[ÆX]

omG!

 

[ÆX]

awsome pic

 

[dw]

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

Sorry to drag this old thread up, I have been away for a few weeks. I had a quick read, and there is one veryimportant point that I think needs to be addressed.

If you are running a concentric pivot suspension, with a gearbox or not, and using the same size sprocket front and rear, the size of the sprcket does not change the anti-squat amount. It is identical no matter how close the chain is to the pivot. The only thing that changes is the amount of force in the chain, but that change is balanced by the lever arm distance created by the rear wheel/ sprocket combination.

There is no benefit to using a smaller sprocket combination.

Linkage suspensions really can have the same benefits for gearbox vehicles as they do for derailler driven bicycles.

Just a quick set of #s to consider. A concentric pivot gearbox bicycle with an output shaft 100mm above the center of the BB, and a common 30mm BB rise will have 25.8% anti squat at zero sag, and 17.1% at 70mm travel (roughly sag for an 8" travel bike). These numbers are identical for any size matched front and rear sprockets. The suspension will have a more forward axle path than a higher anti-squat linkage bike through the same point, 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) 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

 

[dw]

BTW, I sat with Karl once at dinner and later at the show in Taipei. He in fact has ANOTHER new gearbox that he has built, seperate from the Suntour gearbox. Looks trick. The name is under "Universal Transmissions" It's good to see so many people working in this direction.

Dave

 

[dw]

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?

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?

I can GUARANTEE you that use of dw-link would reduce lap times on a motorcycle in Moto GP or Supercross. You won't have to take my word for it on this for long.

BTW, the Sunday has less moving parts and fewer links than a Honda CR 450F.

I will take one simple link and pivot over massve internal shock complexity any day, especially when the linkage system is superior in performance.

It sounds to me like you want the linkage suspension, you just dont realize it.

Dave

 

[zedro]

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

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]

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.

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.

Thanks for your support.

Dave

 

[ÆX]

.............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

well, all this is true. no argument there.

but i don't run a over sprung over damped suspension. i run my settings for bump absorption! NOT TO ELIMINATE BOB. that is what i am saying here. i make DH bikes to absorb bumps better with sacrificing some anti-squat.

you get some 200 bruiser putting out way more leg power than say
Nico or a med rider like most of the DH community you are not getting the anti-squat numbers you are talking about.
bob, can be tuned with 170 cranks and a round pedal stoke with less mashing. not by altering your rear shock to co promise the rear suspension action.

 

[downhill66]

that is some crazy ****

 

[ridetoofast]

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

jeez...this guy sounds authoritavtive...what did he design a bike or something...



















kidding of course. thanks for the perspective dw

 

[zedro]

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.

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.

 

[Heath Sherratt]

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.

SO, Gary, are you going to answer the question?

 

[Wilhelm]

I found some news about the G-Boxx on the website of SR SUNTOUR today (http://www.srsuntour-cycling.com/SID=si6305404b68da5ed24071c814c64fe7/index.php?screen=ne.detail&pid=48&type=news):


"SR SUNTOUR presents first gear box "V-BOXX V-15" | 06 march 2006

The next generation of shifting

This bike has already been presented at the 05 Eurobike show
but not to public. Since we finished our rideable and testable
production gear box "V16" there's no reason anymore to hide our
latest project. Yes we did develop a whole new gear box system
and yes, it is definitely rideable!

Watch out for our V-16 gear box evolution, very soon to come.

Technical details
number of gears: 9 speed
G-CON international gear box mounting standard: YES
future features: 16 gears, magnesium cast housing,
weight (N/A) (...not far away from XT group)"


There are two pictures of the NUCLEON TFR prototype made by Karlheinz NICOLAI for SR SUNTOUR from the Eurobike 2005 show on this website. A third picture was published in issue 10 of the German MTB journal "BIKE" in 2005.


Best regards
Wilhelm

 

[CreeP]

holy f-socks that's a lot of bolts!

 

[bikenweed]

Yeah. Interesting how it's used structurely, holding the down tube and seat tube together.

