[Cary]

I was flipping through the new MBA and notice the advertisement for the Marin Quad FRS. If you look at the pictures is looks strangely like the Blur VPP design. Here is the blurb from Marin's Web Site:

"Marin's new QUAD suspension design is a four-bar linkage system with a patented Intelligent Pivot. The Quad system is designed by ex-Formula One engineer, John Whyte and has been developed to give the most responsive and efficient ride over a variety of terrain. This is achieved by allowing the Intelligent Pivot center to mechanically adjust itself, offering riders better traction and control in all conditions. The Quad uses a patented Intelligent Axle Path, its arc is defined by a quadratic equation. The result is a bike that sprints and climbs like a hardtail and is still able to absorb the bigger hits."

and

"Intelligent Wheel Design:
By moving the wheel backwards early in its travel, the system's ability to respond to square edged bumps is greatly improved. Even the smallest bump activates the suspension, keeping the wheel in constant contact with the trail while dramatically improving traction. About 1/3 of the way through the travel, the wheel's arc returns toward the bottom bracket, optimizing chaingrowth and virtually eliminating pedal induced feedback."


What do you guys think, is this a VPP by a different name or not? It sure looks like an exact copy of the VPP design except the pivot locations are slightly different. Their description also seems to mirror exactly the working of the VPP design.

 

[dante]

well, here's the thing...

here's the thing... it's trying to mimic the VPP without actually infringing on patents. The crux of it is, there is a suspension design that has a solid front triangle, a solid rear triangle and two linkages connecting them together. Look at the Canfield Bros bikes (F1 or Sig) for a pretty simple layout. (Karpiel also uses this technology.) The linkages allow for a motionary pivot point, so instead of a SP or a 4-bar, the pivot point moves as the wheel goes through its travel. VPP takes this a step further by manipulating the linkages in relation to each triangle. The Marin definitely uses the same IDEA, with the big swing arm as one triangle and the main triangle as the other, and then there's the two linkages connecting the two. Obviously they had to change it enough to get aruond the VPP patent but whether this is enough to make it handle differently than the blur is a good question.

dante

 

[Brown_Teeth]

I agree VPP is just the i-drive but less efficent, seems marketing rules and physics is just for fun these days. The Marin sounds interesting but its just spliting hair's for less than a hair's worth of gain for an extra grand? Wish all well but still happy with the old single pivot TARA and a idrive for XC fixes.

 

[Gnarlygig]

Besides the links not rotating the same, the axle paths differ as well.

The Blur's links rotate in opposing directions, while the TARA's links work in the same direction. The Blur's axle path is more vertical than the TARA, which arcs rearward more noticably. Note that while the TARA pivots can be mapped in Gergely's Linkage program using the VPP mode, it only serves to show pivot rotation and axle path, thus the weird looking shock link (in blue), and wrong shock movement, as it's trying to simulate a true VPP shock mount.

Hope this helps, I was looking at the TARA myself, but went with an HH. I may still get something bigger travel later, but would rather have a full 6" travel front and rear. You might want to consider the Rocky Mountain Switch SL and the GT Ruckus Flowta I Drive as well if you want a true six inch rig, they're heavier, but can handle bigger stuff.

 

[Disaster]

The Blur's links rotate in opposing directions, while the TARA's links work in the same direction. The Blur's axle path is more vertical than the TARA, which arcs rearward more noticably. Note that while the TARA pivots can be mapped in Gergely's Linkage program using the VPP mode, it only serves to show pivot rotation and axle path, thus the weird looking shock link (in blue), and wrong shock movement, as it's trying to simulate a true VPP shock mount.

Hope this helps, I was looking at the TARA myself, but went with an HH. I may still get something bigger travel later, but would rather have a full 6" travel front and rear. You might want to consider the Rocky Mountain Switch SL and the GT Ruckus Flowta I Drive as well if you want a true six inch rig, they're heavier, but can handle bigger stuff.

Those TARA linkage pics don't look right at all. The shock looks to be getting longer...actually looks like it is being driven over center so it would first compress, than decompress....actually pushing the bike downward.

The Marin bike suspension is considerably different from your TARA pics. The link faces forward in the front, and backward in the rear. There are quite a few reviews of the Marin available on the web. It seems to be quite popular in the U.K. and has a lifetime warranty on it's linkage. The reviews say it is quite plush, however the rear suspension is highly progressive and it gets fairly harsh toward the end of suspension travel. Seems like it might benefit from a shock with a less progressive curve itself.

By the way, what is "Gergely's Linkage program?" Is it freeware? Where can it be found?

Thanks,
Danny

 

[Gnarlygig]

Arrgghh!, I knew someone would say that! You may have missed this part of my post...

