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Evaluations of Full Suspension Mountain Bike Designs

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Evaluations of Full Suspension Mountain Bike Designs

Post by auhcyelnats on Tue Dec 04, 2012 7:21 am

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Evaluations of Full Suspension Mountain Bike Designs

Understanding how a design works will make you a better rider on the bike. Use this information and our unique experience to help you know the bikes we sell. After you have had your fill of reading the evaluations below, be sure to check out our DREAMRIDE F-SERIES
Here at Dreamride we offer four distinct rear suspension design philosophies. We carry YBB softail designs from Moots that are quite effective without any pivot at all, and 29ers that roll over obstacles that small wheels have to deal with by resorting to suspension, but since we do specialize in long travel for the rougher terrain here in Moab, Utah, we offer the best pivoting linkage designs we could find. After more than a decade, we favor classic four bar linkage and the Moots M-Arc system and here is why:

First, Take a Good Look at the Bottom Bracket Yoke

Below is information on how various systems operate, recommendations and warnings about the various quirks, advantages and disadvantages of different designs, but even if a suspension design looks and feels OK and works well enough for your needs in the parking lot, it may have an obvious flaw that you haven't considered. For example, if you look in front of the rear wheel behind the crank and see a bunch of suspension parts resting right behind the bottom bracket (Pivot bikes come to mind), you can expect problems from mud, sand or anything the rear wheel might deposit on that shelf of moving parts. You will understand after you ride it in nasty muck. You will have a clean up job ahead that will have you spraying water at high pressure onto your pivots, or worse still, spending time on the trail trying to claw the mud out of voids in the aluminum struts. So, you bought a light bike that now weighs a few pounds more every time you ride through wet sand or mud.
Now, look at the finish. If it is anodized, I wouldn't buy the frame for personal use, unless it was a smoking deal and that is what you are looking for. Anodizing signifies a disposable frame. They market this nasty process as stronger and easier to maintain. This is a lie. If you want a stronger frame, get an aluminum frame that has been peened and painted, not peened and put in an acid bath, destroying tight tolerances and creating a surface that cannot be refinished without removing the ano and etching the frame in another acid bath. One manufacturer we know of charges a lot for their anodized hype-machines, even if they have been in the bath up to four times to correct cosmetic flaws when the anodized color streaks and runs. They will even sell these flawed frames as a "Special Edition" by painting the ones that are have been in the bath more than four times. This makes manufacturers of mostly anodized frames suspect for selling seconds at a higher price (paint is much more expensive than ano). Powdercoat is the best surface for an aluminum frame! If a manufacturer uses ano as a primary finish in their overall line, beware.

Is the frame made out of thin water-formed sheets, boxes and strange shapes? A lot of these frames have stress risers all over them just because these methods of construction can shape a bicycle into something that will scare grandma. Weight wheenies beware. Straight gauge tubes and strong-looking CNC machined yokes and junctions are best for full suspension. Simpler is better when it can happen. Weight reduction at the expense of rigidity and longevity is for people with disposable income and a disposable body.

Four Bar Linkage

The best four-bar variation comes from Ventana. Instead of the more vertical mild to extreme S-shaped axle paths of Horst Link and VPP designs, a well designed 4-bar rear axle moves in a perfect arc around the bottom bracket pivot. There are advantages and disadvantages to an arcing axle path. The first feature of the arcing axle is that it is easier to damp an arc with a tuned shock stroke. The rear axle pivot in a four bar system is on the seat-shockstay above the axle. On our Dreamride F-Series bikes, which utilize the Ventana rear suspension design, the rear axle is directly connected to a quad bearing bottom bracket pivot via a stout swingarm. This creates an impressively rigid pedaling platform that takes full advantage of current "stable platform" shocks on the market.
A rarely considered feature of a well thought out four bar design is a seat tube pivot placed to allow the shock to operate in a linear fashion. If you see a bike with this pivot BEHIND the seattube, beware. It will not get the same plush linear travel as those with a more forward pivot mount.

It is obvious at a glance that the Ventana four bar rear is as triangulated a system as possible within the confines of a four bar design. Every junction states the strong, no-flex theme. The rocker is only as long as it needs to be, forming obvious three sided structures anywhere it can happen. All connecting parts within the arc of the stroke restate this triangulation, even if they are connected with a pivot. At all seatstay pivots there are two bearings per bolt to eliminate flex. Pedaling and braking forces are dealt with in very well thought out rocker and seatstay pivot placement, favoring a bit of squat over "jacking" effects (brake hard and the frame will hunker a bit, not jack up and throw you forward).