Eh, my derailure works fine, was super cheap, and is easy to adjust. Please, everyone, buy this and work all the bugs out, so I can one day find a cheap one to use myself. This stuff must cost an arm and a leg, and it's for sure that things will end up breaking on the first production runs and models. But it's still rad. Poco a poco!

 

[xy9ine]

thats really neat using the gearbox as stressed member & integrating the pivot - very moto. *edit* - ^beat me to it^. though the viability as a "universal" gearbox seems suspect as it dictates frame layout & suspension design.

 

[zedro]

though the viability as a "universal" gearbox seems suspect as it dictates frame layout & suspension design.

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

 

[xy9ine]

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

i was referring to the suntour box above (with integrated concentric pivot).

 

[zedro]

i was referring to the suntour box above (with integrated concentric pivot).

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]

yeah, and i'm saying you dont have to mount the swingarm there. It gives you the option but theres no reason not to.

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]

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.

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 well

 

[xy9ine]

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.

 

[ChrisRobin]

. 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.

I still wonder why Rohloff hasn't jumped on that option. Must be a question of money.

 

[zedro]

I still wonder why Rohloff hasn't jumped on that option. Must be a question of money.

or maybe because reducing the number of gears doesnt make it significantly lighter

 

[ChrisRobin]

or maybe because reducing the number of gears doesnt make it significantly lighter

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.

 

[xy9ine]

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.

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...

 

[ÆX]

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...

i talked to them about this in 2001.
but they had just gotten the hubs going and didn't want any more r&d.

it is possible though.

Alex

 

[EVRAC]

Keep in mind this is a prototype from '05. The unit I posted pics of looks much more refined.

Also:

http://www.g-boxx.org

Has finally seen some updating.

 

[EVRAC]

Correction, try this:

http://www.g-boxx.org/index.htm

Not a tonne of new info though.

 

[Shyrmp]

Off-topic but transmission related....

Ellsworth made it in our local regional newspaper with an article regarding a transmission a local techie shop (who's been doing a lot of creative bike tranny concepts for years) is working on for Tony Ellsworth. The printed article showed a mock of the tranny device that is being designed. Pretty cool stuff.

the article:
http://www.nctimes.com/articles/2006/03/15/business/news/17_03_123_14_06.txt

 

[EVRAC]

That's neat. Ellsworth had been working with Hayes/Petespeed on their derailleur in a box. I wonder if this will replace that or be on a different line of bikes. The NuVinci unit is a CVT with a nice simple mechanism, but the problem is slippage and friction. I didn't think it would work for DH, but we will see.

 

[ÆX]

there are some new stuff in history page.

 

[xy9ine]

more pix of that rb. no idea what's in the box.

 

[zedro]

pretty cool but that shock linkage is worse than RM has ever done

 

[ÆX]

more pix of that rb. no idea what's in the box.

]

this general triangle shape indicated a der-in-a-box.

diab is the new word for it.

so you would say this: "the new fuji dh bike had a diab."

alex

 

[ÆX]

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.

yeah, i see all dh bikes being split into two groups"

• radical suspention designs:
  these will be companys that have a tried and true suspention design that will not take a gearbox.

• bikes with simpler single pivots that use gearboxs:
  these will be new companys or ones that have already used gearbox's and aren't stuck with there "selling point suspention designs"

 

[atrokz]

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......

 

[ChrisRobin]

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...

This is like beating a dead horse cuz we know they're NEVER going to do it. But I think all the insides would have to get modded. If you take that multiplier out, you're left with 7 gears where only a couple of those gears are actually usefull. So, either you take out that multiplier and change those remaining 7 gears into usefull ones, I think you'd have to redesign most of the mechanism.

Second thing, a trigger shifter would make the hub more atractive to people riding DH...but that's a really tough one to figure out.

Speaking of the Rohloff boat anchor, I need to find a place that sells the cleaner/refill kit to service mine.

 

[zedro]

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......

thats what DW (and others) keep saying. It's just that people still think concentric is the optimum for some reason

 

[zedro]

If you take that multiplier out, you're left with 7 gears where only a couple of those gears are actually usefull.

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.