tr450 & scalp have brake jack?
I never hear about brake jack or floating brake adapters these days on newer bikes, but still see forms of single pivot bikes. Do bikes like tr450s and nukeproof scalps have noticeable brake jack?
Brake jack as you feel it through your feet is mostly a combination of the chain and the pivot point acting against each other when you're on the brakes. It gives you that stiffer 'hanging up' feeling that really sucks.
Current bikes have main pivots much lower/further back than they did in the floating arm's hay day, much closer to being in line with the chain.
It's still there, but not nearly as pronounced as it used to be.
No that term is well not accurate. The current bikes have almost none and in fact many faster riders prefer it to some degree look at Barel's old KONA that did not use a floater. That term got hot in the late 90's because Mr. Cunningham used it in an article to describe 1 bikes suspension action.
It was what FSR claimed to have over the lowly SINGLE PIVOT keep in mind the RN1 was a lame single pivot. So to answer your question NO the TR450 is not noticeable at all with any rear stiffening while applying brakes.
Would it be fair to say that ''brake jack'' on a DH bike is similar to ''chatter'' that can be experiened through the rear of a mx bike?
Where and if exists on a particular bike/shock set-up.
Brake Jack was a term coined by Richard Cunningham in the late 1990s. About the same time Specialized bought the Horst Link off AMP Research. And about the same time they began their marketing push saying it was awesome.
Essentially while applying the brakes the rear suspension will stiffen and not track over rough terrain. Now this varies HUGELY in relation to chainline on a Single Pivot design. The Orange I owned from 2000-2002 had it but just barely.
So not that dissimilar in terms of meaning, in cause and effect that is. Poorly set-up shock on a mx bike will produce the same result when using the rear brake, losing traction and brake performance into braking bumps and deep ruts. Cheers fella
Brake jack (the rear suspension extending when the rear brake is applied) is not an issue in any modern mainstream dh bike.
Most have brake squat rather than jack.
I don't know of any suspension design that will behave exactly the same when braking vs not braking. Some exhibit more change than others.
IMO I think there are a lot of uneducated riders now days who really don't know the difference,...I can feel the brake jack on my M9 it is slight but it is still there...
I think the lack of brake jack threads are:
A) Not as pronounced on some bikes
B) people don't know the signs/feeling of brake jack
C) people don't ride bumpy enough trails to get there bikes to produce brake jack
the trick is ENJOYING YOUR LIFE EACH DAY, don't waste them away wishing for better days
Concise info guys, thanks for explanation. As you see from my post count I'm somewhat of a ''noob'' in regard to DH bikes and coming across the OP, it caught my interest.
So was curious to know whether it was something of a common set-up problem, that was cured by getting the bike dialled in or whether it was something that was inherent it most DH rigs, simply because the way the bikes are designed.
I now know
The quality of brakes are so much better now days that it's automatically easier to apply smooth brake stiffening suspension action (anti-dive is the proper term), rather than the sudden rear braking chatter or "jack" where the rear tire skids and regains traction in rapid oscillation over irregular and semi-loose trail, that used to happen with the old on-off brakes with poor modulation of 10 years ago.
Also shocks are much better now, having much less stiction which would also cause choppy rear braking action.
neither of those have any "Brake Jack" which is the extension of the suspension under braking...
now "Brake Squat" on the other hand, which is the compression of the suspension under braking, yes, they both have it...
talk about "uneducated". your M9 has 'brake squat' designed into the suspension characteristics. no 'brake jack' anywhere to be found...
Originally Posted by SHIVER ME TIMBERS
Last edited by .WestCoastHucker.; 12-27-2012 at 12:29 PM.
AGAIN I NEVER NOTICED THE TR450 STIFFENING EVER!!!! I tested it for 6 months...our trails are plenty steep. I am testing the 2013 Norco Aurum "FSR" system the TR had no more detectable stiffening than the Norco does.
The suspension can be compressed only while there is good traction. But when it skids from the spring firming compression load it extends or "jacks" towards top-out from spring rebound until traction is regained to squat the suspension again.
Originally Posted by .WestCoastHucker.
The very old term "jack" is not really an accurate term, but the feeling is something like a jack-hammer, more of a chatter effect as the rear skips and regains traction, oscillating the suspension to compress and release compression repeatedly on irregular traction trail conditions.
Brake modulation is so much improved, and shock stiction reduced, that we done hear complaints about "brake jack" any more.
The difference now in floating type 4-bar brake suspension is how much more or less rear brake power can be modulated before skidding. The difference is subtle, riders quickly adapt to modulate what brake power they have. Some 4-bar rear brake suspension designs are just as stiffening and squatty reacting while braking and skid as easily as a monopivot.
In general I agree with others that say that almost all suspension designs have no brake jack problem. Some have brake squat, which may or may not be a problem.
If you look at the forces on the bike during downhill braking, there are normally 2 forces that tend to compress the shock when the brakes are applied (which is the definition of brake squat)
1. The ground reaction force with the tire, causing a backwards horizontal force at the wheel axle.
2. The transfer of intertia from wheel to swing arm as the rear wheel goes from spinning to not spinning (this is why you can put a bike in a repair stand, spin the wheel and then brake, causing the shock to compress even though there is no ground reaction). This normally isn't the main concern, unless you are going from high speed to locking the wheel suddenly.
The location of the swingarm pivot effects how much of a moment is created by the ground reaction force, and how much squat there will be.
So squat happens when you brake, the shock compresses, and the rear suspension feels stiffer.
Here's why it has often been overstated as a problem: During downhill braking your front fork dives, and your front end lowers. Having the rear end squat keeps the bike more level and the geometry better, so some squat could actually be a good thing. And even if there is some loss of travel (stiffening), that is more noticable on short travel bikes than on the downhill rigs mentioned above.