The mild compression ratio offered by a well designed 4-bar design creates a softer stroke. Adjustments are much more refined and wide, and the life of the shock is increased. The rear is quite efficient under pedaling and braking, though not as "plush" while these forces are active compared to parallel beam systems. Plushness is the best way to think of the difference, not efficiency. Efficiency is gained by limiting the effects of the suspension on the rider's inputs into the bike. For us the swingarm mounted pivot (Horst Link) is not worth the flex, which is THE factor in robbing the rider of power to control the bike efficiently, especially in hard turns. We are not as concerned with "super plush" as with strength, lateral rigidity, and predicability at speed in fast technical situations. To some, these handling qualities translate into valuable efficiency more attuned to hardcore trail riding.

Horst Link and Parallel Beam Systems

An interesting trend in mountain bike manufacturing has come about by the expiration of the patent for the Horst Link pivot design. Even before the Horst Link became public domain, manufacturers using it began to move to traditional four bar linkage. The reason? Marketing! Specialized's patent was supported by ream upon ream of magazine ads and the influence that those ads purchased. Any manufacture wishing to piggyback onto the Specialized band wagon got a boost, if not a free ride. For many years I have watched the magazines tell you that Horst Link suspension works best, but it was a farce from the start. A ton of marketing money each month for a single magazine tends to get their attention. Horst Link was originally marketed to hardtail riders, telling them that the rear wheel actually dug into the ground on the power stoke. In other words, it bobbed like crazy in the small chainring. One man's power is another man's bob. A Horst Link, especially the Specialized variety, flexes, bobs and breaks on a regular basis. Eliminating the seattube eliminates triangulation. Using a pivot on the chainstay puts a lot of mush between the power source and to where the power hits the ground. Horst Link is but one design in the parallel beam pool, but they all share the same flaw: Flex!
In minimal terms, parallel beam technology focuses on using parallel linkages to counter pedaling and braking forces, trying to place the four arms in as perfect an alignment as possible to keep chain length the same throughout travel and effectively eliminate chain torque and braking effects on suspension action. The ultimate goal is for the suspension to remain active at all times, with no squat and no dive on braking or acceleration. The closer those parallel beams get to being lined up, the better it works, and the more we see that all these designs are the same. In theory, longer travel parallel beam frames work better at defeating brake effects and pedal forces, though in certain gearing combos there is always bob input from pedaling. As the arms become less and less parallel in shorter travel versions, effects like brake jack and bob start to appear. These effects can be minimalized through weight shifts and a more specific body position defined by the build of the bike. The pivots at either end of the seat-shockstay are especially important in creating a desired shifting "virtual pivot" to allow the rear axle to take a specified path as the shock compresses. Lawill and Specialized Horst Link frames use similar ideas in various structural forms, but basically, these are all operating off of the parallel beam and are truly the same idea.

