

Thank you very much for any help.
Regards, Pavol Kianicka

Thanks for your interest in ABP and how it works.
Explaining exactly how ABP works would take much more than a simple blog posting to fully explain. What I can tell you is that we measure and compare our bikes to the competition in exactly the same way, so our comparisons are accurate.
There are a number of motorcycle design books and vehicle dynamics books that give some insight into this and how brakes interact with acceleration and suspension. However, something to always remember is that a bicycle and rider's CG and mass ratio is VERY different to what a motor cycle has.
What you ultimatly have to do is take all your engineering experience and basic laws of physics and dynamics, and reapply those principles to the bicycle and rider "system."


In my new Fuel EX 9 the lever of the quick release is on the drive-side, unlike most published photo's where it is on the opposite side. Since the adjuster nut stays attached to the frame, it is not just interchanging the skewer and the nut. How can I change it so the adjuster nut is on the drive-side and the skewer on the other side?

Answer: There are two ways to change that. The skewer nut is held into the ABP nut with a tight fit o-ring. First remove the skewer, then by a combination of turning, pulling and wiggling, you can pull the skewer nut out of the ABP nut. Then simply press and twist it to get it back in the other side.
The other way to simply remove the skewer, remove both of the ABP nuts - whilte keeping the skwer nut attached to the ABP nut, and swap sides that the ABP nuts go on. Then simply retighten the ABP nuts to the torque printed on the nut.


How about the complexity of removing the rear wheel?

"It's as simple as removing any other bike's wheel. There is simply the added step of unscrewing the skewer a few more times than usual after flipping open the skewer, and then pulling it out. After that, the wheel is removed as usual. The wheel is a standard, QR hub type wheel, and once the wheel is removed, you can see the slots in the frame that are the same shape as any other QR type dropout.
Once the skewer is pulled out, there are no other pieces to worry about: the QR is a sinlge unit, and the QR adjuster nut stays attached to the frame.
Putting the wheel back in is the same as normal, too. Simply put the wheel in like normal, slide the QR back in, give it a few turns to thread it in all the way, and then adjust the QR tension and close using the QR nut as you normally would.
- Dylan"


Am I missing something here? The caliper still relies on a part of the suspension linkage for a reaction force. Thus, a moment is still induced on the swing arm. And, now there is independent motion between the caliper and the rotor. Causing the brakes to both slow wheel rotation, but also induce rotation as the suspenion articulates. At least before they moved together. Something is just not sitting right with me on this one.

You're exactly right - there is independent motion between the caliper and the rotor, which is exactly what we want. You’re right that they did used to move together. You’re also right that it does induce a moment on the swing-arm.

However, you’re ignoring the biggest and major braking forces – that it weight shift due to braking, and the braking force between the wheel and the ground. Those two forces far outweigh all others. The force that really has the ability to cause a moment about the suspension system – and remember, you have to look at the whole system – is that force at the bottom of the tire, pulling backwards around the main suspension pivot axle.

The brakes still have the ability to slow the wheel’s rotation, however it does not “induce” rotation, it ALLOWS rotation as the suspension cycles. Before when the brake caliper and the wheel moved together, the interaction of the ground and the tire inhibited rotation because the wheel doesn’t want to rotate against the friction between tire and ground. With that very small rotation, the tire can move relative to the swing-arm as the suspension cycles, but rotation between ground and tire is kept to a minimum. It is all about reducing suspension stiffening during braking.

Still don’t believe that? Take a bike – single pivot bikes generally show the most stiffening during braking – and push the bike against a wall. Keeping the bike pushed against the wall, push down on the seat to cycle the suspension (taking a lot of air out of the shock will help demonstrate this just so you can push the suspension deep into its travel easily). Now put the brake on and do it again – you’ll feel the suspension stiffen because the wheel doesn’t want to rotate against the ground, and the brake holding the rotor keeps the wheel from rotating against the swing-arm. Doing this again with an ABP equipped bike will show you a marked decrease in the suspension stiffening. You can also visibly see this by watching how much the brake rotor rotates through the caliper with the brakes off. On the ABP equipped bike, this rotor rotation will be much less than other suspension designs.
- Dylan Howes


In response to my earlier question.
That's awesome, it's exactly the kind of concrete answer I couldn't find anywhere else. Thanks a bunch.


Nice work Dylan!


So, bottom line: it's better at separating brake forces, but does it do it as efficiently as a brake therapy style floating brake caliper?

ANSWER: It absolutely does just that more efficiently than a floating caliper mount. The most obvious way it's more efficient is that we don't have the extra weight of a separate floating mount. The floating mounts add about a half a pound of weight to a bike, not the mention the extra complexity of more parts, more bearings, and long brake rods that must be run through the frame.

When we started developing the ABP system, one of the bikes we tested it on was a Session 7. We already had a floating brake mount developed for this bike by Brake Therapy. Using the Session 7s as a test bed, we were able to directly compare the bike without any braking assistance, with the Therapy mount, and with ABP, giving a very "apples to apples" comparison. The ABP system was more efficient at keeping the suspension active under braking - and we showed this not only with the math and science behind ABP, but on the trail in real world testing conditions, on a bike we already had a lot of experience with.

Every good suspension system has to have a solid theory behind it based on math and physics. But it is ultimately the ride on the trail that matters above all else. This is where ABP really shines and proves the theory behind it. -DH

Jon medina


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