bcd said:well, there are a lot of us making concentric pivot bikes out there
so i will type some words in our defense.
you are right, they do have pedal bob. BUT! not nearly the amount you are saying. the closer the drive chain is to the pivot the less leverage it has. the less bob you will have. a roller of 18T at a pivot
point is unperceptive when riding a dh bike. we are talking dh bike performance here. no XC. i don't recommend CP for xc at all.
that is exactly how a good gearbox is geared. bb to gears has all the
ratio change.
then from a CP to rear use as small as you can with a 1-1 ratio. like a 18-18.
we make different bikes but some people like to know both sides.
its give and take. your bike pedal the best that is possible. that is the way you designed them.
gearbox bikes are more concerned about the QUALITY of the rear suspension. less about pedaling.
Alex
Have you ever considered that maybe, just MAYBE, Honda hasn't realized the benefits of linkage suspensions for their engine powered vehicles yet because the engines dont complain when they have to push harder?Heath Sherratt said:The original question and the surprising lack of observation is this- ALL MOTO bikes have single pivots-ALL. Yet they have no chain problems. Honda obviously used this information to build their mountain bike-I don't want extra pivots, i don't want the newest and hypest linkage system. I want simplicity, function, and form. That's it. So how did they=honda, do it?
that 'model' seems a bit exargerated from reality. My bike has a 230mm pivot above and 90mm foward of center and if anything feels like it has too much anti-squat on a gradient. Granted it doesnt use a concentric pivot chainline but a modified swingarm mounted chainline, but the difference shouldnt be that dramatic i would think.dw said:Another interesting fact to consider is that in order to even approach 100% anti squat (which you do want to do on any bicycle, regardless of discipline) with a concentric pivot bicycle using identical front and rear sprockets, main pivot height would have to be in the range of 500mm above the bb center, or even with your fully raised seat height. Thats not too practical, and wouldn't corner all that well really.
Hope that this helps.
Dave
zedro said:that 'model' seems a bit exargerated from reality. My bike has a 230mm pivot above and 90mm foward of center and if anything feels like it has too much anti-squat on a gradient. Granted it doesnt use a concentric pivot chainline but a modified swingarm mounted chainline, but the difference shouldnt be that dramatic.
well, all this is true. no argument there.dw said:.............and additionally will have to run higher spring rate and damping rates to compensate for acceleration performance. This will leave the bike oversprung and overdamped when coasting.
Another interesting fact to consider is that in order to even approach 100% anti squat (which you do want to do on any bicycle, regardless of discipline) ...................
Hope that this helps.
Dave
dw said:A concentric pivot does absolutely NOTHING to minimize pedal bob. Actually, in almost all cases, it PROMOTES pedal bob. The reality of the situation is that with layouts that are useable for a bicycle, you will be stuck with a maximum of about 35% anti-squat at the beginning of the travel, and it will rapidly move to the pro-squat range by the sag point, menaing that you will waste away acceleration energy in your damper. With pro-squat, every time you accelerate, every pedal stroke, some of your energy will go into actually forcing the suspension to compress. This of course will require a platform shock, which will give up traction in deference to pedaling ability. Its a lose-lose situation.
The only way that zero chain growth can remove pedal feedback is through using identical sprocket sizes front and rear. Pedal feedback is vastly overrated anyways in my opinion.
Derailleurs are going to be here for a long time.
Dave
well not sure what BB height your 'model' uses (or if you took into account my own personal COG while hammering a hill :wonky2: ), but at 14.75" for a 9 incher with lots of sag, it aint exactly a tall bike in the saddle (ask my pedal pins and Supercharger, they'll tell you). Anyways just pointing out that having a pivot at half of what you stated can produce the inch-worm effect.dw said:The "model" IS reality.
Additional spring and damper can help a lot, but gives inconsistent performance between pedaling and braking. Hence the point of a linkage system. Keep in mind BB rise. Higher BB rise will require less pivot height.
SO, Gary, are you going to answer the question?zedro said:i'm surprised at your surprising lack of observation that bikes and motorcycles are completly different vehicles, and that a person pedalling a bike one third his weight is a tad different from a smooth and powerfull engine driving a moto almost twice the riders weight. Ever since designers stopped 'observing' moto design, suspension designs have been getting better.