The downside of any parallel beam four bar linkage design assignment is that things like seatpost and cranks and brakes get in the way of how the thing is going to work. Specialized's FSR designs eliminate the seatpost, causing problems like exposed seatpost bottom, interference between seatpost and shock, structural failure from flex due to stress risers from the elimination of the classic triangle, etc. We once carried the best example of the Horst Link system, the Turner 5-Spot (stopped using the system when the Horst patent expired!) which combines the Horst rear pivot with a four bar rear end that maintains the seatpost mounted rocker arm and bushing pivots in an attempt to minimize lateral flex, but the most nagging downside with all these designs is lateral compliance. The dirty word is "FLEX!" These designs, even when executed well, squirm and twist. The parallel beam four-bar is truly between a physics rock and a design hard place. A parallelagram does not have anywhere near the geometric strength of a triangle. It is a Rube Goldberg engineering task to eliminate lateral twisting from a four-sided structure that hinges at every corner, especially when the swingarm has a pivot at the rear end. There are ways to lessen the effect--beefier rocker and swing arms, shortened rockers, adding structure between the parallel working pieces, using the four-bar configuration by including a seatpost mounted rocker, but all these designs interfere with the desired effect, monkey with rider position and geometry, and seriously effect high speed handling, especially in high speed turns. We considered a cross-over rocker arm that sweeps over the rear tire like the Manitou reverse arch, but finally just gave up and moved on to four bar linkage designs that focus more on rigidity and less on that measely 2% or so pedal efficiency you get from the parallel beam. It's always a trade-off. For some people who go slower and want comfort in the saddle advantages of efficient pedaling outweigh compliance issues. It is only when the speeds increase and the turns get fast that you have to think about forces of nature that could make that rear end twist, load, wind up and release like a slingshot. The faster you go, the more you are going to like straight ahead four bar or canilever beam designs. A downhill bike is for going downhill, so a single pivot is very smart and you can eliminate brake effects with a floating brake system. A freeride bike needs pedaling efficiency, but cannot tolerate flex, so the four bar design is more appropriate. With good parallel beam four bar linkage designs the longer the travel, the better it works, but as you pour on the travel more flex is introduced into the system. Understand that the reason a short travel XC suspension bike feels so sweet to a novice convert is that the shorter the suspension travel, the less sophisticated the design has to be to work efficiently. Good four bar designs shine when the wheels start to move up and down more than three inches.

The Virtual Pivot Point design now owned by Santa Cruz has received a lot of attention. It is a fine design, especially pedaling over level ground on roots and rocks. But the huge chink in the VPP hype armor is found when climbing steep hills. The design's main feature is that chain torque pulls the wheel to a specified point along the "S" when SAGGED, and keeps it there. Therefore, there IS torque input when you point the bike up and weight shifts to the rear wheel and the bike sags more into its travel. The chain tries to move the wheel into that specific point on the "S" and when SAG is over or under that chosen point along the "S", chain tension pulls it back to that spot. SAG can be caused by hitting a bump, too, right? I read glowing reviews in magazines about the Blurr, but nowhere do they concentrate on the bike's climbing attributes. MBA did state that the bike would "scratch" its way up a hill. Give them credit. They didn't say it was perfect. Reading between the lines, it gets a little clearer. One review spoke of a certain "deadness" engineered in there somewhere. Of course, by virtue of the design, it is right where you will be pedaling from. Dead is dead. Flex happens, too. So, we still prefer Ventana's take on four bar, without the marketing hype.

One more thing about VPP: MADE IN CHINA. NO ENVIRONMENTAL STANDARDS. NO HUMAN RIGHTS STANDARDS. NO TAXES.

Single Pivots

This is the category which has benefited most by recent rear shock design developments. There are good reasons to consider a single pivot frame over a linkage bike. The best are simplicity and strength. The origins of the best front pivot location were the Santa Cruz Hecklers and the Pro-Flex bikes of the early 90's. The single pivot location is most important in controlling pedal and braking forces into the rear suspension. If you are thinking single pivot, make sure the frame carries weight low and has geometry suitable for your intended purpose. Stiffness is a prime concern in single pivot designs (see the pictured Superlink). Expect some pedal kickback on impacts and stiffening of the suspension during hard pedaling even with the best single pivot designs. Avoid bikes with high or very low pivot points and any single pivot that does not reinforce the swingarm with solid design. Brent Foes does the best with this design and includes floating rear brakes on most models, eliminating harsh braking effects of the simple pivot design.

The Gibson Superlink is just one of the reasons why the Ventana El Chamuco WAS far superior to other single pivot designs. Now it is a thing of the past, but we expect to see some Chinese manufacturer pick up the ball and run and have seen a few copies on much lesser frames.
Moots M-Arc Suspension

The Moots M-Arc, our favorite at four inches of travel, is a 4-Bar/Single Pivot hybrid. It is a Goldilocks system for XC racers, and is especially suited for 29 inch wheels. At four inches of travel there is really no need for more sophisticated linkage designs. The real reason for the arc is to manage the shock location without creating problems associated with S-curve stroke designs. M-Arc consists of a pivot behind the bottom bracket and a top rocker system that guides the rear section in a perfect arc and drives the shock with a perfect progressive stroke. Because it has no rear section pivot, it is amazingly rigid. The M-Arc design keeps the frame triangulated and puts weight low on the frame. It also pedals extremely efficiently. Four inches of travel is the maximum amount of travel for the M-Arc. The Moots Zirkel models use the M-Arc design with the Mooto-Xz being the best example of just what this system works best for. No other system is more attuned to the use of the Fox RP-23 rear shock.
The Evolution of XDreamTrail (XDT) and ClimbMAX

