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There's some new oranges out, so that means the internet commentators are talking about brake (or sometimes break) jack.
Can someone explain in words a technically minded (but bicycle illiterate) can understand?
braking forces being transmitted along the swing arm to the shock and causing unwanted suspension (in)activity) - often seen as the swing arm effectively being locked out under heavy braking.
Most modern suspension systems are designed to be unaffected by braking forces.
cue lots of typing and no resolvable force vector diagrams.
<pulls up a chair>
Related reading...
https://singletrackworld.com/forum/topic/simplicity-vs-performance-suspension-design/
But you might be better off getting a ride on an Orange and making your own mind up.
This article explains almost every different suspension design and their various characteristics, including anti-rise aka brake jack
BIKERADAR.COM Basically the torque from the rear brake acts on the suspension to compress the shock and hence jack the back of the bike down. In reality it means the rear stiffens up under braking, which can be a good or bad thing depending on the degree and personal preference.
Yeah, stiffer rear end going into a corner, more stones n'rocks going everywhere and a bit more drama. But that doesn't matter on an orange as it'll be noisy everywhere so no-one notices a bit more corning racket. I quite liked that trait when I had one.
I think.....
If you try and explain it you just end up with a headache and an argument.
The solution is you want the calliper to move 'more backwards' relative to the axle as the suspension compresses. Rather than on a single pivot where the caliper is rotating with the swingarm.
Look at examples like kona's DOPE system, orange 223's with floating brake arms, trek abp or Lawill suspension (which is kinda like a dw and a horst link but makes it easier to visualise how it deals with brake jack due to the pivot placement).
The advantage of having some, is it goes a long way towards stopping the fork diving and the whole bike getting too steep just as you hit the braking bumps.
… something … than Fleetwood Mac.
brake jack means a 200m single picot downhill bikes is harsher over braking bumps than a 140mm trail bike. I'll never ride another single pivot again. Maybe i'm just getting soft/old.
I have never understood the basis for the "stiffening". The spring rate hasn't changed, so suspension "jacked" by x mm will respond to a bump of y mm in the same way as if it wasn't.
There may be an effect to do with locking the brakes and how the sudden transfer of angular momentum from the wheel to the suspension jacks it up further, then unlocking the brakes and repeating, gives rise to a lumpy feeling?
I used to have a Trek Diesel... Very like an Orange.
It had the option of running this brake therapy arm thing which was supposed to stop brake Jack.
I never had the arm thingy. Rode the bike on many uk dh tracks and Morzine too.
Can't say I noticed anything negative happening.
I test rode an Orange something-or-other many years ago when every other rider at a trail centre seemed to have one.
Absolutely hated it. The kickback and jack from the rear end was horrendous. To be fair, I'd come off many years of riding true 4-bar linkage full sus which had none of those issues. I could barely ride the Orange, it just felt dreadful. Maybe I needed to learn to ride it in a different way.
I have never understood the basis for the “stiffening”. The spring rate hasn’t changed, so suspension “jacked” by x mm will respond to a bump of y mm in the same way as if it wasn’t.
There may be an effect to do with locking the brakes and how the sudden transfer of angular momentum from the wheel to the suspension jacks it up further, then unlocking the brakes and repeating, gives rise to a lumpy feeling?
Most suspension designs (but not all) have a progressive spring rate through their travel. Plus you lose sensitivity if the back end is trying to compress while you are hitting a load of braking bumps, hence skipping over rather than following the terrain more precisely up and down. On the plus side however, it does help to counteract the forward weight transfer under braking. As ever there is always a compromise to be had. Personally I like my rear suspension to be as active as possible on the brakes and use my own body mass to compensate for the weight transfer. So I'm not a big fan of excessive anti-rise.
Plus you lose sensitivity if the back end is trying to compress while you are hitting a load of braking bumps
This is the bit I don't see. There will be less travel available until you bottom out, but I don't think the effects involved will get you anywhere near there. Plus, the "jacking" will be offset by the reduced load on the rear due to weight transfer. You could argue you would lose sensitivity with a neutral braking ararngement, because the weight transfer will cause the rear suspension to extend, meaning there is less travel available to push the wheel into holes.
The back end isn't trying to compress, it is compressed. The suspension will (as far as I can see) be operating completely normally, just at an offset in the travel compared to where it would be with no brake jack (because the braking force is independent of speed and displacement, it is a constant). Unless you lock the wheels.
The suspension will (as far as I can see) be operating completely normally, just at an offset in the travel compared to where it would be with no brake jack
I do see where you are coming from, it's a bit like having a pre-load except in reverse. I think in reality most suspension systems tend to stiffen through their compression stroke, so that offset will tend to put the suspension into a stiffer part of its curve. I expect very few (decent) modern bikes would have a linear rate and even less a falling rate. Most are progressive rising rate. As you say it's balanced against extension from weight transfer, so it is all about balance of forces, riding style and simple personal preference.
I would think you'd have to be riding very strangely and have an extreme version of it for the weight going forwards not to outweigh the braking force compressing the swingarm.
In reality it's just something you need to balance out rather than obsessing about. I doubt very much that all modern bikes eliminate it, and I have a feeling that it's never going to be as much of a problem as dive under braking - yet nobody runs anything but telescopic forks.
This is how I tried to describe it to a mate at a demo day when he couldn't figure out why his dream bike didn't feel so good....
Picture an Orange swingarm as the suspension compresses. The swingarm, and therefore the brake caliper, rotates around the rear axle, and the caliper around the rotor.
Lock the brake, and the caliper can't rotate around the rotor, the swingarm can't rotate around the axle. Then the rear wheel, while trying to move out of the way suddenly feels like a hammer crashing into bumps.
