Author Topic: Let's talk geometry... (Read 8250 times)

Dugo · « **on:** February 19, 2003, 02:43:33 am »

I've been thinking lately about how well my '98 Animal seems to climb. I was looking at it the other day and for a single pivot design, it's interesting how Proflex(K2) set the shock to be almost parrallel to the swing arm and closely aligned with the swing arm pivot and crank BB points.

I really don't notice a whole lot of "bob" from my bike and I believe it's because the forces of the shock against the swing arm are pushing "back and down" rather than straight "up and down" as in the other EVO designs.

Now what this means I think is that the rear suspension will be slightly less responsive but more stable. If you take a big hit, it moves, smaller hits don't get as much reaction. I think it may be due to the fact that there is a slight leverage effect of the shock against the swing arm that needs to be over come by the swing arm moving up and changing the shock angle. Does this make sense?

I know the '98 Animal's and Beast's are a little disparged on this board when compared to the Oz's and stuff. I guess some of it has to do with the lack of after market support for the Animal's shock geometry. (and why did they run it through the seat down tube?)

However, I actually believe that Proflex got the geometry pretty close to perfect on the Anmial/Beast but their implementation of it left eveyone scratching their head when it came to the shock design (not to mention the weakness in the extension shaft).

So I'd like to see how others feel about "bob" and the various geometries we see in the EVO frames. Is the Animal conceptually superior in design or am I just being partial to my bike? Wasn't the factory racing on these at one point in time? And if that's the case, they must have represented the best design they had to offer at that point, right? And how about other single pivot design's from other manufactures? Who has some experience with other bikes that have a similar geometry to the Animal/Beast?

Well, now that I've painted a giant bullseye on my head, fire away...

Scott · « **Reply #1 on:** February 19, 2003, 08:34:55 am »

I don't recall the factory riding the Animal in xc but maybe it was used in dh? I do recall an article stating it climbed very well for a bike that descended as ably as it does not to mention they are a sharp looking frameset too. Isn't the shock setup , angles anyway, similar to a pull shock Razorback only with a conventional coilover? If so that may explain the efficiency of the design.

IFO · « **Reply #2 on:** February 19, 2003, 11:11:13 am »

98' Animal roks...

i wanted one SO bad a few years back...

sadly i never managed to get one...

[smiley=nod.gif]

p.s. the fact your shock lays flat vs. a angled slope of the EVO wont make any difference to the way teh bike rides...

the shocks leverage ratio/ bike ride mannerisms are built into the frame geometry...its all in the pivot location and the way the shock is valved...

dont stress your bike is a wicked nice bike... maybe not a HUGE-dropin freeride bike, but still plenty able to be taken seriously...

GET · « **Reply #3 on:** February 19, 2003, 11:22:05 am »

I love my '98 Animal. On general trail riding, I use my 5500C. But, when I'm taking the trails with large rocks and drops on steeper descents, I take the Animal. Great ride either way!

Dugo · « **Reply #4 on:** February 19, 2003, 02:04:41 pm »

Quote

I love my '98 Animal. On general trail riding, I use my 5500C. But, when I'm taking the trails with large rocks and drops on steeper descents, I take the Animal. Great ride either way!

Hi Get,

So you have both...I guess from what you're saying they ride about the same. No difference in "bob" or climbing ability?

If that's the case I guess that shoot's my theory to hell. It just seems the laid down shock design would behave differently from a straight up and down design.

IFO · « **Reply #5 on:** February 19, 2003, 02:12:56 pm »

im actually curious as to why u would think a shock orientation to the frame would make a difference to how it behaved....

all things being equal the shock shouldn't notice any diffrence... basicly a well designed frame will/should hold the shock in a perfect plane of motion so its not exposed to lateral loads or other types of friction induced forces....

wether it be flat/angled or strait up...

Dugo · « **Reply #6 on:** February 19, 2003, 03:15:40 pm »

Quote

im actually curious as to why u would think a shock orientation to the frame would make a difference to how it behaved....

all things being equal the shock shouldn't notice any diffrence... basicly a well designed frame will/should hold the shock in a perfect plane of motion so its not exposed to lateral loads or other types of friction induced forces....

wether it be flat/angled or strait up...

Well, I guess I look at it like a linkage. If you have a link that is perpendicular to another link and you raise that link, all of the displacement is going right into the other link. It moves straight up (spring compression at a linear rate, ie; 1" of displacement = 1" of compression)

Now, If you angle the perpendicular link at 45 degrees and raise the other link, some of the displacement is actually changing the link angle and some of it is going into displacement of the spring. I believe in this case you are actually going to have a "rising rate" of spring compression. What I mean is non-linear compression, initially the deflection is going more into changing the angle and as the angle shifts the compression rises, hence "rising rate".

Now it all get's interesting when you have a link that is basically parallel to your displacement link. What happens I believe is that there is a leverage effect that actually works to counter the intial displacement until the angle is changed to a point where the shock begins to react. That's why there's perhaps less bounce or "bob" when you have a laid down shock design.

