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Black Lion
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WheelsForHeels said:
By the way, to everyone suggesting that I do a demo, I'm working on it. Trying to get a six point to try in the NYC area. Will be interesting to compare the ride to the suspension ideas... Glad you all like your rides. I have to say the new models from Iron Horse look incredible.
If you are ever in the New England area specifically Mass.
I could make that demo happen.

Greg
 

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M070R-M0U7H FR3NCHI3
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For me it’s simple…when I test ride a bike, I’m asking myself the following questions:

Does the bike linkage get the claimed amount of travel?
Does the bike pedal well in all the gamut of gears?
How does the suspension perform under hard braking?
How does the suspension work when pedaling over rough stuff.
How does the suspension deal with hard fast hits and small bumps.

All stuff a graph won’t tell you…you need to ride the bike to find that out. In addition, if you ride the bike, you’ll be able to find out a whole lot of other thing like:
Is the geometry right for me?
What size is right for me?
Do I feel any flex?
And more…

okay...I need to finish my beer...it's getting warm ;)
 

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www.derbyrims.com
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WheelsForHeels said:
let's do a thought experiment: Imagine that a rider with 6 inches of rear suspension travel is pedaling at constant speed over a large rock--not an uncommon situation for an all-mountain rider. The first inch of the path over the rock has a gentle incline of, say, 20 degrees. But the next inch of of the path over the rock has a steep incline of, say, 80 degrees. When the rider's rear wheel hits the first inch of the path, the chain will grow at relatively slow rate; but when the rear wheel goes over the next inch, the chain will grow at a faster rate due to the greater vertical travel required for an equal amount of movement over the surface. Thus, when the rear wheel is going over an irregularly inclined surface--which is typical of "bumps" found in natural-terrain--chain growth rate will be irregular as well.
WheelsForHeels
Warning, more brain pain…

When a wheel hits a bump the rear wheel rolls faster (and feeds chain faster to the crankset) on the bump faces compared to the top and bottom of bumps due to the trail surface's longer distance from point to point than a smooth surface. With near constant rider input to pedaling cadence, the bike slows a little but the wheel speeds up a lot while the suspension compresses then later rebounds for a bump slope. Some amount of rearward path is required to keep a rather constant resistance of pedal spin cadence from chain tension. The wheel slows passing over the top of a bump, and again slows traveling across the trough.

The dw-Link's rate of increase is greater than low monopivot near sag, close to high monopivot, but then the dw-Link very more rapidly decreases in tension increase to be more low-monopivot/ICT-like in tension increase just a little deeper than sag (and even less tension increase than low monopivot/ICT very deep in compression travel).

Combined with wheel speed fluctuating increase and decrease timing over bumps, the dw-Link's rapid chain tension digressive increase during travel compression maintains a rather constant pedal resistance tension through bumps and feels low monopivot like in feedback, but without the low monopivot's energy draining acceleration squat and slower acceleration.
 

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Very true when I tested bikes those were my questions..... and choose the 7point over... the Highline, DHR, Specialized, Kona, and tons of other similar bikes AND the HUFFY.(JK)

The completeness of the bike is what sold me. The price was the last deciding factor. It brks very well, pedals when I need it to, suspension is smooth at all times. What more can you have???
 

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Discussion Starter · #27 ·
Confused...

Derby, your latest response is interesting. It seems that what you are suggesting is that the effect of the wheel moving faster over a bump balances out the effect of the suspension moving rearward. I can only imagine the equations that would be necessary to demonstrate this idea with meaningful precision.

Aren't you contradicting a previous post of yours, though, when you say that the DW Link behaves first like a high pivot and then like a low pivot? Wouldn't this changing behavior result in a nonlinear increase in chain tension as the rider goes over a substantial bump? And wouldn't this nonlinear increase be noticable to the rider? I think that in a previous post previously you said the increase was linear.

Yogreg, I'm working on getting a demo out on Long Island, but will let you know if I fail.
 

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www.derbyrims.com
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WheelsForHeels said:
Derby, your latest response is interesting. It seems that what you are suggesting is that the effect of the wheel moving faster over a bump balances out the effect of the suspension moving rearward. I can only imagine the equations that would be necessary to demonstrate this idea with meaningful precision.

Aren't you contradicting a previous post of yours, though, when you say that the DW Link behaves first like a high pivot and then like a low pivot? Wouldn't this changing behavior result in a nonlinear increase in chain tension as the rider goes over a substantial bump? And wouldn't this nonlinear increase be noticable to the rider? I think that in a previous post previously you said the increase was linear.

Yogreg, I'm working on getting a demo out on Long Island, but will let you know if I fail.
I can't fully explain all the factors of chain tension fluctuation. But is must be more to it than a constant chain-stay length.

I suspect that if measured the rate of chain-stay growth drops quickly just below sag and then grows at a regressive rate. The path may be more parabolic or elliptical than more common round monopivot and Horst link paths. I'm guessing the softer feel than low monopivot hits a square bump is due to that.