....["Note that while the TARA pivots can be mapped in Gergely's Linkage program using the VPP mode, it only serves to show pivot rotation and axle path, thus the weird looking shock link (in blue), and wrong shock movement, as it's trying to simulate a true VPP shock mount."]....By this I mean disregaurd the shock movement and phantom blue link which does not appear on the TARA. I could have spent alot of time running the illustrations through my Windows XP Paint and erased the blue link and laboriously drawn in the shock by hand to show the correct position, but that still would not have made use of the other feature of Linkage, being spring curves and such.

Gergely's Linkage is indeed freeware and is unfortunately not easy to find, I had to scour the old forum to find the thread that had a link to it, if I locate it again, I'll post it Danny.

 

[Gnarlygig]

OK Danny, I found it. You may want to store this URL as you'll only see a download...

[/QUOTE] By the way, what is "Gergely's Linkage program?" Is it freeware? Where can it be found?

Thanks,
Danny[/QUOTE]...box when you click on it.

http://www.mtbcomprador.com/pa/english/Chapters%20and%20Documents/Linkage2/linkage2.exe

Here's some tips on using it, as the readme is overly complex except for engineers. When choosing a bike pic to map pivots from, look for large, high resolution pics. If you're on the website of the bike brand, always click to enlarge the bike pic before saving it in your pictures file. The pic needs to be a good profile shot at eye level of the frame to really work well. The program will ask you for either BB to rear axle distance or wheelbase, it's best to know the BB-RW for acurate rear suspension movement. The main problem you will encounter in trying to precisely click pivot locations is the main or swingarm pivot, as it is quite often obscured by the chainrings. In cases like this you can look for diagrams on the bikes website, illustrating, geometry, suspension technology, etc. which might show it's actual location. You can then use reference points like how it lines up with the back of the seat tube, chainstays, or BB to better pinpoint where to click for the main pivot. If you have any questions on how to use it other than that, let me know in another post, good luck.

 

[Disaster]

Arghh....is right.

I guess I should have read more and looked at the pretty pictures less. Thanks for the link to the progy.

There are a lot of things going on when a suspension is acting, pedal load, chain force, rider weight shift, bump load, braking input...etc. The marketers love to focus on just one thing that the suspension does well and compare it to other suspensions from other companies. This will always be a grossly unfair comparison. One suspension might be the king at addressing pedal feedback while allowing braking input to reduce it's effectiveness otherwise. It is the whole picture you have to look at. I'd love to see a program that tried to address all the variables. Of course, that is just the next step, then there are the dynamics...the interactions of tire and suspension mass vs. shock and damping.

 

[zonoskar]

You can also visit my website, it has a large number of linkagefiles already defined and you can submit your own files as well.

http://212.238.216.189/MTB2/Bikes/Linkage/index.php

 

[Gnarlygig]

I've reworked the TARA illustrations via Paint....

I guess I should have read more and looked at the pretty pictures less. Thanks for the link to the progy.

There are a lot of things going on when a suspension is acting, pedal load, chain force, rider weight shift, bump load, braking input...etc. The marketers love to focus on just one thing that the suspension does well and compare it to other suspensions from other companies. This will always be a grossly unfair comparison. One suspension might be the king at addressing pedal feedback while allowing braking input to reduce it's effectiveness otherwise. It is the whole picture you have to look at. I'd love to see a program that tried to address all the variables. Of course, that is just the next step, then there are the dynamics...the interactions of tire and suspension mass vs. shock and damping.

but as mentioned earlier, it's really not going to give you any more dat, just for looks.

If you'll notice, the forward link is pretty much in the same position at 0mm as 100mm, this is because it rotates clockwise like the rear link, then counterclockwise, very interesting design, and many say it works great. I'm a bit skeptical about it having so much chaingrowth regaurding climbing efficiency though. Too bad the Linkage program will not plot it's linkage rate, I'm guessing it starts out as rising rate, but changes to falling rate about the point where the forward link starts rotating counterclockwise, though I'm certainly no expert.

 

[derby]

Ouch! No wonder I didn't like the test ride of the Marin Quad. It's got a sharply rearward path throughout. Although I'm not convinced the Linkage path graphic is accurate, the forward link isn't rotating much from top-out to bottom-out in the graphic. If the path illustration is near correct, it's overly counter squat throughout, thus harsh pedaling on bumps. That's what the ride felt like too. The classic Gurvin Proflex, which the Marin monopivot designs improved upon a lot, is more smoothly bump compliant with very little bob.

The VPP has a very vertical path to the ground, which is very bump compliant at top out and effectively ramps up counter-squat progressively throughout travel from progressively increasing pedaling chain tension during travel compression. It feels very buttery over most terrain, only bigger more full travel bumps produce noticeable pedal kickback.

Thanks for doing and posting the Linkage graphics. And especially, thanks to Gergely for giving us the Linkage program.