Orange's can feel good but you have to know how to ride them to their advantages. Plus the people who go mega fast on them aren't dragging the brakes everywhere.
Personally I CBA and I ride a 4 bar.
"Picture an Orange swingarm as the suspension compresses. The swingarm, and therefore the brake caliper, rotates around the rear axle, and the caliper around the rotor.
Lock the brake, and the caliper can’t rotate around the rotor, the swingarm can’t rotate around the axle. Then the rear wheel, while trying to move out of the way suddenly feels like a hammer crashing into bumps."
And that's true for every full-sus that doesn't have near-parallel links on the suspension. A single-pivot (not just simple ones like Orange but all the linkage driven ones like Cotic and Evil and Kona and Commencal and...) "suffers" the most but so do all counter-rotating short link bikes, most co-rotating short link bikes, all counter-rotating four bars and a fair few conventional four bars too.
The flip side of this is that brake SQUAT (that's what it is, not brake jack) stabilises the geometry, so if you brake hard before a corner you'll enter the corner with the bike more balanced. Yes, you'll have a bit less grip on the rear tyre when braking but judging by the storming performance of Commencal's DH bikes for the last two seasons (which have far more extreme suspension interaction under braking than any Orange) that isn't a problem.
My current full-sus (Specialized FSR four bar) has much more active suspension under braking than my old full-sus (Banshee KS-link co-rotating short link) but I preferred how the Banshee squatted as you braked before turning. Fortunately I prefer everything else about the Levo so I'm prepared to work around that.
"I would think you’d have to be riding very strangely and have an extreme version of it for the weight going forwards not to outweigh the braking force compressing the swingarm."
Lots of bikes have close to 100% anti-rise (brake squat), which means the weight going forwards is cancelled out by the rear suspension squatting. Yes the fork will still dive but the back end will not rise, so you'll finish braking with the attitude of the bike the same as on a hardtail with the same fork. Full-sus bikes with low anti-rise require you to shift your weight more to keep the bike balanced.
I used to have a Klein Mantra. It used to throw me off on a regular basis going downhill when the brakes were applied. Most scary bike ever. My Orange 5 is perfectly fine.
I am not sure that is what that 100% means? For it to mean that, an assumption about wheelbase, rider height and riding position etc. would have to be made. It may be a % of the braking force that is going into suspension compression.
Lock the brake, and the caliper can’t rotate around the rotor, the swingarm can’t rotate around the axle. Then the rear wheel, while trying to move out of the way suddenly feels like a hammer crashing into bumps.”
If you lock the brake, the rear wheel will move upwards as its angular rotating energy is transferred to the spring. But that will happen on a downslope, when contact force is reducing, which is when you want your suspension to be doing the opposite - extending. When you hit the next bump, the suspension will not be in a good position to absorb it.
Yeah, yeah I know all that. That was the the best description I could come up with at the side of the trail when my mate was wondering why a top spec Orange 5 felt like a jackhammer compared to his Stumpjumper.
I am running a 160 mmm rear disc on my Orange alpine, and the rear suspension is much less affected by brake jack,I think locking up the rear wheel, even a small amount will upset a single pivot rear end, I think its best to be as smooth as possible, and use the front brake a bit more than other designs.Just saying like.
If you lock the brake, the rear wheel will move upwards as its angular rotating energy is transferred to the spring. But that will happen on a downslope, when contact force is reducing, which is when you want your suspension to be doing the opposite – extending. When you hit the next bump, the suspension will not be in a good position to absorb it.
But do you really want the back end to be freely extending when you are braking hard down a steep slope? Obviously it does extend due to the forward weight transfer, while the fork dives for the same reason. But in an ideal world you would probably want the bike to stay more or less flat. Hence why anti-dive / anti-rise geometries exist, both in bikes and cars alike. It's all a question of degree and finding the right balance and compromise. For example too much anti-squat/dive in a car suspension tends to make the ride feel harsh and insensitive, but too little makes the body pitch like a boat (previous generation Volvo XC60 comes to mind).
I've never ridden an Orange, but it sounds like the back end has tons of rear anti-rise. Possibly just too much for some tastes, while others might like it?
So does the shock effectively lock in the compressed or extended position?
The shock doesn't lock, it stays moving, but not necessarily in a good way. Well that's my view anyhow.
@moshi - yes, anti-rise at the back (as with anti-dive at the front) is in principle a good thing. But it does appear to give rise (sic) to issues with mtbs. My theory is that this is becasue of what happens when the brakes lock/unlock as you go over braking bumps, not because the suspension is locked out by the brakes. That issue would not arise with road vehicles which don't lock their brakes or encounter braking bumps, also the relative inertia of the wheels compared to the vehicle as a whole will be way less. It is a bit unfair to pick on Oranges, plenty other bikes with similar arrangements out there.
@greyspoke - just to be clear I wasn't picking on Oranges and I don't even know how little or much anti-rise they actually have under braking. I was just talking in general about the potential pros and cons of anti-rise in any mtb suspension system. My gut feeling as a mechanical engineer is that you wouldn't want too much brake-induced suspension compression as it would be inconsistent unless you were super smooth on the brakes. I can easily imagine this causing issues over multiple braking bumps, especially for an average rider.
I recall that brake jack was much bigger issue with rim brakes than with disk brakes, at least partially because you had to brake for much longer duration to slow down. With modern brakes a small blip on the brakes reduces speed efficiently.
My SC Superlight with V-brakes was particularly bad with certain fast and steep trails, runs without braking were fast and exciting, brakes on and the bike turned into jumpy scary beast.
LINKAGEDESIGN.BLOGSPOT.COM Thanks chief, that's a cool link for engineering nerds like me!
Danny Hart’s custom floating brake mount on his linkage driven single pivot Saracen DH bike.