But also unlike VPP there's no deep travel pedal-resistance and cadence stall, or when standing and climbing it doesn't jack and drop in the middle and granny rings.

But bumps also increase and decrease the wheels cover and so feed a little more chain in a given distance than when the trail is smooth, so that is some chain tension fluctuation introduced than must be counterbalanced with the DW link better than other designs do.
 

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Discussion Starter · #30 ·
Hmmm... Derby, you have many interesting ideas. It seems to me, though, that we're basically throwing a whole bunch of different forces out there and then speculating as to how they all balance each other out. With so many forces to consider and no hard numbers for any of them, we're just guessing about how they all come together. I'm going to test ride a six point this weekend and see if real world experience helps add to the picture.
 

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WFH,
Maybe you should read the DW-Link patent(s). I haven't read them but once DW commented that it was all explained there. Go to uspto.gov and search issued patents under author's name and you should be able to find them. You seem to crave explanation so maybe those would help. Just a thought -
 

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6.8 test ride/more brain torture

This is WheelsForHeels. Signed in under my other name by mistake. Darn... Keep forgetting to use my psuedonym!

Anyway... Just had a pavement test ride of the 6.8. Unfortunately, it was raining out and the dealer (quite reasonably) didn't want me taking his brand new, white bike onto the liquifying trails.

My pavement test ride was inadequate to guage the performance of the bike. However, I did notice very limited movement of the suspension under hard pedalling in both chainrings. I also found the geometry and general feel of the bike to be great.

I did not find any magical level of efficiency in the bike, but again my test was inadequate. However, the more I think about the arguments that the DW Link is superior, the more I question them.

Derby, if our body mass makes the suspension want to compress under acceleration and therefore causes the rear axle to move rearward, and if at the same time our pedalling force counteracts this by pulling the axle in the opposite direction, doesn't this mean that we're using some of our body's energy to resist suspension compression? Why is this any worse than using some of our body's energy to induce suspension compression in less rearward systems? Maybe we're wasting similar amounts of energy with both types of systems, even if we're wasting the energy in different ways. And even if you could do the math to show slightly less waste with the DW link, it seems to me there are other tradeoffs with having the wheel move backward: less stable center of gravity, less control in hard corners, etc. These things could cause the body's muscles to work harder and induce fatigue as fast as, or even faster than, in "less efficient" systems.

Hey, I'll be the first to admit that I'm just being an armchair engineer here. It's quite possible that the DW Link is the best thing ever created in the history of bicycle suspension. But I haven't yet seen any proof of this claim yet. I feel like these forums are religious--everyone's got an argument for why their suspension is divinely great, and a lot of people get very passionate about the matter, but a compelling rational argument showing that any one suspension is the best remains elusive.

Hmmm... maybe there's no such thing as a best suspension... Maybe the 6.8 is a great bike and there are other bikes just as great too.
 

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lbortman said:
Hey, I'll be the first to admit that I'm just being an armchair engineer here.
Indeed you are.

I wouldn't even begin to debate this topic with you - I'm no e-engineer. I will say that having owned Santa Cruz and Intense VPP bikes, Specialized and Ellsworth Horst-link bikes, and various single-pivot bikes, that the dw-link has impressed me as offering the most balanced suspension design I've encountered. Excellent braking properties, minimal pedal feedback, awesome traction both climbing and cornering, and all-around great handling.
 

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Discussion Starter · #36 ·
6.8

Hey, Dogboy, yes, no pretense here. I'm just a man on a learning mission and in search of a new bike... reading all the contradictory opinions of everyone on this Website and testriding the different bikes that various people rave about. Thanks for your own opinions. I'm going to give the 6 point another test ride soon, at a time and place that let me hit the trails with it.
 

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some info

Hi WFH,

From a traction and energy conservation standpoint, dw-link is truly superior to any other suspension that has been marketed in the bicycle industry previously. This can be backed up in two ways. 1) through physical modeling, and 2) through ride testing.

dw-link is not magic. dw-link is not a fictitious marketing campaign trying to back up some random links and pivots with impossible claims. Actually, there has never been a dedicated dw-link advertising campaign in the history of its existence. Not one print ad, not even a banner ad. Pretty much everything you hear about dw-link is the enthusiastic responses of riders who have ridden the system and made their own decisions, the ride testing part if you will.

Physical analysis is a little less easily absorbed by most people, especially on the interweb. The intertrode is full of so called "experts" regurgitating what they hear without really having an understanding about what they are discussing. Physical analysis of vehicles is not simple, but it is not that complex either. To me there are much more complicated things that I have dealt with. Motorcycles and bicycles are analyzed a little differently than a typical automobile. This has caused huge amounts of misunderstanding, especially over the years on MTBR. I personally gave up trying to discuss the finer points here years ago. It's like talking to a wall sometimes. Thus, this thread will not become a roundtable discussion (with my input at least) on the finer points of physics. It is what it is.

That being said, EVERYTHING that you could ever want to know about dw-link, the physics that define our world and govern how it works, can be found on dw-link.com, and in the second dw-link patent 7128329.