- ray

 

[Gnarlygig]

I haven't ridden an XC or TARA Marin QUAD, but I'm not surprised...

...at your review. They (Jon Whyte) really emphasize the way it's design pulls the rear axle to the ground, and you're going to have a rearward axle path or high swingarm pivot in doing so. I would think this would adversely effect the braking causing jack, ala the Proflex. To their defense though, the illustrations I posted only show the first 100mm of travel, it does start arcing forward after that, though not soon enough to keep the bugs out IMO. I find consistently though Ray, that every frame I run through the Linkage program no matter how sophistocated, Horst or not, always has more chaingrowth at full travel than the manufacturers claim. The best are under 7mm, the worst upwards 16mm. The exceptions of course, are the concentric swingarm pivots at the BB, which are known to be overly active and require platform suspension to quiet them down. For the most part, I'm still thinking the Horst Link technology is superior, if nothing else, for achieving it's intended purpose in a lightweight, simple fashion.

 

[Disaster]

This pic is NOT the same as the Marin Quad suspension.

...at your review. They (Jon Whyte) really emphasize the way it's design pulls the rear axle to the ground, and you're going to have a rearward axle path or high swingarm pivot in doing so. I would think this would adversely effect the braking causing jack, ala the Proflex. To their defense though, the illustrations I posted only show the first 100mm of travel, it does start arcing forward after that, though not soon enough to keep the bugs out IMO. I find consistently though Ray, that every frame I run through the Linkage program no matter how sophistocated, Horst or not, always has more chaingrowth at full travel than the manufacturers claim. The best are under 7mm, the worst upwards 16mm. The exceptions of course, are the concentric swingarm pivots at the BB, which are known to be overly active and require platform suspension to quiet them down. For the most part, I'm still thinking the Horst Link technology is superior, if nothing else, for achieving it's intended purpose in a lightweight, simple fashion.

The Marin's front pivot is on a forward link, not a reward link. This could totally change the path of the 4 bar linkage.

"Chain growth", isn't the only important factor in a suspension with regard to pedal feedback. If this were so, the BB swingarm would be the ideal suspension to eliminate pedal/suspension feedback. As the BB swingarm suspension is driven up it necessarilly has to drive the tire to the exact ratio of the gearing...just like you were pedaling. This is the bio-feedback or bio-pacing that some suspensions try to counter. A single link swingarm (that isn't a unified triangle) can't address this. It has to be done with a 4 bar linkage that places the rear axle on a link that is at least one linkage away from the link that pivots the swingarm.

The Marin has the swingarm properly isolated but I haven't gone through the analysis to see if it addresses the biopacing issue.

 

[derby]

Yes, gear ratio also produces pedal kickback or forward. Low gears increase kickback, high gears reduce it. For example mount a wheel in a stand by the rim, hang a granny ring and chain off the biggest cog. Then swing by hand the ring all the way around the wheel's cog holding the chain tight. You'll see the ring revolves more than one revolution. Only a 1:1 gear ratio doesn't mechanically modify the steady pedal kickback produced by the growth of the axle path from the BB (effective chain-stay growth).

There are external to suspension plus drive-train kicks to the bike. Bumps and rocks suddenly slow the wheels, spiking the damping, and kick the bike away from otherwise freely forward progress. Combined with mechanical kickback the momentum can be very much disturbed, and this is the tradeoff and the wizardry required by designers to balance anti-squat with free momentum.

Gnarlygig, I appreciate your close studies of Linkage. I agree it is not entirely accurate and it has travel limits. It's close enough for comparisons between most common designs now. Compound mechanical curves, paths, are more than a handful to calculate with the trigonometry required. Gergely Korvak has provided a great illustration tool for all of us. It must have taken many months of hours to produce. I hope he is well employed by human conservation efforts we who love this earth really need his help.

The Horst link is the most elegant design to address the effective pedaling and braking efficiencies. The VPP and DW link (IH Hollowpoint (another low-life name for a bike) have produced some very interesting alternatives to effective pedaling, but they don't integrate the higher quality braking that the Horst link accomplishes so well, at least not yet.

The geometry of pedaling and braking are quite separate.

For pedaling the axle path swingarm line and drive-chain-line cross to form an effective IC (Point of Moment), where the acceleration line from the ground traction passes through, and the inertia of the suspended CM interacts in balance with gravity and spring to the PofM, with unbalanced suspended inertia, slowed by damping.