We expect all bicycles to be able to climb efficiently, even longer travel bikes. It is important to be able to get to the top without fighting the machine, and you need to be able to pedal through and over obstacles without the bike feeling top heavy. We have found that 5.5 to 6 inches of rear wheel travel is where Goldilocks lives. All of our bikes pedal well, and if they didn't, we would not offer them. We try to balance the capabilities and energy-saving effects of long travel with needs of bike to handle the terrain and speeds required by the individual rider. On the way up, the bike must pedal. On the way down, even when it gets really rough, it should allow you to relax and get back some of that oxygen. While shorter travel bikes bounce around, the longer travel steads put power and braking forces to the ground. The difference between 5 and 6 inches of travel on the back of a mountain bike is pretty drastic. The difference between 6 and 7 is minimal. A well-built long travel full suspension bike with that magic 6" of travel takes less energy and, as the terrain gets rougher, it forgives your mistakes, . . . to a point, of course. The bikes are built to slam obstacles, pedal, point, and shift, smoothly over rough stuff.
In the case of the longer travel All Mountain (XDT) bikes we offer, extra weight (35 pounds maximum) actually helps create momentum, so short rollies are a piece of cake, impacts during the climb vanish, and the bike is stable on the ground and in the air. A bike's weight only becomes a negative on a long steady smooth climb when momentum runs out, or when the rider is not fit, and even then the bike is still a capable climber. The more you lean toward light weight for climbing sake, the more tentative you will have to be on the descent. The XDT and ClimbMAX bikes offer the best equation for your personal needs, because we have tried all the parts, beat up the frames, and know the right place for each. If you ride one of our Moab-oriented builds long enough, even if you may consider it to be on the heavy side of things, it simply becomes your mountain bike. Legs get stronger. Lungs get larger and more efficient, when repeatedly challenged. If you want more info on this subject, click on WEIGHT RANT. If you want to go the other way, toward light weight for the sake of light weight, we now offer the FEATHER, the most recent of our Dreamride F-Series mixed wheel size bikes.

Testing Platforms

Dreamride currently uses the following frames exclusively for testing component formulas: DREAMRIDE FULLY; DREAMRIDE F-69; DREAMRIDE MUTANT; VENTANA EL CHAMUCO; MOOTS MOOTO-XZ; MOOTS VAMOOTS; PEGORETTI MARCELO; DREAMRIDE WHITE RIM 69ER. The Dreamride F-69 gets most of the attention nowadays due to its amazing superiority in performance. Some manufacturers used Dreamride testing data and input to design frames currently on the market, or to market their product effectively. For our own Dreamride frames there has been a lot of attention given to finding effective ways to massage geometry and wheelbase for longer travel bikes for a range of purposes, from cross country to freeride. Ultimate results of testing can be seen in the current model year Dreamride F-Series.
About pedaling longer travel bikes:

The way a bike feels is effected by the bike you were on before. It goes like this: If you are coming from other designs that are less plush (hardtails, short travel and poorly designed full suspension bikes that beg you to set the bike with little or no sag), you will have to concentrate on pedal stroke. To get started, sit down and spin. Concentrate on the power of the pedals moving you forward. After over a decade on four bar linkage bikes, I now stand and chug on a smooth climb, adjusting body position to counter shifts in weight or effects of chain torque in upper gear ratios, but the real secret, at first, is to sit and keep a steady spin--torquing the rings evenly all the way around, scraping that dog crap off the bottom of your shoe, and pulling up on the back stroke with your quads. This is not such a good way to push a heavier bike up a steep climb for long, because your knees will suffer, but once you get the feeling of where the bike likes to see your weight, you can stand up and pedal in any gear.
One trick that cooks riders on hardtails or lesser full suspension rigs, is to accelerate in the saddle up a loose and rocky slope away from them. The bikes we have chosen for our "Black Diamond" kits show their muster when the going gets very rough, the speed increases and power goes into the pedals.

Lee Bridgers
Dreamride Mountain Bike Tours and Sales
Moab, Utah

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auhcyelnats
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Join date : 2012-07-24
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