I could be full of shit, but my mechanical engineering background tells me there's something inherently different in how a suspension will react given a particular shock angle to the swing arm.

What are your thoughts IFO?

GrimJack · « **Reply #7 on:** February 19, 2003, 07:21:20 pm »

Nope.

The alignment of the shock makes zero difference.

The only factors that matter are the travel path of the shock mount on the swingarm and the location of the other shock mount in relation to the pivot(s).

Mind you, you'll notice that these factors are not all the same from the EVO to the ANIMAL series frames, so they will have small differences in performance on the trail. These will be very small differences, as both are single pivot bikes with awfully similar pivot locations.

GET · « **Reply #8 on:** February 19, 2003, 09:28:31 pm »

I do not have a problem with bob with either bike. Most of the trails I ride are wooded single track over limestone rock ledges. I am hopping and bopping over rocks and roots alot of the time and the K2 suspension is fantastic for this. The only times I catch myself with a little bob is after fatique has started setting in and I happen to be on smooth climb (not very often.) Even then, it is minimal and I fix it by smoothing out my cadence.

I think the secret to this (K2/Proflex) single pivot design is the leading pivot (forward of the BB). Also, if you draw a line from the rear axle to the pivot, you can see that this line is close to the BB axis, thus minimizing misalignment effects. This is true for both the 5500C and the Animal.

Some of the K2 guys can probably explain the technology better, but I know it works for me.

Dugo · « **Reply #9 on:** February 20, 2003, 02:00:32 am »

Quote

Nope.

The alignment of the shock makes zero difference.

The only factors that matter are the travel path of the shock mount on the swingarm and the location of the other shock mount in relation to the pivot(s).

Mind you, you'll notice that these factors are not all the same from the EVO to the ANIMAL series frames, so they will have small differences in performance on the trail. These will be very small differences, as both are single pivot bikes with awfully similar pivot locations.

...well there you go..."the location of the other shock mount in relation to the pivot(s)" is quite a bit different on the Animal and EVO frames. However, I guess the impact IS negligable, because GET has both, rides both and doesn't notice much difference.

Can't argue with the real world...but this did catch my interest. Thanks guys....

Steve O · « **Reply #10 on:** February 20, 2003, 07:35:10 am »

Is there a difference in shock stroke between a 98 Animal and an Evo?

Steve O

Steve O · « **Reply #11 on:** February 20, 2003, 08:10:04 am »

I tried to stay out of this one, but it bothered me too much, where are the teahers (physics,geometry)when you need them.

The K2 page shows a different stock spring weight for the same weight riders on the Evo and on the Animal/Beast. the Evo uses a 450lb sping for a 100lb rider. The Animal/Beast uses a 600lb spring for the same weight rider.
That alone should tell you there is a difference in the leverage the swingarm puts on the shock!

Steve O

Dugo · « **Reply #12 on:** February 20, 2003, 08:14:32 am »

Good point...I'm running a 750lb spring and I only weigh 180 lbs. I like the fact that the rear is so taut and maybe that's a big reason why I don't get much bob. But your point about the difference in leverage is a good one...it obviously is different for the different geometries.

Now, I can see this. The laid down design of the Animal/Beast means it doesn't have as much resistance to displacement so it would need a stiffer spring.

Who here has played around with spring rates and what have you found??? Like I said, I seem pretty happy with a 750lb spring on my Animal but I think for my weight a 600lb is recommended.

SteveO...I measured my 98' Animal and the NR-2 stroke is about 1 1/2" to bottom out. Don't know what the EVO strokes are.

They say the rear wheel travel is 5", but I'm not sure how reliable K2's assessment is of that. It seems less to me, but I could be wrong.

GET · « **Reply #13 on:** February 20, 2003, 08:40:15 am »

I'll make two points to clarify. First, there is definitely a difference in the mechanical advantage due to the shock angles between the Animal and the EVO geometries. The support is much more direct in the EVO. (This goes as the sine of the angle between the shock and the pivot/wheel axle line ... if you're interested.) However, this doesn't change the swingarm travel pattern, just the amount of force needed to support the bike. Second, the bikes do handle a little differently, but I don't notice any real difference in their tendancy to bob (which I think was part of the original question.) I have set my Animal up to take bigger hits. On faster trails, I really love throwing my 5500C around. Even though its only about 5 pounds lighter, its easier to hop and jump. (For one thing, I have Frogs on the 5500C.)

jimbo · « **Reply #14 on:** February 20, 2003, 08:57:05 am »

Don't know about the various K2 single pivot design. My Evo will BOB if I loosen the rebound. It will not BOB if I tighten the rebound. I prefer to keep the rebound tight. It's not as springy for launching stuff, but then it doesn't kick me in the ass

as much when the rebound is loose.

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Author Topic: Let's talk geometry... (Read 8250 times)

Steve O

Steve O

jimbo