Hell, even Honda does have their pivot remotely in the same location, nor bothers with shock linkages etc...their bike is nothing like their moto designs.
every so often someone has to bring up MX like it's a huge revelation know one yet noticed after all these years.
no more than a normal bike. You dont have to mount the swingarm concentrically to the final drive, you could do anything you want reallyxy9ine said:though the viability as a "universal" gearbox seems suspect as it dictates frame layout & suspension design.
i was referring to the suntour box above (with integrated concentric pivot).zedro said:no more than a normal bike. You dont have to mount the swingarm concentrically to the final drive, you could do anything you want really
yeah, and i'm saying you dont have to mount the swingarm there. It gives you the option but theres no reason not to.xy9ine said:i was referring to the suntour box above (with integrated concentric pivot).
ah yes. i do agree that alternative arrangements may be technically feasible, but with an allready integrated pivot solution, i don't see any manufacturer using THIS box & not using that feature - for instance using a high pivot in the frame above the box / adding a tensioner, etc.zedro said:yeah, and i'm saying you dont have to mount the swingarm there. It gives you the option but theres no reason not to.
well if theres a glut of identical systems, then i think they would. You could use the pivot as part of a 4 bar system as wellxy9ine said:ah yes. i do agree that alternative arrangements may be technically feasible, but with an allready integrated pivot solution, i don't see any manufacturer using THIS box & not using that feature - for instance using a high pivot in the frame above the box / adding a tensioner, etc.
I still wonder why Rohloff hasn't jumped on that option. Must be a question of money.xy9ine said:. i still wonder if a lightweight dh-friendly gearhub (ie, an 8spd rohloff lite) is a more reasonable proposition - it would certainly circumvent alot of engineering headaches.
or maybe because reducing the number of gears doesnt make it significantly lighterChrisRobin said:I still wonder why Rohloff hasn't jumped on that option. Must be a question of money.
I'm guessing that would be by removing gears somehow out of the current gear hub. Redesigning the insides to make them lighter with less gears is where the lack of cash comes in. Who knows.zedro said:or maybe because reducing the number of gears doesnt make it significantly lighter
apparently the rohloff is essentially a 7spd with a geared multiplier to get the next 7. gutting that mechanism (if its possible) probably wont net a huge weight savings (anybody willing to donate one for research?). be kinda fun taking one of these apart. the chance of getting it back together & functioning, tho...ChrisRobin said:I'm guessing that would be by removing gears somehow out of the current gear hub. Redesigning the insides to make them lighter with less gears is where the lack of cash comes in. Who knows.
i talked to them about this in 2001.xy9ine said:apparently the rohloff is essentially a 7spd with a geared multiplier to get the next 7. gutting that mechanism (if its possible) probably wont net a huge weight savings (anybody willing to donate one for research?). be kinda fun taking one of these apart. the chance of getting it back together & functioning, tho...
xy9ine said:more pix of that rb. no idea what's in the box.
]
yeah, i see all dh bikes being split into two groups"xy9ine said:true. the problem of finding a frame-mounted transmission layout that may be applicable to the greatest range of suspension designs is a tough one. i still wonder if a lightweight dh-friendly gearhub (ie, an 8spd rohloff lite) is a more reasonable proposition - it would certainly circumvent alot of engineering headaches.
xy9ine said:apparently the rohloff is essentially a 7spd with a geared multiplier to get the next 7. gutting that mechanism (if its possible) probably wont net a huge weight savings (anybody willing to donate one for research?). be kinda fun taking one of these apart. the chance of getting it back together & functioning, tho...
thats what DW (and others) keep saying. It's just that people still think concentric is the optimum for some reasonatrokz said:If the DW link is being developed for MX use, what is to stop it or a similar system being used for a ID bike? Last time I checked motorcycles dont have derailuers and only have one external......
huh? they're all usefull, it would be spaced like a road cassette (actually probably with a near geometric progression of 13%-14%). Remember their 14 speeds cover a 27 speed drivetrain; it's chainwheel/cog systems that have redundant ratios.ChrisRobin said:If you take that multiplier out, you're left with 7 gears where only a couple of those gears are actually usefull.