Please take a look. I think that the physics is well defined enough on dw-link.com to make it understandable, but I am open to any input for clarification for the site. I know that it can use it, its just tough to get all that information into easily digestible little packets.

A couple points to address thoughts that I read in this post.

1)
Remember Newton's 3rd Law; "every action has an equal and opposite reaction". Mass transfer is a part of any movement. Whether walking, on a bike, in a car, mass transfer happens, and you can feel it and use it.

A bicycle has the highest ratio of center of mass height to wheelbase of any vehicle (other than a unicycle obviously). When you ride a wheelie, all of your mass transfers to your rear wheel. When you do an endo, all of your mass transfers to the front wheel. When you accelerate, your mass is accelerated, and mass transfers to the rear wheel. When you brake, your mass transfers to the front wheel. Anyone who has ridden any bicycle can relate to the human tactile feelings of the physics at work here.

This mass transfer happens on all bikes. Road bikes, to downhill bikes, on some level the mass transfer is happening and being mitigated by the chassis. On a road bike, when you accelerate, the sprung mass (rider +frame) transfers rearward, and the seatstays see a load increase. If one were to put a gage to measure force in the seatstays, you would plainly see this force increase. The seatstays may only deflect by a small amount, and you may have only a millimeter of wheel travel, but the movement is there on some level. If it helps, think of a full suspension bike as a normal bike with a very flexible seatstay. Every time you accelerate, your mass transfers rearward. Your suspension is designed to be compliant to reduce vibration and harshness, as well as allow your tires to maintain optimal grip with the road surface. Every time you accelerate (with no control for the wheel at all) your suspension will compress until the acceleration, and therefore the mass transfer stops.

2) Acceleration and mass transfer are directly proportional. If there was no damper attached to your suspension, just a spring, you would have 100% conservation of energy. All of the energy put into the spring would be released back into the system. This however, is not the case with a suspended vehicle. The suspension system needs a damper to control spring oscillations resulting from bumps; otherwise the suspension would vibrate uncontrollably and be more of a detriment to traction and comfort than an aid. This damper is the double edged sword. Many (almost all actually) suspension systems sold today rely on over damping the suspension at low speeds in order to control the suspension's reaction to mass transfer. A damper is a device whose sole purpose is to convert mechanical energy to heat and dissipate it as waste energy. When you accelerate a vehicle, and the suspension compresses due to mass transfer, a significant percentage of that energy is converted to heat and dissipated.

3) In addition to mass transfer, you have another important factor to consider on a human powered vehicle. The "engine" for a human powered vehicle is YOU. As an engine, you operate at very low RPM and with very heavy 15-40 lb unbalanced pistons oscillating vertically (your legs). Get on your bike, any suspension bike, get up to coasting speed on the road, and backpedal. Look at your shock oscillate up and down. This is your suspension reacting to the mass of your legs moving up and down as you pedal.

4) OK, so before we get into any further explanation, I have one thing we need to all repeat together. Write it down, tell your kids, tell the neighbors and the dog.

TWO FORCES CREATE A SQUAT RESPONSE; THE FIRST IS DRIVING FORCE, THE SECOND IS CHAIN PULL FORCE. DRIVING FORCE IS ALWAYS THE GREATER FORCE.

If you don't consider mass transfer and driving force in a kinematical and dynamic analysis of a suspension, (like 99% of dw-link's predecessors) then the analysis is useless/ inaccurate/ rubbish.

Summary:

Dw-link is the world's first and only suspension system that counteracts the effects of mass transfer and the unbalance of a rider's legs moving up and down on the suspension system. Dw-link uses position sensitive anti-squat to accomplish this. The end result is a suspension that can use much less compression damping than other systems, which increases traction, and conserves energy at the same time.

Many companies will try to spin a yarn and give you some story. I am just one guy, a rider like you who just happened to have a dream and pursued it. All I ask is that you take the time to set the bike up and ride it. See how it feels. I cannot guarantee that the bike you ride will be your favorite bike that you ever rode. I can however, guarantee that the physics that dw-link uses to its advantage, and the words used to describe them here are as real as the flesh on your bones. Physics is timeless.

Thanks for reading.

Dave

Supporting references:

a. www.dw-link.com
b. US Patent 7,128,329
c. pending patents in Europe, UK, Japan, etc…
 

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www.derbyrims.com
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WFH you asked if rider energy is wasted resisting squat compression. No, the rider energy is balanced in leverage to move the bike and rider forward rather than storing the energy in the spring to pogo the rider upward upon rebound.

Using an automatic semi to full lockout platform shock can be set up for minimizing wasted energy to pogo and acceleration losses, but the suspension remains more firm when coasting and braking for a choppier handling ride with worse bump compliance and less traction.

Only bumps move the dw-Link suspension, not rider energy. When compressed below sag, pedaling ant-squat leverage is relaxed in sync with the spring's greater ability to resist pedaling squat. The relaxed leverage maintains smooth pedal feedback as the bump compression stretches the chain length.
 
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