Braking locks the rear wheel to the link the brake pads are attached to (I say lock because at some slow speed any brake drag will stop the wheel. The torque relation is the same at any moment.) Follow the geometry of the brake locked link to its IC or a monopivot with the frame. The IC or pivot rotates with the wheel around the axle and tugs down or lifts the frame from that point. The inertia from the ground traction through the suspension when braking the rear wheel is like tying a rope from the IC or pivot anchored at the ground contact point with the rear wheel. The inertia of the rider swings more towards horizontal when decelerating and weight shift removes weight from the rear of the frame. For the rear tire to maintain traction the suspension must relax compressing tensions from the anchor-drag braking effect between the wheelbase. If the pivot or IC is in front of the front wheel, the anchor drag effect to that point of the frame fulcrums across the front wheel and helps extend the rear suspension down against rebound damping. But the frame and rear suspension can become too rapidly rising when the IC is far in front of the front wheel frame fulcrum and tension can bind against rebound damping or suspension topout and lift the rear wheel from the threshold traction required to avoid skidding and wheel jack. (A rider must exaggerate her reposition further behind the seat to compensate for the exaggerated frame pitch). An IC or pivot behind the rear wheel is extremely extending to the rear suspension.

It's a complicated balancing of pedaling and braking to combine a nice balance. Many DH bikes use separate suspensions for pedaling and braking, adding a floating linkage system for tuning braking.

- ray

 

[DeeEight]

How do the designs like late-model versions of the Lawhill rear suspension work out as far as pedalling and braking efficiency?

 

[Axe]

Your links are wrong.

Look at the Marin design, and fix it, before offering analysis.

 

[derby]

The wheel path produces a big ring height, rear side of seat-tube, very constantly located virtual pivot with the Schwinn 4 inch travel version of a Lawwill. That would produce a high monopivot ride pedaling much like a San Adreas monopivot. The Yeti DH has a lower, middle ring height constantly located virtual pivot about 2+ inches behind the seat post, which would pedal much like a Horst link.

They both would have stock floating disc brakes with a rearward IC, producing quick suspension extension as the IC rotates downward and seat post upward with the locked wheel tension. Lawwill design DH racers use a separate add on tunable floating brake system to reduce or eliminate the top out tension of the stock disc mount, most XC riders wouldn't notice the problem or adjust with lighter use of the rear brake. V brakes on the seat or chain stay of the Schwinn XC bike looks like it should be very stable, compressing the frame in tension with the wheel rotation much like a seat-tube located monopivot I’m guessing, having an IC sky high between the wheels (the wheel is not attached to the same link as the V brake on a Lawwill, but close enough for a very similar effect like typical seat-stay pivots with V brakes uses the IC of the brake link for the tension path.).

Interesting to comment on the Lawwill. I just met Mert Lawwill briefly for the first time this afternoon at the Trips-For-Kids benefit at the Broken Drum in San Rafael. I’d like to interview him for his ideas on design, but it was too loud and busy to talk much at the party. Other pioneers supporting the benefit there were Joe Breeze , Gary Fisher, Tom Richey, and Jackie Phailen as well as many more infamous sub-dudes.

- ray

 

[Gnarlygig]

Disaster, you are not apparently noticing that this is an illustration...

...taken directly from the TARA pivot points, NOT the XC bike. The TARA pivots are placed just as shown, and BOTH links are fixed to the frame at their FRONT end, not like the XC bike.

If you look closely at this picture of the TARA, which is the bike I mentioned was the illustration, you can clearly see what I mean. As for chaingrowth, yes many bikes do have it and benefit from it, and I never said that other factors do not come into play regaurding efficiency. It is my opinion however, that the more chaingrowth there is, the less efficient the climbing traits on rooty, rocky terrain, that is not to say it would be a detriment on smooth terrain, where it would provide better traction. I do believe as well though, that bikes with minimal chaingrowth, pedal better than those with 0 chaingrowth, which can be overly active and lack control.

 

[Gnarlygig]

I believe you as well Axe, are not noticing what frame I'm illustrating here.

Look at the Marin design, and fix it, before offering analysis.

These pivot points are taken directly from the TARA bike, and their fixed points, being the front end of each link, is correct as well. This is NOT an illustration of the XC bike, which differs from the TARA. I've also gone to great length just to remove the triangular link and improper shock location, as explained above, so people won't be confused by it. This illustration does not work for linkage rates in the current Gergely program, due to having to use the VPP mode just to get the pivot points to show correctly. Once you've plotted the pivot points correctly however, it does suffice to show both axle path and chaingrowth.

 

[Gnarlygig]

Yeh, Mert's a pretty meticulous dude, I remember my older brother...

...raving about his mechanical skills while racing flat track, shaving grams on his engine parts here and there to juice more power out of his bike. It seems to me the Lawill design was originally intended to give DH bikes a stable topped out sprint capability on flat sections where you need to pick your speed back up. I think it was taken too far when they adapted it to the Schwinn 4 Banger, I sat on one and couldn't believe how bad the saddle wanted to rise up with firm pedal pressure, I knew it would have driven me nuts on rocky, rooty climbs.